Skip to main content

Utilizing Natural Dynamics for Reliable Legged Locomotion

Periodic Reporting for period 2 - NatDyReL (Utilizing Natural Dynamics for Reliable Legged Locomotion)

Reporting period: 2020-10-01 to 2022-03-31

The NatDyReL (Utilizing Natural Dynamics for Reliable Legged Locomotion) project aims at a fundamental paradigm shift in the design and control of humanoid robots. In contrast to the now mature technology of torque-controlled drives, the robot developed in NatDyReL will be based on highly compliant actuators. This technology has the strong potential to enable physical robustness against external impacts and allows for periodic energy storage and release during highly dynamic motions. The robot will be able to adapt its dynamic behaviour at runtime to the current ground conditions and to the desired walking speed. In addition, part of the kinetic energy can be temporarily stored in the elastic drives at each step, thus enabling robust and energy-efficient execution of dynamic walking movements. In order to successfully implement these concepts in practice, it is necessary to take the actuator dynamics fully into account in the planning of the overall body movement as well as in the real-time control. Considerable effort thus will be spent on the fusion of whole-body locomotion algorithms with novel concepts for the control of elastic actuators. The project requires close interdisciplinary cooperation between experts from different disciplines, especially from robotics, control engineering and mechatronics.
* In work package 1 we developed a generic control framework for controlling elastic actuators. The control framework is based on the concept of a structure preserving coordinate and input transformation. Instead of compensating the nonlinear elastic system dynamics, the controller shapes the overall behavior such that it resembles a well damped compliant actuator which has the desired stiffness and damping terms for the link motion included.

* In work package 2 we extended our locomotion framework to include reactive step adaptation in order to react to external disturbances at the body and the feet (stumble reaction). Moreover, we developed an algorithm for the generation and control of angular momentum during balancing and locomotion. Both algorithms were verified on the exiting torque-controlled robot TORO.

* Highly dynamic motions for running and jumping were developed based on simulation models. Particular emphasis in the motion generation was paid on the smooth transition between walking and running motions.

* The evaluation of the mentioned concepts was done based on extensive simulations for walking, running, and jumping motions. Selected algorithms are currently being verified in the lab on the experimental test-bed C-Runner.
The main focus of our current activities is the preparation for the design of a new elastic robot platform. Detailed requirements for the actuation and the motor selection are drawn from simulations of different dynamic locomotion trajectories, both at the rigid body level and under the consideration of elastic actuators. The considered actuation system includes several couplings between the joints and a mix of compliant and quasi-rigid actuators.

In parallel to the mechanical design we will intensify or efforts on the harmonization of the whole-body locomotion controllers with the elastic actuation and the ESP control framework for elastic actuators.
Overview of the NatDyReL project