Steerable needles offer a minimally invasive method to deliver treatment to hard-to-reach tissue regions. We introduce a new class of tape-spring steerable needles capable of sharp turns ranging from 15 to 150 degrees with a turn radius as low as 3 mm, which minimizes surrounding tissue damage. In this work, we derive and experimentally validate a geometric model for our steerable needle design. We evaluate both manual and robotic steering of the needle along a Dubins path in 7 kPa and 13 kPa tissue phantoms, simulating our target clinical application in healthy and unhealthy liver tissue. We conduct experiments to measure needle robustness to stiffness transitions between non-homogeneous tissues. We demonstrate progress towards clinical use with needle tip tracking via ultrasound imaging, navigation around anatomical obstacles, and integration with a robotic autonomous steering system.

Urban winds are a serious hazard for low-altitude autonomous aerial operations in urban airspaces. Previous methods for motion planning in urban winds require global knowledge of the obstacles and flow field and do not lend themselves to real-time application. In this paper, a planning and control framework is proposed for safe and energy-efficient navigation through urban flow fields that strictly relies on onboard sensing. The algorithm incorporates predictions of local wind flow fields into a receding horizon optimal controller, balancing energy consumption with obstacle avoidance on the fly to reach a goal destination. Simulation studies on a procedurally generated urban map with diverse wind conditions demonstrate that the energy-aware motion planner reduces energy consumption by as much as 30% and results in 32% fewer crashes on average compared to the wind-agnostic baseline. Comparisons to a global wind-aware planner indicate only minor trade-offs associated with planning on a local horizon.

Recent progress in reinforcement learning (RL) and tactile sensing has significantly advanced dexterous manipulation. However, these methods often utilize simplified tactile signals due to the gap between tactile simulation and the real world. We introduce a sensor model for tactile skin that enables zero-shot sim-to-real transfer of ternary shear and binary normal forces. Using this model, we develop an RL policy that leverages sliding contact for dexterous inhand translation. We conduct extensive real-world experiments to assess how tactile sensing facilitates policy adaptation to various unseen object properties and robot hand orientations. We demonstrate that our 3-axis tactile policies consistently outperform baselines that use only shear forces, only normal forces, or only proprioception. Videos and details available on the project website.

This paper presents a Continuous Impact-Minimizing (CIM) rolling locomotion method for Variable-Topology Truss (VTT) robots, addressing limitations of conventional stepwise motion. Traditional VTT locomotion depends on discrete reference transitions, resulting in pauses, slow progress, and unintended ground impacts. Inertia-driven rotation at each step also generates impact forces on joints, raising durability concerns. CIM rolling continuously adjusts joint lengths by tracking the center of gravity in real time, enabling smoother motion and minimizing impacts. This approach allows VTTs to move directly to targets without unnecessary resets. Simulations validate the effectiveness of CIM rolling, demonstrating a 50% increase in speed and a 49% reduction in nodal impact force compared to conventional methods.

Despite their growing popularity, swarms of robots remain limited by the operating time of each individual. We present algorithms that allow a human to sculpt a swarm of robots into a shape that persists in space perpetually, independent of onboard energy constraints, such as batteries. Robots generate a path through a shape such that robots cycle in and out of the shape. Robots inside the shape react to human initiated changes and adapt the path through the shape accordingly. Robots outside the shape recharge and return to the shape so that the shape can persist indefinitely. The presented algorithms communicate shape changes throughout the swarm using message passing and robot motion. These algorithms enable the swarm to persist through any arbitrary changes to the shape. We describe these algorithms in detail and present their performance in simulation and on a swarm of mobile robots. The result is a swarm behavior more suitable for extended duration, dynamic shape-based tasks in applications, such as entertainment, agriculture, and emergency response.

THE sense of touch is an indispensable requirement for humans to effectively interact with the physical world around them and perform dexterous tasks. Similarly, this should be no different for robots. Imagine, for example, a robot that can open a bottle of medicine and dispense pills to an elderly person. Although this might seem a straightforward task for a human, it remains a significant challenge for a robot. Critically, the completion of the task depends on tactile sensing: the robot needs to receive and interpret the feedback from interacting with the bottle, determine the appropriate force based on the size and hardness of the pills, and adjust its pose to safely dispense them. Each step involves contact-rich interactions that can only be effectively deciphered through tactile sensing. Typically, tactile sensing works in conjunction with other modalities, such as vision, enabling the robot to adjust its actions dynamically and complete the task. In response to this vision of robots interacting with the physical world through touch, tactile robotics has now emerged as a key research area. Tactile robots can be defined as intelligent systems equipped with tactile sensors that can extract and process tactile data to guide their operations and interactions. The development of tactile robots presents scientific challenges, ranging from the design and fabrication of tactile sensors to methodologies for processing tactile data, integrating tactile feedback into task execution, and combining it with other sensory modalities to improve robot perception. As a result, tactile robotics demands collaborative efforts across several disciplines, involving material and data scientists …

Modular self-assembling systems typically assume that modules are present to assemble. But in sparsely observed ocean environments modules of an aquatic modular robotic system may be separated by distances they do not have the energy to cross, and the information needed for optimal path planning is often unavailable. In this work we present a flow-based rendezvous and docking controller that allows aquatic robots in gyre-like environments to rendezvous with and dock to a target by leveraging environmental forces. This approach does not require complete knowledge of the flow, but suffices with imperfect knowledge of the flow's center and shape. We validate the performance of this control approach in both simulations and experiments relative to naive rendezvous and docking strategies and show that energy efficiency improves as the scale of the gyre increases.

This paper proposes a new locomotion algorithm for truss robots on irregular terrain, in particular, for the Variable Topology Truss (VTT) system. The previous Polygon-based Random Tree (PRT) search algorithm for support polygon generation is extended to irregular terrain while considering friction and internal force limitations. By characterizing terrain, unreachable areas are excluded from search to increase efficiency. A one-step rolling motion primitive is generated based on the kinematics, statics, and constraints of VTT. The locomotion planning is completed by transforming and connecting multiple motion primitives with respect to the desired support polygons. The algorithm's performance is verified by conducting simulations in multiple types of environments.

We introduce a multi-modal reconfiguration planner for the Variable Topology Truss (VTT) modular robot system. The VTT system is a truss-architecture modular self-reconfigurable robot. When a VTT is restricted to a single topology, the collision constraints between the truss members divide the configuration space into many connected components, which makes collision-free planning difficult. This new planner leverages a mathematical invariant based on link theory to find topological reconfiguration actions that can connect these different regions and make progress towards a goal. We show that this planner is effective at finding paths between configurations with different truss topologies.

We propose a mechanism for low Reynolds num-ber walking (e.g., legged microscale robots). Whereas locomotion for legged robots has traditionally been classified as dynamic (where inertia plays a role) or static (where the system is always statically stable), we introduce a new locomotion modality we call buoyancy enabled non-inertial dynamic walking in which inertia plays no role, yet the robot is not statically stable. Instead, falling and viscous drag play critical roles. This model assumes squeeze flow forces from fluid interactions combined with a well timed gait as the mechanism by which forward motion can be achieved from a reciprocating legged robot. Using two physical demonstrations of robots with Reynold's number ranging from 0.0001 to 0.02 (a microscale robot in water and a centimeter scale robot in glycerol) we find the model qualitatively describes the motion. This model can help understand microscale locomotion and design new microscale walking robots including controlling forward and backwards motion and potentially steering these robots.

