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Hubs, Gearboxes, Sprockets and Chains Can't find 'em, grind em - hubs and transmissions, problems and modifications to make you run smooth and trouble free


homemade derailleur transmission?

Can't find 'em, grind em - hubs and transmissions, problems and modifications to make you run smooth and trouble free


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  #21  
Old 12-31-2013, 06:40 PM
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Default Re: homemade derailleur transmission?

This may be an unpopular view and I mean no disrespect, but you may well be "fixing" the wrong end of the problem as the 212 is simply an ill-suited engine for retrofitting to a bicycle, it's primary attraction it's low price... initially.

While reliable with a growing aftermarket parts supply, it's also bulky with a poor power to weight ratio, an auxiliary engine with a limited RPM range it's inexpensiveness often negated by the lack of any sort of powertrain, a costly, complicated endeavor to address in most cases, which is what inspired this thread I suspect.

While I advocate "to each their own" & build what you will, if your primary intent is to build affordable & reliable four stroke motorized bicycles, even fast ones with gears you may wish to consider researching other engine & transmission options rather then attempting to redesign a bicycle's derailleur system, it's limitations well known and well short of your needs.

Just for one example, as length & breadth are apparently of little concern as you're a fabricator (I've checked your build, nice custom BTW) this engine type while initially twice the cost of the 212 utility come complete with your choice of transmission options, 3, 4 & 5sps, auto, semiauto & standard - your choice & because of that often cost less, sometimes much less than a completed utility motor build and range from 49cc on up, they've a far better power to weight/displacement to HP ratio as well as full charging systems, electric starters and a vast selection of aftermarket goodies: http://motorbicycling.com/showthread.php?t=19630


Please don't take this the wrong way, the pred is responsible for many a unique build and it's not a bad engine - it just bothers me as it seems many see the displacement vs cost and think that's all there is to it, then get trapped into trying to reinvent the whee... erm, transmission or forced into buying expensive aftermarket custom parts to make it work, pulleys & plates that cost twice as much or more then the engine itself...

If you're a fan of the 212, don't want to buy expensive solutions & not worried about the above, I'd skip the derailleur redesign (they're not all that great in even people powered bicycles lol) & stick w/the sheave drive you've already built, which looks to be a good design & application BTW;




edit: As for the suitability of a cassette/derailleur transmission for motorized application, while the freewheel puts up with it and the normal wear is negligible I can with no more then one missed shift (accidental neutral drop), blow all the teeth off even a quality cassette's cog even with just the stock 49cc four stroke referenced above... granted that's abuse inadvertent or otherwise, but also bodes poorly for it's ability to handle a 212.

Last edited by BarelyAWake; 12-31-2013 at 06:52 PM.
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  #22  
Old 12-31-2013, 06:44 PM
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Default Re: homemade derailleur transmission?

its all good, I completely understand
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  #23  
Old 12-31-2013, 06:54 PM
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Default Re: homemade derailleur transmission?

David Staton once did something similar to what you have. He put a 7 speed freewheel on one of his outside drive gearbox. There was a single sprocket on the left side of the rear wheel. He designed a shifter for it as well. I see he no longer carries this kit. So I'm going to assume it either didn't sell well or didn't work well. You may be able to design your system to work but at what expense?
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Old 12-31-2013, 06:58 PM
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Default Re: homemade derailleur transmission?

well I went ebay and mfg supply and I can possible build this transmission for 50 to 80 dollars easily, if do a redesign even lower
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Old 12-31-2013, 07:04 PM
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Default Re: homemade derailleur transmission?

Hey for that price I say go for it. I was told my autoshift bike wouldn't work either. Yet this is going on my forth year riding it. I'll soon be building a 5 speed automatic using a Strumy Archer 5 speed hub.
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Old 12-31-2013, 07:06 PM
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Default Re: homemade derailleur transmission?

shoot for the stars and knock one out
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  #27  
Old 12-31-2013, 07:34 PM
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Default Re: homemade derailleur transmission?

Give it a whirl, why not I figure & it will definitely work lol, it's for how long I wonder about is all, they're temperamental & comparatively delicate even in the best of situations - then again an $80 experiment is worth every penny even if it turns out to be no more than a learning experience.

Some stuff I've learned - chain whip/slap can be an issue at the higher speeds we have - a stronger or additional return spring may aid this & if you use a thick/tacky lube or cheap chain the links may bind, snarling in the derailleur & ripping it apart. If the power application is too abrupt (engagement/torque) the freewheel pawls may fail and/or sheer teeth off the cogs. Oddly, chain/cog wear doesn't seem to be a problem but the potential for the occasional catastrophic failure shouldn't be dismissed as even a slight maladjustment can have grave consequences (chattering between gears/indexing failure can and will cause serious damage w/this load).

Example of (mild) chain whip w/a new chain & fresh, light lube during one of the seemingly endless indexing sessions: http://youtu.be/_GTS0xG8BPM

This design of yours looks promising, I would hazard the guess that you may have issues with the "input shaft" to "gears with derailleur" chain as it looks quite short, the closer the two points the greater the angle the chain has between it's lowest & highest gears, causing indexing issues and problems with the chain skipping off the forward cog;




...and I would remind some there's a difference between saying "it can't be done" and advising of problems that have been experienced, between nay-saying and trying to help.

Last edited by BarelyAWake; 12-31-2013 at 07:36 PM.
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Old 12-31-2013, 07:37 PM
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Default Re: homemade derailleur transmission?

Yes sir, with that said let experimentations commence!
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