Belt vs. Chain

[Chris is me]

Belts have benefits and drawbacks. Like most engineering decisions, there isn't one definitively better option.

Kevlar backed timing belts have some pretty neat advantages. Belts never stretch - once you get the tension right you never, ever need to adjust them, ever. "Set it and forget it". If you precision machine to exact center distances, you may not need a tensioner at all, which is really cool. Belts are also fabulously light.

What you gain in ease of maintenance you lose in versatility. You need to design your robot around the belts. Unlike chain, you actually have to plan the belts out and make sure they are of proper length and tension. Belts are more sensitive to being undertensioned than chain is, so you really do have to get it right. Also, belt pulley stock may be hard to come by.

Chain is great because it's flexible and customizable. It can be any length, just break and relink. Everyone has chain handy, and sprockets are easy to come by and not too hard to make. The main drawbacks are that 25 chain in particular needs attention to tension and alignment, and 35 chain is pretty heavy.

I would say that if you typically CAD your full drivetrain before you build it, belts can be a good solution. If you put that much planning into the drivetrain already, belts are not going to be a hassle. If you'd prefer a simpler, less worrisome drivetrain, use chain. It's important not to reach beyond your abilities in FIRST.

We used belts on our drivetrain and chain for our arm. We put a lot of planning into our drivetrain, but our arm was much more of a "build it and go" job, so we didn't want to take chances there.