How to measure contact force between a surface and a point cloud?

I'm trying to model the interaction between a tire and uneven surface.

I'm using the "Spatial Contact Force" block to model the contact. I modeled the surface with the "Grid Surface" block, and the tire uring the "Point Cloud" block. This is similar to the Mars rover model example.

This works great, but the problem is that sensing of normal force and friction force is disabled for the "Spatial Contact Force" block with this combination of contact.

How can I get the normal force and friction force at the tire-surface contact point without it?

I tried measuring forces at the hub revolute joint, but that doesn't seem to match the contact forces that I can measure when I redo the simulation with a solid tire and solid road. I cannot use the solid tire and road since, my surface has to be uneven and cannot be represented by a convex hull.

Answer 1

[Steve Miller]

Through R2022b, it is not possible to enable the Normal Force or Friction Force measurements at the Spatial Contact Force block for the combination of Point Cloud and Grid Surface. Your approach at the hub seems like it should work as long as the vehicle is not rolling or pitching too much.

The other approximation you could use is to measure the x-y-z position and velocity of the wheel center, pass that to a lookup table to determine how deep (and fast) the tire is penetrating into the surface, and calculate the normal force that way. This will also be an approximation, only looking at the point directly below the wheel center.

--Steve

[Ashwin Rao]

Thanks. I ended up implementing a collision detection algorithm between a circle and arbitrary interpolated line to get all the forces. I skipped the contact force block entirely.

[Vi-Hung]

Can you get the Fn force from the contact block with the newest version of matlab (2024a)?

Answer 2

[Yuchen]

I met the same problem as you. Could you please tell me in detail how you solved it? thank you