what Chain size and tensioner to use for the drivetrain

Originally Posted by Darunada

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]

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.

[Cory]

Originally Posted by kE7JLM

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]

Originally Posted by Cory

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]

Originally Posted by Cory

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]

Originally Posted by Otaku

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]

Originally Posted by kE7JLM

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]

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]

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

[artdutra04]

Originally Posted by Kat Kononov

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 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]

Originally Posted by kE7JLM

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

.

[DPTeam270Driver]

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]

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...)

[Clifford]

Where did you guys get your Pps? We're thinking about using it for tensioing our drive chain. Thanks.