Quote:
Originally Posted by Chris is me
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.
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I think a lot of people are debating belts is its possible to put too much load on certain combinations in a drivetrain. The smallest chain system you can buy is #25 chain with 16t sprockets. The torque calculations with 4 inch wheels are still within spec of #25 chain, even with 6 cims. Whereas with 9mm belts and 24t pulleys, you are out of spec for the belts. I saw alot of teams (including us) use that combination this year, and it did not work out well. Had we gone up to 30t pulleys we most likely wouldn't have broken a single belt, but if you have a baseplate mounted under 2x1, like in most WCD's, you actually cannot fit a 30t pulley without pocketing the baseplate, or spacing it out. And inside a standard WCD its harder to fit 15mm belts.
So if you make sure to put the right size belts in, they can be a great system. But I would not use 9mm belts with 24t pulleys. You will most likely have a bad time if you do.
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All statements made are my own and not the feelings of any of my affiliated teams.
Teams 1510 and 2898 - Student 2010-2012
Team 4488 - Mentor 2013-2016
Co-developer of
RobotDotNet, a .NET port of the WPILib.