DIYbanter - View Single Post

wrote:
because of the high proce of gas, would putting a motor on a bicycle be
practicle to get to work a few days a week? I live about 18 miles away
it is all highway with a wide berm for bicycles. I have a spare 5 horse
motor from an old tiller. Could I mount a bracket and put it above my
back wheel to drive the back wheel on my 10 speed mountain bike? Would
I be able to pedal it home if the engine failed? How would I rig a
clutch of some sort or would I even need it? Seems like an interesting
project.

How fast could you go with a 5 horse motor?

I've done exactly this project with a motor from a weed whacker...
but I don't remember the horsepower (it was probably less than 5 though)

The basic problem is gas engines like high rpm to provide high torque.
In practice once I got going about 25kph, I could get cruising speed to
happen, and accelerate a little as well)

My clutch was a brake cable attached where one brake normally would go,
my transmission was a rollerblade wheel attached directly to the shaft
of the motor. The size of the wheel is critical in the distribution of
power to your bike (it acts as a gear, but doesn't always start with a
useable ratio, I had to take a little material off of one I used).

I physically pressed the rollerblade wheel using my "clutch" into the
rear tire by having the motor slide at one contact point(nearer the
shaft) on the motor mount, and fixed (but freely rotateable) at it's
other mount point (farthest the shaft). Using this method, I used the
rotating rear tire to start the motor (no pull cord for me).

For safety reasons, I included an electric kill switch located at one
handlebar.

Eventually I had to retire the contraption. The vibrations shook the
bike apart eventually causing faliure of many things (it was a drum
brake bike, and the drum was shaken apart). You could prevent this, but
the engineering time would be significant.

My top speed was over 75kph downhill (I often passed regular vehicles,
and that does get one some rather surprised looks), and this was clearly
a dangerous speed (I wore no helmet).

The gas was excessively cheap, and your 18 mile commute would have cost
pennies.

I often rode it with the engine off, and the weight was not too much
trouble.

Having done all that (and I encourage you to give it a shot, and let us
know how it goes), I would highly recommend however that you do an
electronic conversion instead.

Electric motors like to give you high torque at low rpm (which a lot of
biking demands), and doesn't totally **** out at higher rpm. The
vibrations would be less, hence less repair worries, but the final
weight will be much higher due to batteries.

My drawing board stage project is for an electric bike with an enclosure
so I can drive in the rain, and have better aerodynamics, and it will
be a recumbent... If I only get the time. My commute is slightly over a
marathon.