Fitting belts within your frame

[Chris is me]

Originally Posted by Joey Milia

22t is the absolute largest you can fit in 2in 1/8 wall tubing. We offset the baseplate rivets from the belts and we do the center drop by pushing the outer wheels up 1/16 and the middle wheel down a 1/16th. I think if you did it all from just the center or just the outer you would get some rubbing. Going 3/32 either side of center to get 3/16 total should be possible though. (please check in CAD though I haven't looked at it for a while)

This is similar to what I had to do in order to comfortably fit 24T pulleys in a 2.5" tall frame design I worked on last year. Ultimately I think we're going to go with drop tuning in 2015 (sanding down Colsons until the drop feels "just right") so this isn't an issue for us.

We chose to go with 2x2 instead of 2x1.5 because of how tight the belts are in the tube. 1.5 doesn't leave much room for things poking into the side of the tube (like gearbox bolts or the caps for access holes) and we were worried about rubbing the sides of the tubes. How well does your set up work with 1.5in wide tubing?

1.5 is a bit of a pain, but not impossible to work with. As mentioned before the main thing to keep in mind is the bearings. You either need to put a spacer between the bearing flange and the tube or counterbore the pulleys to clear the OD of a bearing. I guess VersaBlocks are also a way around this. As for bolt heads, we design around where the belts should be, aiming to put bolt holes in the middle of the tube when possible. Most things we do rivet to the top of the frame anyway. As for access hole caps, we don't even cut them anymore, but when we did we left a 1/16" thick tab to rivet a plastic cover to.

[chrisfl]

Would you be able to create a slot in the top and bottom of the tube to allow clearance for the pulley to extend out of the tube a bit? Then the belt would be going along one or two outer sides of the tube. I haven't done this before. This would help save space within the interior of your frame for electronics and subsystems.

[Mike Marandola]

Originally Posted by chrisfl

Would you be able to create a slot in the top and bottom of the tube to allow clearance for the pulley to extend out of the tube a bit? Then the belt would be going along one or two outer sides of the tube. I haven't done this before. This would help save space within the interior of your frame for electronics and subsystems.

If I am understanding what you are saying correctly, you wouldn't be able to get the belt in since it can't be split. Unless you are talking about making one long cutout running the length of the tubing. In that case, a lot of strength will be lost.