It is important to consider the advantages of both based on specific applications.
Pros of Chain:
- Sprockets can be more compact (Slimmer than pulleys.)
- Chain can be broken to allow for easy servicing.
- Chain, #35 in particular, can support higher load than belts.
- Sprockets can be found in COTS solutions in more sizes than belts.
Cons of Chain:
- Chain, particularly #35 chain, can be heavier than belts.
- Chain can stretch over time (Chain should be fine for at least 2 regionals if properly tensioner or set for an exact c-c distance).
- Chain comes in links, it can be a PAIN to deal with chain if you don't use a whole number of links.
- Chain probably shouldn't be run at higher rpms. I've seen a team explode #25 chain by running it at 5K RPM.
Pros of Belts:
- Belts come in many sizes. (You may need to buy from sources other than VEX or AndyMark, however.
- Belts can be much lighter than chain if used in applications within their load range. (Provided you use larger pulleys, you should be able to push their load rating in FRC applications.)
- Belts are much quieter than chain.
- Belts do not stretch as much as chains when properly loaded.
- A broken belt will not shatter (from what I've seen at least!). Flying belt material is safer than flying steel or aluminum.
Cons of Belts:
- Belts require pulleys than can be much wider than sprockets.
- Belts are more likely to stretch or break if misaligned or if their C-C distance is inaccurate. (Belts in Drivetrains and many other FRC applications are already being pushed beyond what they're rated for; you will see catastrophic results much easier than chain that isn't being pushed well beyond what it is loaded for.)
- Belts require a higher accuracy to properly use in comparison to chains. (I've been told ~.003in is optimal).
This document is really helpful for finding information on belts:
https://www.gates.com/~/media/files/...ion-manual.pdf
If you want additional information, post here or look for Travis or Austin Schuh. I learned most of this information by reading posts from those two and they are very experienced with using both belts and chains on their robots.