Monopedal robot branch-to-branch leaping and landing inspired by squirrel balance control

Locomotors traversing arboreal environments must often leap across large gaps to land
on small diameter supports. Balancing these dynamic landings is challenging due to high incident
momentum, restricted foothold options, and reduced capacity to produce reaction torques on
narrow supports. We hypothesized that leg length control to enhance branch reaction control
authority would dramatically expand the range of successful landing conditions, drawing on the
same powerful leg actuation required for leaping. Exploring this balance strategy, the monopedal
robot Salto-1P demonstrates branch-to-branch leaps including some upright balanced landing
despite negligible grasping torque. We also compared this landing strategy to the landings of
squirrels which similarly lack the grip strength found in other arboreal species. We demonstrate
that greater radial force control reduces the inertial body torque and/or grasping torque at the
support required to balance a given landing. Adding simple radial force balance control strategies
to conventional balance controllers greatly expands potential landing conditions, increasing the
range of initial angular momentum that can be balanced by 230% and 470% across ranges of
landing angles for low-order models of the robot and squirrel, respectively.