what Chain size and tensioner to use for the drivetrain [Archive]

edBringas

08-01-2008, 19:41

Hi,
We are trying to decide our drivetrain this year, the question came up when discussing the chain size. I'm of the belief that the standard #35 is fine but others think a thinner chain might be better. Any thoughts?
Also in the past we created our own tensioners with store bought pvc but this year we want to buy a manfactured tensioner to prevent the chain to fall off. Does anyone have a good online source?

Thanks
-Ed

davidhoughton

08-01-2008, 19:55

personally i would go with the larger burlier chain due to strength but if you are needing to save weight it would probably be better to go with the smaller chain

as far as a tensioner gos im not sure

hope i have been of some help

CraigHickman

08-01-2008, 20:00

We use #25 for everything. As long as you run it/tension it properly, there is no conceivable way you could break it. Please note I'm not saying it's invincible, I'm saying when done correctly, it is more than strong enough.

As for tensioners, that depends on your drivetrain setup. Some teams buy idler sprockets from McMaster, or some equivalent, and then put it on a U bolt so it's adjustable. I personally prefer to go with live Axles, and pull bearing blocks. But that requires more machining and materials.

Good luck! Post some pictures once you finish it, so we can see!

Tristan Lall

08-01-2008, 20:07

This depends on your application. Teams have used either #25 or #35 with success (and rarely, other sizes as well), but there have been some ugly instances where the wrong chain for the job was used.

Estimate the loads on the chain by consulting a design manual like this (http://tsubaki.ca/pdfs/sectionA.pdf) (look for ANSI roller chain, e.g. RS25 or RS35) to get an idea of the power that the chain will accept, at a given speed. (That manual lists the allowable horsepower for each chain type, for a given sprocket size, at some speed, assuming the full working load is applied. Note that the working load is significantly less than the breaking load, because the manufacturer has selected a factor of safety.) Then have a look at the Tsubaki troubleshooting guide (http://tsubaki.ca/pdfs/roller.pdf) to avoid the situations that can damage chain or reduce performance.

As a general principle, the tensile load in a chain is inversely proportional to the sprocket diameter. Big sprockets are safer than small ones, if the chain is at risk of breaking.

waialua359

08-01-2008, 20:39

We are going with something totally different this year. Bike chain with custom made sprockets. Lighter and stronger like #35 chain but with the #25 chain weight. The pitch on the sprockets are different from the standard 25 and 35 chain. We made our own. :D

RTTComanche17

08-01-2008, 20:52

our team has only used 35 chain. we have absolutely put it to the test too, and it has never broken. our bot in 2006 outpushed every ither bot we went up against, even the ones with outback style track designs. we bent our frame causing the chain to rub the inner frame rail, the wheel, be out of alignment, and have excess slack. it never failed. we had to replace our wheel cuz the chain started to eat throuth the aluminum side plate. 35 chain is cheap insurance. use it!

artdutra04

08-01-2008, 23:31

25-pitch chain will work fine for drive-train applications if you can manage the manufacturing tolerance required, and save you a fair amount of weight over 35-pitch. Team 190 has always used 25-pitch roller chain, and Team 228 will be going with 25-pitch this year.

As for tensioning roller chain, Team 228 always uses an extremely simple method of using HDPE bar stock with an off-center hole. As you rotate the HDPE around the center hole, the diameter changes and works perfectly for adding tension to roller chain. Here's a photo of three applications of these simple chain tensioners from our 2007 robot:

http://www.team228.org/gallery/63/slideshow/S4300211.jpg (http://www.team228.org/media/pictures/view/3009)

Otaku

09-01-2008, 13:58

#35 chain, and might I be the first to suggest sliding motor mounts? Leave some tolerances and mill out slots so that your motor mounts and bearingplate supports can slide back and forth -- then there's no use for tensioners, and you save some extra weight. It does take a bit more thought, though. 675 used sliding motors last year and we used tensioners the year before, and all I can say is we're not going back to tensioners.

Scott Morgan

09-01-2008, 14:04

We'll be using #25 chain for our drive this year. We'll tension it by sliding the front and back wheels, center wheel is direct driven.

Jeff Waegelin

09-01-2008, 14:43

I always use #35 for drivetrains. I've found that it's much more forgiving when dealing with misalignment. If you've got the skills and resources to keep your tolerances tight, your chain properly tensioned, and a relatively short chain, #25 can work just fine. For something as mission-critical as the drivetrain, though, I prefer the security of the bigger stuff.

EduardoVemny

09-01-2008, 22:12

Thanks for the info, Though my gut said #35 chain, my skill set has always been electrical/programming and thus wanted to make sure. To bad we don't have a mechanic/engineer to confirm what I thought this year.
As for the tensioner I think we are going with artdutra04 idea. Alas we do not have access to a mill and this might be the best route.
Thanks

burkey_turkey

09-01-2008, 23:15

25-pitch chain will work fine for drive-train applications if you can manage the manufacturing tolerance required, and save you a fair amount of weight over 35-pitch. Team 190 has always used 25-pitch roller chain, and Team 228 will be going with 25-pitch this year.

As for tensioning roller chain, Team 228 always uses an extremely simple method of using HDPE bar stock with an off-center hole. As you rotate the HDPE around the center hole, the diameter changes and works perfectly for adding tension to roller chain. Here's a photo of three applications of these simple chain tensioners from our 2007 robot:

I def agree. We started using HDPE two years ago and have never looked back. Its easy light simple and effective.

Darunada

09-01-2008, 23:57

DonRotolo

10-01-2008, 00:02

We use #25 for everything. As long as you run it/tension it properly, there is no conceivable way you could break it.
Read the highlighted phrase above again. #25 is fine, but only IF...

