Belts vs. Chains
 

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?

Re: Belts vs. Chains
 

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.

Re: Belts vs. Chains
 

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

Re: Belts vs. Chains
 

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.

Re: Belts vs. Chains
 

Belts:

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

Chain:

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

Re: Belts vs. Chains
 

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?

Re: Belts vs. Chains
 

#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.

Re: Belts vs. Chains
 

It might be nice if this were a poll.

Re: Belts vs. Chains
 

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.

Re: Belts vs. Chains
 

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. :cool:

Re: Belts vs. Chains
 

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

Re: Belts vs. Chains
 

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).

Re: Belts vs. Chains
 

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.

Re: Belts vs. Chains
 

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.

Re: Belts vs. Chains
 

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).

Re: Belts vs. Chains
 

I was just throwing the counter to "#25 chain breaks" out there because in my use, it doesnt.

Yes run the numbers on your own, make sure it works, then pick the lightest and easiest..

Re: Belts vs. Chains
 

Belts rely on alot of friction to transfer power from pulley to pulley. By design, they're less efficient (albeit only slightly) than chain/sprocket setups.

The reason chains break is due to lack of tension. Chains in general are most vulnerable to a break during a sudden change in direction (e.g. full power forward to full power backwards, or from dead stop to full forward). The slack in the chain creates a huge change in force that is spread (use integral physics to exactly calculate) almost equally among the links when the slack becomes taut.

If the chain were already in tension, the change in force is almost negligible, but due to the slack before the change in direction, it is MUCH greater. The weakest link will then break -- usually it's the master link, which is why you only ever want 1 master link per chain run.

If you never change directions usually you're ok if there's not too much slack, but that is never the case in a FIRST robot -- you WILL be bumped, you WILL change directions & speeds. Bicycles on the other hand, do not receive such change in force, therefore by design bicycles can use #25 chain and undergo the same torques as a FIRST bot but the chain will never break.

Tension is your friend. You also want to pre-stretch the chain during practice so that it doesn't stretch during a match. This can be done by tensioning the chain very well, then running a battery down by running the drive train and making it change directions alot. This will prevent the chain from stretching during a match and inadvertently giving you some undesired slack.

Re: Belts vs. Chains
 

Thanks for information! Sounds good....

Also when we say that a chain "stretches", does that mean it is wearing in? or is the metal really stretching? I would think that new chain will wear down the high spots at each link rather quickly, then as there is now greater surface area, the wear will slow down.

Re: Belts vs. Chains
 

You can get toothed belts and pulleys for those, like what came in the kit. That can help a little.

Re: Belts vs. Chains
 

I think it is actually stretching. I have no solid evidence to back up my opinion, but I did watch as my team's arm prototype's #35 chain went from really tight to so loose that it was barely touching the teeth of the lower sprocket in under half a second. (There was a lot of force on that chain though)

Re: Belts vs. Chains
 

CHAINS ARE BETTER THAN BELTS. The belts will tend to slip, while chains stay put. Also, a new link can fix a broken chain in 5 to 10 minutes.

Re: Belts vs. Chains
 

I have broken #25 chain before, use #35 chain coming from the trans to the drive wheels. OR we use 25# chain to connect our wheels in the 6X6 config.
personaly i like 35# better becuase it doesnt strech like 25# does.

Re: Belts vs. Chains
 

we use #35 chain for whatever we do. ive only ever see one team break 35 chain, but that was only because they took a fish from the master link on and off one too many times. (it bent and they lost the master link) #35 chain is awesome cuz it can handle so much. our 2006 robot used 35 and we bent our frame, causing the chain to misalign, rub the wheel, rub the frame, and we were still able to out push any one and every one that chose to take us on. #35 can handle the abuse. i dont think a belt woulda survived.

35 is cheap insurance.

Re: Belts vs. Chains
 

I agree that the chain gets longer when you first use it, then it kind of settles in and stays the same length for a while.

I was just saying that I think this is caused by initial wear, not by the metal exceeding it's yield strength.

Kind of nit-picky of me

Re: Belts vs. Chains
 

Chains will stretch and they won't stretch evenly. The more abuse a chain takes, the more likely it will develop tight and loose spots.

