When Rolling Gets Weird: A Curved-Link Tensegrity Robot for Non-Intuitive Behavior

Abstract

Conventional mobile tensegrity robots constructed with straight links offer mobility at the cost of locomotion speed. While spherical robots provide highly effective rolling behavior, they often lack the stability required for navigating unstructured terrain common in many space exploration environments. This research presents a solution with a semi-circular, curved-link tensegrity robot that strikes a balance between efficient rolling locomotion and controlled stability, enabled by discontinuities present at the arc endpoints. Building upon an existing geometric static modeling framework [1], this work presents the system design of an improved Tensegrity eXploratory Robot 2 (TeXploR2). Internal shifting masses instantaneously roll along each curved-link, dynamically altering the two points of contact with the ground plane. Simulations of quasistatic, piecewise continuous locomotion sequences reveal new insights into the positional displacement between inertial and body frames. Non-intuitive rolling behaviors are identified and experimentally validated using a tetherless prototype, demonstrating successful dynamic locomotion. A preliminary impact test highlights the tensegrity structure's inherent shock absorption capabilities and conformability. Future work will focus on finalizing a dynamic model that is experimentally validated with extended testing in real-world environments as well as further refinement of the prototype to incorporate additional curved-links and subsequent ground contact points for increased controllability.

Figures (11)

• Figure 1: Tensegrity robot locomotion speed comparison among five different mobile tensegrity robots with published experimental speeds bohm_etal_mechatronics_2016paul_etal_ieee_transactions_robotics_2006chen_etal_mechanisms_robotics_2016kim_rapid_2014chen_inclined_2017. The four straight-link designs are significantly slower than the curved-link design when normalized to body lengths per second (BL/s).
• Figure 2: TeXploR prototype on the right (red) and TeXploR2 on the left (black). The two curved arcs in each iteration are held together with a network of 12 elastic cables. Rolling is achieved via internal mass shifting along the arcs, which shifts the overall CoM of TeXploR2. TeXploR2 is signficantly larger and weighs nearly triple that of TeXploR.
• Figure 3: Motor carriage design. a) Cross-section view of the v-groove and ball bearing configuration in the motor carriage that grip the T-track. b) Isometric view of the motor carriage attached to the T-track. This view emphasizes the v-groove bearing attachments at both ends of the motor carriage, preventing motor rocking during increased velocity.
• Figure 4: Curved arc with motor assembly. a) Motor carriage underside with matching arc curvature for smooth rolling along the top of the T-track. Six embedded ball bearings promote smoothness. Pinion gears are connected via bolts anchored into heat set inserts on the underside and sides of the carriage. b) The motor carriage fixed to the curved arc. c) Internal geometry of the sister gear racks. Partial assembly highlights the connection points.
• Figure 5: TeXploR2 electronics. All electronics are rigidly connected to an electronics mount that sits on top of a motor.