Systematic study of limb-body coordination during sandfish burial

The ~10 cm long sandfish lizard can bury into dry granular media within a half-second. Unlike its subsurface sand-swimming behavior, in which propulsion is generated by a head-to-tail traveling-wave of body bending, sand-diving uses both undulatory body motion (typically 1-2 cycles) and a stereotyped pattern of limb use (and disuse). In previous work [Maladen et al, ICRA 2011], a limbless sandfish robot could bury 75% of its body within 5 undulation cycles. To gain insight into the importance of limb use, we performed biological and robophysical experiments. In animal studies, when all limbs were bound (taped to the body), the animal could not effectively bury; hind limb binding increased burial (~4 cycles) but not effectiveness, whereas forelimb binding decreased burial probability (40% success rate using ~6 cycles). To systematically study the morphology, timing and coordination of the sandfish’s limbs and body undulations, we constructed a new sandfish robot with five position-controlled servo motors which generate a travelling body wave, and mounted to the body four rotational servo motors with 3D printed limbs. We expect that a properly coordinated limb use pattern in our robot will improve burial performance.