How to model Concave Hull Contact Force in Simulink Simscape

Hi,

I modelled a Quarter Pipe in Simulink Simscape Multibody and try to get the contact force with a colliding object via the Spatial Contact Force Block.

First experiment with a convex surface (or alternatively a plane surface) works very nice, the Ball (green) rolls down the contour:

In the second experiment with the quarter Pipe matlab seems to approximate the surface what results in a cord (blue dotted line) between both ends. The Result is that the Ball hovers over the surface instead of following it:

I fist used the "file solid" Block (yellow part) with no success. As a second approach I modelled the Quarter Pipe in a "Revolved Solid" Block (I uncommented the yellow part then) with the same result.

Is there a Way to model spacial contact force to a concave surface?

I attached the sample program but could not upload the step file. Can be tested with the revolved solid though.

Thanks for any help,

Tobi

Answer 1

[Yifeng Tang]

For a generic solid, Multibody only support exporting the Convex Hull for contact modeling (as of R2025a). So that quarter pipe geometry won't work directly.

You can try "Point Cloud" for the quarter pipe. See documentation here: https://www.mathworks.com/help/sm/ref/filesolid.html

There may be some overhead, but my experience is that it's not bad. You can try keeping the solid, having the point cloud but hiding the point cloud in Mechanism Explorer, so it looks better :)

Answer 2

[Jan Janse van Rensburg]

I have a Work in Progress to make it easy to add point clouds to STLs (Any Shape) and Some basic shapes (Brink, Cylinder, Sphere) You could solve your problem by converting the quater-pipe section to STL and then using the the "PC_STL (Upsample)" Block on the STL of the pipe and then use a normal spherical solid and a spatial contact modelling block between them.

I would stress that this is a WORK-IN-Progress so you would need to look under masks to modify the mass properties and some other settings. But this would make you life a bit easier.

PointCloudAndGridSurfaceHelper.mlproj - Link only valid until 5 May 2025

See the screenshot of the Demo Model and Library below: