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Originally Posted by magnets
I disagree with all three of your claims.
1. You can run chain considerably looser than exact C-C (because of alignment slop), and it will work, though it will be noisy/sloppy. It will continue to transmit torque until it is loose enough for the chain to slide off of a tooth, which requires the chain to be quite loose. Belts will slip if there is slop or if the center to center is to small, and snap if they are too tight. Chain is much more tolerant of C-C misalignment.
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I have never, ever, ever seen a HTD belt come off of a sprocket, no matter how hastily or imprecisely-assembled. I've used quite a few HTD belts. I've seen sprockets buck chain regularly for my entire experience in FRC. So I think we'll just have to disagree here.
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2. I don't understand this comment. Belts require an integer number of grooves/teeth, and chain does too. I don't see how this can be an advantage of either.
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You're correct here, I meant to edit that out of my post but you responded first.
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3. Belts stretch, but admittedly, less than chains.
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Not by any appreciable amount in any drive I've worked with.
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I have been in charge of drive chain on the past 6 robots I've been involved with. We have never had a single issue. We've never broken a chain, as they're rated for considerably larger loads than belts, we never thrown a chain on a competition robot, as we always cover them and ensure sprockets are aligned, and we've never had any other failures. We haven't always had access to great machining resources, and we've never had a problem.
I have been in charge of one belt drive, so I realize my experience with them is limited, but they're thicker, they slip, and we had a belt snap. So we're going back to chains.
On the original topic, I find that putting in a floating idler sprocket, like this (http://www.team228.org/gallery/106/s...998-37b1e.jpg), is the way to go for chain. If you want it tighter, move it closer to the smaller sprocket, and if you want it looser, move it away. It's easy, cheap, light and adjustable.
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It seems we've had different experiences. It'd be nice to know what we've been doing differently, since I've never ratcheted a belt nor have had one snap in competition, but have thrown plenty of chains (due to misalignment, bad masterlinks, and other causes).