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Old Nov 17, 2014, 02:35 AM
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United States, TX, Lipan
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Go Kart Chain PSRU

I'm seriously considering using #35 chain and sprockets to reduce prop speed and gain efficiency of a larger prop while reducing prop noise. Seeing several engines so equipped it doesn't appear to be a major task. Since chain is a no-slippage drive the thought of adding a starter/generator also seem possible. Has anyone had similar ideas or have completed making a chain Propeller Speed Reduction Unit? Ed
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Old Nov 17, 2014, 06:29 AM
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What size engine and prop ? For many smaller applications #25 may be a better bet . The chain either way is pretty heavy , as are the sprockets , unless you use nylon sprockets . Nylon is a lot quieter as well . You should also fit a chain retention "guard" of some kind to contain the chain should it happen to dismount .

Toothed belt drives are probably a better solution . Perhaps a bit less efficient from a power standpoint but lighter and quieter than the roller chain . Again nylon sprockets win at the scales .
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Old Nov 17, 2014, 10:41 AM
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This has been done successfully in the past.

http://www.bing.com/images/search?q=...electedIndex=1
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Old Nov 17, 2014, 10:52 AM
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Well the Wright Brothers used a chain drive to power the dual props on their Wright Flyer. I remember seeing a few engines with reduction drives using chains and sprockets before too. So it is possible, Usually most everyone opts for a toothed belt drive or gears though. There were some planetary gear drive units made in the past too.
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Old Nov 17, 2014, 03:34 PM
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tony clark and another european manufacturer also do belt reduction drives. ultralights and PPGs also use reduction drives and it's either belts or enclosed gears, never seen chains used. belts are going to be quieter, lighter, last longer and are just more suitable at these speeds. mcmaster-carr is your friend...
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Old Nov 17, 2014, 04:49 PM
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You could look up some of the chain suppliers to see what the maximum recommended running speed would be.

I'd agree that a timing belt would probably be a better alternative.
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Old Nov 17, 2014, 08:39 PM
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A while back I saw some old common combustion engines that were used in large RC helicopters at the time. I am talking something with a ten foot rotor span or more. There was a two cylinder setup and a three cylinder setup. They all used a chain to connect the engines together to keep them in sync.

So it isn't really a bad idea to use a drive chain as a gear reducer for driving larger propellers. Now it may not be the best way to do it though. But it would work.

For belts, sprockets, chains, pulleys, gears et cetera, I suggest perusing Stock Drive Products out.
http://www.sdp-si.com/
You can easily spend days going through their catalog perusing things and coming up with ideas for all the neat stuff they have. They have pretty much everything one could want too.
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Old Nov 18, 2014, 01:17 AM
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some examples of chain or belt driven engines, last two pics are the smallest model chain I know off by Kyosho and a mere 3mm wide ( note that sprocket was home made for my Blériot wingwarping system ) large chain driven engine is obviously missing a spring tensionner ! The Kyosho chains are used on the gokart.
pm : noticed there are quite a few Kyosho chains on ebay and some include sprockets, never knew that
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Old Nov 18, 2014, 09:15 AM
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Are we talking about just chain, or PSRU units in general? What size engine/prop?

