Fig. (a) A quadruped robot "Kotetsu" on the split-belt treadmill. (b) Experimental setup of Kotetsu for split-belt locomotion with hindlimbs.

Frigon et al. (J. Phys. 2017) conducted hindlimb locomotion experiments using spinal cats. In these experiments, the forelimbs of the spinal cat were positioned on a fixed platform located 1 cm above the treadmill. We followed these procedures using a quadruped robot, “Kotetsu.” The forelimbs were stopped, and the hindlimbs were stepped on a treadmill using PD control. We conducted two types of hindlimb locomotion experiments, tied-belt locomotion (RH:LH = 13.2 [cm/s]:13.2 [cm/s], speed ratio: 1), and split-belt locomotion, using speed ratios (fast belt speed/slow belt speed) from 1.25 to 2.5 in Frigon’s experiments.