Design and Development of a Wheel-less Snake Robot with Active Stiffness Control for Adaptive Pedal Wave Locomotion

Abstract

This paper presents the design and manufacture process of a wheel-less, modular snake robot with Series Elastic Actuators to reliably measure motor torque signal and investigate the effectiveness of active stiffness control for achieving adaptive snake-like locomotion. A Polyurethane based elastic element to be attached between the motor and the links at each joint has been designed and manufactured using water jet cutter, which made the final design easier to develop and more cost-effective, compared to existing snake robots with torque measurement capabilities. The reliability of such torque measurement mechanism examined using simulated dynamical model of pedal wave motion, which proved the efficacy of the design. A distributed control system is also designed, which with the help of an admittance controller, enables active control of the joint stiffness to achieve adaptive snake robot pedal wave locomotion to climb over obstacles, which unlike existing methods does not require prior information about the location of the obstacle. The effectiveness of the proposed controller in comparison to open-loop control strategy has been shown by the number of experiments, which showed the capability of the robot to successfully climb over obstacles with the height of more than 55% of the diameter of the snake robot modules.

Snake Robot with Driving Assistant Mechanism

“…However, to overcome environmental irregularities, such as those that are found following disasters, snake robots need to use the optimal gait type according to the terrain, and a complex mathematical model to find the optimal gait type for each terrain is required [12][13][14][15][16]. In addition, a complicated semi-autonomous algorithm is needed to change the optimal gait type based on the terrain after receiving information about the terrain from additional sensors [17][18][19]. Furthermore, to support locomotion of snake robots in extreme environments, a mechanical design to overcome rough terrain, such as a wheel-based snake robot [20,21] or a skin drive snake robot [22], has to be considered.…”

“…There has been no research into the additional mechanisms or body shapes of a snake robot that can help snake robots to move efficiently on steep slopes, like those shown in Figure 1. In addition, the body shape of conventional snake robots is cylindrical or rectangular [1][2][3][4][5][6][9][10][11][12][13][14][15][17][18][19][20][21][22]. For this reason, when the snake robot moves sideways on the steep slope, the robot rolls down, and the stability is highly decreased.…”

Dynamical Modeling and Control of Modular Snake Robots With Series Elastic Actuators for Pedal Wave Locomotion on Uneven Terrain

“…On the other hand, more recently in Ref. [22], we proposed a cost-effective snake robot design equipped with series elastic actuators (SEAs), where an elastic element is attached between the motor and the links to reliably measure the servomotor output torque and regulate the motor torque (force) for adaptive motion [23]. Such a snake robot with SEAs and similar ones, such as Ref.…”

“…[27] with a cam mechanism (see Ref. [22] for more details), which makes them ideal for locomotion on uneven terrain. However, the introduction of an elastic element between the robot servos and the links adds a new level of complexity to the snake robot model [28], which to best of our knowledge is not considered in any snake robot model presented in the literature.…”

“…Moreover, although it is shown in Refs. [29] and [22] (by conducting experimentation on the robot) that adaptive lateral undulation and pedal wave motion can be achieved by incorporating a torque feedback signal (by measuring the deflection of the elastic element) into the joint controller, no formal modeling framework exist to be employed for investigation of such control methods.…”