#35 is far more forgiving, but heavier.

artdutra04

10-01-2008, 01:14

the chain doesn't eat the HDPE away?Not any appreciable amount over the course of a competition season.

If you use softer or lower density plastics, the roller chain will start eating away the plastic rather quickly. But the High Density property of HDPE is great to act as a low-friction surface for the roller chain, without being eaten away.

On our previous robots, after four or five competitions, all we'd notice on our chain tensioners would be a two small grooves about 1/16" of an inch deep.

CraigHickman

10-01-2008, 01:44

the chain doesn't eat the HDPE away?

The reason I ask is because the chain ate away a good half inch into our robot when some bolts rattled loose on a pneumatic tire, causing it to expand and push the sprocket (and thus, chain) into the frame.

For non idler chain runs, we use Glass infused Delrin (use masks when machining this crap, it's NASTY to your lungs!), which held up incredibly well, and never wore down during our whole season.

kE7JLM

10-01-2008, 01:45

Cory

10-01-2008, 01:58

Best not to go with Chain tensioner it is more friction and more work for your CIMS. Just make the chain as tight as possible and don't worry if it take you a full day to mount the wheels. It is one of the most important parts.

This is poor advice.

Any properly designed chain tensioner will not rob your drive of any power.

Every drivetrain should have some provision for tensioning chain. If you don't, it will eventually stretch enough to be too loose, even if you calculated the exact center-center distance to allow you to use a whole number of links.

kE7JLM

10-01-2008, 02:10

This is poor advice.

Any properly designed chain tensioner will not rob your drive of any power.

Every drivetrain should have some provision for tensioning chain. If you don't, it will eventually stretch enough to be too loose, even if you calculated the exact center-center distance to allow you to use a whole number of links.

It has work for us for two years...

Otaku

10-01-2008, 02:16

If you don't, it will eventually stretch enough to be too loose, even if you calculated the exact center-center distance to allow you to use a whole number of links.

This is true.

However, will it really exaggerate itself over the 3-9 days that I'm guessing most teams compete (that's 1-3 events)?

Not that I advocate not having a tension system. I still stand by sliding motor mounts.

Cory

10-01-2008, 03:13

This is true.

However, will it really exaggerate itself over the 3-9 days that I'm guessing most teams compete (that's 1-3 events)?

Not that I advocate not having a tension system. I still stand by sliding motor mounts.

We put hundreds of hours of drive time on our robots. Some teams clearly put a lot less on theirs.

A blanket statement that tensioners are unnecessary is never a good thing, imo.

artdutra04

10-01-2008, 11:22

Best not to go with Chain tensioner it is more friction and more work for your CIMS. Just make the chain as tight as possible and don't worry if it take you a full day to mount the wheels. It is one of the most important parts.Making the roller chain as "tight as possible" would be a larger load on the motors than a properly tensioned drive train.

Jeff Waegelin

10-01-2008, 11:53

I have had some robots that functioned fine for a whole season, while never having to adjust the chain. I've had others that had to be constantly adjusted. Sometimes you can get away with not having tensioners, but it's like playing a game of Russian Roulette with your drivetrain. It's better to come up with a tensioning solution (HDPE, idler sprockets, sliding motor/wheel mounts) than to risk having your drivetrain fail in a critical situation because the chain got too loose.

Kat Kononov

15-01-2008, 17:20

Where can we get HDPE and do we have to make the tensioners or do they come pre-made?

artdutra04

21-01-2008, 11:44

Where can we get HDPE and do we have to make the tensioners or do they come pre-made?
Check out page 3498* of McMaster-Carr's (http://www.mcmaster.com/) catalog for the HDPE (high density polyethylene) solid rod between about 1" and 3" diameter.

* Just type in 3498 in the search box on McMaster.

DonRotolo

21-01-2008, 12:32

Best not to go with Chain tensioner it is more friction and more work for your CIMS. Just make the chain as tight as possible.Properly tensioned chain is far better than "as tight as possible". This puts unreasonable loads on the components, and actually reduces its ultimate strength since the load is oscillatory and subject to fatigue.

The fraction of a watt consumed by a tensioner can be measured, but you'd never notice it.

Maybe doing it wrong works for you and your team, and that's cool for you, but that doesn't make it good engineering practice.

Don

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DPTeam270Driver

21-01-2008, 15:04

team 270 always had a problem w/ chain tensioning
if u would like to be cheap, you can use zip ties to tension the chains
or this year we found cim motor tensioners in one of the old KOP bins, we just made plates and they are great. they provide constant tension and are easy to maintain

Dick Linn

21-01-2008, 19:00

HDPE is readily available in cutting boards, laundry detergent bottles and other things marked with the #2 recycling symbol with the HDPE or PE-HD printed below the triangle. Think milk jugs, eh?

If you keep your chain runs short, use quality components and align them and occasionally lubricate the chain, you shouldn't have a lot of chain tensioning problems. I agree that if your design allows the primary drive/gearbox to be adjusted or shimmed slightly, it makes life simple. One time, we needed a tensioner for a long chain run, so we cut a guide groove in some skateboard wheels and used them as rollers. Worked marvelously, and cost virtually nothing. The only other time, we stuffed a narrow piece of HDPE into a channel in some 80/20, as the chain needed to go over a rather misplaced structural rail in its path. frtgtgf'ikb n

(The last comment is from our kitten, who jumped up on the laptop twice and managed to shut everything down a few minutes ago. Thank goodness Firefox cached everything... I wouldn't want to deprive y'all of these words of wisdom amongst the cussing...)