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Increased Millirobot Traction in Running and Jumping through Leg Spines


In this thesis leg spines have been used in a variety of systems including traction for horizontal running, and a gripping mechanism for jumping on inclines. These spines were inspired by collapsible leg spines found on insects and spiders that provide a passive mechanism for increased traction while running over complex terrain. I used this architectural advantage as biological inspiration to increase the traction with a VelociRoACH, a high speed terrestrial robot. These spines exhibited anisotropic properties in the fore-aft and lateral directions, with a 2:1 holding-to-release force ratio on corkboard (0.2 N to 0.1 N). This increase in effective friction coefficient at the foot-to-surface contact points increased the running speed on flat ground and 20 degrees inclines and the maximum incline the robot can traverse by 10 degrees. The VelociRoACH with spines is able to engage the surface and pull up to 0.36 N whereas without spines it slips while pulling 0.2 N, increasing the useful work in pulling a load. The spines also allow the robot to remain dynamically stable and resist torque disturbances.

After preliminary experiments using bio-inspired spines on the VelociRoACH, the various structures insects use to enhance interaction with the substrate during jumping were examined. The effectiveness of spines at the base of cricket tibia and attachment pads on tarsi were tested in providing traction on various surfaces by measuring jump kinetic energy using high-speed video. Both substrate and attachment structure significantly affected jump kinetic energy, but most significantly spines increased jumping performance by 82% on Styrofoam.

Inspired by crickets, similar experiments were performed on a 2.5g jumping robot for more controlled tests. The addition of spines increased jump kinetic energy on Styrofoam by 65%, and doubled its jump distance to 40cm. Adding rubber attachment pads allowed the robot to jump on Teflon, increasing the kinetic energy from 0 to 7.8mJ. Leg spines appear critical for maximum jumping performance on surfaces that allow penetration and attachment pads can increase performance on smooth surfaces.

Lastly, spines were used in a gripper mechanism for the monopedal jumping robot, Salto, to reduce slip and provide adhesion capabilities. The mechanism pushes in angled spines along their length and is kinematically constrained to engage/disengage with leg crouch/extension. The resulting gripper introduces no new actuators, enables jumping on penetrable inclines up to 60 degrees, as opposed to a rubber ball foot that works up to 20 degrees, and enables static adhesion to hold 7.5 times the robot's weight from a ceiling.

Overall leg and foot spines have been shown to be an effective means of increasing performance in traction and jumping without requiring additional actuators, degrees of freedom, batteries or control. This is especially useful for small robots that have limited real estate and weight constraints. However, using spines as a passive mechanical solution for traction can be used in larger robots and other applications as well.

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