Belt vs. Chain

[Jon Stratis]

The difference in belts versus chains, as others have mentioned here and as our team has experienced, is really one of time. Using belts typically takes more time, as you need to work our more precise distances, figure out precise lengths of belt to order, etc. Chain is quick and easy - you can get a kitbot assembled in a day with a chain drive. For a belt drive, unless you have the exact length of belt on hand, it'll take longer (lead time on ordering new belts).

We've always used chain on our drive system. It's quick, easy, and reliable (we've never had much of a problem with it). We've used belts in some other places as well - most notably in our claw/roller assembly this year and in our shooting turret for Lunacy. In both cases, we had to obtain belts of the appropriate length, and build in tension adjustment (this year, mounting the Banebots motors in slots for adjustment, for Lunacy we mounted CIM motors on rotatable armatures). Both of those tension adjustments were set and forget... but they needed to be planned out ahead of time. Contrast that with our drive system this year, where we through it together and added tensioners after the fact.

As we've told our team countless times... there are a multitude of ways to solve any one problem, and many of those ways are going to provide equivalent results.Chain versus belts is one of those comparisons... they'll both give you the same results, it's really a decision on what you would rather do, and where you want to spend your time.

[Akash Rastogi]

Originally Posted by Andrew Schreiber

Use what you know and don't fix what ain't broken.

OR try some set ups out in the offseason!

[lemiant]

Originally Posted by Ether

You didn't ask if re-engineering their process to use belts would be an insurmountable task for a powerhouse team like 1114.

It's not a question of being scared. Experienced successful teams generally allocate their limited resources to tasks that have the greatest benefit/cost ratio.

I would just think that with a 10% performance gain, some of the big teams would have put in the time to work it out.

[Andrew Schreiber]

Originally Posted by Akash Rastogi

OR try some set ups out in the offseason!

More important things to prototype than a system that can only be marginally improved.

[Ether]

Originally Posted by lemiant

I would just think that with a 10% performance gain, some of the big teams would have put in the time to work it out.

You have to ask yourself the question, "10% of what?".

When you're talking about teams like 1114, they probably already have a drivetrain that more than meets their needs.

If the day ever comes that they believe they could gain a competitive advantage by allocating resources to re-engineer their drivetrain, I'm sure they will consider doing that.

[AdamHeard]

We've considered belts in out drivetrain, but have always turned them down for a few reasons.

Currently, we almost exclusively use chain; we know chain, we have lots of sprockets, no pre-planning required to chain something up. With belts, we now have an entirely separate set of parts that need to be identified, purchases etc...

The disassembly is a huge disadvantage too. We've never lost a chain on our drive, but if need be we could replace one in under a minute. Switching to belts requires a redesign of our gearboxes, or partial disassembly of a gearbox to install a spare.

[Akash Rastogi]

Originally Posted by Andrew Schreiber

More important things to prototype than a system that can only be marginally improved.

Depends on what your team is trying to accomplish. Designing and prototyping something new to you is better than just accepting the fact that you're only going to build within the constraints of what you already know. Never said you have to use it during season. Your offseason design can help you decide if a change is the right thing for your team to do based on your own results as well as feedback from others with experience with something like belts vs. chain.

[artdutra04]

Originally Posted by lemiant

Ok, so I read 234s paper, and it pretty unequivocally states that belts are better. How come everyone still uses chain?

• We already have a lot of roller chain and sprockets.
• Belts are application specific, you design for an exact length belt. On the other hand chain can be taken off, and shrunk or lengthened for use on future robots.
• 25p roller chain (and its sprockets) are narrower than equivalent timing belt; this is one of the main reasons why we stick with 25p roller chain in the drive train.

Rarely is there ever a truly universal "better" in engineering.

[Karthik]

Originally Posted by Ether

The reasons were right there in the paper:

• Belt requires a more integrated design and precise manufacturing
• Wheels and belt must be assembled concurrently, unlike chain
• Belt requires more physical space because of the width differences for varying load capacities
• Chain drive is a known, proven system for transfer of power from the drive motors / transmissions to the drive wheels and between the wheels

Originally Posted by lemiant

I doubt 1 & 2 would be insurmountable for a team like 1114 (who I happen to know uses #25 chain), or 228. I'm not sure about #3, how much extra space are we talking here.

We've often talked about moving from chain to belts for our drivetrain. Most of our reasons for not making the switch have already been mentioned, but there's one big one missing, which is very specific to FRC. The lead time on the exact belts and sprockets we would want, imported into Canada, is about 2 weeks. We used belts on our elevator and roller claw this year, and acquiring the belts was the largest bottleneck. There's no way we'd sacrifice that much programming, practice and systems integration time on our drivetrain, for the marginal benefit that belts provide. Now, if we could find a way to reduce these lead times, belts would become a very attractive option.

Originally Posted by lemiant

And #4 has never scared a powerhouse out of doing anything.

Hardly. Number four keeps us from doing things all the time. We'll always take a solution that we know works 100% of the time over a solution where we have less confidence. Reliability is one of the keys to a successful FIRST season. We will not give it up for a new solution until we've proven the new solution is just as reliable as the established one.

As our founding mentor Stephen Rourke used to say, "The most effective solution is the simplest one that works".

[AdamHeard]

Originally Posted by sdcantrell56

In the past I have used th sdp-si calculator to find the exact distance and it seems to work very well. Aren says they did the same thing for there drive and it worked perfectly as well. Our drive this year used tensioners but next year we will be going to a tensionerless exact spacing set-up.

Did you use their number as is, or did you add/subtract a small amount?

[Chris is me]

Originally Posted by AdamHeard

Did you use their number as is, or did you add/subtract a small amount?

As-is works well. Adding some dead space is a bit risky with the belt and pulley tolerances.

[sdcantrell56]

Originally Posted by AdamHeard

Did you use their number as is, or did you add/subtract a small amount?

We did as-is.

[Chas_G]

Gates has scholarships offered to students whose teams use belts also!

We however use chain for all of our energy transfer solutions.

[emekablue]

What about belts being used not for the drive, but for the arm. We have had quite the problem with tensioning our arm's chain (other tensioners are too large, and we have about an inch of slack), I think because we are over-torquing the motor. Will putting in belts help solve this problem? Or will a simple change in gear ratio do the trick?

[lemiant]

Originally Posted by emekablue

What about belts being used not for the drive, but for the arm. We have had quite the problem with tensioning our arm's chain (other tensioners are too large, and we have about an inch of slack), I think because we are over-torquing the motor. Will putting in belts help solve this problem? Or will a simple change in gear ratio do the trick?

Correct me if I missed something, but couldn't you just remove the extra links?