Belts vs. Chains

[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).

[Brandon Holley]

Originally Posted by EricH

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).

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..

[JesseK]

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.

[MrForbes]

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.

[lukevanoort]

Originally Posted by squirrel

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.

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)

[MrForbes]

Originally Posted by lukevanoort

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)

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

[Capt. Quirk]

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.

[cobrawanabe1699]

Originally Posted by squirrel

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

#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.

[Dick Linn]

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.

[EricH]

Originally Posted by JesseK

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.

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

[AndyH]

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!