Is SimMechanics suitable for Models with a lot of contact force?

Hello,

I tried to build a model of a walking apperatus in SimMechanics but the simulation is extremely slow so I can't use the model properly. It assume the reason why it is so slow is that there is a lot of contact force calculation going on.

At some times there is simulatanious contact force calculation of two objets against the floor and calculation of three revolute joint limits. All these restrictions to keep the object falling through the floor and keep rthe joints from going over their limits are implemented with spring-damper-systems.

Did I just build a poor model or is it so slow because SimMechanics isn't made for such models with a lot of contact force calculation?

[Deinse]

Hi Philipp, I'm looking into building a similar model in SimMechanic and I was wondering if you were successful or found a good way to model the contact forces?

Answer 1

[Sebastian Castro]

@ Philipp: How is your contact modeled? Is it with spring/damper forces? If so, you want to make sure the springs aren't too stiff because this means high frequencies, which in turn means fast dynamics that the solver gets hung up on. Also, make sure you're using stiff solvers like ode15s or ode23t for your model.

If your contact is interfacing with Simulink blocks, make sure you don't have any warnings about algebraic loops. You can remove these by low-pass filtering the signals with an appropriately tuned first-order transfer function 1/(T*s + 1).

@ Denise: If you want to get started with contact modeling in SimMechanics, MathWorks File Exchange has a really nice unofficial contact library.

http://www.mathworks.com/matlabcentral/fileexchange/47417-simmechanics-contact-forces-library

- Sebastian