[ale] OT geek motorcycle?

[Danny Cox]

Stephen,

On Sun, 2004-04-18 at 07:46, Stephen Turner wrote:
> hey im playing with the idea of an electric motorcycle, figured since we
> got some geeks here that like living outside the box maybe a couple played
> with the idea themselfs? if nothing else i will most likely make a
> electric gokart :D

	Once upon a time, in a galaxy called Milky Way, I made an electric
mini-bike for a science fair project.  We (I found some guys at an
electric motor rewinding company to help) took a old six volt generator
from an old junked truck, they rewound the rotor, sand-blasted the
housing, and welded a mounting bracket to the frame.  With one "compact"
12 volt battery, the speed was unimpressive at maybe 6 miles per hour. 
With two though, it was pretty fun!  On the other hand, it was pretty
heavy!

	The main problem with electrics, as always is the throttle, or more
precisely, the lack thereof.  The mini-bike had an on/off switch.  If
you use a rheostat, you lose the energy as heat, and the batteries wear
down as if you were full throttle all the time.

	The answer is to get to big (in terms of current) FET transisters,
usually ganged together.  You feed 'em a square wave, I think in the
6-10K Hz range, and vary the on-time to the off-time (pulse width
modulation) to achieve the throttle control.  It's not hard (for an EE),
but it's certainly beyond me (a software weeny).  For a go-kart or
mini-bike, it's much safer (lower voltage).  For a car, you need 6-800
volts, and the danger of touching body parts across live contacts gives
a new meaning to the word "terminals".

	So: that's about my knowledge limit.  Any other input?

	Stephen: go fer it!

-- 
kernel, n.: A part of an operating system that preserves the
medieval traditions of sorcery and black art.

Danny