They look like switches, but these wheels will actually actuate with pneumatic cylinders. The front will actuate together and the back will actuate together, but independent of the front. This should help with turning and maneuverability. (at least in theory, we need to test it though). (see this video for how we are hoping to make it work
https://www.youtube.com/watch?v=PtRewwr59d8 )
We'll get an updated render up also. We are new to rendering in Solidworks (making the change from Inventor) so we are a little rusty.
As far as tensioning goes we are going to use the measurements from the online calculators to drive our distances. If we have to, we can make "positive stops" between the pieces and mount to the 80/20 to set the distances.