Truss robots are highly redundant parallel robotic systems that can be applied in a variety of scenarios. The variable topology truss (VTT) is a class of modular truss robots. As self-reconfigurable modular robots, a VTT is composed of many edge modules that can be rearranged into various structures depending on the task. These robots change their shape by not only controlling joint positions as with fixed morphology robots but also reconfiguring the connectivity between truss members in order to change their topology. The motion planning problem for VTT robots is difficult due to their varying morphology, high dimensionality, the high likelihood for self-collision, and complex motion constraints. In this article, a new motion planning framework to dramatically alter the structure of a VTT is presented. It can also be used to solve locomotion tasks that are much more efficient compared with previous work. Several test scenarios are used to show its effectiveness.

This paper develops a decentralized approach to mobile sensor coverage by a multi-robot system. We consider a scenario where a team of robots with limited sensing range must position itself to effectively detect events of interest in a region characterized by areas of varying importance. Towards this end, we develop a decentralized control policy for the robots-realized via a Graph Neural Network-which uses inter-robot communication to leverage non-local information for control decisions. By explicitly sharing information between multi-hop neighbors, the decentralized controller achieves a higher quality of coverage when compared to classical approaches that do not communicate and leverage only local information available to each robot. Simulated experiments demonstrate the efficacy of multi-hop communication for multi-robot coverage and evaluate the scalability and transferability of the learning-based controllers.

The Modboat is a low-cost, underactuated, modular robot capable of surface swimming. It is able to swim individually, dock to other Modboats, and undock from them using only a single motor and two passive flippers. Undocking without additional actuation is achieved by causing intentional self-collision between the tails of neighboring modules; this becomes a challenge when group swimming as one connected component is desirable. In this work, we develop a control strategy to allow parallel lattices of Modboats to swim as a single unit, which conventionally requires holonomic modules. We show that the control strategy is guaranteed to avoid unintentional undocking and minimizes internal forces within the lattice. Experimental verification shows that the controller performs well and is consistent for lattices of various sizes. Controllability is maintained while swimming, but pure yaw control causes lateral movement that cannot be counteracted by the presented framework.

Soft robotic actuators are safe and adaptable devices with inherent compliance, which makes them attractive for manipulating delicate and complex objects. Researchers have integrated stiff materials into soft actuators to increase their force capacity and direct their deformation. However, these embedded materials have largely been pre-prescribed and static, which constrains the actuators to a predetermined range of motion. In this work, electroadhesive (EA) clutches integrated on a single-chamber soft pneumatic actuator (SPA) provide local programmable stiffness modulation to control the actuator deformation. We show that activating different clutch patterns inflates a silicone membrane into pyramidal, round, and plateau shapes. Curvatures from these shapes are combined during actuation to apply forces on both a 3.7 g and 820 g object along five different degrees of freedom (DoF). The actuator workspace is up to 12 mm for light objects. Clutch deactivation, which results in local elastomeric expansion, rapidly applies forces up to 3.2 N to an object resting on the surface and launches a 3.7 g object in controlled directions. The actuator also rotates a heavier, 820 g, object by 5 degrees and rapidly restores it to horizontal alignment after clutch deactivation. This actuator is fully powered by a 5 V battery, AA battery, DC-DC transformer, and 4.5 V (63 g) DC air pump. These results demonstrate a first step towards realizing a soft actuator with high DoF shape change that preserves the inherent benefits of pneumatic actuation while gaining the electrical controllability and strength of EA clutches. We envision such a system supplying human contact forces in the form of a low-profile sit-to-stand assistance device, bed-ridden patient manipulator, or other ergonomic mechanism.

Hardware platforms for socially interactive robotics can be limited by cost or lack of functionality. This article presents the overall system—design, hardware, and software—for Quori, a novel, affordable, socially interactive humanoid robot platform for facilitating noncontact human–robot interaction (HRI) research. The design of the system is motivated by feedback sampled from the HRI research community. The overall design maintains a balance of affordability and functionality. Initial Quori testing and a six-month deployment are presented. Ten Quori platforms have been awarded to a diverse group of researchers from across the United States to facilitate HRI research to build a community database from a common platform.

We describe a docking mechanism and strategy to allow modular self-assembly for the Modboat: an inexpensive, underactuated, oscillating, surface-swimming robot powered by a single motor. Because propulsion is achieved through oscillation, orientation can be controlled only in the average; this complicates docking, which requires precise position and orientation control. Given these challenges, we present a docking strategy and a motion primitive for controlling orientation, and show that this strategy allows successful docking in multiple configurations. Moreover, we demonstrate that the Modboat is also capable of undocking and changing its dock configuration, all without any additional actuation. This is unique among similar modular robotic systems.

Flying Modular Structures offer a versatile mechanism that can change the arrangement of constituent actuators according to task requirements. In this work, we extend a modular aerial platform that can expand its actuation capabilities depending on the configuration. Each module is composed of a quadrotor in a cage that can rigidly connect with other modules. The quadrotor is connected with the cage by a revolute joint that allows it to rotate with respect to the cage. Modules located in the structure are either parallel or perpendicular to one another. The task specification defines forces and moments needed during the execution. We propose two search methods to find a configuration that can satisfy the specification. The first approach consists of an exhaustive search that yields optimal structure configurations by exploring the whole search space. The second approach proposes a heuristic based on subgroup search, reducing the problem complexity from exponential to linear. We validate our proposed algorithms with several simulations. Our results show that the proposed heuristic is computationally efficient and finds a near-optimal configuration even for flying modular structures composed of a large number of modules.

The Modboat is an autonomous surface robot that turns the oscillation of a single motor into a controlled paddling motion through passive flippers. Inertial control methods developed in prior work can successfully drive the Modboat along trajectories and enable docking to neighboring modules, but have a non-constant cycle time and cannot react to dynamic environments. In this work we present a thrust direction control method for the Modboat that significantly improves the time-response of the system and increases the accuracy with which it can be controlled. We experimentally demonstrate that this method can be used to perform more compact maneuvers than prior methods or comparable robots can. We also present an extension to the controller that solves the reaction wheel problem of unbounded actuator velocity, and show that it further improves performance.

In this study, based on an analysis of experimental results, we propose a method for slip modeling of Spiral Zipper. The Spiral Zipper is a prismatic actuator that extracts a length-changeable cylindrical tube from a flexible ABS band. The band tube is driven by a friction wheel; the slip results due to the lack of synchronization between the motion of the band and that of the friction wheel. Through experiments, we verify that the flexibility of the band causes an impact force between the band and the friction wheel. Additionally, we verify that the tube extraction process causes resistance, which contributes to the increase in the relative angular velocity. Considering the factors mentioned above, we develop a slip model by employing different numbers of contact patches that express the flexibility of the band. Subsequently, we validate the model’s performance through simulations. In addition, we propose a coefficients standardization method for obtaining similar results with different number of contact patches We expect that this study will be a basis for design optimization and control system development of the Spiral Zipper.

