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-   -   Multi gear weed whacker powered bicycle (http://www.diygokarts.com/vb/showthread.php?t=9296)

Suicidaltendencies 10-24-2010 03:21 PM

Multi gear weed whacker powered bicycle
 
As the title says: I wanna make a multispeed bike. I have a mountian bike sitting in my backyard. I also have a weedwacker that was written off by my dad as dead so i have takin it in and got it running, now i wonder if it is possible to mount the engine to the bike and use the rear gears of the bike still.

devino246 10-24-2010 03:28 PM

Bike gears wont be able to stand up to the RPM of the weedeater engine.

Suicidaltendencies 10-24-2010 03:35 PM

Dang. well thats why i asked

Russ2251 10-24-2010 03:46 PM

Weedie engines do not produce a lot of power.
Should work if properly planned out. Centrifugal clutch is a must. The fewer the teeth...the better.
Engine should be mounted to drive the pedal sprocket. The rest is cake.

devino246 10-24-2010 04:10 PM

Quote:

Originally Posted by Russ2251 (Post 117958)
Weedie engines do not produce a lot of power.
Should work if properly planned out. Centrifugal clutch is a must. The fewer the teeth...the better.
Engine should be mounted to drive the pedal sprocket. The rest is cake.

Considering the amount of offset between multi-speed bike sprockets, i would think the chain would frequently jump. Although, if its geared down to near-human speeds, I suppose it would work.

Russ2251 10-24-2010 04:26 PM

Quote:

I suppose it would work
Again...If planned properly, it will work.
RPM must be kept low when shifting.

Doc Sprocket 10-24-2010 06:08 PM

RPM has to be calculated, but I would think the engine would have to drive a jackshaft for a primary reduction, then the jackshaft would drive say, the larger sprocket on the crank, then the smaller sprocket would go to the wheel. You'd lose the high-low shift, but retain the shifting at the rearend. Alternately, if you could find a way to add another sprocket to the pedal crank, the engine could drive IT, leaving the factory shifting intact.

Suicidaltendencies 10-24-2010 06:35 PM

Well the pedals have 3 gears the rear has 8 so ill see what i can think up

Russ2251 10-24-2010 06:36 PM

Use the largest of the 3 to start.

Suicidaltendencies 10-24-2010 06:38 PM

Will do

Kenny_McCormic 10-25-2010 02:56 PM

Keep in mind most gears on a bike are overdrive gears, so a lot of reduction will be needed before you apply power to the bikes crank.

GreyhoundOfYerfDogs 10-25-2010 03:05 PM

I did this as a teen with a strange off-brand engine I had found in an alley (small 4 stroke.) Rather than use the bicycle gears I used a rubber wheel about 4" diameter bearing against the rear tire. Using scrounged parts only, the gearing wasn't good at all, but it would propel my bike along faster than I could pedal. Running through even a little water made the wheel slip. If I did it again, a better drive wheel would probably solve these issues; rock-hard solid rubber with grooves is NOT the hot tip. Using the bicycle gears isn't that great of a plan unless you can get some mad reduction gearing.

robbie 10-25-2010 03:59 PM

If your engine drives the largest sprocket on the pedal assembly I think you could make it work.

When you cruise on a normal mini bike and then let off the throttle, the spinning wheel keeps the clutch engaged until you slow down enough for it to let go. On a bike, the pedals drive the wheel but not the other way around. This would allow you to release your throttle and coast. Then you could probably shift gears with little engine bursts, without everything going bonkers the whole time you're moving.


If you set up the engine to drive the large pedal sprocket, you can use the two smaller sprockets as normal. You may need a reduction between the engine and the pedal sprocket, but that's another issue.

Russ2251 10-25-2010 05:08 PM

Just do it...
As I previously stated, it will work.
Most difficulty will be in mounting engine.
Keep driving chain as short as possible, meaning keep engine PTO as close as possible to pedal sprocket.


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