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Unread 09-01-2008, 22:12
EduardoVemny EduardoVemny is offline
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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.
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Unread 09-01-2008, 23:15
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Re: what Chain size and tensioner to use for the drivetrain

Quote:
Originally Posted by artdutra04 View Post
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.
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Unread 09-01-2008, 23:57
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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.
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Unread 10-01-2008, 00:02
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Re: what Chain size and tensioner to use for the drivetrain

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Originally Posted by 114ManualLabor View Post
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.
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Unread 10-01-2008, 01:14
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Re: what Chain size and tensioner to use for the drivetrain

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Originally Posted by Darunada View Post
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.
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Unread 10-01-2008, 01:45
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Re: what Chain size and tensioner to use for the drivetrain

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.
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Unread 10-01-2008, 01:58
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Re: what Chain size and tensioner to use for the drivetrain

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Originally Posted by kE7JLM View Post
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.
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Unread 10-01-2008, 02:10
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Re: what Chain size and tensioner to use for the drivetrain

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Originally Posted by Cory View Post
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...
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Unread 10-01-2008, 02:16
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Re: what Chain size and tensioner to use for the drivetrain

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Originally Posted by Cory View Post
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.
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Unread 10-01-2008, 03:13
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Re: what Chain size and tensioner to use for the drivetrain

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Originally Posted by Otaku View Post
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.
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Unread 10-01-2008, 11:22
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Re: what Chain size and tensioner to use for the drivetrain

Quote:
Originally Posted by kE7JLM View Post
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.
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Unread 10-01-2008, 11:53
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Re: what Chain size and tensioner to use for the drivetrain

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.
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Unread 15-01-2008, 17:20
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Re: what Chain size and tensioner to use for the drivetrain

Where can we get HDPE and do we have to make the tensioners or do they come pre-made?
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Unread 21-01-2008, 11:44
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Re: what Chain size and tensioner to use for the drivetrain

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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.
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Unread 21-01-2008, 12:32
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Re: what Chain size and tensioner to use for the drivetrain

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Originally Posted by kE7JLM View Post
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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