Please help me? I'm trying extremely hard to get our telepresence covid robot to climb stairs. It has tri-wheels and I have been trying many different combinations of mates but not getting anywhere.

I've uploaded some pics. two are of a wheel assembly on their own, I thought I'd start simple. Ha! And the other is of the robot in its entirety.

As well as this I've been attempting to mate the two adjacent sets of wheels so that they move at the same time with the symmetric mate and a plane in-between. However, this only worked with one set and not the other, and I'm baffled as to why?