Hi Alessandro,
I tried to find where you had put your force of 100N downwards but couldn't find it.
Then I tried to find the iam I previously made but couldn't find it either. Please find enclosed a new built assembly with your parts in it. I just used normal constraints in the assembly environment as I am more familiar with them.
When entering the DS environment first I go to the simulation settings and turn off "Automatically Convert....Joints" then when prompted I choose "remove automatic generated joints"
Then I add a spatial joint and a planar joint manually. The planer joint I don't edit, it just keeps the parts from moving through each other.
By the spatial joint I define the dry friction of 0,5 by dof6(T) and the imposed motion (see pictures).
Then by dof4(T) I set the downforce of -100N.
The simulation player is set to 1 sec. Then run simulation and in the output grapher you can see the U-imposed6 of the spatial joint giving you the expected 50N.
I hope this helps you out.
Kind regards,
Joshua