This work investigates the deployment of an affordable socially assistive robot (SAR) at an older adult day care setting for the screening of COVID-19 symptoms and exposure. Despite the focus on older adults, other stakeholders (clinicians and caregivers) were included in the study due to the need for daily COVID-19 screening. The investigation considered which aspects of human-robot-interaction (HRI) are relevant when designing social agents for patient screening. The implementation was based upon the current screening procedure adopted by the deployment facility, and translated into robot dialogues and gesturing motion. Post-interaction surveys with participants informed their preferences for the type of interaction and system usability. Observer surveys evaluated users’ reaction, verbal and physical engagement. Results indicated general acceptance of the social agent and possible improvements to the current version of the robot to encourage a broader adoption by the stakeholders.

The Variable Topology Truss (VTT) is a new class of self-reconfigurable robot that can reconfigure its truss shape and topology depending on the task or environment requirements. Motion planning and avoiding self-collision are difficult as these systems usually have dozens of degrees-of-freedom with complex intersecting parallel actuation. There are two different types of shape changing actions for a VTT: geometry reconfiguration and topology reconfiguration. This paper focuses on the geometry reconfiguration actions. A new cell decomposition approach is presented based on a fast and complete method to compute the collision-free space of a node in a truss. A simple shape-morphing method is shown to quickly create motion paths for reconfiguration by moving one node at a time.

In this work we introduce ModQuad-DoF, a modular flying robotic structure with enhanced capabilities for yaw actuation. We propose a new module design that allows a one degree of freedom relative motion between the flying robot and the cage, with a docking mechanism allowing rigid connections between cages. A novel method of yaw actuation that increases the structure control authority is also presented. Our new method for the structure yaw control relies on the independent roll angles of each one of the modules, instead of the traditional drag moments from the propellers. In this paper, we propose a controller that allows the ModQuad-DoF to control its position and attitude. In our experiments, we tested a different number of modules flying in cooperation and validated the novel yaw actuation method.

We propose a serpentine type tendon driven underactuated end-effector design with a closing mechanism that is triggered upon contact with an object. This end-effector can grasp objects without knowing the size a priori and is able to grasp a new object while securing another one previously grasped, and so grasp multiple objects sequentially with a single DOF actuation. Design parameters based on the object dimensions are proposed. A low-cost prototype demonstrates two implementations (radius estimation and autonomous grasp of circular objects by torque control, and sequential grasps of multiple objects) of the end-effector through several experiments. A method for estimating applied internal forces is also proposed. This end-effector can benefit robotic manipulation in tasks such as fetching applications, industrial pick-and-place of single or multiple objects and human-robot hand-off interactions.

Modular robotic systems with self-repair or self-replication capabilities have been presented as a robust, low cost solution to extraterrestrial or Arctic exploration. This paper explores using ice as the sole structure element to build robots. The ice allows for increased flexibility in the system design, enabling the robotic structure to be designed and built post deployment, after tasks and terrain obstacles have been better identified and analyzed. However, ice presents many difficulties in manufacturing. The authors explore a structure driven approach to examine compatible manufacturing processes with an emphasis on conserving process energies. The energy analysis shows the optimal manufacturing technique depends on the volume of the final part relative to the volume of material that must be removed. Based on experiments three general design principles are presented. A mobile robotic platform made from ice is presented as a proof of concept and first demonstration.

This paper is an initial step toward the realization of an aerial robot that can perform lateral physical work, such as drilling a hole or fastening a screw in a wall. Aerial robots are capable of high maneuverability and can provide access to locations that would be difficult or impossible for ground-based robots to reach. However, to fully utilize this mobility, systems would ideally be able to perform functional work in those locations, requiring the ability to exert lateral forces. To substantially improve a hovering vehicle's ability to stably deliver large lateral forces, we propose the use of a versatile suction-based gripper that can establish pulling contact on featureless surfaces. Such contact enables access to environmental forces that can be used to further stabilize the vehicle and also increase the lateral force delivered to the surface through a possible secondary mechanism. This paper introduces the concept, describes the design of a new self-sealing suction cup based on a previous design, details the design of a gripper using those cups, and describes the arm and flight vehicle. It then evaluates the cup and gripper performance in several ways, culminating in physical grasping demonstrations using the arm and gripper, including one in the presence of simulated flight noise based on data from preliminary indoor flight experiments.

Flying modular robots have the potential to rapidly form temporary structures. In the literature, docking actions rely on external systems and indoor infrastructures for relative pose estimation. In contrast to related work, we provide local estimation during the self-assembly process to avoid dependency on external systems. In this paper, we introduce ModQuad-Vi, a flying modular robot that is aimed to operate in outdoor environments. We propose a new robot design and vision-based docking method. Our design is based on a quadrotor platform with onboard computation and visual perception. Our control method is able to accurately align modules for docking actions. Additionally, we present the dynamics and a geometric controller for the aerial modular system. Experiments validate the vision-based docking method with successful results.

This paper presents an algorithm to do motion planning for a new class of self-reconfigurable modular robot: the variable topology truss (VTT). Modular robots consist of many modules that can be configured into various structures, and motion planning problem for modular robots with many degrees of freedom and many motion constraints is a significant challenge. In this paper, we propose a novel motion planning algorithm for modular robots to handle this problem with huge state space inspired by DNA replication process - the topology of DNA can be changed by cutting and resealing strands as tanglements form. In a variable topology truss, a single node with enough edge modules can split into a pair of nodes and two separate nodes can be merged to become an individual one. This self-reconfiguration ability results in more potential applications for this type of robots in unstructured environment, such as space and underseas but also leads to more challenges for reconfiguration planning. A novel way to model the robot in a nonuniform grid space is presented and a simple local planner is also developed to check the validation of possible actions. This approach significantly simplifies the problem and some experiment results show that the complicated problem can be solved in a reasonable time.

This paper presents a novel manipulator for aerial vehicles to perform grasping and manipulation tasks. The goal is to design a low-cost, relatively light but strong manipulator with a large workspace and compact storage space that can be mounted on an unmanned aerial system. A novel design solution based on the Spiral Zipper, an expanding tube, combined with tether actuators is presented. A model of the system is introduced and the control method and pose estimator are developed and tested with some experiments showing the reliable performance of the overall system. An experiment with a self-sealing suction cup gripper demonstrates manipulation while mounted on the aerial vehicle frame.

We present a novel flying modular platform capable of grasping and transporting objects. It is composed of four cooperative identical modules where each is based on a quadrotor within a cuboid frame with a docking mechanism. Pairs of modules are able to fly independently and physically connect by matching their vertical edges forming a hinge. Four one degree of freedom (DOF) connections results in a one DOF four-bar linkage that can be used to grasp external objects. In this paper, we propose a decentralized method that allows the Flying Gripper to control its position, attitude and aperture angle. In our experiments, we tested the hovering performance for different aperture angles and with a grasped object. The performance for a closing and opening motion was also verified.

