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This paper presents our newest findings in planning a dynamically and kinematically feasible center of mass motion for bipedal walking robots. We use a simplified robot model to incorporate multi-body dynamics and kinematic limits, while still being able to meet hard real-time requirements. The vertical center of mass motion is obtained through interpolation of a quintic spline whose control points are projected onto the kinematically feasible region. Subsequently, the horizontal motion is computed from multi-body dynamics which we approximate by solving an overdetermined boundary value problem via spline collocation based on quintic polynomials. The proposed algorithm is an improvement of our previous method, which used a parametric torso height optimization for vertical and cubic spline collocation for horizontal components. The novel center of mass motion improves stability, especially for stepping up and down platforms. Moreover, the new method leads to a less complex overall algorithm since it removes the necessity of manually tuned parameters and strongly simplifies the incorporation of boundary values. Lastly, the new approach is more efficient, which leads to a significantly reduced total runtime. The proposed method is validated through successfully conducted simulations and experiments on our humanoid robot platform, LOLA.

This paper presents recent and ongoing hardware and software upgrades to our humanoid robot LOLA. The purpose of these modifications is to achieve dynamic multicontact locomotion, i. e., fast bipedal walking with additional hand-environment support for increased stability and robustness against unforeseen disturbances. The upper body of LOLA has been completely redesigned with an enhanced lightweight torso frame and more robust arms with additional degrees of freedom, which extend the reachable workspace. The mechanical structure of the torso is optimized for stiffness with the help of an experimental modal analysis performed on the real hardware, while the new arm topology is the result of kinematic optimization for typical use-cases in a multi-contact setting. We also propose extensive changes to our software framework, which include a complete redesign of the onboard, real-time perception and navigation module. Although the hardware upgrade is finished and the overall software design is complete, the implementation of various modules is still work in progress.

Bipedal walking while keeping the upper body upright is a complex task. One strategy to cope with this task is to direct the ground reaction forces toward a point above the centre of mass of the whole body, called virtual pivot point (VPP). This behaviour could be observed in various experimental studies for human and animal walking, but not for the humanoid robot LOLA. The question arose whether humans still show a VPP when walking like LOLA. For this purpose, ten participants imitated LOLA in speed, posture, and mass distribution (LOLA-like walking). It could be found that humans do not differ from LOLA in spatio-temporal parameters for the LOLA-like walking, in contrast to upright walking with preferred speed. Eight of the participants show a VPP in all conditions ( R 2 > 0.90 ± 0.09), while two participants had no VPP for LOLA-like walking ( R 2 < 0.52). In the latter case, the horizontal ground reaction forces are not balanced around zero in the single support phase, which is presumably the key variable for the absence of the VPP.

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