Wheel assembly rolling down stairs with contact library

I'm trying to simulate 2 wheels on 1 axle rolling down stairs. I'm having an issue with the transition of contact forces from one plane to another. The ball rolls on one surface and starts falling down when half of the sphere is over the edge, the wheel falls down with half of it inside the stairs, when it reaches a certain height the 2nd plane starts acting on the wheel and it is flung through space. Here are 3 images visualising the issue. I want the transition to be just as if it was a normal ball/wheel falling down the stairs, so the outer contour should align with the vertical surface. I have 3 coordinate systems defined on the stairs model and I am using a sphere to plane block for each. See image 4 and 5.

Answer 1

[Nicolas Schmit]

The Sphere to Plane Contact Force (3D) block models a force normal to the contact plane, active only when the projection of the center of the sphere on the plane is inside the plane. It does not model contact at the edges of the plane. Thus, the rolling sphere(or wheel) starts falling as soon as its center is not above the plane anymore.

Possible workaround for your problem:

1. Mechanically connect the edge of the step to the center of the sphere using a revolute joint and prismatic joint in series.
2. Connect the prismatic joint to a mechanical hard stop from the mechanical translational domain, and configure the hard stop so that the minimum distance between the edge of the step and the center of the sphere is the sphere radius.

You can find examples on how to interface Simscape Multibody with the foundation domains in the Simscape Multibody Multiphysics Library.