Reality Check Please (Newbie)

["Ashley Roll" <ash@digitalnemesis.com>]

Hi Everyone,

I've been lurking on the list for a few weeks now and trying to plan a
project and I would like to ask for a bit of a reality check - Is what I'm
planning possible.

First off, I'm in Brisbane Australia, are there any "local" list members?

For my real job I design electronics (mainly embedded control systems) so
I'm reasonably comfortable with the electrics, my main problem is
understanding the motor "size" that I need.

I would like to build an electric motorcycle. However I want it to be a
cruiser type motorcycle like a Harley (I'm quite tall and I don't fit
comfortably on most other styles of bike). This would be mainly for riding
around the city on errands.

I would like it to be able to get up to highway speeds (max legal is 110Kmh,
but a bit over that just so I can get out of the way of things would be
good.. lets say 130Km/h)

As for range, maybe 50Km would be ok, but obviously more would be better :)
I'm not a "lead foot", but being a motorcycle, you do need to be able to
accelerate reasonably quickly.

If I was to use a Harley Davidson (or similar) rolling chassis, I'd keep the
5 speed transmission, the gear ratios are (including chain gears to drive
wheel):

1st: 10.110   2nd: 6.958   3rd: 4.953   4th 3.862   5th: 3.150

so, if we assume the wheels are 60cm diameter, this gives us a wheel
circumference of about 188cm, and therefore a "wheel RPM" of just over 1150
RPM to reach 130 Kmh. This would mean that I would need a motor to be
spinning at a little over 3620 RPM in 5th to reach this speed.

I'm pretty sure I can change these as needed with out too much difficulty.
It would be a case of experimenting and optimising I guess.

Now the mass of a standard Harley with ICE is about 330kg. Perhaps a third
of this is engine and related stuff. As a reference, the standard engine
delivered 110Nm @ 3100 RPM.

If I were to use say 6 Optima YTs.. giving me 72V (assuming I can fit them
all, I would add as many as I could) each weighing about 20Kg, that would
add 120Kg and a motor and controller say another 30Kg I'd be ending up with
a weight of about 370Kg + rider.

Is this actually feasible? What size of motor would be usable? I'm looking
at some motors in a catalogue that have a stall torque rating of 26, 33, 56
or 82 Nm. (would need rewinding to work with 72V). the 26 and 33Nm motors
are rated to 6800RPM, the 56 and 82PRM are only rated to 2800RPM so some
messing with gearing may be needed to match the required speeds.

Using the stall current rating and the rated voltage, they workout at about
4.2KW, 3.8KW, 10KW, 13.8KW would any on these be usable? These are 3 phase
AC Servo motors. Yes I know they are more difficult to drive, but lets
assume that I can do that for now, I'm really just interested in the kind of
"size" of motor I need - I may switch to a DC motor later :)

Any comments. I'm I going in the right direction? Is this doable and what
sort of range could I expect? or am I totally nuts? :)

Where can I find info about calculating motor requirements?

Cheers,
Ash.

---
Ashley Roll
Digital Nemesis Pty Ltd
www.digitalnemesis.com
Mobile: +61 (0)417 705 718