[Hugh Meyer]

It looks like you are planning to move the traction wheel up and down with the mecanum wheel fixed. If you switch that and float the mecanum wheel you can use air pressure to create a suspension system and set the pressure to assure you have all four wheels in contact with the floor. This makes a much better driving mecanum if the floor is uneven. When one wheel goes off the ground driving goes bad.

Don't forget about the side thrust created by the mecanum wheels. You need some way to react against that force.

-Hugh