Chains main weakness is their master link. Installing the clip, so the open end of the clip is facing the direction of rotation, is a quick way to eject a master link clip as soon as it rubs against some part of the bot.

Improper installation of the clip leads to bending the clip and again increases the chance of loosing the clip.

Chain alignment is important

Chassis flex will also eject a chain.

A tight chain robs the motors of power and will require more power to spin the drive train.


If you use a chain, buy a pair of Snap-On "Duck-Bill" Pliers (basically a wide, flat version of a needle nose pliers) to install and remove your master clip. Replace your master clip often (if you are removing the clip often), Be sure your chain is aligned perfectly. Be sure there is about 3/8" to 5/8" of up & down play in the Chain (get in the habit of checking your chain after each use). Minimize frame flex. Make sure the chain can't rub on any parts.

Always install the open end of the clip facing the opposite direction of rotation and safety wire the master clip to the chain.

Re: Belts vs. Chains
 

#35 chain will stretch about 1/8" for every 4 feet. I MTB, so I have ALOT of experience with this stuff. #35 will stand up to just about anything. Ive slammed it on rocks, trees, roots, etc and never had it break. Also, the torque exerted on it during a rough ride is astounding. I've never broken #35

Chain stretch usually slows down the more it is stretched. After that 1/8", the chain will settle in and stay put for the next 10 years if you want it to. As long as you don't abuse a #35 chain, it will work perfectly for you.

Re: Belts vs. Chains
 

Here is some technical information about chain. Think in terms of initial "elongation", not "stretch".

http://www.diamondchain.com/support/.../wear_life.php

and from their FAQs: 12. Roller Chain Stretch (Elongation)

Why is my chain "stretching", elongating, too quickly?

ANSWER: Proper lubrication is critical in achieving the maximum wear life of any roller chain. As the chain articulates around the sprockets, the pin and bushing wear. This wearing causes the elongation, or "stretch", in the chain. Lubrication of these surfaces through proper lube application or the utilization of Diamond Duralube or Ringleader O-ring chains can greatly increase the wear life of the chain.


I've found that a decent quality chain has less initial elongation than the no-name-brand stuff sold for cheap go-karts.

Re: Belts vs. Chains
 

cables

Re: Belts vs. Chains
 

1323 has gone with a chain drive #25. The reason for that is if you use a tensioner from mcmastercarr, the chain will never pop off. The belts are good everywhere else besides the drivetrain. We using belts to power our wheels on the hand

Re: Belts vs. Chains
 

last year 612 went 20 matches or so through regionals and championships with belts and pulleys and all we had to do was check that they were tight - no maintenance

Re: Belts vs. Chains
 

Team 612 has originally been using chains, but after many problems in 2005 including tensioning problems, chain slippage, and chains breaking we switched to belts and pulleys in 2006.

Simply the greatest decision we have ever made.

Our kevlar belts are stronger, lighter, quieter, more robust, and less prone to slipping and snapping. Once we used ours last year we didn't have a single problem through 2 regionals, championship, and tons of offseason practice. The only problem was our wheels being to weak:rolleyes: . We have changed that this year with a more robust wheel design. The only big change we have made was the belt teeth shape, we went from rectangles to trapezoids to handle the 4 cims we are putting on them.

You guys trust the belts in your car right?

Re: Belts vs. Chains
 

there are lots of factors that are common for both chain and belt:
stretch, slippage, tension, surface area on the pulley/sprocket, weight, maintenance, and load capacity.
Gates has a good informative page(albeit a bit biased i think;) ) on the pros and cons of belt and chain drive systems.
it seems that chain is a more forgiving design wise, allowing for some mistakes in tensioning and load distribution.

Re: Belts vs. Chains
 

I believe that it depends on the drive deisgn. Just have to keep the specs in mind when choosing the application. We used #25 on our racerbot. (see topics, St Louis Regional & 1098 Ferrari) We had great sucess with it on the drive, 6:1 single stage reduction from 2 CIM motors per wheel. Only threw chain when we took a direct hit on the wheel at speed. We kept going as we were running 4 CIM motors, and ackerman steering. We could get 20.7 fps on th field.

Had a great time at St Louis Regional and congrats to the champs!

Re: Belts vs. Chains
 

not for high-speed applications though.

in the early 1900s all the big machinery used cables.