Micro air vehicles exemplified by quadrotors generate downward thrust in their body fixed frame and may only maneuver spatially by changing their orientation. As a result of this underactuation they are fundamentally incapable of simultaneously regulating orientation and position. Furthermore, their feasible maneuvers are limited to spatial trajectories with continuously differentiable acceleration. We present a coaxial helicopter which emulates full actuation over forces and torques (six degrees of freedom) using only two actuators. The orientation of the thrust vector from each rotor is governed by the drive motor by exciting a cyclic flapping response in special articulated blades. The useful separation of orientation and translation dynamics is demonstrated in flight experiments by tracking spatial trajectories while maintaining flat body attitude as well as tracking desired orientations near hover while station keeping.

We introduce ModQuad, a novel flying modular robotic structure that is able to self-assemble in midair and cooperatively fly. The structure is composed by agile flying modules that can easily move in a three dimensional environment. The module is based on a quadrotor platform within a cuboid frame which allows it to attach to other modules by matching vertical faces. Using this mechanism, a ModQuad swarm is able to rapidly assemble flying structures in midair using the robot bodies as building units. In this paper, we focus on two important tasks for modular flying structures. First, we propose a decentralized modular attitude controller to allow a team of physically connected modules to fly cooperatively. Second, we develop a docking method that drives pairs of structures to be attached in midair. Our method precisely aligns, and corrects motion errors during the docking process. In our experiments, we tested and analyzed the performance of the cooperative flying method for multiple configurations. We also tested the docking method with successful results.

We present a system enabling a modular robot to autonomously build structures in order to accomplish high-level tasks. Building structures allows the robot to surmount large obstacles, expanding the set of tasks it can perform. This addresses a common weakness of modular robot systems, which often struggle to traverse large obstacles. This paper presents the hardware, perception, and planning tools that comprise our system. An environment characterization algorithm identifies features in the environment that can be augmented to create a path between two disconnected regions of the environment. Specially-designed building blocks enable the robot to create structures that can augment the environment to make obstacles traversable. A high-level planner reasons about the task, robot locomotion capabilities, and environment to decide if and where to augment the environment in order to perform the desired task. We validate our system in hardware experiments.

Physical connectors with self-aligning geometry aid in the docking process for many robotic and automatic control systems such as robotic self-reconfiguration and air-to-air refueling. This self-aligning geometry provides a wider range of acceptable error tolerance in relative pose between the two rigid objects, increasing successful docking chances. We present a new method for computing the error range (or area of acceptance) for a pair of rigid connector objects with self-aligning geometry capable of higher dimensional analysis which was previously limited to three. The method is based on the configuration space obstacle model, which gives us a representation of the space of contact states between the two objects. Using an approach direction as analogous to gravity, and assuming the target docked configuration is stable, the set of misaligned points that lead to docking is the target configuration's watershed for an arbitrarily dimensioned configuration space obstacle. It is well known that the watershed of a height map on a discrete grid can be found using any number of algorithms from image segmentation. We present an implementation based on Meyer's flooding algorithm to determine this watershed and measure the AA for simple connectors in 2D and 3D. Results are presented for systems including unconstrained motion in SE(2) and motion constrained to four dimensions (ie. x,y,z,pitch) in SE(3).

In this paper a novel telescopic manipulator was adapted to a mobile robotic base to perform manipulation tasks in an elder care facility. As indicated by our previous work, leisure activities and engagement in socialization were desirable among elders, and a physical game assisted by the robot was chosen to investigate both its acceptance and interaction with the older adults. The robot was deployed at an assisted living center and performed multiple interactions. The manipulator was able to successfully retrieve items from different heights as part of the game and results from post-interaction surveys with elders indicated high perceived usefulness and comfort in having the robot as an assistant in the game.

Holonomic systems are often complex and expensive with poor terrain handling capabilities. This paper introduces HAMR, a platform that is simple and low-cost with good terrain handling capabilities which was designed using a new method for characterizing mobility. A mobility ellipsoid (analogous to a manipulability ellipsoid) is introduced as a design tool. A metric called holonomicity measures the extent to which a vehicle can move equally in all directions. The holonomicity of HAMR is measured experimentally. It is shown that non-holonomic vehicles can have relatively high holonomicity as well.

The goal of Piccolissimo is to create a small, simple, and self-powered flying vehicle. Piccolissimo has just one motor and two rigid bodies, which are propellers that spin in opposite directions. The mass distribution and relative rotor speeds are designed to maintain passive stability in hover. Cartesian velocity control is obtained by introducing an asymmetry in the rotation axis of the two rotating bodies and pulsing the thrust at appropriate times. The dynamic model for this device is developed and presented, highlighting the terms that enable a workable design. Two devices are discussed: a vertically controllable version that is 28 mm in the largest dimension and Cartesion controllable version that is 39 mm in the largest dimension.

The PaintPot manufacturing process is a new way to create low-cost, low-profile, highly customizable potentiometers for position sensing in robotic applications. It uses widely accessible materials, requires no special expertise, and creates custom potentiometers in a variety of shapes and sizes, including curved surfaces. PaintPots offer accuracy and precision performance comparable with commercial (non-customizable) options through a calibration process that trades small computation for cost. This paper includes detailed PaintPot manufacturing and calibration processes, and experiments that validate the accuracy, precision, and lifetime performance of PaintPots, comparable to commercial sensors. We also provide a case-study application in the SMORES-EP modular robot, and show how the PaintPot process can be used to create resistive surfaces capable of sensing position in 2D on planes and spheres.

The advantage of modular robot systems lies in their flexibility, but this advantage can only be realized if there exists some reliable, effective way of generating configurations (shapes) and behaviors (controlling programs) appropriate for a given task. In this paper, we present an end-to-end system for addressing tasks with modular robots, and demonstrate that it is capable of accomplishing challenging multi-part tasks in hardware experiments. The system consists of four tightly integrated components: (1) A high-level mission planner, (2) A design library spanning a wide set of functionality, (3) A design and simulation tool for populating the library with new configurations and behaviors, and (4) Modular robot hardware. This paper condenses the material originally presented in Jing et al. 2016 into a shorter format suitable for a broad audience.

Physical connectors which have geometry to passively guide mating increases robustness in attachments. This is a key design area for self-reconfigurable modular robots, which frequently make and break connections. By repurposing the interpretation of a well-known motion planning tool in configuration space obstacles for its encoding of contact geometry, we present a method for determining a metric of error tolerance (area of acceptance) in multiple dimensions by construction. Watershed analysis is run on this configuration-space model to determine the full shape and area of the capture region for the connector pair. We show the results of this process for several connector types.

This paper presents findings from two deployments of an autonomous mobile robot in older adult low income Supportive Apartment Living (SAL) facilities. Design guidelines for the robot hardware and software were based on query of clinicians, caregivers and older adults through focus groups, member checks and surveys, to identify what each group believed to be the most important daily activities for older adults to accomplish physically, mentally and socially. After data analysis, hydration and walking encouragement were found to be critical daily activities, becoming the focus of our deployments. The aim of the deployments was to understand the efficacy of human-robot interaction and identify ways to enhance the robot design and programming. Through observation of older adults interacting with the robot and post-interaction surveys filled out by the older adults, conclusions were drawn for further advancement of the robot development to be tested in future deployments. Results overall indicated high perceived usefulness and growing acceptance of the robot by older adults with increased interactions.

