Measuring forces in scene

[Roman Byrtus]

Hello, I have a trident snake robot, set up in the following way:


Now what I am interested in are (in general all the forces acting on the objects, but more importantly) the friction forces between the wheels on each arm of the robot and the floor. I am using the Vortex dynamics engine. Currently I am using the sim.getContactInfo(sim.handle_all, Arm1LW, sim.handleflag_extended) command to return the forces between the wheel and hte floor. I have a few questions about the values that this function returns:

1) This function returns a single contact point between the wheel and the floor, however, when I turn on "Display contact points", it shows 4 contact points between each wheel and the floor. Is there a difference between the contact points displayed and the single one returned? As in, are the displayed ones calculated by V-REP and the one returned by the function calculated by the Vortex dynamics engine?

2) If I want to know how this force is calculated, I should inspect just the theory guide of the Vortex engine, or is there something in V-REP affecting this as well?

Thank you for any answers.

Roman

[coppelia]

Hello Roman,

by default the physics engines will run 10 sub-steps of 5ms, for each simulation step (50ms). This can be adjusted of course, but this is the default. And this also means that the physics engine might produce 10 contact points, where a single would be expected.

So you can parse those contact points with sim.getContactInfo. You can try to evealuate them for each dynamic step, or average them for the simulation step.

The calculated contact forces are handed from the physics engine to V-REP, without modification.

Cheers