Hi, Simone. Congratulations on getting a custom mobilizer to work -- very nice! I think you are correct that that's the only way to implement the singularity-free behavior you want. The fact that MobilizedBody::FunctionBased assumes 3 angles for rotation dooms it. (BTW that is itself a custom mobili...

Sorry for the delay in responding to this. I ran your program to see what's happening. My guess is you didn't realize that when you apply a mobility force it is applied equal and opposite to the two connected bodies. So a torque is being applied both to the actuated wheel and the free-floating chass...

Hi, Simone. Simbody's integrators interpolate when a reporting time doesn't coincide with a step completion.

That's on by default but can be controlled by Integrator methods like setAllowInterpolation().

Regards,
Sherm

Hi Simone. If you use one of SImbody's variable step integrators, it should be able to figure out to take small steps over the rapid transition automatically.

Regards,
Sherm

Awesome! Thanks, Walter.

Sadly, no. There is a nice Assembly analysis in Simbody but no InitialVelocity analysis (there should be!) You can work around that by adding a velocity constraint (or Motion object) to one of the dofs (assuming a net-1-dof system). Then constraint projection will figure out all the other velocities...

You could try:
- CPodes limited to Order 1 (that makes it implicit Euler)
- SemiExplicitEulerIntegrator
- Use fixed step or very loose accuracy requirement, like 10%
- Use less damping or large masses to avoid extreme stiffness

Optimization is still probably the most direct approach.

Assembly analysis is for satisfying position constraints. In this case it sounds like you would like the spring to minimize its stored potential energy, that is have the system relax so that it is in a steady state. That's a "static" or "equilibrium" analysis, if I understand your question. Simbody ...

I think all you need is a C-style cast like
SimTK::MobilizerQIndex(int)

Hi, Andrea. The entire System (including all its Subsystems) needs to be built before any computations are done. It looks like you are adding a Subsystem later, would be good to get that sorted out (might not be the problem but could cause trouble). Also, the GeneralContactSubsystem is old and super...