Why does the Mecanum trolley go off track?

Why does the Mecanum trolley go off track?
First find the reason from the mechanical part:
Part 1: After the Mecanum Wheel is assembled, whether the Mecanum wheel is perpendicular to the ground.
The second part: whether the forces of the four mecanum wheels are consistent.
Part III: Inspect the small rubber wheels on each Mecanum wheel for damage.
The above are the problems I encountered when making a Mecanum wheel robot. If it is the first case, it can be solved by making a wheel seat or other methods, so that the Mecanum wheel is vertical to the ground. If it is the second case We have encountered this situation before, using a suspension structure, and then placing four wheat wheels on four electronic scales, adjusting the suspension stiffness so that the pressure of the four wheels is basically maintained at a similar pressure, the third type Basically, just change the small rubber wheel.
Secondly, from the aspect of electric control, it is mainly whether the four motors form closed-loop control. Generally, if the mechanical aspects are not serious, the four motors of the closed-loop control should make the car run straight!