Chain vs. Belts?!?

Hey everyone. I’m from team 240 T.E.M.P.E.S.T.

The past 2 years we have used chain everywhere. There was one thing that happened, we had to fix the chain a lot more than we liked too. I know this could be due to poor alignment, etc. but next year we plan on using belts.

What are your thoughts on Chains? Belts?

Thanks, Drew

This is a topic that is discussed quite often.

There is a good white paper written by team 234 which evaluates the power transmission methods:

https://www.chiefdelphi.com/media/papers/2216

Thank you! I’ll check it out

Its worth mentioning that if the issue was alignment whether you are using chains, belts or interlocking plastic monkeys the issue wont be solved.

If you are using #25 chain and there are alignment issues switching to #35 could help but really the best thing to do is fix the alignment.

If your issue has to do with master links I would buy a dark soul chain remover.

iirc belts actually are more sensitive to being out of alignment so switching to belts is only going to make things worse.

After seeing what 5172 did with poly cord this year, im excited to use it more in the future. Belts don’t stretch which is nice, but you have to design around belt size more so than you do with chain. Personally I’m sick of chain, but that’s because it cost me a ton of time during Ri3D. It’s more difficult to align a chain than it is a belt in my experience.

You can’t go wrong either way if you do it correctly. I would suggest looking into poly cord belts as an option.

For the uninformed, what did 5172 do with polycord?

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/gates/industrial/power-transmission/manuals/light-power-and-precision-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.

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They used it everywhere! Most of the mechanisms on their robot were powered by polycord. It was cool to look at, and obviously functional.

A quick skim of the 20 pages of search results for chain vs belt gave me these:

https://www.chiefdelphi.com/forums/showthread.php?t=144963&highlight=Chain+vs+belt

https://www.chiefdelphi.com/forums/showthread.php?t=142390&highlight=Chain+vs+belt

https://www.chiefdelphi.com/forums/showthread.php?t=138335&highlight=Chain+vs+belt

My FTC team is looking at it as complete replacement for gears and chain.

I wouldn’t trust it in high torque situations such as drivetrains, as I haven’t worked with it yet. If anybody can speak to polycord’s power transfer ability before slipping that’d be awesome. I can’t wait to test the stuff in many different applications.

It could just come down to what your team already has or is familiar with. CD has no consensus on whether belts or chains are better. So, I just use chains because that’s what the team already has.

Whatever you choose, make sure you have good alignment. We had a regional last year where we broke about nine belts because of poor/weird alignment. We also had to disassemble the third stage of our gearboxes for at least six of those belts, so we basically got so sick of replacing belts that we went with #25 chain this year. But again, alignment.

Also, be sure you can tension your chain because it will stretch.

I like belts for everything other than drivetrain. Why drivetrain? Because for a given strength, chain is more compact than belts, and with the 4-cim loads in the drivetrain compactness is a high priority for me. That’s a point that’s often overlooked in the belts vs. chain debate.
It’s also possible to run chain in tube in a 2x1 easily and reliably, whereas doing the same with belt is a lot harder.
Belts run quieter than chains, so for anything else- from shooters to intake to arms- I prefer them. In the specific case of arms, the belt will likely slip before the gears start shearing teeth (in theory), so I get a bit of a safety factor there.

We tried using it this year for driving our intake. Our intake was designed to pinch the ball between the wheels and a churro and we could not spin the ball out. The polycord would just slip. We were attempting to use it more like a traditional belt, which was probably our mistake, and only had 2 cords. However, in 2015 we used it for a conveyor belt and it worked fine. I think the main dlfference is we had a lot more cords (4 or 5) and it was a lower torque application.

QFT.

If alignment or tolerance is what is causing you problems now, switching to belts will make the situation much worse.

We successfully used a Polycord drive system in the past. One of the center wheels was direct driven by a custom super shifter based gearbox. The other wheels are all direct driven by Polycord using custom pulleys directly attached to the wheels (Dead Axles). This is the best picture I could find of the drive train. (This is one of our signature Round Robots)







Out of curiosity, what year was it? Also, did you have any problems with the polycord slipping in shoving matches or other high-torque situations?

There’s no single correct answer (despite what some CDers would say) of what you should use. It all depends on your situation. If you need the weight, you may need to go with belt. If it’s going to be a giant PITA to change a belt, you may need to go with a chain.

In my opinion, the “default” choice, when nothing really matters, you just need a reliable drivetrain, is to go with #35. It doesn’t break, it’s dead simple, it’s forgiving, but is heavy. However, the “nothing really matters” portion is rarely the case and each situation needs to be handled on a case-by-case basis. What is important is knowing the tradeoffs (which have been outlined pretty well already in this thread). I wouldn’t, however, deviate from the “default” of #35 chain without a good reason. The good reason may be weight related or space related, but you should at least have one.

Agreed. My team has learned the hard way to just use #35. The way I like to think about it is that #35 is complete overkill for FRC, which is why its the best option for FRC. Since it is overkill, it is a lot harder to mess up and will just work, which is exactly what you want for a drive train. The question you should be asking whenever you use chain should be why should I use #25, not why should I use #35.