Issues with contact point and contact force

[Niyi]

Hello,

I am using coppeliasim to simulator a contact task based on a UR5 robot. But the contact point and contact force/torque seems not right. Here is the scene:
https://www.imghippo.com/i/XcS5142Vw.png
The cylinder was driven downward by the robot using IK. The engine I use is mujoco. But when the contact happens, there's only one single contact point and the position is not at the centor of the contact surface, causing torques which should not exist. My questions are:
What determines the position and numbers of the contact points?
How can I make the correct contact?

Cheers

[coppelia]

Hello,

with Mujoco, indeed, only one contact point is reported in some situations, strangely (e.g. a cylinder sitting in the exact center of the scene). But from my understanding it is a consolidated contact point, that groups/averages several contact points.
If you need several contact points, you can always group several shapes, or cuboids. But in your case, I suspect another problem, not sure from a picture.

Cheers

[Niyi]

Thanks,

I was trying to get the accurate contact force and torque, I was suspecting it is the contact point numbers causing the non vertical forces. The vedio is provided by the link below.
https://drive.google.com/file/d/1Vp-X0o ... drive_link

Just tell me if anymore more information is needed.

Cheers

[coppelia]

You need to give access to the video/file...

[Niyi]

sorry, now the video is unlocked.

[coppelia]

Indeed it appears strange to display only one contact point. The yellow point contact display only shows the contact points that happened in the last dynamics iteration (there are 10 such iterations by default in a simulation step, i.e. by default simulation time step is 50ms, and dyn. time step is 5ms).
So use the contact display add-on instead to get more insight (or use sim.getContactInfo directly).

Cheers