Chain vs. Belts?!?

[asid61]

Originally Posted by Knufire

The pulleys that VEX and AM sell are 5mm pitch HTD, so that's what most FRC teams use. Usually 9mm or 15mm wide. You can also run GT2 tooth profile belts on HTD pulleys.

If you use a GT2 profile with HTD pulleys, it's not supposed to add any benefit, so generally speaking it's better to just stick with HTD for availability purposes.
The lower limit (and it's a sketchy one) for 5mm pitch 9mm wide HTD belt pulleys is 24t apparently for a typical year (read: not this year). I believe that 36t is safer than using 24t, especially if it's your first time. If you use 15mm wide belts I'm not sure, but 24t is supposed to be safe with those.
You would be better served asking "Chris is me" because I'm just parroting what he says at this point. A quick search on google should turn up some relevant threads about belt sizes.

[GeeTwo]

Originally Posted by DrewMatic

But back to the belts... What sizes would you recommend. I know 100% that the sizes may vary between years and robots.

We ran belt our second year (2013 Ultimate Ascent) for the lighter-duty portion of our climber, and for our frisbee feeder (or more precisely, frisbee arrestor), and in our fourth year (2015 Recycle Rush) for the drive system exactly according to the AM-14U2 plans. IIRC, all were stock 15 tpi belt.

Obviously an edit:

Originally Posted by troy_dietz

I think you may have your games mixed up a bit.

Yes, RR is RR is RR. I also fixed this above...

[troy_dietz]

Originally Posted by GeeTwo

...(2015 Rebound Rumble)...

I think you may have your games mixed up a bit.

[Cothron Theiss]

Originally Posted by DrewMatic

But back to the belts... What sizes would you recommend. I know 100% that the sizes may vary between years and robots. But I'm not sure on the standard belt sizes due to the inexperience with the topic.

Others who have run custom drivetrains with belt would be able to tell you better, but the numbers Sam posted are great to start with. Though if you need to run smaller sprockets than what is recommended, you can always incorporate idler sprockets/bearings into your belt run to increase the amount of wrap you have on your pulleys. This adds weight and complexity, but it is an option.

[lark95]

Sorry it took a bit longer than expected to get the pics but here they are. This is the chain break that we made to break #35 chain so that we could get away from using master links. The chain is aligned in the line of of holes on the bottom while a pin is pressed down with the handle. It works great for us and is really fast as it does not use any other tools at all.

[Lireal]

Originally Posted by lark95

Sorry it took a bit longer than expected to get the pics but here they are. This is the chain break that we made to break #35 chain so that we could get away from using master links. The chain is aligned in the line of of holes on the bottom while a pin is pressed down with the handle. It works great for us and is really fast as it does not use any other tools at all.

https://mail.google.com/mail/u/0/?ui...92c66_0.1& zw

https://mail.google.com/mail/u/0/?ui...d904a_0.1& zw

The links don't work right now. It looks like they are links to email attachments. Can you upload them to google drive or similar and share them that way?

[lark95]

Originally Posted by lark95

Sorry it took a bit longer than expected to get the pics but here they are. This is the chain break that we made to break #35 chain so that we could get away from using master links. The chain is aligned in the line of of holes on the bottom while a pin is pressed down with the handle. It works great for us and is really fast as it does not use any other tools at all.

Fixed it, the pics are visible now.

[Monochron]

Originally Posted by lark95

Sorry it took a bit longer than expected to get the pics but here they are. This is the chain break that we made to break #35 chain so that we could get away from using master links. The chain is aligned in the line of of holes on the bottom while a pin is pressed down with the handle. It works great for us and is really fast as it does not use any other tools at all.

How do you assemble chain onto the robot? Or do you always create a loop of known length and wrap it around un-tensioned sprockets?

[lark95]

Originally Posted by Monochron

How do you assemble chain onto the robot? Or do you always create a loop of known length and wrap it around un-tensioned sprockets?

We always just create known length loops like you said. With how much #35 stretches on something like a drive train through out a season, we find that we always need chain tensioners anyway so it really is not to big a deal.