Byron used to use a of of PSRU's in his bigger stuff, even gear drives? If looking smaller, wasn't too long ago there were a lot of belt reductions used with electric installs.
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Old Nov 26, 2014, 01:55 AM
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After researching chain drives and viewing several in action on 30cc and bigger engines commonly used for large scale RC, it appears to be a viable option for PSRU's. Roller chains appear to be the most commonly used type drives on motorcycles which are easily purchased and replaced. Most belt OEM's advise against using tooth belts preferring multi-vee for PRSU's due to torsional stress. Like belts some basic guidelines are; keep shaft centers < 80 pitches, running speed <3000 ft/min slower is better, drive sprocket should be >17 teeth, chain tension should be some what loose i.e. like chainsaw or use a spring tensioned idler or nylon rider once set with a new chain DO NOT READJUST. Normally a roller chain is considered worn out when stretched 1.5% allowing additional stretch will also damage sprockets which should be avoided. Obviously the sprockets will need replacement, this time can maximized by timely maintenance and measuring wear. All motorcycled dealers and websites have custom chain lubricates which greatly reduce sling off since most riders like to show-off their bikes without chain lube splattered on rim and fender. Considering most roller chains meeting RC needs are #25 & #35 (1/4 & 3/8) pitch are normally sold in 10' lengths for <$20 there should be no reason to except excessive wear. It's is advisable to purchase extra master links when ordering chain. Like belts, chain quality is usually price related with premium chains costing more. Motorcyclist seem to favor o-ring chains made by Tsubaki but, that is just my observation. Since weight is always a concern aluminum driven sprockets are preferred, in the event you have to purchase a steel one consider making lightening holes to reduce weight. Likely your drive sprocket will be hardened steel, it is advisable to avoid single digit ratios i.e. 2:1 3:1 and so on to cancel engine harmonics while still increasing propeller efficiency. It is advisable to use smaller diameter shafts since they also help reduce harmonic vibrations along with lower prop speed. Depending on your airplane's design and engine performance curves most props work best in 1800-2300 rpm range, again this is based on general aviation airplanes with 5-6' props. As you already know even light planes are noisy so don't expect a stealth model either but, lower frequencies are considered better.

See this link for how to measure wear: http://www.chainweargauge.com/roller...hain-wear.html
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Old Nov 26, 2014, 06:09 AM
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Goooood luck ..............
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Old Nov 26, 2014, 07:32 AM
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One thought it that with motorcycles, they gear down the engine using a transmission. The final drive sprocket is thus turning low RPMs compared to the engine. Maybe 1,000 RPMs tops. That has me wondering what the maximum speed is for a chain drive. If the engine is turning say 12,000 RPMs and the sprocket and chain is running at that speed, will that be a problem? Even with a large gas engine turning 6,000 RPMs is still a huge speed for the chain and sprocket. Now I know the overhead cam engines use a chain drive, but the load stresses are different than being driven for power off the crankshaft. So it had me wondering what speeds the chain and sprockets can handle.
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Last edited by earlwb; Nov 26, 2014 at 07:34 AM. Reason: add more info
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Old Nov 26, 2014, 07:50 AM
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The speed ratings are specified in manufacturer's data . Most motorcycles also employ torsional dampers to minimize shock loads . Chain slack tends to magnify the problem .
We are somewhat at a disadvantage here since the OP has provided little information regarding engine type and size , prop specs etc . The chain maintenance tutorial is a given , Not sure what it has to do with the question at hand . Most of the #25 roller chain is plain bearing , unsealed if I recall correctly . Unlike belt drives , plain chain usually requires regular lubrication . Noise is cumulative so chain will add noise and absent isolation will also tend to transmit noise .


I know there have been quite a few successful toothed belt drives for model aircraft . Multi vee or poly grip belts generally require a measure of radial loading to provide adequate grip . Our engines are designed primarily to absorb end thrust loads , less so radial loading . Chain drives will increase the radial loading to some extent , I suspect a multi vee drive could generate an even higher load .
Often there is need for a spring loaded idler to keep the belt adequately tensioned and take up belt stretch .
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Old Nov 26, 2014, 08:26 AM
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To the point I just don't see it being practical in the rpm ranges we would be talking. Even if were were talking about a multiple stage reduction, the initial stage is going to be turning a lot faster than anything I've seen turning - except for maybe the cam drive chain on some bikes. Of note there is that they're using some pretty good size sprockets (much bigger than 17t). If this is a can it be done project, I'd say it is. If it's a can it be done practically exercise, I'd have to change my vote....

"Chain drives will increase the radial loading to some extent."
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Old Nov 26, 2014, 08:27 AM
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Having raced go-carts, I would shy away from chain for RC applications. #35 is not and I assume #25 chain are not true roller chain as in there is no roller on the link. I found wear to be excessive. But in a racing application it was part of the game. I would go the belt direction if at all possible. It will be a much smoother drive and should last much longer with fewer issues.

Ken
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