Can't get a soil body to follow a closed-trajectory using the spline and point on curve contraint

Hi!

I'm using "point on curve constraint" together with a sppline to move a sphere along a closed path.

the model looks as follows:

which gives me the following result:

I would like the sphere to follow the complete trajectory, however I can't manage to get it.

I created a signal that I input to the movement in the x axis. The signal looks as follows:

The sphere stops at in the middle of the curve, just before the middle of the circle on the right and then comes back to the origin. The heighest point of the triangle is the farthest point to the right in the spline curve.

A work around I thought about was to actuate also the Y axis, however, for this I wouldn't need the curve contraint anymore.

My final goal is to create the tracks of a vehicle (tank like tracks).

I hope I could get some help