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#25 chain drive


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Cyber



Joined: 26 Aug 2015
Posts: 59
Location: Melbourne


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#25 chain drive

Hi all! Smile

I'm building my bot using a pair of those 100W scooter motors and some #25 chain driving some of those scooter wheels, a bit like the setup on the SubKor bot. I was just wondering if there's any things I should look out for using chain, like does it stretch? Does it need a spring loaded tensioner to handle shock or will it be fine with a manually adjustable idler?

Cheers!

Post Wed Oct 28, 2015 9:01 am 
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Nick
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Some builders have terrible problems with chains coming off. As long as you align the sprockets really carefully and keep the chain reasonably tight, you shouldn't have any problems.

Chain doesn't need dynamic spring loaded tensioning but having some way to adjust the tension when the chain stretches is a good idea. Typical ways are an idler sprocket, half links (short chain links you insert or remove) and moveable drive components. I would go for the idler sprocket as it also helps guide the chain and increases the wrap around the drive sprockets.
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Post Wed Oct 28, 2015 11:53 am 
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Valen
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isolate the motor + drive sprocket from any plausible mechanism of getting bent out of alignment. Most common is the outside shell of the bot bending when it gets hit, warps the drive line and the chains run off.
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Post Wed Oct 28, 2015 1:48 pm 
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Glen
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quote:
Originally posted by Valen:
isolate the motor + drive sprocket from any plausible mechanism of getting bent out of alignment. Most common is the outside shell of the bot bending when it gets hit, warps the drive line and the chains run off.


This, built it into its own solid, isolated unit with as short a run as possible with maximum wrap on the sprockets. The frame on no robot will stay aligned or straight so of course alignment critical chains will jump off if attached to it.
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Post Wed Oct 28, 2015 2:14 pm 
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Cyber



Joined: 26 Aug 2015
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Location: Melbourne


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thanks guys. I'm building the wheels+motor frame section very rigid and then shock mounting that to the rest of the frame which should hopefully prevent any movement that throws things out of whack. Looking at it now I might throw in a couple more braces - I'd intended for it to have some flex but I can see how that'd be a bad thing for the chain.

It might be a good idea to 3D print some chain guides to prevent big lateral knocks throwing the chain around too much and leading it off the sprockets.

Post Wed Oct 28, 2015 2:49 pm 
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Valen
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it doesn't need to be over done, it just needs to be strong enough not to bend when you load it up, and when the robot decides to go flying across the arena and the frame is trying to encourage the motor to go with it ;->

I dunno about the chain guides, ideally you shouldn't have any long runs of chain like glen said, IE you should be sprocket || sprocket with almost no gap between. and like glen said the chain wrapping almost 180 degrees on each one.

Of course nothing is ever ideal but the closer you can get to that the better, the shock mount is good but be wary of it ripping apart, mostly you just attach the drive unit to the bot in such a way that you let the bot chassis deform it won't drag the frame around. (Like say 2 bolts on one side of the wheel hole, rather than 4 bolts around the entire hole, so if the hole gets deformed it won't drag the drive module out of square)
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Post Wed Oct 28, 2015 4:34 pm 
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miles&Jules
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Every chain i have ever done has fallen off…..We don't use them anymore. There is a planetary gearbox that goes on the front of scooters which is good but its a lot of lathing to get it to work. The other problem is weight…those scooters weigh twice as much as a drill. That said scooters never burn out so the motor part of them is very reliable….But belts are better.

I noticed Gary has chain weapon drive in Badger his full body spinner. He was saying that they work best with lots of teeth rather than just a few on the smaller pinions.
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Post Thu Oct 29, 2015 12:19 am 
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Rob Team Rotwang



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Chain on the incomplete Ref bot, plan is to have it for unsticking robots or putting them out if they're on fire. One way to get an 8 to 1 reduction, allows for all the weight to be on the two wheels mounted on a solid shaft with big bearings and lets the motor just do what it does best. Chains a bit vulnerable to derailment, hard to guard against all spikes in any wheel openings. Motors shimmed at the back to tension the chain.



