compact, lightweight, gear reduction for hobby project

[svejkovat]

I'd like to attach a 26cc Ryobi 4 cycle weed trimmer motor to a commuter bicycle to supplement pedaling. I'd like to do this as efficiently and elegantly as possible.

Versions I've seen resort to friction drive direct to the tire or enormous pulleys to acquire speed reduction straight off of the motor's shaft. I'd rather see if it's possible to mount the engine more traditionally within the frame (like a motorcycle) and bolt a small planetary gear reducer directly to the back of the little gas engine. In this fashion I could more easily integrate the motor right into the bicycle's original drivetrain.

A cursory look at such reducers on the web reveals the tiny sets for use within power hand tools, and the industrial sized versions that weigh many time more than I can use.

Can anyone point me in a direction to start looking for a gear box that would be in useful range for this project?

 

[MikeHalloran]

Does a mo-ped need tags and insurance where you are?

Find out before you invest more effort.



Mike Halloran
Pembroke Pines, FL, USA

 

[svejkovat]

Yes it does. Tags, but no addit insurance. I have two Puch mopeds with current tags on them. I'll do likewise with this machine.

I'm thinking that the most straightforward answer may end up being a toothed belt to a jackshaft and then chained from there to the left side of the pedal crankshaft.

The Puchs are not really true 'mopeds' despite the label. In fact, few mopeds really are. The pedals are used to start the engine and that's about it. When forced to pedal primarily (out of gas or engine breakdown) it soon becomes apparent that walking it is preferable.

What I'd like to achieve with a supplemental little 4 stroke is the ability to truly supplement the pedaling power and arrive at some approximation of the 'best of both worlds'. Pedaling would still be the primary input, with the motor injecting comfort, range, and speed. This 26cc motor, with proper muffler, is whisper quiet.

But If I could find a robust and very lightweight planetary gearbox around 10 to 1, I might be steps ahead.

 

[MikeHalloran]

Friction drive direct to the tire is really the elegant way, from an engineering perspective.

Your way, you get to fabricate some nice shiny brackets, I'm guessing aluminum billet, drilled for lightness, and color anodized with polished highlights. That kind of stuff is elegant from an artist's perspective.

Unfortunately, you will also run into problems with the frame and the pedal crank bearings not being designed for the motor's chain pull. Similarly, the chain is undersize, as are the sprockets, as are the spokes, etc.

When you are done you will have one more, very expensive, moped.





Mike Halloran
Pembroke Pines, FL, USA

 

[svejkovat]

"Thank MikeHalloran for this valuable post!"

Thank you mike!

You're guessing alum billet, color anodized with polished highlights? Why on earth would you guess that mike? You in a bad mood?

This is simply for the challenge of seeking to integrate a 26cc 4cycle weed trimmer motor into an otherwise fully functional Specialized mountainbike. With a 26cc ryobi trimmer motor you couldn't overstress the componentry or the frame of a modern bicycle frame like this. Most bicycle athletes far exceed the capacity of this little motor's torque.

Nothing really constructive to add? Why even weigh into this then? Just can't stop yourself from being an irritating prick?

Yeah, yeah, yeah. I'll go away. Post some sniffling retort if you must. Doesn't seem to be worth my while here to stick around and have to read it anyway.