Foot Placement in the Simplest Slope Walker Reveals a Wide Range of Walking Solutions

We show that the simplest slope walker can walk over wide combinations of step lengths and step velocities at a given ramp slope by proper choice of foot placement. We are able to find walking solutions up to slope of 15.42°, beyond which, the ground reaction force on the stance leg goes to zero, implying a flight phase. We also show that the simplest walker can walk at human-sized step length and step velocity at a slope of 6.62°. The central idea behind control using foot placement is to balance the potential energy gained during descent with the energy lost during collision at foot-strike. Finally, we give some suggestions on how the ideas from foot placement control and energy balance can be extended to realize walking motions on practical legged systems.