what Chain size and tensioner to use for the drivetrain
 

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

Re: what Chain size and tensioner to use for the drivetrain
 

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

Re: what Chain size and tensioner to use for the drivetrain
 

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!

Re: what Chain size and tensioner to use for the drivetrain
 

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 (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 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.

Re: what Chain size and tensioner to use for the drivetrain
 

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

Re: what Chain size and tensioner to use for the drivetrain
 

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!

Re: what Chain size and tensioner to use for the drivetrain
 

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:

Re: what Chain size and tensioner to use for the drivetrain
 

#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.

Re: what Chain size and tensioner to use for the drivetrain
 

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.

Re: what Chain size and tensioner to use for the drivetrain
 

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.

Re: what Chain size and tensioner to use for the drivetrain
 

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

Re: what Chain size and tensioner to use for the drivetrain
 

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

Re: what Chain size and tensioner to use for the drivetrain
 

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.

Re: what Chain size and tensioner to use for the drivetrain
 

Read the highlighted phrase above again. #25 is fine, but only IF...

#35 is far more forgiving, but heavier.

Re: what Chain size and tensioner to use for the drivetrain
 

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.