This paper details the development, modeling and performance of AmphiSTAR, a novel high-speed amphibious robot. The palm size AmphiSTAR, which belongs to the family of STAR robots, is a "wheeled" robot fitted with propellers at its bottom that allow it to crawl on the ground and run (i.e. hover) on water at high speeds. The AmphiSTAR is inspired by two members of the animal kingdom. It possesses a sprawling mechanism inspired by cockroaches, and it is designed to run on water at high speeds like the Basilisk lizard. We start by presenting the mechanical design of the robot and its control system. Then we model AmphiSTAR when crawling, swimming and running on water. We then report experiments on the robot to measure its lift and thrust forces in its on-water running mode and evaluate its energy consumption. The results show that in the on-water running mode, the lift forces are a function of the work volume of the propellers whereas the thrust forces are a linear function of the propellers' rotating speed. Based on these results, the final version of the 3D printed robot was built and experimentally tested in multiple scenarios. The experimental robot can crawl over the ground with performances similar to the original STAR robot and can attain speeds of 3.6 m/s. The robot can run continuously on water surfaces at speeds of 1.5 m/s. It can also swim (i.e. float while advancing by rotating its propellers) at low speeds and transition from swimming to crawling (see video).

In a recent study, we developed a minimally actuated wave-like robot and analyzed its kinematics. In this paper, we present the dynamic locomotion analysis of a miniature version of this wave robot. We examine different crawling environments, determine under which conditions it can advance, and evaluate its propulsion force. We first developed two locomotion models to characterize the cases where the robot is crawling between two straight surfaces or over a single flat surface. We specified the conditions in which the robot will advance and the advance time ratio as a function of the friction forces and weight of the robot. Next, we developed highly flexible tube-like shapes that we molded from silicone rubber to experimentally test the forces acting on the robot inside these tubes. Finally, we designed a miniature model of the robot and experimentally validated its crawling conditions (see video).

This paper presents Flying STAR (FSTAR) a reconfigurable hybrid flying quadcopter robot. FSTAR is the latest in the family of the STAR robots fitted with a sprawling mechanism and propellers allowing it to both run and fly using the same motors. The combined capabilities of running and flying allows FSTAR to fly over obstacles or run underneath them and move inside pipes. The robot can reduce its width to crawl in confined spaces or underneath obstacles while touching the ground. We first describe the design of the robot and the configuration of the wheels and propellers in the flying and running modes. Then we present the 3D printed prototype of the FSTAR robot which we used for our experiments. We evaluate the energy requirements of the robot and the forces it can generate. The experimental robot can fly like an ordinary quadcopter but can also run on the ground at a speed of up to 2.6 m/s to save energy (see video).

This paper presents “1STAR,” which is the first robot that is driven by a single actuator but can be directly commanded to move straight or turn clockwise or counterclockwise. The legged robot relies on a novel actuation gait, which exploits the compliance disparity between alternate stance tripods, to generate rotation by continuously accelerating and decelerating the legs. The direction of turning depends on the configuration of the legs-tripod left or right-and the timing of the acceleration and deceleration. Alternating leg acceleration in successive steps allows for continuous rotation in the desired direction. The turning radius can be varied by changing the timing of the leg acceleration and deceleration without changing the cycle frequency and linear speed. A simplified kinematic motion model of a robot is presented, and a dynamic simulation is performed to analyze the behavior and optimize robot parameters. The locomotion gait is verified experimentally using our newly designed “1STAR” robot.

We present a novel dynamic gait to control in-plane locomotion [1] (forward, back, clockwise and counter clockwise rotations) of a compliant legged hexapedal robot using a single actuator. The gait exploits the compliance disparity between alternate stance tripods, to generate rotation by controlling the acceleration of the robot [2]. The direction of turning depends on the configuration of the legs- tripod left or right- and the direction of the acceleration. Alternating acceleration in successive steps allows for continuous rotation in the desired direction. A simplified model of a robot is made and a numerical simulation was performed to analyze the behavior and optimize robot parameters. The robot is capable of rotating with a coefficient of friction as low as 0.2 but its performance improves as the COF increases up to 0.6. Beyond that, little change is noticed.

