Body Lift and Drag for a Legged Millirobot in Compliant Beam Environment

Much current study of legged locomotion has rightly focused on foot traction forces, including on granular media. Future legged millirobots will need to go through terrain, such as brush or other vegetation, where the body contact forces significantly affect locomotion. In this work, a (previously developed) low-cost 6-axis force/torque sensing shell is used to measure the interaction forces between a hexapedal millirobot and a set of compliant beams, which act as a surrogate for a densely cluttered environment. Experiments with a VelociRoACH robotic platform are used to measure lift and drag forces on the tactile shell, where negative lift forces can increase traction, even while drag forces increase. The drag energy and specific resistance required to pass through dense terrains can be measured. Furthermore, some contact between the robot and the compliant beams can lower specific resistance of locomotion. For small, light-weight legged robots in the beam environment, the body motion depends on both leg-ground and body-beam forces. A shell-shape which reduces drag but increases negative lift, such as the half-ellipsoid used, is suggested to be advantageous for robot locomotion in this type of environment.Comment: First three authors contributed equally. Accepted to ICRA 201

Rapid-Manufacturable Hair Sensor Array for Legged Millirobots

Abstract — We present a rapid-manufacturable, hair-actuated contact sensor array designed for use on legged millirobots. The sensor is an array of sensitive contact switches. Each switch is activated by loading a hair mounted at the switch tip. The hair sensor array is sufficiently sensitive to detect the small contact forces experienced by a lightweight robot, with an average normal sensitivity of 0.8 grams/hair. The compliant polymer hairs detect both normal and shear contact, allowing the array to detect a variety of contact forces. By virtue of its design, the hair sensor array can be fabricated using a roll-to-roll layered process. We demonstrate a straightforward application of the sensor technology on a hexapedal millirobot, using the array to both estimate average ground speed and detect high-centering when running over obstacles. This application is of particular interest for milliscale robots operating in rough terrain, where the risk of entrapment is high. Our results indicate that the hair sensor array can estimate ground speed and detect highcentering when running over simple geometric obstacles. I