E-puck model problem when set speed to zero

[Pat]

When I use the e-puck model given in V-REP, I find if I set the speed of the two wheels to zero in the script, the e-puck will rotate around itself little by little. Why does this happen and how can I avoid it?

[coppelia]

Hello,

what you describe is directly linked to the Bullet engine (version 2.78), right? In that case the joint doesn't really rotate, but the wheels do micro-jumps (because otherwise you could use the checkbox Lock motor when target velocity is zero). To resolve your problem, simply increase somewhat the inertia of object ePuck.

Cheers

[Pat]

Many thanks for your help.
I have tried to use the checkbox Lock motor when target velocity is zero, and the e-puck do micro-jumps as you said. I change the inertia matrix of the e-puck and it resolves the problem when the value is set very small (down to zero) or very large (1000). Could you tell me why is this the case?

Thanks again!

[coppelia]

This is directly linked to the way each physics engine works. You will notice that with some physics engines, you do not see that little jumps, even if you adjust the inertia. A too small inertia or mass is always dangerous. They should not be too large either.
Make sure to read the design considerations 7 and 8 here.

Cheers