[fargus111111111]

Belt vs chain, in my 4 years, relatively short compared to many of these people, I have not seen a lot of difference if the shafts the belt/chain is on are attached to the same plate, when you start getting joints in between it gets a little hairy with belts, but we have only broken a chain once, and that was on our t-shirt shooter while driving in the grass and all its drive is 25 chain, our 2012 robot, a very similar design, uses 35 chain from the gearbox to the center axle, then 25 from the center axle to the end axles and we have never had any problems. On the belt side, the past 3 years we have used belts in the drive and never experienced any issues, our 2014 bot is still running all original parts, except the wheels. 2014 and 2015 we used the standard kit base and 2016 we used a modified version of the Rhino Track system. (custom fit to our Breckoflex tracks) We have used poly cord in the past as well, the last time was 2012, but the stuff is quite useful for intakes, our 2006 robot uses a crazy pulley system and a bunch of poly cord to run the intake and spiral ball storage system off one motor. Poly cord can't take too much torque, but sometimes that is a good thing and the cord is not near as picky about alignment as long as you have deep pulleys and if needed you can even make it turn on multiple planes.

[Oblarg]

Some thoughts, from my personal experience:

Belts are more sensitive to C-C distance. Chain is more sensitive to alignment. I've never once, in my many years of FRC, seen a timing belt jump off a pulley (exclusively using flanged pulleys, admittedly, has helped with this). I've seen chain jump off not-quite-aligned sprockets more times than I can count. However, I've seen plenty of not-quite-tight-enough belts ratchet, whereas chain will only ratchet if it's basically falling-off-loose.

Complicating this fact for chain is the tendency to stretch, which is not a problem with belt. Once a belt is properly set up, you can forget about it. Chain, not so much.

The upshot of this is that chains will (almost) always require either tensioners or adjustability at one end of the run. On the flip side, if you don't have the machining capability do to precise C-C distances, so will belt.

Belts are much, much quieter, which is a bigger benefit than you'd think.

Chain can be put on in-place without moving a sprocket, via. masterlink. Belts cannot.

Chains can transfer a much higher maximum load, given the size of belts used in FRC. If you're limited in your pulley diameter or belt width, or if you just have a mechanism with whopping forces involved, this can matter.

This isn't rigorous at all (so take it with a grain of salt), but belts seem to be less-prone to bizarre one-off undiagnosable failures than chain. A fair number of times I've seen chain fall off drives with no visible faults, with no hint of the cause and no subsequent failures despite nothing being changed. I have seen a grand total of one belt failure in my entire time in FRC.

My teams tend to use belts, because we value reliability and belts basically never fail.

On #25 vs. #35 chain, my advice is to avoid the former unless you are certain of your team's machining precision. As I mentioned, #35 chain is already more sensitive to mis-aligned sprockets than belts - but #25 chain is *far* more sensitive than #35 chain, still. If you cannot align the sprockets extremely well, it will fail. My teams, which machine almost exclusively with a chopsaw and a drillpress, have abandoned #25 chain for this reason, and we do not regret it one bit.

[GeeTwo]

Originally Posted by Oblarg

On #25 vs. #35 chain, my advice is to avoid the former unless you are certain of your team's machining precision. As I mentioned, #35 chain is already more sensitive to mis-aligned sprockets than belts - but #25 chain is *far* more sensitive than #35 chain, still. If you cannot align the sprockets extremely well, it will fail. My teams, which machine almost exclusively with a chopsaw and a drillpress, have abandoned #25 chain for this reason, and we do not regret it one bit.

+1. #25 has only worked well for us when alignment was due to COTS parts, rather than our own machining. Then again, I wish we did more machining with a chop saw and a drill press; I am fighting an uphill battle against the hand drill and the Dremel tool.

[S1LK0124]

I know for a fact that my team has published a paper evaluation this very topic. If you'd like, I can post a link to it!

[S1LK0124]

You can find it here, scroll down until you find the "Belts vs Chains presentation" PDF.

[C.Lesco]

Chains suck if you dont know how to instal them or get that finicky half link in however used correctly i think its fine. As for belts, a good belt is better in my opinion "but belts might stretch" people argue. Youre using the thing for 6 hours flat out total at most, it doesnt matter in the time span of build and comp unless youre using a multiyear old belt. BELLLTSSSS