A Nitinol-Actuated Worm Robot Bends for Turning and Climbing Obstacles

Earthworms, Lumbricus terrestris, are multi-segmented invertebrate animals that have the ability to crawl over land, burrow beneath the soil, and bend their bodies to turn and coil. Each of these motions can be performed while maintaining a small form factor. The low profile locomotion is made possible via peristalsis, a locomotion method in which waves of circumferential and longitudinal contraction propagate in a retrograde manner (opposite to the direction of motion) down the length of the animal’s many-segmented body. We have previously tested peristaltic locomotion on planar surfaces, but here we explore additional actuators in a smaller form factor for bending a pre-fabricated mesh body with nitinol shape memory alloy springs. This new robot, MiniWorm, has a minimum diameter of 1.7 cm, is capable of moving forward at a speed of 0.88 cm/min and can lift its front segment 1.5 times its diameter. We show that without lifting, the robot cannot cross even very small obstacles (14% of diameter), but that a head-lifting gait enables this motion. Future work will enable the robot to move farther with better integrated electronics.