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 A Few Chain Drive Questions

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Alex
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PostSubject: A Few Chain Drive Questions   Sun Nov 22, 2009 6:19 am

Hey guys, i'm looking at using chain drive for a new 15# robot. I'm looking at either a #25 or #35 chain. Would these hold up in combat? The #25 had a load of 140lbs and the #35 had 480lbs. How much is common to see in a drive train? I've used xl timing belts before would the results be comparable? Any help would be much appreciated.

Some people may ask to why i'm using chain not timing belts. I am planing on doing a two stage reduction to a 4wd robot, making for a total of 8 belts or chains, in 4 different sizes. I figured by using chain reductions i wouldn't have to design the robot around the different size belts like i have done in the past.

Thanks for your help
Alex Udanis
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SenaiERI
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PostSubject: Re: A Few Chain Drive Questions   Sun Nov 22, 2009 12:47 pm

I don't know if it's such a good idea to use belt reduction in this competition. There are plenty of motors out there with gear reducing transmissions, but I don't think I would trust moving belts in this environment. I'm not saying it can't be done, but it better be incredibly stout to hold up against your opponents attacks.
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Alex
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PostSubject: Re: A Few Chain Drive Questions   Sun Nov 22, 2009 1:00 pm

SenaiERI wrote:
I don't know if it's such a good idea to use belt reduction in this competition. There are plenty of motors out there with gear reducing transmissions, but I don't think I would trust moving belts in this environment. I'm not saying it can't be done, but it better be incredibly stout to hold up against your opponents attacks.

Well we did a 1/1.3 reduction in aftershock using belts. We were using 16:1 Banebots and two inch wheels, to get where i want to be i would need to use 3" wheels or 10-12:1 gearhead with the 540 motors.

I am looking for something close with chains
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rdubard
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PostSubject: Re: A Few Chain Drive Questions   Sun Nov 22, 2009 1:24 pm

Chains have the same sorts of restrictions as toothed belts (synchronous/timing belts) in the sense that you can only get chain lengths in integer units of links, and sprockets come only in certain sizes (again with integers of teeth). It is true that, for a given width, a chain will handle more tension, but unless you've got increased downforce (magnets or vacuum) belts can handle things just fine (see below)

I guess what I'm trying to say is that I do not understand yet the advantage you are seeking from chains that belts lack.

Also, though I am sure you know this, chains are much heavier than belts. This makes for less weight to put into things like armor, batteries, etc. Less obvious is that chain drives are less efficient than timing belts, because you are expending more energy moving the chain and flexing the link joints.

BUT, to answer your question, even if you had only 2 wheels driving the entire robot, and crazy good traction (coefficient of friction = 2), and a big wheel (4 inch radius), driven by a small sprocket (1 inch diameter), and you are pushing an opponent with the same traction, all of which are 'worst case' scenarios, the chain would only have 120 pounds of tension force in it. So, I don't think the chains are likely to break.

All of the above are theoretical--my only experience with chain drive was when a student built a notoriously crappy robot called gatorbot, which had so many other problems that the chain drive difficulties went unnoticed.
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rjw
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PostSubject: Re: A Few Chain Drive Questions   Sun Nov 22, 2009 9:30 pm

why not go to a bigger ratio in the gbox and use single belts?

Or use timing belts in a size that has many different length offerings

SDP (stock drive products) has lots of belts in some sizes..like maybe XL's? not to mention the weight savings????

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rdubard
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PostSubject: Re: A Few Chain Drive Questions   Mon Nov 23, 2009 6:13 am

Stock Drive Products www.sdp-si.com has over 100 sizes of XL belts, and every pulley size ranging from 10 teeth/appx 5/8" up to 30 teeth/appx.2", (after that it does skip around a bit, but those are some large pulleys)
Their website also has a GREAT design utility
http://www.sdp-si.com/Cd/default.htm

I have no affiliation with SDP, just a satisfied customer.

However, this still doesn't address the original point--what is appealing about chains that belts lack?

Aha! I can think of two advantages-
you can repair a chain, but a b
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rdubard
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PostSubject: Re: A Few Chain Drive Questions   Mon Nov 23, 2009 6:23 am

And if you don't hit 'return' before you are done typing, your comment wont get cut off Very Happy

As I was saying, there are two three advantages I can think of that chains have over belts--

1) If you have the correct tool, you can repair a chain.

2) Furthermore, when doing R&D, you can change around your chain size without having to have multiple sizes pre-ordered and laying around (as would be necessary with belts)

3) Chains can sometimes be installed in tight quarters without removing covers, loosening axles, or removing sprockets. (To put on a belt, you've generally got to be able to get the pulleys off.)
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rjw
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PostSubject: Re: A Few Chain Drive Questions   Mon Nov 23, 2009 6:26 am

Timing belts have better power transfer than chains and sprockets. I think that efficency is in the mid 90% range, IIRC.

MLEC is STILL using the ORIGINAL belts on both Rattlers...lol... affraid

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Cody
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PostSubject: Re: A Few Chain Drive Questions   Mon Nov 23, 2009 8:32 am

we've snapped a bunch of belts on Aftershock and lost matches cause of it

He's up to something but i'm not sure what
Maybe to save space?!
idk lol
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Alex
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PostSubject: Re: A Few Chain Drive Questions   Mon Nov 23, 2009 9:22 pm

Cody Harris wrote:
we've snapped a bunch of belts on Aftershock and lost matches cause of it

He's up to something but i'm not sure what
Maybe to save space?!
idk lol

You'll see i have some idea's cooking up......i just ordered a 12x12x1.5" block of al from mcmaster
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Will Bales
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PostSubject: Re: A Few Chain Drive Questions   Tue Nov 24, 2009 8:00 am

oh... I know wha you're up to..
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