Recent work in the field of bio-inspired robotic systems has introduced designs for modular robots that are able to assemble into structures (e.g., bridges, landing platforms, fences) using their bodies as the building components. Yet, it remains an open question as to how to program large swarms of robotic modules so that the assembly task is performed as efficiently as possible. Moreover, the problem of designing assembly algorithms is compounded by the scale of these systems, and by the lack of centralized guidance in unstructured environments. The main contribution of this work is a decentralized algorithm to assemble structures with modular robots. Importantly, we coordinate the robots so that docking actions can be parallelized. We show the correctness of our algorithm, and we demonstrate its scalability and generality through multiple scenarios in simulation. Experiments on physical robots demonstrate the validity of our approach in real-world settings.

This paper introduces a new class of self-reconfigurable robot: the variable topology truss (VTT). Related to an existing class of robots, the variable geometry truss (VGT), variable topology trusses have the additional capability to change the topology of the truss through self-reconfiguration. The hardware necessary to achieve this is introduced, and the constraints and capabilities of this new type of robot are analyzed by introducing the concept of a topology neighbor graph. Lastly, the minimal reconfigurable VTTs, which require 18 members, are identified and their achievable topologies are enumerated.

A novel prismatic joint called a Spiral Zipper is used to create a 3DOF robot arm in a spherical robot configuration. The Spiral Zipper can be very compact as it has a large extension to compression ratio. An initial prototype has shown a ratio of over 14:1. The Spiral Zipper is very strong in compression, but maybe loose under tension and moments. A tether based system ensures the prismatic joint is always in compression while enabling spherical coordinate positioning with a long reach, high force, low mass design. While having typically an order magnitude higher strength to weight ratio for a given reach compared to standard industrial robot arms, the arm is slower and was not designed for high precision. These characteristics may be applicable for mounting on mobile robots or flying vehicles. This paper introduces the design and testing of several prototypes.

This paper addresses assembly sequence planning for constructing planar structures of the common brick wall pattern collectively with mobile modular robots that have the same rectangular footprint. Here we present a new algorithm for target structures with internal holes that our previous algorithm was not able to address. Our new algorithm constructs a feasible assembly sequence where robots do not have to pass through narrow corridors while approaching their target positions. The algorithm is provably correct and complete and runs in time that is linear in the size of a target structure, that is, the number of its parts. We also present software implementing our algorithms and a set of numerical experiments using the software. Finally, we extend our algorithms to address other symmetric patterns formed by a collection of congruent rectangles on the plane.

We present the EP-Face connector, a novel connector for hybrid chain-lattice type modular robots that is highstrength (88.4N), compact, fast, power efficient, and robust to position errors. The connector consists of an array of electro-permanent magnets (EP magnets) embedded in a planar face. EP magnets are solid-state magnets that can be turned on and off and require power only when changing state. In this paper, we present the design of the connector, manufacturing process, detailed experimental characterization of the connector strength under different loading conditions, and compare its performance to existing magnetic and mechanical connectors. We also illustrate the functional benefits of the EPFace by demonstrating reconfiguration with the SMORES-EP robot.

We address the problem of detecting embeddability of modular robots: namely, to decide automatically whether a given modular robot design can simulate the functionality of a seemingly different design. To that end, we introduce a novel graph representation for modular robots and formalize the notion of embedding through topological and kinematic conditions. Based on that, we develop an algorithm that decides embeddability when the two involved designs have tree topologies. Our algorithm performs two passes and involves dynamic programming and maximum cardinality matching. We demonstrate our approach on real modular robots and show that we can detect embeddability of complex designs efficiently.

We present the control design, system integration, and free flight evaluation of a novel 227 g swashplateless coaxial helicopter. This micro aerial vehicle (MAV) achieves authority over roll, pitch, and yaw orientation as well as maneuvering thrust using only two propellers directly affixed to two motors. No additional aerodynamic control surfaces or actuators are introduced. Instead, cyclic control is obtained through the underactuated dynamic response of the main rotor itself to a modulated drive torque. Comparisons are drawn to conventional four-motor quadrotors and four-actuator fixed pitch coaxial helicopters in terms of mechanical complexity and actuator mass fraction. Trim power consumption in hover is reported across a range of symmetric and asymmetric loading states. Closed loop trajectory tracking maneuvers are demonstrated in a motion capture environment.

The paper presents a model for adding stabilizers to a flying device without rotational momentum (such as quadrotors or ornithopters) that will create passively stable vehicles in hover. This model enables the design of the size and location of these stabilizers that will vary the stability and performance of the vehicle. The model is verified with nine experimental vehicles that span the stability design space. Passive stability allows the removal of costly inertial sensors and increases the robustness of the vehicle. Analysis of the cost and drag that impacts flight performance is also discussed.

We present the methodology, algorithms, system design, and experiments addressing the self-assembly of large teams of autonomous robotic boats into floating platforms. Identical self-propelled robotic boats autonomously dock together and form connected structures with controllable variable stiffness. These structures can self-reconfigure into arbitrary shapes limited only by the number of rectangular elements assembled in brick-like patterns. An O(m2) complexity algorithm automatically generates assembly plans which maximize opportunities for parallelism while constructing operator-specified target configurations with m components. The system further features an O(n3) complexity algorithm for the concurrent assignment and planning of trajectories from n free robots to the growing structure. Such peer-to-peer assembly among modular robots compares favorably to a single active element assembling passive components in terms of both construction rate and potential robustness through redundancy. We describe hardware and software techniques to facilitate reliable docking of elements in the presence of estimation and actuation errors, and we consider how these local variable stiffness connections may be used to control the structural properties of the larger assembly. Assembly experiments validate these ideas in a fleet of 0.5 m long modular robotic boats with onboard thrusters, active connectors, and embedded computers.

Alignment of module connectors is a crucial component of self-reconfiguration in modular robotics. Accomplishing this process using passive mechanical geometry saves resources such as space and power for the modular robot. We present concepts for evaluation of these geometries as well as a new 3D geometry, the 3D X-Face. For comparing different connectors independent of the rest of the robot, figures of merit are presented which are based on the ability for connectors to mate in the presence of position and orientation errors (offsets). Figures of merit for many current connectors are presented. The 3D X-Face alignment behavior is simulated in Gazebo over several sets of initial conditions to estimate the full area of acceptance, and the connector is tested on a CKBot robotic platform. For the situation without rotation, results indicate a 27% improvement over current gendered connectors and a 467% over ungendered connectors. The 3D X-Face is further simulated over a full five-dimensional set and metrics are estimated on that set.

