So our team wants to use a modified version of the kit chassis with 4 wheels (2 traction on the front, 2 omni on the back). The wheels in question are 6" and to put the axles through the middle mounting holes on the chassis instead of the farthest out ones. We did some measurements for 42 teeth 5mm HTD pulleys and found that the two closest available belt sizes for the hole spacing (about 18.5") were 225T which space 18" apart and 250T which space 20.5" apart.
Is it reasonable to tension out 2" on the top and bottom(potentially using some funky shapes) or should we try something else, like putting a dead pulley in the middle that they both attach to.
It’s reasonable to tension a belt that is just a bit too big for the application. You could probably use a delrin sleeve, with a slip fit bore over a bolt as a tensioner. Start with a big sleeve, turn it down on a lathe until it feels like a “just right” size, set it and forget it. Once you get the tension right you’re good to go all year.
We just notched the end rails, so they would clear the 6 inch wheels using the longer belts. This increases our robot’s wheelbase by two inches, compared to getting the 160 belts, which helps to increase robot stability. it kept a couple students busy for an hour or two. No problems so far.