Belt vs. Chain

Any thoughts on belts vs. chain for powering wheels in drivesystems?

What about for articulation systems?

Well belts are lighter and in my experience they don’t stretch much if at all. However they require some pretty good tension in order to run nicely. If a belt snaps it is pretty tricky to change out.
Chain is pretty heavy but you van easily adjust its length and if it were to snap it is easy to replace it.

We have always used chain on our drive-trains (sometimes 35 sometimes 25) and we have had really good luck with it. We have used belts on things like arms and grippers and I have personally liked it a lot. You can have long belt runs without worrying about weight too much. Belts also just seem to lead to a smoother motion of an arm to me.

~DK

My only experience with belts was when we used them to power the steering for our swerve drive last year. We had so many issues with the belts slipping that we eventually replaced them with chain. My team uses chain rather exclusively for the ease of adjustment and the ability to prevent slippage. I’m sure belts have an advantage in certain areas, but we’ve gone through many years with chain alone and had success.

we use belts for anything that exceeds the maximum RPM on #25 chain.

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.

One other thing to watch out for: Chassis flex. 1293 attempted to use belts on their kit-framed entry, Stephen Colbot. They discovered the tower for their arm caused the chassis to flex just enough that the belts started slipping off the gearbox. As I recall, they fixed this by using standard #35 chain from the gearbox to the near wheels, then retaining the belt drive from the center to the fronts.

Belts require you to do your homework ahead of time, but definitely have some advantages over roller chain. We typically use belts in various mechanisms on our robots; this year we used 5mm HTD pitch belts in our roller claw.

http://www.team228.org/gallery/142/slideshow/build-season-week-six_5032f-5e2fd.jpg](http://www.team228.org/media/pictures/view/6885)

These belts only appear loose as the other side plate for our roller claw has been removed for the photo; with the second side plate installed we never had any problems (nor any need for a tensioner) with the belts. The smaller sprockets were machined from aluminum timing belt stock, and the larger ones are hybrid aluminum hub/polycarbonate body sprockets; both of these we purchased from SDP/SI. The belts are from Gates.

What is your method for designing the exact C-C?

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.

My alma mater team did an analysis of the difference between using belts and chain back in '08. Here is the link:

http://cyberblue234.com/site/wp-content/uploads/2011/01/2009-234_Belt_vs_Chain_CHP_Forum1.pdf

That being said, we used belting for our drive system at one regional. We accidentally got some WD-40 on them, and they were shredded the first time heavy defense occurred. Otherwise, they worked great.

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

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

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

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

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

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.

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

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.

OR try some set ups out in the offseason!

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.

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

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.

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