Vehicle motor and friction problem

[Moroz]

Hello everybody,

I and my team mate are trying to make vehicle (tank) using PGS (SI) with wheels attached via hinge joints with spring-damper for vertical support. The model has a body with attached wheels on the bottom and on the corners of the body. All wheels are driven.

We deduce equations for PGS impulses taking joint constraints and spring into account. The vehicle is set in motion by angular speed in wheels and so begins to move according to frictional impulse propagated to the body from wheels. Friction is anisotropic (with two direction t1 and t2), one direction along wheel and one along hinge axis.

It moves and turns on ground very plausible, but we have a following problem. When tank comes to some vertical obstacle it begins to climb up even with not big friction coefficient. We think that the problem may be in incorrect motor modeling or we are not right with model parameters (such as friction, spring, damper or elasticity). If somebody can share his experience or make an advice it would be a great pleasure for us.

Thank you in advance, and excuse me for possible lingual errors.