[ODE] Pushing through collisions

[Nguyen Binh]

Hi Jon,

JW> Anyway, my question still remains: how much force is supposed to 
JW> be exerted by the ODE contact constraints?

     Force is supposed to be exerted by the ODE contact constraints is
    to be determined by the solver base on penetrate depth. So the
    penetration depth is trivial, i.e collider's jobs.

      Those problems are raised by not robust colliders. I think of the
     the most "not robust" part of ODE is colliders.

     I'm working on cylinder-vs anything collider for ODE now
     (originated from Croteam's SE 2.0 engine). There is case in
     cylinder vs sphere I have to exaggerate the depth value to make
     the huge object didn't go through small one. Let's wait and see
     how it survives when you drop a big cylinder over a tiny sphere.
     :)

     Of course, solver is important also. If you use original step,
     your simulation is safer from interpenetrate than using StepFast.

JW> Does ERP or CFM affect this, and if so, how?

    Yes!

    <From ode doc>
    The ERP specifies what proportion of the joint error will be fixed
    during the next simulation step. If ERP=0 then no correcting force
    is applied and the bodies will eventually drift apart as the simulation
    proceeds. If ERP=1 then the simulation will attempt to fix all joint
    error during the next time step.
    <End>

    So, small ERP can cause very large penetration


-- 
Best regards,

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   Nguyen Binh
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