Drive Train Design - Weight & Belts

[Jared]

Originally Posted by Oblarg

To provide some counterpoint:

I have seen a grant total of one belt failure in my 7 years in FRC (out of 4 years of belt drives), on a belt that was overtensioned, at an offseason event after several competitions. Both 4464 and 449 ran belt-driven 6 CIM drives last year without incident (modified KOP on 4464, 9mm belts on 36-tooth pulleys in a WCD on 449).

I have seen more chain failures than I can count, mostly due to master links or slightly out-of-alignment sprockets.

Thus, I can't honestly say that I wholly buy the robustness argument for chain over belt. As far as failure rates go, my observations are precisely the opposite. Belt is far more forgiving in terms of alignment slop between the pulleys, and if you don't have the machining capabilities to have exact C-C distance you can do fine by having one end of the belt run be adjustable (versablocks are a great way to do this). The lack of stretch means that you need less adjustability than a comparable length of chain, as well.

The only downside I've ever noticed for belts is that they demand that you pick a length and stick with it, so there's little potential for last-minute design changes (unless you purchase a new belt). In a drive, this isn't so much of a problem - frame dimensions are usually decided on very early and seldom changed.

I don't disagree with anything that you're saying, but I think chain is still an okay choice for drive. Remember, most of the belt drive robots you see are kitbots that are easy to build correctly, and all chain robots you see are custom drives, which are much easier to mess up.

It's possible to be successful with #25, #35, 9mm, and 15mm belts with a 6 CIM drive. Team likes 118 and 254 have been running #25 chain drives for years, and they don't have chain failures.

That said, you do need to be accurate when you're using the chain (especially #25). With all the off the shelf solutions, getting a reliable chain drive shouldn't be impossible.

Also, do you have any data to prove that a 6 CIM drive is out of specification for the #25 chain?