Quote:
Originally Posted by Chris is me
If you have the manufacturing capability, there is no reason not to use exact centers for belt drivetrains. Absolutely none. It's effective, idiot proof, and reliable. It's not that hard to under tension or over tension a belt, which leads to reduced belt life. I just don't understand how people can prefer tensioners for a system whose tension never needs to be adjusted (in the context of an FRC robot life span).
15mm is far safer than 9mm for a drivetrain. We had poor experiences with 9mm belts and 18T pulleys our first year using the system. Since we've gone to 15mm the problems have gone away for our particular wheel size and pulley tooth counts. This year we used 15mm belts and 24T pulley stock with zero problems.
The bigger the pulley tooth count, the more you can get away with using a 9mm belt in the drive. I'm not entirely convinced yet that 9mm 24T belt drives are a reliable way to do a "West Coast" style drive. Bigger tooth counts should be fine. Any discussion of the strength and validity of belts *must* include the pulley tooth count or else the anecdote isn't useful.
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I believe one benefit of tensioners is that, because of manufacturing tolerances in the belts, exact centers won't always provide the same tension. For this reason, if you're using 9mm belt I think you should have tensioners to dial in the exact tension you need without relying on perfectly accurate belt lengths
That said, we use fixed centers but add a bit to the distance depending on how the belts fit. We've been very successful the past two years using 15mm wide belt on 22t pulleys inside our DT tubes driving 3.5in wheels. We have 1/2in hex in the pulleys in the tube, 1/2 in round bearings, and 7/16 hex in the wheels. It's a set up I hope stays around for a while.