Simulating friction on floor for a humanoid in simmechanics second generation

I am currently working on a humanoid simulation on simmechanics 2G and working on getting the friction on the floor working. For the normal force, we are using the overdamped spring model for the floor. I have tried out the following ways to simulate friction:

1) Put overdamped springs in the two horizontal axes.

2) I tried to adapt the same function as used in the simmechanics 1g stiction block for friction: F = -drag_coef*v - constant - k*exp(-trans_coef*v)

Both of them don't seem to work, as the humanoid still keeps slipping on the floor. Any other suggestions on how else it can be implemented?

Answer 1

[Steve Miller]

As long as your friction force depends on the normal force, you have the signs correct, and you make it into static friction (relative velocity close to zero) this should work. You can try the Spatial Contact Force block, added in R2019b, to get rough values for the parameters in your friction model.

--Steve