Reply To: how can i constraint the compression of the spring to be in one direction ?

[peteroznewman]

Promote the Remote Force to a Remote Point.  Apply a Remote Displacement and scope it to the Remote Point you just created. If the axis of the spring is the Y axis,  set X = 0 and Z = 0 and leave Y to be Free. That will constrain the Remote Point to move only along the Y axis.