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What is the best way to find ground reaction forces?

Posted: Mon Nov 22, 2021 10:12 am
by Amerile
In order to calculate the zero moment point (ZMP) of the robot I need to find the total reaction of the plane, currently I'm using "getContactPoints()" which gives me the normal reactions of the ground applied to robot's feet, the only way I can think of to also find the applied forces in x and y directions (friction) is to find the direction of the feet link's velocities and, using friction coefficient (which I don't know what is the default in pybullet!!!) and find them my self. by I really doubt that this would give me acceptable results cause in lots of cases there are already weird occasions when the contact point between foot and plane are one, two, or three and I'm not sure whether in these occasions the link velocity in x and y direction are what I want or not.
Furthermore, I wanted to check whether I have understood the returned contact point correctly or not. According to my understanding when the foot is placed on the ground 4 contact point are returned which indicate 4 corners of the foot rectangle. but the unusual thing is that sometime even-though the foot is on the ground I get less than 4 contact points!

PS: My model is in URDF and the parts are STL. And as the forum indicates general Bullet support I think I need to specify that I am using Pybullet :)

Thanks :)