Kinematic performance of a quadruped robot is determined by the mechanical structure. This article presents a novel leg structure for legged robots that integrates a differential mechanism into the conventional design. This approach enables all actuators to be positioned within the robot's torso at fixed locations, significantly reducing the leg's inertia. Furthermore, the new structure introduces a parallel transmission system that balances motion and torque distribution among the joint actuators, effectively reducing torque peaks and enhancing the drive capability during dynamic motions. A family of configurations of differential leg structures is constructed, and their mapping to the classic serial leg structure is dissected in kinematic and mathematic. Simulations of various single-leg models are conducted to validate the performance of the new configuration under typical gait conditions. Subsequently, a leg prototype is designed, manufactured, and tested in experiments involving tasks, such as trajectory tracking, weighted squats, and squat jumps. The development of a prototype quadruped robot featuring this novel leg structure is also presented.

The importance of mobile robots for the nuclear disaster response has been realized after Fukushima Dai-ichi nuclear power plant accident. In this paper, we propose a tracked robot for rescue and search in nuclear environment. A gamma-ray irradiation test of the robot's control system is conducted, in order to evaluate the performance of the robot in nuclear environment. The parallel test method is described and the test result is reported.

To improve the mobility of locomotive devices on loose, sandy terrain, protrusions or convex patterns called lugs (i.e., grousers) are attached to the surface of a locomotive modulus. Following our previous study, in which the effects of angular speed, lug sinkage length, and soil cumulative deformation on lug-soil interaction forces during the fixed-axis rotational motion were experimentally confirmed, this study proposed an approximation equation to formulize the relationship among the normal force, lug sinkage length, and lug rotational angle. Moreover, the measured tangential force is compared with values calculated from a conventional tangential force model for discussing its accuracy of predicting the tangential force. Conclusions from this study present the fundamental principles for understanding the lug-soil interaction mechanics for a lug that is performing arbitrary planar motion on sandy terrain.

The planar rimless wheel (PRW) is a classic and simple passive dynamic mechanism to simulate biped walking, different simplified PRW models have respective descriptions and limited applications. This paper focus on constructing the general PRW model, and analyzing the intrinsic and mathematical relation between different PRW models. Based that, the limit cycle of symmetric PRW and asymmetric PRW are proposed separately. Moreover, the stability in universal domain are investigated in detail. Furthermore, simulation and experiment results show that the 2-period limit cycle motion of the asymmetric PRW is more effective, flexible and self-adaptive compared with regular rimless wheel, and more actual applications would be achieved by adopting the general model.

To gain high mobility on challenging terrains, a mobile robot based on eccentric paddle mechanism (ePaddle) with locomotion versatility has been proposed. In this paper, a paddle-aided stair-climbing motion is presented for this ePaddle-based robot. The robot can roll on the stair as a traditional wheeled vehicle and also can climb up the stair under the help of its paddles. Robot-stair interaction modes are presented and typical feasible postures of the robot in stair-climbing are discussed. Frictional requirements for the robot to hold a desired posture are evaluated by modelling statics of the robot. Analyzed results reveal that two critical scenarios in wheeled mode occur when the front-wheel is at the bottom of the riser, and when the rear-wheel is at the top of the riser, respectively. In contrast, frictional requirements of the paddle-aided stair-climbing postures confirm that the robot can climb up the stair with all feasible postures by touching the stair with the paddle, which verifies the effectiveness of the proposed paddle-aided stair-climbing.

Sandy terrains are widely distributed on this planet and include desert, beach, and area affected by volcanic eruption where covered with ash. Currently, these environments still present a challenge for mobile robots due to their poor trafficability. One of the most essential requirements on such terrains for mobile robots is to generate enough drawbar pull with a small amount of slippage. For this purpose, protrusions or convex patterns called lugs (i.e. grousers) are attached on the wheels. However, oscillational drawbar pull generated by lugs results vibration of the robot body and therefore disturb the stability of the robot. In this paper, we aim to reduce the oscillation of the drawbar pull by proposing a novel wheeled mechanism integrated with an actively actuated lug. The drawbar pull on the sandy terrain in fabricated testbed is firstly measured on a prototype mechanism. Based on measured force, a strategy of tuning sinkage length of the active lug for generating stable drawbar pull is proposed. This method has the advantage of that it requires neither prior knowledge on terramechanic models nor physical properties of the terrain. The performance of the proposed method is finally verified by comparing the generated drawbar pull with that of a wheel with a fixed lug.

