IT WORKS!

It's been a while since I used aim constraints and it took me a while to figure out how to rig that piston part (wheel part), but it's done now and it works fine! (check pic)

So if I move that circle controller underneath the wheel, the whole thing will follow and rotate along nicely and the upperbody won't move. If I move the upperbody, then the wheel will stay put on the ground, and the piston parts will aim toways the central sphere of the upperbody. :)

C.