This paper addresses the self-assembly of a large team of autonomous boats into floating platforms. We describe the design of individual boats, the systems concept, the algorithms, the software architecture and experimental results with prototypes that are 1:12 scale realizations of modified ISO shipping containers, with the goal of demonstrating self-assembly into large maritime structures such as air strips, bridges, harbors or sea bases. Each container is a robotic module capable of holonomic motion that can dock in a brick pattern to form arbitrary shapes. Over 60 modules were built of varying capability. The docking mechanism is designed to be robust to large disturbances that can be expected in the high seas. The docking mechanism also incorporates adjustable stiffness so that the conglomerate can comply to waves representative of sea state three, and have the ability to dynamically stiffen as required. The component modules for autonomous assembly, docking and simultaneous collision-free planning as well as the software architecture are presented along with the description of experimental verification.

In this work, we present a low-cost, flying research MAV, comparable to common quadcopter platforms. We propose a flyer with only two moving parts (a rotor and a stator) and a single actuator that is capable of hovering flight without active attitude control. The passive stability is analyzed and reduced to two mechanisms that are a function of the relative offset of the center of pressure and center of mass, the angular momentum of rotor and stator and the differential lift of the spinning elements. The design space over these parameters is explored with a dozen models that are unstable and one that is stable. Interestingly, the two stability mechanisms are not compatible requiring opposing design emphasis. Passive stability of this model is verified by Routh Hurwitz criterion, in simulation and a physical prototype. The vehicle has the added benefits of low complexity and favorable size scaling compared to other MAVs. The vehicle design guidelines derived from both theory and experimentation are presented.

Connection and disconnection occur often in modular robotics. Furthermore, position errors increase in chain-style modular robots as chains get longer. This paper presents a passive (unactuated) compliant two-layer latching mechanism compatible with planar docking mechanisms such as the X-Face, with design considerations and important design parameters empirically identified. Design parameters such as alignment, face curvature and overhang width are shown to have unintuitive effects on the behavior and strength of the connectors. The latch mechanism has a bonding ratio (force of the bond over force required to engage bond) in the range of 20 to 76, depending on the design parameters used. The paper also presents a reconfiguration control sequence that combines the module actuation forces with the connectors' natural forces to increase the reliability of the connection process and reduce the maximum force required. In addition, several types of reconfiguration are performed, including reconfiguration with a 12 module long chain that demonstrates the connectors' robustness to error.

Disaster scenarios involve a multitude of obstacles that are difficult to traverse for humans and robots alike. Most robotic search and rescue solutions to this problem involve large, tank-like robots that use brute force to cross difficult terrain; however, these large robots may cause secondary damage. H.E.R.A.L.D, the Hybrid Exploration Robot for Air and Land Deployment, is a novel integrated system of three nimble, lightweight robots which can travel over difficult obstacles by air, but also travel through rubble. We present the design methodology and optimization of each robot, as well as design and testing of the physical integration of the system as a whole, and compare the performance of the robots to the state of the art.

Traditional coaxial helicopter micro air vehicles use a large propeller motor in conjunction with two small servomotors to control thrust, pitch, and roll forces and moments. Quadrotors similarly generate these necessary forces and moments through the coordinated control of multiple actuators. We present a novel propeller architecture which allows a single motor and rotor to express such control by modulating the torque applied to one passively hinged, underactuated propeller. Flight tests of a two-motor coaxial helicopter demonstrate that such a system can provide active stability and control in a real flight system.

Grippers have been shown using jamming of granular media grasp a large range of objects by pushing against them (with an activation force) to conform the gripper to the object's shape before grasping them with the intent to make universal grippers. This paper presents two effective modifications to jamming gripper designs (adding small nubs and fluidizing the granular media) resulting in significantly larger holding forces (typically 60%) and increasing the range of object geometries. The paper presents the design and fabrication of these devices and explores the range of objects and conditions empirically. Experiments also show that the nubs enable the grasping of smaller objects in which the gripper can engage interlocking forces in the granular media.

Self-reconfigurable robots are capable of changing their shape to suit a task. The design of one system called SMORES (Self-assembling MOdular Robot for Extreme Shape-shifting) is introduced. This system is capable of rearranging its modules in all three classes of reconfiguration; lattice style, chain style and mobile reconfiguration. This system is capable of emulating many of the other existing systems and promises to be a step towards a universal modular robot.

Connection mechanisms are critical to many modular reconfigurable systems. This paper introduces the ModLock manual connection system which is both easy and fast to attach/detach (requires seconds) as well as strong (failure at 2.2kN tensile load). This low cost, low profile connection system has been demonstrated on a variety of robot configurations including legged walkers, flying quadrotors and wheeled robots.

There is a need in the field of modular robotics for a low-profile docking face with a wide range of performance. Mechanical self-aligning geometry features for docking faces of modular reconfigurable robot systems can be varied to improve the reliability of connection systems. This paper presents a new two-layer mating face design for robots that are constrained to move in a plane. It has a provably larger area of acceptance than any to date. We present an analysis of both position and orientation misalignments with simulated results over a two parameter design space comparing this connector with two other best-in-class shapes. The results show an average acceptance area increase approximately 88% over gendered mating faces and approximately 138% over non-gendered mating faces.

Biomechanical studies suggest that animals' abilities to tune their effective leg compliance in response to changing terrain conditions plays an important role in their agile, robust locomotion. However, despite growing interest in leg compliance within the robotics literature, little experimental work has been reported on tunable passive leg compliance in running machines. In this paper we present an empirical study into the role of leg compliance using a composite tunable leg design implemented on our dynamic hexapod, EduBot, with gaits optimized for running speed using a range of leg stiffnesses, on two different surface stiffnesses, and with two different payload configurations (0 kg and 0.91 kg). We found that leg stiffness, surface compliance, and payload had a significant impact on the robot's final optimized speed and efficiency. These results document the value and efficacy of what we believe is the first autonomous dynamic legged robot capable of runtime leg stiffness adjustment.

Micro air vehicles have emerged as a popular option for diverse robotic and teleoperated applications because of their inherent stealth, portability, and disposability. In this work, we adopt a system-level perspective for the development of a rotary-wing micro air vehicle and propose a new design that utilizes gyroscopic dynamics for attitude control. Unlike traditional vehicles where attitude control moments are generated by aerodynamic control surfaces, the proposed vehicle will leverage the existing angular momentum of its rotating components to generate gyroscopic moments for controlling attitude. The capacity to rapidly generate large gyroscopic control moments, coupled with the precision gained from eliminating the need for complex and restrictive aerodynamic models, improves both agility and adaptability. We present the design and analysis of a new flying machine including the dynamic model with simplified aerodynamics and a control scheme based on a model linearized around hover. Simulations show the responsiveness and stabilization of a simple linear controller for hover.

We describe a mobile modular robot system that can generate foam to make structural elements. The mobile platform itself is built of CKBot modules and carries extra modules along with a foam generation device. We demonstrate the system synthesizing new robot morphologies: a snake-like robot and a legged robot. We also use the foam structures to encapsulate and pick-up objects and to modify the environment by blocking a door. Our presentation describes the issues that arose in implementing and using this technique.

