Kinodynamic planning for spherical tensegrity locomotion with effective gait primitives

Abstract

Tensegrity-based robots can achieve locomotion through shape deformation and compliance. They are highly adaptable to their surroundings, and are lightweight, low cost, and physically robust. Their high dimensionality and strongly dynamic nature, however, can complicate motion planning. Efforts to date have primarily considered quasi-static reconfiguration and short-term dynamic motion of tensegrity robots, which do not fully exploit the underlying system dynamics in the long term. Longer-horizon planning has previously required costly search over the full space of valid control inputs. This work synthesizes new and existing approaches to produce dynamic long-term motion while balancing the computational demand. A numerical process based upon quasi-static assumptions is first applied to deform the system into an unstable configuration, causing forward motion. The dynamical characteristics of the result are then altered via a few simple parameters to produce a small but diverse set of useful behaviors. The proposed approach takes advantage of identified symmetries on the prototypical spherical tensegrity robot, which reduce the number of needed gaits but allow motion along different directions. These gaits are first combined with a standard search method to achieve long-term planning in environments where the developed gaits are effective. For more complex environments, the various motion primitives are paired with the fall-back option of random valid actions and are used by an informed sampling-based kinodynamic motion planner with anytime properties. Evaluations using a physics-based model for the prototypical robot demonstrate that modest but efficiently applied search effort can unlock the utility of dynamic tensegrity motion to produce high-quality solutions.

Robustness evaluation for rolling gaits of a six-strut tensegrity robot

“…Though the rolling gaits listed in Table 3 are all represented as using TC-6 or TO-5 as the initial touching-ground triangle, they are also applicable to other initial states due to the pyritohedral symmetry of the structure with order S ¼ 24, which means that there are 24 unique combinations of rotations and reflections that result in an equivalent configuration. 22 As a result, the repeated tests for each gait are conducted by switching the starting touching-ground triangle according to the pyritohedral symmetry of the structure. Specifically, six tests are conducted for each gait in gaits 1-12, and the corresponding starting touching-ground triangles are TC-1, TC-2, TC-3, TC-4, TC-6, and TC-7, respectively, in which TC-2, TC-3, and TC-7 can be transformed into each other by a rotation operation with a rotation angle of 120 , and TC-1 and TC-6 can be transformed into each other by a combined rotation(60 )-reflection operation, while six tests are conducted for each gait in gaits 13-30, and the corresponding starting touching-ground triangles are TO-1, TO-2, TO-3, TO-4, TO-5, and TO-6, respectively, in which TO-1 and TO-2 (as well as TO-4 and TO-5) can be transformed into each other by a reflection operation, and TO-3 and TO-5 (as well as TO-6 and TO-2) can be transformed into each other by a rotation operation with a rotation angle of 180 .…”

“…Chang et al 21 presented a path planning method based on basic rolling gaits using the A* algorithm. Littlefield et al 22 proposed approaches to produce long-term locomotion using rolling gaits, in which a standard search method is used for simple environments and an informed sampling-based planner for complex environments.…”

Robust Shape Control of Gyroscopic Tensegrity Robotic Arm

“…A comparison between the modelbased and data-based approach is an emerging topic of recent research [ [29]]. Both of these active control strategies are useful for the deployment of tensegrity-based civil engineering structures [ [30], [31]], and tensegrity robots [ [32], [33], [34], [35]]. In this paper, a model-based output regulation approach for the nonlinear shape control of a general "classk" tensegrity structure using control Lyapunov function is discussed.…”

Jumping Tensegrity Robot Based on Torsionally Prestrained SMA Springs

“…An area where lightweight and high-performance actuators could find use is in the development of space exploration robots such as tensegrity robots. Tensegrity robots consist of interlocking struts and cables that can perform diverse motions when deformed. , However, tensegrity robots that can produce rolling motions using lengthening struts or moving weights have been shown. , Different methods to predict the performance of these gaits have been demonstrated including simulation and reinforcement learning. , Rolling motions with soft actuators has only been demonstrated using McKibben muscles and liquid crystal elastomer–carbon nanotube composite actuators. − Shape memory polymers struts have also been used to realize self-deploying tensegrity structures . However, these soft actuator-based robots remain slow and have not brought forth new locomotion strategies.…”

“…23,24 However, tensegrity robots that can produce rolling motions using lengthening struts or moving weights have been shown. 25,26 Different methods to predict the performance of these gaits have been demonstrated including simulation and reinforcement learning. 27,28 Rolling motions with soft actuators has only been demonstrated using McKibben muscles and liquid crystal elastomer−carbon nanotube composite actuators.…”