Rigid body motion when using moving springs

Hello,

When I try to build my moving vehicle ASE occasionally returns an error citing rigid body motion and instability as the cause. My vehicle is modelled using 3 layers of springs connected to two beams, see figure below (only section of the vehicle shown). It was solved by introducing lateral and longitudinal stiffnesses in the springs (CT). However, if these values are high, the system will not move when an initial velocity (V0) is applied, or bounce back. In addition, when modifying the beam dimensions, i.e. make it larger and therefore stiffer, or adding finer beam meshes, ASE seems to have the same problem even though there are lateral and longitudinal stiffnesses. This was again solved by adding an even higher CT in the springs, which again makes the motion a problem . Any suggestions on how to avoid the rigid body instability problem, but at the same time make it possible to prevent the moving springs bouncing back to the original position?

Moving spring model

Best regards,
Fredrik