Something we currently have under way its going to be a special effects robot for a theatre company. Originally this bot was designed for an offroad competition with speed and stability mainly in mind. The sprockets are attached to the wheels and they’re huge 80 tooth sprockets which wasn't good when fighting maestro another Light weight. it all got bent and the chain came off. Mayve been better to have more reduction in the motor and smaller sprockets. Or multiple stage reduction.
Theres a video of us making those adapters. https://www.youtube.com/watch?v=j7VKHdyJIkg


Weasel our light weight. Breaks all the rules with chain guides and hardly any chain on the drive motor. Never lost a fight as far as I know. Could be top ranking light weight in the country. Light weights are much better to utilize chain with the weight to play with. I dont think this could be done with a feather and still have armor. Yet in its class its a good way to get '4 wheel drive' with 2 motors, so the chains really doing two things, being the transmission of power to the wheels and also being the gearbox.


This might be the most you would do in a feather weight, keeping it all close together. the small teeth are good the chain has to climb a long way to fall off. the small number of components here is good, you get a good amount of wrap around. The closer the components are to the same size the better u get 180 wrap if they’re the same size but don’t get reduction. if you get it right you got a strong combination, you get it wrong, it falls off. it can be done.

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Post Sun Nov 08, 2015 1:28 pm 
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Cyber



Joined: 26 Aug 2015
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Location: Melbourne


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thanks again guys

Rotwang that last photo with the scooter wheel is pretty much my exact setup but with the motor sprocket and wheel sprocket even closer than that. i'm looking at putting some industrial ball rollers on the front to get it moving nicely. like these:

https://www.google.com.au/search?q=ball+roller&espv=2&biw=1366&bih=643&site=webhp&tbm=isch&imgil=DsDkmXJOyAtRHM%253A%253BMdnfc65xc0QynM%253Bhttp%25253A%25252F%25252Fwww.aliexpress.com%25252Fpopular%25252Fball-roller-table.html&source=iu&pf=m&fir=DsDkmXJOyAtRHM%253A%252CMdnfc65xc0QynM%252C_&usg=__4FWFkoptz_xfec_2yb1LnM4b9Oo%3D&ved=0CCkQyjdqFQoTCKXDvrL2_8gCFSSqpgodrZwHmQ&ei=48Y-VuXFKaTUmgWtuZ7ICQ#imgrc=DsDkmXJOyAtRHM%3A&usg=__4FWFkoptz_xfec_2yb1LnM4b9Oo%3D

I'd like to make it four wheel drive but for my first bot I think that's a stretch too far

cheers

Post Sun Nov 08, 2015 1:59 pm 
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Nick
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I used transfer rollers like that for several years - they don't last very long, even if they are heavy duty types. I found they either jam solid from picking up material from the floor, or the internal balls fail from shock damage. You will get much better performance for less weight from UHMW skids IMHO.
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Post Sun Nov 08, 2015 2:10 pm 
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MikeNCR



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I've primarily used #35 roller chain on featherweight bots and thus far I've had very good luck when following a few design rules-

-Use chain calculators to get an axle spacing that results in an even number of links.
-Mount both shafts such that flex is minimized.
-If feasible place the sprockets close enough to a chunk of material that they have to be fed through the opening on the sprocket.

I've broken chains a few times, but I've yet to have one de-rail.

Example pics:
Nyx v2- http://nearchaos.net/WordPress/wp-content/uploads/2013/02/PresentingNyx.jpg
Styx/Nyx v1- http://nearchaos.net/StyxUp.jpg (Yes, it's using a bolt as a tensioner, and yes, it works well.)
Spanky- http://nearchaos.net/WordPress/wp-content/uploads/2013/02/IMAG0564.jpg

Post Sun Nov 08, 2015 2:24 pm 
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