Efficient, Dynamic Locomotion through Step Placement with Straight Legs and Rolling Contacts

TL;DR

Efficient, dynamic locomotion for near-flat-ground walking is addressed by combining ALIP-based step placement with direct stance-leg-length height control and a biologically inspired heel-to-toe rolling CoP strategy. The Quickster controller is validated on the Nadia humanoid in simulation and hardware, achieving forward walking at 0.75 m/s with robust disturbance rejection and multi-directional motions, while delivering improved gait efficiency over a baseline CoM trajectory controller. The results demonstrate that straight-leg walking and rolling contact reduce both positive and negative work, suggesting a practical, real-time approach for energy-efficient bipedal locomotion with potential real-world impact on humanoid robotics. Overall, the work provides a cohesive, implementable framework that enhances speed, stability, and efficiency for flat-ground walking in real robots.

Abstract

For humans, fast, efficient walking over flat ground represents the vast majority of locomotion that an individual experiences on a daily basis, and for an effective, real-world humanoid robot the same will likely be the case. In this work, we propose a locomotion controller for efficient walking over near-flat ground using a relatively simple, model-based controller that utilizes a novel combination of several interesting design features including an ALIP-based step adjustment strategy, stance leg length control as an alternative to center of mass height control, and rolling contact for heel-to-toe motion of the stance foot. We then present the results of this controller on our robot Nadia, both in simulation and on hardware. These results include validation of this controller's ability to perform fast, reliable forward walking at 0.75 m/s along with backwards walking, side-stepping, turning in place, and push recovery. We also present an efficiency comparison between the proposed control strategy and our baseline walking controller over three steady-state walking speeds. Lastly, we demonstrate some of the benefits of utilizing rolling contact in the stance foot, specifically the reduction of necessary positive and negative work throughout the stride.

Figures (8)

• Figure 1: Our humanoid robot, Nadia, during forward walking hardware tests of the Quickster walking controller.
• Figure 2: Stages of stance leg length control. Leg length is initially held constant, then increases with a constant acceleration towards a maximum length, and finally decreases with a constant acceleration to motivate touchdown of the swing foot.
• Figure 3: CoM height and height acceleration comparison between controllers at 0.7 m/s steady-state walking.
• Figure 4: Left: biological walking can be modeled using arc-shaped feet at the base of the inverted pendulum hansen2004roll. Right: rolling contact CoP defined based on CoM position, resulting in a modified LIP time constant hansen2004roll.
• Figure 5: Quickster's full implementation of rolling contact. The non-rolling contact CoP is shown in green. The rolling contact CoP (black) starts at the back of the foot upon heel strike, remains there until toe strike, moves forward toward the toe in full support, and finally reaches and remains at the front of the foot until toe-off.