Belts vs. Chains

[Mikhail_Pham]

We're from a rookie team in Irvine (TUSD) California, and while working, we came across the issue of whether to attach a chain or a belt to the sprocket. We figured the belt was lighter and more efficient, but, looking around, a lot of teams seem to prefer chain.

Why? I understand that older teams may like the dependability and long lasting quality of a good metal chain, but other than that, why?

[Elgin Clock]

Chains (if & when) they break, are easier to fix than belts in most cases.

Here's my logic behind that from using chains for a number of years now.
If you break a chain, just add some more pieces to it very simply.

In a belt system, you (more than likely) need to access the entire run of it, and replace the full belt.

I don't know why other than that, but I just know they are easier to replace than a full belt when dealing in confined spaces of the footprint we personally (as a team) use to run our chain.

Don't get me wrong, a break in the system is still a pain in the butt to fix no matter if it's made out of chain or anything else for that matter, but it's easier to get to one part of it than to get to the entire running path most times (in our designs anyways).
Your results may vary.

/my 2 cents.

[Alex_Miller]

Belts can also slip. We learned that the hard way when trying to left two robots. A chain hopefully wont slip as easily.

[ALIBI]

We have been using timing belts from McMaster-Carr in our drivetrain for years and have never had a failure, check the specs., they keep getting stronger and stronger ratings. We have used slots for tensioning (transmission/CIMS slide back and fourth). Belts do require more work to replace, we just have never had to. We have a four wheel drive 06' (kit tranny w/ two cims each driving 8' wheels) with four belts that are still original with no sign of wear. On short runs I would recommend timing belts, longer runs are probably better served by chains.

[Justin M.]

Belts:

Quiet, Light, Smoother, more flexible
Weaker, can slip, crack, break, strip

Chain:

Strong, robust, more efficient
Heavy, abrasive, can pop off, stretch

[Richard McClellan]

Has anyone actually broken a chain on a drive system before? I've never heard of something like this and would think it'd be very difficult to do on a FIRST robot, even if you're only using #25 chain.

Is there anything special to watch out for or particular situations to avoid when designing a chain system to prevent the chain from breaking? What kind of situation in a match would cause this?

[henryBsick]

#25 can break
I am not sure of other team's frequency with such an event, but I have seen in personally twice.
That is over 5 robots and lots of chain chain though.

[Courtneyb1023]

It might be nice if this were a poll.

[MrForbes]

Think about the load on the chain when the robot is pushing and the weight is mostly all on the rear wheels....about 70 lbs per wheel, times the wheel to sprocket diameter ratio, is pulling on each chain. Design working load for #25 chain is generally a bit over 100 lbs, so it is possible that the chain can break.

[Elgin Clock]

Originally Posted by richardmcc2

Has anyone actually broken a chain on a drive system before? I've never heard of something like this and would think it'd be very difficult to do on a FIRST robot, even if you're only using #25 chain.

Is there anything special to watch out for or particular situations to avoid when designing a chain system to prevent the chain from breaking? What kind of situation in a match would cause this?

Yep... It happens when you replace a screw very quickly between matches in the path of your chain with a head that is too big (re: socket head cap screw as opposed to a nice button head, or better yet, a countersunk screw).

Those protruding heads tend to put stress on not only the chain itself, but the retaining clips and "break" your chain when it is very much unwanted... (re: in the middle of a match. )

Leasson learned: Use countersunk screws in the path of a chain, and have plenty of extra's around in case you need more.

[Chris Fultz]

Originally Posted by richardmcc2

Has anyone actually broken a chain on a drive system before? I've never heard of something like this and would think it'd be very difficult to do on a FIRST robot, even if you're only using #25 chain.

YES, #25 can break and will, especially on a drive train. We have an absolute rule that no #25 on the drive.

We do use it in some other lower stress / lower power areas.

There is a good write up of chain vs. belt on the gates website -
http://www.gates.com

[EricH]

Originally Posted by Chris Fultz

YES, #25 can break and will, especially on a drive train. We have an absolute rule that no #25 on the drive.

We do use it in some other lower stress / lower power areas.

Same here. In 2001, we had #25 in the drive. During 2003, when it was our practice robot, we spent more time replacing chain than we did driving.

We used some in our shooter in 2006 (intermediate pulley system to the shooter wheel). The rest of the power transmission there was a belt, and we never had a problem. Actually, most of our shooter/loader was belting, either for transport (timing belt driven by an FP) or for shooting (Big CIM to intermediate axle, where we put chain the rest of the way).

[Brandon Holley]

Originally Posted by EricH

Same here. In 2001, we had #25 in the drive. During 2003, when it was our practice robot, we spent more time replacing chain than we did driving.

We used some in our shooter in 2006 (intermediate pulley system to the shooter wheel). The rest of the power transmission there was a belt, and we never had a problem. Actually, most of our shooter/loader was belting, either for transport (timing belt driven by an FP) or for shooting (Big CIM to intermediate axle, where we put chain the rest of the way).

Originally Posted by Chris Fultz

YES, #25 can break and will, especially on a drive train. We have an absolute rule that no #25 on the drive.

We do use it in some other lower stress / lower power areas.

There is a good write up of chain vs. belt on the gates website -
http://www.gates.com

On the contrary to the above posts...

I have personally used #25 chain on 3 robots. 1 of which did ALL of the gear reduction through chain and sprocket (yep thats right 12 chains per side) and I have never had a chain break.

A lot of people tend to think that #25 chain is weak and will not work. Our team looked extensively at the numbers of #25 vs #35. The result was us using #25 chain on our robot (and not a chain broke).

Tension. Tension. Tension. Keeping those chains tight is the miracle cure of chain breakage.

[aztech75]

Before we started to use belts, we were breaking chains left and right. In the four seasons that we used belts we broke one at battlecry and thats it. If you get the belts with teeth, and pulleys that are designed to fit those specific belts, than they will never slip.

[EricH]

Originally Posted by Brandon Holley

Tension. Tension. Tension. Keeping those chains tight is the miracle cure of chain breakage.

The last time we used #25 was on our shooter in 2006. It was pretty tight; we did use a belt for most of the motor-wheel connection and chain was only on the last six inches or so.

I would say run the numbers and go with the easiest and lightest solution that will work (in that order, probably, except work comes first).