1Maximilian Raff , C. David Remy1 maximilian.raff@inm.uni-stuttgart.de

Optimization of Gaits with a Soft Contact Model

Motivation

Soft Contact Model

Model Verification

Gait Optimization

Conclusion

Remy, C. David, Keith Buffinton, and Roland Siegwart. "Comparison of cost functions for electrically driven running robots." 2012 IEEE International Conference on Robotics and Automation. IEEE, 2012.

Hereid, Ayonga, and Aaron D. Ames. "FROST*: Fast robot optimization and simulation toolkit." 2017 IEEE/RSJ International Conference on Intelligent Robots and Systems (IROS). IEEE, 2017.

Schumann, Ethan, et al. "Effects of Foot Stiffness and Damping on Walking Robot Performance." 2019 International Conference on Robotics and Automation (ICRA). IEEE, 2019.

Neunert, Michael, et al. "Trajectory optimization through contacts and automatic gait discovery for quadrupeds." IEEE Robotics and Automation Letters 2.3 (2017): 1502-1509.

Observable foot-compliance during ground interaction

Are fully rigid contact models superior to

soft contact models in gait optimization?

[Schumann 2018]

measuered hard soft

Simulation results of RAMbi (squatting)

- deformations ( ) of a single foot

normal force

displacement

Hard contact model

series of foot-drops

- -continuous in C1

- smoothing coefficient

- no sticking forces:

rigid body (hybrid dynamics):

- no foot deformation

- holonomic non-slipping constraint in stance

7 DoF monoped

Both contact models were implemented for a monopedal robot

- fixed horizontal speed in periodicity constraints

Objective function:

- thermal losses in motors

Initial guess:

- upright standing trajectory

The soft contact model is showing substantial compliance

- resembles experiments much closer than the rigid contact model

Contact models in gait optimization: soft contact model

- contact invariant

(single-phase optimization)

- about twice as fast

- requires fewer mesh points

hard contact model

A good initial guess is essential for both contact models

Ins�tute forNonlinear Mechanics

inm

Model Properties

Soft contact model

Transcription Direct collocation

- Hermite-Simpson splines

(similar to Frost [Ayonga 2017])

Implementation

- multi-phase (hard contact model)

- exploits sparse structure, analytic gradients

- mesh refinement

References