How to model ground contact with contact library for a hopping human?

Hello everyone,

I am implementing a model of a human that is hopping. I use Simmechanics second generation and the contact force library to model ground contact. The model consists of two legs (thight and shank), hip and two feet. I use the sphere to plane contact on 4 points on each foot: one on the heel and 3 at the toes. How do I set the parameters for stiffness and damping to simulate a realistic ground contact? At the moment my human is sometimes falling through the ground.

I would like to know what impact the stiffness and damping parameters have on the contact and how to set the paramters for the error tolerances of the solver correctly. I already have read the readme file of the contact force library and tried out the suggestions there.

Thanks alot

Answer 1

[Steve Miller]

To set the stiffness parameters properly, you should determine what is the maximum penetration the feet can have with the ground and set the stiffness parameter so that when the maximum force is applied the foot does not penetrate too far.

For the cases where the robot falls through the floor, it could be the stiffness parameter is not high enough. Another issue could be that the solver is taking steps that are too large and it is missing the floor. If you make the floor thicker, it should not pass through the floor without seeing it.

--Steve