We present our findings on the first application of motion planning methodologies to the recently introduced Sprawl Tuned Autonomous Robot (STAR). The reported results provide a first glimpse on the capabilities of this novel, 3D-printed robot in performing autonomously non-trivial motion planning tasks in environments populated with obstacles. We employ methods from sampling-based motion planning under nonholonomic constraints, and implement in open loop the generated path on the physical robot for various environments of increasing complexity.

For maximum maneuverability, terrestrial robots need to be able to turn precisely, quickly, and with a small radius. Previous efforts at turning in legged robots primarily have used leg force or velocity modulation. We developed a palm-sized legged robot, called TAYLRoACH. The tailed robot was able to make rapid, precise turns using only the actuation of a tail appendage. By rapidly rotating the tail as the robot runs forward, the robot was able to make sudden 90° turns at 360 °s-1. Unlike other robots, this is done with almost no change in its running speed. We have also modeled the dynamics of this maneuver, to examine how features, such as tail length and mass, affect the robot's turning ability. This approach has produced turns with a radius of 0.4 body lengths at 3.2 body lengths per second running speed. Using gyro feedback and bang-bang control, we achieve an accuracy of ± 5° for a 60° turn.

In this work we analyze the cost of transport of in-plane hexapedal robots. The robots are modeled as a rigid body with six massless legs, each having two compliant degrees of freedom and the contact is modeled using Coulomb's model. We start our analysis by formulating the cost of transport for rigid legged robots as a function of their geometry, friction coefficients, actuation velocities and slope angle and compare it to the results of a dynamic multibody numeric simulation. In the second part, we estimate the cost of transport in the more general case when the legs and surface are compliant. We evaluate the energy consumptions factors, sliding, work against gravity, elastic losses of the legs and the surface, and kinetic energy and compare them to the total energy input of the actuators. This analysis allows us to evaluate the work range of the robots and determine the optimum locomotion paths for improved battery performance.

This paper presents a six-legged, sprawl-tuned autonomous robot (STAR). This novel robot has a variable leg sprawl angle in the transverse plane to adapt its stiffness, height, and leg-to-surface contact angle. The sprawl angle can be varied from nearly positive 60 degrees to negative 90 degrees, enabling the robot to run in a planar configuration, upright, or inverted (see movie). STAR is fitted with spoke wheel-like legs which provide high electromechanical conversion efficiency and enable the robot to achieve legged performance over rough surfaces and obstacles, using a high sprawl angle, and nearly wheel-like performance over smooth surfaces for small sprawl angles. Our model and experiments show that the contact angle and normal contact forces are substantially reduced when the sprawl angle is low, and the velocity increases over smooth surfaces, with stable running at all velocities up to 5.2m/s and a Froude number of 9.8.

In a previous investigation, the minimum energy and power requirements for earthworm locomotion over flexible surfaces were analyzed. The optimum conditions of locomotion were obtained as a function of the number of cells, friction coefficients, stroke length, energy recovery factor, and tangential compliance. In this paper we focus on the energy requirements of inchworms which, unlike earthworms, consume energy both during the locomotion of the cells and the clamping. In order to estimate the energy requirements, an experiment was performed on the aorta of a bull in which the normal and tangential compliances were obtained. The analysis allows us to compare between inchworms, regular earthworms and earthworms with lower forward coefficient of friction, and determine which of the devices is more efficient with given environment conditions. We also propose a new gait of locomotion for inchworms which reduces the energy consumption.

Turning while running at high speeds remains a difficult task for legged robots, but this capability is crucial for maneuvering quickly in a real-world environment. In this work we present a 10 cm long novel robot, SailRoACH, the first running robot that uses aerodynamic forces to turn. We present a scale analysis of aerodynamic steering, showing this steering method is most effective for small robots. Modeling and simulations were performed, and validated with experiments, that showed the robot is capable of stably turning in a 1.2 m radius at 1.6 ms-1. We also show that aerodynamic steering is superior for high speed turns at high forward velocity, compared to existing methods. Additionally, aerodynamic steering allows us to introduce a constant yaw disturbance to the robot. This is useful for studying legged locomotion, and is difficult to achieve otherwise.