This paper addresses the miniaturization of the modules of a modular robot - a major challenge in the field. State of the art modules typically use electromagnetic motors for mobility and self-reconfiguration. However, electromagnetic motor performance reduces upon downscaling to the mesoscale. The smallest self-contained module uses shape memory alloy which is inherently inefficient, slow, and difficult to position control. This work surveys available actuation technologies with respect to appropriate figures of merit. It concludes that dielectric elastomer actuation is promising. We present the design and experimental analysis of an agonist-antagonist dielectric elastomer actuator configuration 7 times smaller than previously demonstrated. Demonstrations with two modules show module bending up to 15° in various modular robot morphologies. In addition, we demonstrate parallel actuation: a pair of modules acting in parallel can lift twice the load a single module can.

Passive robotically-reconfigurable truss structures offer considerable utility as they can quickly adjust to changing functional requirements and resources at a level of sophistication that no human builder could match. Furthermore, robot built structures can be constructed in environments such as surface of Mars or in micro-gravity, which would otherwise be too time consuming or dangerous for humans. In this paper we discuss some of the mechanical design challenges of developing a passive robotically-reconfigurable truss system, and present the concept of the factory floor, which can construct truss-like structures without climbing on them. In the proposed system, each level is constructed on a ground plane using a truss and node configuration and is elevated to make room for the next level. This process is repeated to create 3D truss structures or reversed to decompose the structure for the next task.

An energy efficient joint-locking mechanism that works in conjunction with the main actuator of a robot module is presented. The mechanism will enable chain-style modular reconfigurable robots to perform a wide array of tasks such as dynamic motion and bio-inspired locomotion while consuming less power. The design process for developing this mechanism is presented, and analysis is provided. This mechanism is ideal for modular reconfigurable robot systems, but can be modified to suit many applications. A prototype is developed that outperforms comparable devices such as those that utilize piezoelectrics, magnetic particles, and electromagnetically-actuated disc and drum brakes in terms of power consumption and specific torque.

Miniaturization of Programmable Matter is a major challenge. Much of the difficulty stems from size and power requirements of internal actuators. This paper demonstrates that external energy can be used to both move modules and actuate their bonding mechanism. It presents a lattice style Programmable Matter system whose neighbor to neighbor lattice distance is 14mm. Previous work has shown a chain of edge connected right angle tetrahedrons can fold to arbitrary shapes. To form useful shapes such as tools, the chain should be folded to meet the functional requirements of the task such as mechanical strength. This paper also introduces the analysis of the strength of Programmable Matter systems. Module connections are defined by 6DOF stiffness matrices. The paper analyzes the strength of a heterogeneous system with some rigid and some soft connections.

Inspired by the pseudopod mobility mechanism found in amoebas, we propose a toroidal robot which can fold in on itself to generate the same overall motion of the amoeba. One of the advantages of such a robot is its ability to squeeze under obstacles and through holes smaller than its nominal diameter. These abilities make it particularly well suited for unstructured and highly constrained environments such as medical and search and rescue applications. We present several actuation mechanisms which are being investigated towards the development of an everting toroidal robot. For smaller scale applications, we present contracting ring actuators made up of shape memory alloy rings or electroactive polymer rings that create a differential stress and drive the motion. For larger scale applications, we present a tape spring mechanism which uses a membrane composed of treads arranged in a circular pattern. Another large scale mechanism uses a snake-like robot that can be formed into a torus which can ascend and descend cylindrical structures. We also present a chemical actuation method which utilizes chemically induced swelling in crosslinked polymers to produce forward motion. Finally, we describe a novel torus shaped actuator being developed which uses shape memory alloy rings to generate an everting motion.

Modular robots are a powerful concept for robotics. A modular robot consists of many individual modules so it can adjust its configuration to the problem. However, the fact that a modular robot consists of many individual modules makes it a highly distributed, highly concurrent real-time system, which are notoriously hard to program. In this work, we present our programming framework for writing control applications for modular robots. The framework includes a toolset that allows a model-based programming approach for control application of modular robots with code generation and verification. The framework is characterized by the following three features. First, it provides a complex programming model that is based on standard finite state machines extended in syntax and semantics to support communication, variables, and actions. Second, the framework provides compositionality at the hardware and at the software level and allows building the modular robot and its control application from small building blocks. And third, the framework supports formal verification of the control application to aid the gait and task developer in identifying problems and bugs before the deployment and testing on the physical robot.

We present a novel approach to controlling the locomotion of a wheel by changing its shape, leading to applications to the synthesis and closed-loop control of gaits for modular robots. A dynamic model of a planar, continuous deformable ellipse in contact with a ground surface is derived. We present two alternative approaches to controlling this system and a method for mapping the gaits to a discrete rolling polygon. Mathematical models and dynamic simulation of the continuous approximation and the discrete n-body system, and experimental results obtained from a physical modular robot system illustrate the accuracy of the dynamic models and the validity of the approach.

Much like a falling cat can reorient itself to land on its feet, a climbing robot should also reorient itself to minimize damage during a fall. This paper presents and analyzes the dynamic motion of a modular robot, called CKbot righting itself during a fall. It presents a mathematical model of the falling system that correlates well with experimental reorientation results about one axis. The model also explains why the the process of flipping around is practical only about the long axis of the robot. For more robust orientation correction, a different configuration of CKbot and a new motion plan is presented that corrects for all forms of posture error.

This paper provides proof-of-concept that state-of-the-art sampling-based motion planners that are tightly integrated with a physics-based simulator can compute paths that can be executed by a physical robotic system. Such a goal has been the subject of intensive research during the last few years and reflects the desire of the motion planning community to produce paths that are directly relevant to realistic mechanical systems and do not need a huge post-processing step in order to be executed on a robotic platform. To evaluate this approach, a recently developed motion planner is used to compute paths for a modular robot constructed from seven modules. These paths are then executed on hardware and compared with the paths predicted by the planner. For the system considered, the planner prediction and the paths achieved by the physical robot match, up to small errors. This work reveals the potential of modern motion planning research and its implications in the design and operation of complex robotic platforms.

This paper presents a method for scaling down the size and scaling up the number of modules of self- re configurable systems by focusing on the actuation mechanism. Rather than developing smaller actuators, the main actuator is removed entirely. Energy instead comes from the environment to provide motion in prescribed synchronous ways. Prescribed synchronous motions allow much faster assembly times than random Brownian motion which has been used before. An instantiation of this idea is presented using a motion platform to induce motions based on the inertial properties of the modules and the timed actuation of small latching mechanisms.

This video shows an uncut sequence of a 15 module robot in a bi-pedal configuration subject to a variety of disturbances yet staying on task. As the robot walks, a large disturbance is introduced. A human kicks the robot in its midsection causing the robot to fall into three separate clusters of five modules. Each of these pieces diagnose their state sensing gravity and their connectedness. They each perform a self-righting maneuver, then begin to search for each other. This is a first demonstration towards the development of solving larger self-reassembly problems that include greater levels of randomization and entropy (more pieces more widely distributed.) The 2006 Robotics Science and Systems workshop on self-reconfigurable robots developed as one of the grand challenges for this area, the ability to survive and self-repair after an explosion. This work will push the technologies required for integrated sensing, localization, distributed control, under highly unstructured conditions.

