homemade derailleur transmission?

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Sidewinder Jerry

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Dec 19, 2011
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I've got a 5 speed autoshifting bike. It shifts 5 gears automatically. I use a Sram 890 chain its always held up good for me.
 
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Sidewinder Jerry

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I'm currently using a Robin Sabaru EHO 35. Which has 1.6 hp. I'll be upgrading the engine to a Honda GXH 50 soon. I'm going to put the R/S engine on a Columbia bike. The Columbia will have a wide range 5 speed Strumy Archer internal hub. I've figured out a way to modify the LandRider autoshift derailleur to use it with the S/A hub. It to will shift 5 gears automatically.
 
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Sidewinder Jerry

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Yeah that's a bit much. The cops where I live don't mess with you as long as you use small engines. But here 212 cc would be considered a motorcycle. I'm sure some of the racing guys will be able to help you.
 

maniac57

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I wonder is there a possible way to make an existing derailleur system work to handle the power.

Handle the power of a 212cc pred?
Not going to happen. It will eat gears and chains in short order.
That kind of power would destroy any shift kit I'm aware of.
The best way to get wider speed range reliably would be to use a torque converter/variator/CVT style transmission.
 

mat_man

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Sidewinder Jerry

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Are you asking is there a way to widen the jockey pulley arm for a wider larger chain? Is there a way to get larger jockey pulleys for a larger chains? Can you put sprockets and spacers designed for a larger chain on a freewheel or cassette core? All this for the purpose of running a 212 cc engine through it. This all seems a bit much. You'd probably be better off seeing if you can get a semi automatic transmission off a motorcycle, scooter or moped. There's several 3 and 4 speeds which use a centrifugal clutch. That's probably going to be your best bet.
 

16v4nrbrgr

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I'd check out a CVT for the 212, it's not the HP that'll kill a derailleur but the torque, it would prolly munch a geared hub right off the bat as well. Fortunately there are a lot of minibike CVT's for sale for the 3/4" shaft four strokes. I don't think a derailleur would work with a cassette of gears for wider HD chain, the chain needs to have side play in order to jump gears, the wider the chain, the less it will allow that movement.
 

jazz2561

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Thanks for all the replies, see I would get a CVT or motorcycle transmission. The problem is, im in college and tight on money, so, one day I got the brilliant idea of taking the design of a derailleur system and custom building one with 5 or 6 plate sprockets and 35 or 41 chain. The idea seems kind of promising considering ebay.
 

Sidewinder Jerry

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There's nothing wrong with brain storming. What you're suggesting may be possible but it would require building by means of machining and fabricating a heavy-duty version of a current derailleur. In other words you'd have to build some that currently doesn't exist. Then comes the freewheel or cassette you'd have to fit sprockets and spacers onto them. The freewheel or cassette cores only have two pawls in them and wouldn't be able to handle the torque of a large engine. Last of all you'd have to design a shifter(s) since the spacing would be different between the gears.

As for building a stronger multi speed freewheel I'll be doing a tread on that soon. I'll be showing how o turn a White Industries Trails single speed freewheel into a 5 speed freewheel. The WIT freewheel has six pawls and 72 points of engagement.
 
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Sidewinder Jerry

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Are you talking about a single sprocket on the rear freewheel and using the front derailleur to shift gears on a shift kit? On a Staton inc shiftkit you can put 3 chain rings to drive the rear wheel. Then a modified rear derailleur would be like a chain tensioner but there's several gain tensioners that would work better. I've got two WIT freewheels in my shiftkit. I could actually tell you a way to design a 3 speed system with a shiftkit but it would cost as much as or more than getting a cvt or motorcycle transmission.
 
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jazz2561

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Not exactly, think of it like a standard motorcycle transmission. On the engine is a centrifugal clutch with a chain going to a input shaft. On the input shaft a front chain ring is mounted and a chain goes to 6 gears and the derailleur system. The gears and derailleur system is mounted on the output shaft, and the output shaft has a sprocket with chain running to the rear wheel.
 

Sidewinder Jerry

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Now that I see what you're talking about it could work. You wouldn't have to change the derailleur at all or the freewheel since they aren't bearing a direct load. I would suggest using a Sram 890 chain.
 

BarelyAWake

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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.
 
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