Rapid and consistent turning of running legged robots on surfaces with moderate friction is challenging due to leg slip and uncertain dynamics. A tail is proposed as a method to effect turns at higher yaw frequencies than can be obtained by differential velocity drive of alternate sides. Here we introduce a 100 mm scale dynamic robot - OctoRoACH - with differential-drive steering and a low-mass tail to investigate issues of yaw rate control. The robot without tail is underactuated with only 2 drive motors and mass of 35 grams including battery and control electronics. For some surface conditions, OctoRoACH can maintain heading or turning rate using only leg velocity control, and a basic rate-gyro-based heading control system can respond to disturbances, with a closed-loop bandwidth of approximately 1 Hz. Using a modified off-the-shelf servo for the tail drive, the robot responds to turning commands at 4 Hz and up to 400°/sec.

Biological vessels are characterized by their substantial compliance and low friction which present a major challenge for crawling robots for minimally invasive medical procedures. Quite a number of studies considered the design and construction of crawling robots, however, very few focused on the interaction between the robots and the flexible environment. In a previous study, we derived the analytical efficiency of worm locomotion as a function of the number of cells, friction coefficients, normal forces and local (contact) tangential compliance. In this paper, we generalize our previous analysis to include dynamic and static coefficients of friction, determine the conditions of locomotion as function of the external resisting forces and experimentally validate our previous and newly obtained theoretical results. Our experimental setup consists of worm robot prototypes, flexible interfaces with known compliance and a Vicon motion capture system to measure the robot positioning. Separate experiments were conducted to measure the tangential compliance of the contact interface which is required for computing the analytical efficiency. The validation experiments are shown to be in clear match with the theoretical predictions. Specifically, the convergence of the tangential deflections to an arithmetic series and the partial and overall loss of locomotion verify the theoretical predictions.

This paper proposes a novel dynamic gait of locomotion for hexapedal robots which enables them to crawl forward, backward, and rotate using a single actuator. The gait exploits the compliance difference between the two sides of the tripods, to generate clockwise or counter clockwise rotation by controlling the acceleration of the robot. The direction of turning depends on the configuration of the legs -tripod left of right- and the direction of the acceleration. Alternating acceleration in successive steps allows for continuous rotation in the desired direction. An analysis of the locomotion is presented as a function of the mechanical properties of the robot and the contact with the surface. A numerical simulation was performed for various conditions of locomotion. The results of the simulation and analysis were compared and found to be in excellent match.

Recent attempts at designing untethered devices for locomotion inside compliant biological vessels, highlighted the requirements for energy efficiency for prolonged duration inside living bodies. Quite a number of studies considered the design and construction of crawling robots but very few focused on the interaction between the robots and the flexible environment. In previous studies, we derived the efficiency, defined as the actual advance divided by the optimal advance, of worm locomotion. In this paper, we analyze the force, minimum energy and power requirements for worm locomotion over flexible surfaces. More importantly, we determine the optimum conditions of locomotion as a function of the number of cells, friction coefficients, stroke length, energy recovery factor, and tangential compliance. Optimality is defined with respect to energy and power requirements. The analytical results are obtained by integrating the force over the actuator motion and alternatively by summing up the overall energy losses due to friction and elastic losses with the surface and the efficient work performed by the robot. The theoretical predictions are compared to numerical simulations modeling worm robots crawling over flexible surfaces and are found in perfect match.

An inherent characteristic of biological vessels and tissues is that they exhibit significant compliance or flexibility, both in the normal and tangential directions. The latter in particular is atypical of standard engineering materials and presents additional challenges for designing robotic mechanisms for navigation inside biological vessels by crawling on the tissue. Several studies aimed at designing and building such robots have been carried out but little was done on analyzing the interactions between the robots and their flexible environment. In this study, we will analyze the interaction between earthworm robots and biological tissues where contact mechanics is the dominant factor. Specifically, the efficiency of locomotion of earthworm robots is derived as a function of the tangential flexibility, friction coefficients, number of cells in the robot and external forces.