Hello! I'm having a little problem to figure out the rotation of a spherical mass, maybe you have more clear ideas! Imagine to have a sphere laying (just it weight) on a support with three contact point: 1) one wheel, that has an external torque apply. 2) helping support that touch the sphere in two point with two conical wheels (one shaft mounting two conical wheels). I would like to rotate the sphere, just with the rotation of the driver wheel. Also I would like to know the rotation of the test mass, driver wheel and helping wheels. I know, of course that if the applied torque is less than a certain value there is the pure rotation without sliding, so I am able to relate the rotation of the driver to the rotation of the others. My question regards the start on of the system. Is it possible to find equation that describe the dynamics of the start on of the system? If I have a slide in some contact I'm not able anymore to know the exact rotation of the sphere because I can't not relate it to the driver rotation. Sorry if it difficult to understand what I wrote, if you have question just tell me! Thanks!