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Originally Posted by Saool
Thank you for the feedback. At first we were planning on using a single belt that ran inside the 2x1 but were promptly met with many issues. In this render we were planning on having the back to center wheel's belt on the inside of the frame and the front to the middle inside the tubing.
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Another option would be to use wider tubing. If you aren't riveting to the top or bottom of the tube (so clearance isnt' an issue), I would recommend 2x2 tubing and 15mm belts. If you can make your own pulleys, you can fit it in 2x1.5 tubing with some creative counterbores. Since it does seem like you are riveting, 3x1.5 tube is safer, but that's definitely adding some weight.
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We planned on using belts because of their minimal stretching, but after recieving all this feedback to switch to chains, we will probably be doing so.
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Honestly, I think some of the feedback against belts is a bit unfair, and maybe not based on hands on experience. If you design your belts right, you should never need to perform maintenance on them inside a tube; we're going into season 5 without a belt failure. Even with an in-tube design it is possible to change a belt in 10-15 minutes if you think carefully and know what you're doing. You do not need to remove the entire gearbox to change an (internal) belt - you slide it out a few inches until the pulley is free, then slide it back in once the next belt is in place. An access window above the middle wheel will help with this. If you leave the ends open you do not need access windows on the outer wheels.
All of this said, there are compelling reasons to use chain over belt, particularly if you are running the power transmission external to the tube. Chain drive external saves weight in using a smaller extrusion profile, and I guess it saves a little space too. In the case of using belts outside of the tube, a belt drive failure would require removal and disassembly of the gearbox, and that's no fun. It's really up to preference, and whether or not you want to tension after the fact or not. If you like tensioners and bearing blocks, chain is a lot easier. If you can machine "exact centers", where your wheels are fixed the exact distance apart that a belt calls for, and you don't mind a "fatter" drive tube, belt drives are nice.
So maybe they weren't wrong... Just thought I'd add some data and explain the logic behind internal belt drives a little bit more.