This paper introduces a new challenge problem: designing robotic systems to recover after disassembly from high-energy events and a first implemented solution of a simplified problem. It uses vision-based localization for self- reassembly. The control architecture for the various states of the robot, from fully-assembled to the modes for sequential docking, are explained and inter-module communication details for the robotic system are described.

Modular robotics has been an active area of research for the last decade. In this paper, we argue that it also provides an excellent platform for education. PolyBot is a type of modular reconfigurable robot developed at PARC. The PolyKinetic/spl trade/ System provides a robotic scripting language and programming environment for controlling this type of robot. Based on experience with mentoring high school students, and running a tutorial for robotic researchers at IROS'03, we show that, PolyBot and the PolyKinetic/spl trade/ System is effective for educational activities at multiple levels. These include playing, exploring, building, programming, competing, and most of all, learning while having fun.

A common point of weakness in many path/motion planners is dealing with configuration spaces (C-spaces) that involve narrow gaps of passages. This is caused by the indirect representation of the C-space inherent in those planners. Unfortunately many real environments and tasks give rise to such situations. While a small number of planners do exist which reliably work in these environments, they in turn have problems when the robot has many controllable degrees of freedom. High degree of freedom motion in confined spaces is a typical problem encountered by PARC's PolyBot platform. The algorithm put forward in this paper is designed to work directly with the C-space obstacles' geometry, and so is not hampered by narrow passages. The planner is a homotopic one which solves general problems in n-dimensional C-space. The algorithm's theoretical characteristics are shown to compare very favourably with other contending planners in these specialised domains. Results of some preliminary testing are given.

Modular reconfigurable robots have the potential for great versatility and robustness; however, programming locomotion gaits for hundreds of modules remains a challenge. In this paper we present a formal model for programming locomotion gaits in chain-type modular robots: phase automata. A phase automation is an event-driven state automation with an initial phase delay. The phase delay is normally a real value between 0 and 1. Phase automata are compact representation of locomotion gaits and capable of being embedded and distributed across modules. The concepts of phase automata have been implemented on both PCs and embedded micro-processors. An XML script language and programming interface for phase automata are being built. Locomotion gaits programmed using phase automata have been tested both in simulation with 100+ modules and in hardware with 50+ modules.

A Telecube is a cubic module that has six prismatic degrees of freedom whose sides can expand more than twice its original length and has the ability to magnetically (de)attach to other modules. Many of these modules can be connected together to form a modular self-reconfigurable robot. The paper presents the intended functions, discusses the physical requirements of the modules and describes two key mechanical components: a compact telescoping linear actuator and a switching permanent magnet device.

We discuss the theoretical limitations for reconfiguration of metamorphic robots made up of Telecubes, six degree of freedom cube shaped modules currently being developed at Xerox PARC. We show that by using meta-modules composed of 8 individual modules as a backbone for building the desired shape, we can establish completeness for the reconfiguration as well as time and space bounds for the process. Finally we present several open problems in the field of reconfiguration.

We present a complete, local, and parallel reconfiguration algorithm for metamorphic robots made up of Telecubes, six degree of freedom cube shaped modules currently being developed at PARC. We show that by using 2 /spl times/ 2 /spl times/ 2 meta-modules we can achieve completeness of reconfiguration space using only local rules. Furthermore, this reconfiguration can be done in place and massively in parallel with many simultaneous module movements. Finally we present a loose quadratic upper bound on the total number of module movements required by the algorithm.

Several studies have focussed on robotic systems with many degrees-of-freedom. Such robots often have stringent joint limits. For motion planning, a key question is to find feasible joint solutions of the system of a given position and orientation of the end-effector. In the presence of join limits, the solutions are found by searching the joint space using heuristics. In this paper, we propose a simple algorithm to construct the joint solutions for a robot chain with many degrees-of-freedom and joint limits, using dextrous workspaces. The algorithm provides a set of sufficient conditions to guarantee feasible joint solutions in the presence of limits. The procedures are illustrated by theory and experiments on PolyBot, a modular robot developed at Xerox PARC.

Some engineering applications require structures to expand and contract in size, while retaining their exterior shape. The applications range from mundane daily life objects to more fancy art structures. In contrast to a multiple degree-of-freedom structure, a single degree-of-freedom structure can be driven by a single actuator, reducing the cost and simplifying the control. In this paper, we study single degree-of-freedom structures that can be formed by a lattice of single degree-of-freedom polyhedral expanding units. Due to built-in symmetries, the entire structure can expand and contract as one of the units in the structure is actuated.

A planner for statically-stable motion of a legged robotic vehicle over an uneven terrain is presented that can plan the footplacement of individual legs for highly cluttered terrain. A method for determining the traversability over a generic discretised height map terrain is presented. Planning is broken into two levels of refinement to reduce the overall complexity and incorporates a number of heuristics. The planner has successfully planned the motion of 6 and 8 legged configurations of the XEROX PARC PolyBot modular reconfigurable robot as well as the CMU Ambler in simulation over arbitrarily complex terrain. A distributed implementation of the planner has also been shown on PolyBot's distributed computational platform.

One of the constraints that severely limit the capability of highly redundant manipulator arms is the actuator torque limits. This paper presents a way to achieve large effective forces from weak actuators by exploiting the large mechanical advantage that results from systems near singularities. While large mechanical advantages have been applied near singularities in many instances, this method allows the application of this large force over a large distance. It is applied specifically to closed chain mechanisms and demonstrated on the PolyBot modular self-reconfigurable robot.

Modular, self-reconfigurable robots show the promise of great versatility, robustness and low cost. However, programming such robots for specific tasks, with hundreds of modules and each of which with multiple actuators and sensors, can be tedious and error-prone. The extreme versatility of the modular systems requires a new paradigm in programming. We present a software architecture for this type of robot, in particular the PolyBot, which has been developed through its third generation. The architecture, based on the properties of the PolyBot electro-mechanical design, features a multi-master/multi-slave structure in a multi-threaded environment, with three layers of communication protocols. The architecture is currently being implemented for Motorola PowerPC using vxWorks.

Modular, self-reconfigurable robots show the promise of great versatility, robustness and low cost. The paper presents examples and issues in realizing those promises. PolyBot is a modular, self-reconfigurable system that is being used to explore the hardware reality of a robot with a large number of interchangeable modules. PolyBot has demonstrated the versatility promise, by implementing locomotion over a variety of terrain and manipulation versatility with a variety of objects. PolyBot is the first robot to demonstrate sequentially two topologically distinct locomotion modes by self-reconfiguration. PolyBot has raised issues regarding software scalability and hardware dependency and as the design evolves the issues of low cost and robustness will be resolved while exploring the potential of modular, self-reconfigurable robots.

This paper investigates new modes of robot land locomotion, in particular statically stable non-wheeled, non-tracked locomotion. These locomotion gaits are accomplished by a reconfigurable modular robot called Polypod using a control scheme combining a small number of primitive control modes for each module. The design of Polypod is first reviewed, then two and three-dimensional locomotion gaits are described along with two "exotic" gaits. These gaits have been implemented on Polypod or simulated on a graphic workstation.>