An eccentric paddle locomotion mechanism (ePaddle) was proposed to enhance the mobility of amphibious robots for multi-terrains tasks. There are several feasible terrestrial and aquatic gaits for an ePaddle-based robot. In this paper, we present the method for modelling thrust in one of the aquatic gaits, namely the oscillating-paddling gait, for an ePaddle mechanism. The conception of the oscillating-paddling gait is introduced firstly and followed by the thrust model. In order to verify the proposed model, a thrust measuring facility is built. A series of experiments are carried out with this facility. From the results, we verify the thrust model for the oscillating-paddling gait. Furthermore, we characterize how the amplitude and direction of the generated net thrust force relate with the amplitude, period and oscillation ratio of the oscillating-paddling gait.

The use of rescue robots in disaster response has become increasingly common, but few of them can operate on harsh amphibious terrain, especially on soft terrain. To access such challenging environments, we have proposed a novel eccentric paddle mechanism (ePaddle) which exhibits high environmental adaptability and can achieve six major types of gait, such as wheel-like rolling, two legged walking gaits, wheel-paddle-integrated rolling, and aquatic paddling gaits. In this paper, we present the details of the paddle trajectory generation method for ePaddle to access soft terrain. On such conditions, the paddle can operate as a lug to generate additional pull and lift forces that improve traction performance and prevent wheel sinkage than using wheel-like rolling. We adopt the passive pressure theory to model the pull and lift forces acting on the paddle; these forces are determined by soil parameters and the inclination angle, sinkage length, and moving direction angle of the paddle. Based on this model, we propose a motion planning strategy to control the inclination angle and protruded length of the paddle to generate required pull and lift forces and weaken any fluctuations in them. Then, we verify the effectiveness of our proposed method by using simulations.

To enhance the mobility of amphibious robots for multi-terrains tasks, we have proposed an eccentric paddle locomotion mechanism (ePaddle) with several feasible terrestrial and aquatic gaits. In this paper, we present a rigid paddle model for predicting the thrust force in one of the aquatic gaits, namely the rotational paddling gait. Thrust forces calculated by this model demonstrate the idea that by relocating the paddle shaft eccentrically from its wheel center, the rotating paddles will generate vectored thrust force for swimming. The paddling motion and the validity of the rigid paddle model are verified by experiments in a water tank.

In this paper, we propose a novel configuration of a multi-legged robot which has only one degree of freedom in each leg and a passive body segment joint between each pair of body segments. With this configuration, a robot can perform planar legged locomotion with less actuators than the conventional legged robots. To model the mobility of a robot with this novel configuration, we firstly select candidate configurations from all of the possible configurations by performing mobility analysis on the robot. Then, feasible gait patterns for achieving planar locomotion are designed with these candidate configurations. The idea that legged locomotion is achievable by less actuators as well as the gait planning methods are verified finally by simulations.

In this paper we present a decoupled control method based on kinematic models of an amphibious reconfigurable robot called ePaddle-based quadruped robot (eQuad). The locomotion mechanism of eQuad is a novel eccentric paddle mechanism (ePaddle) that can perform wheeled, legged and paddling actions in both terrestrial and aquatic environments. We first introduce five terrestrial and aquatic gaits. A duty factor of up to 1.0 can be achieved for the legged walking. Therefore, the proposed robot eQuad can walk with a unique gait by eliminating the swing phase of the legs, and it has a large stable margin because all its legs are in contact with ground during walking. Kinematic models of this robot suggest that with this unique gait the reconfigurable ePaddle mechanism has the potential to achieve both legged and wheeled locomotion with the aid of a simple controller. A decoupled controller adapted from the wheeled robot is then built to evaluate this idea. Finally, simulations are performed to verify our proposed decoupled control and gait sequence planning methods.

To achieve versatile locomotion in complex amphibious environments, a robot should be capable of performing different gaits. In this paper we present such a versatile amphibious robot based on a novel eccentric paddle mechanism (ePaddle). We first illustrate the concept of the ePaddle with five major possible gaits and conceptual gait sequences. We then summarize five types of configurations from these gaits. Based on these configurations, two motion behaviors are found and modeled by using kinematic equations for the future gait planning tasks. To verify the proposed ideas, we develop an ePaddle prototype module. Several simulations on these gaits are performed to verify the conceptual locomotion gait and the developed kinematic models. Experiments on five possible configurations demonstrate the valid of the ePaddle concept and the prototype design.

This article focus on the design of a biomimetic control architecture, which can improve the capability of agility and independence of multilegged walking robots. Since this kind of robots are contrived from multiped animals, the thinking and behaviour manners of multiped animals are first researched and are classified into several types, which are the theoretical base of the biological model. The proposed conceptual model and physical model of the biomimetic control architecture, which are software hardware codesigned, are made up of four blocks, that is information sensing, information communication, behavior generation, and joint driver blocks. Furthermore, the architecture model can realize the evolution between different behavior control layers based various behaviour manners. Through simulation and experiment, it is proved that this biomimetic model makes multilegged walking robots adapt the irregular environment well