Re: Reality Check Please (Newbie)

[Michael Shipway <mshipway@speakeasy.net>]

Ashley Roll wrote:
> 
> 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 guess I'm a good one to give some preliminary answers here.
I am just finishing a Honda Goldwing, for similar reasons.  I am 186 cm
tall.
And the Gold Wing has a large weight limit. 455kg(1050 lb.) GVW.
I've only gotten mine up to about 45 kph so far, what with my stuck
brakes.
http://www.generalist.org/madmike

I saw a very similar bike at the US Tour de Sol, that confirmed that my
math was about right.
They had the same motor (6 hp "AdvancedDC" brand, series wound, 72
volt), and twice the battery mass, and also no transmission.
I carry 100 kg (250 lb) of lead, removed the engine and transmission,
which massed 100 kg. together, so the bike is close to the original
mass.

The math says I should go about 10 km at 100kph or 50 km at 50kph.  A
motorcycle has the aerodynamics of a moose with a full rack.
 
> 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.

The math said I'd get more range by swapping transmission for another 30
kg of batteries.
I'd suggest using a belt or chain drive for ease of construction, and
besides you can change ratios easily.
My shaft drive is silent but it was a major headache. 


> 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.
> 

The Gold Wing was 200 kg, about 1/2 engine and tranny etc.
I'm another 100kg.  

> 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


-- 
Michael Shipway
mshipway@speakeasy.net
(301) 237-5563 (cell, any time)
(240) 683-0620 (home, evenings)
PO Box 1511
Washington Grove, MD 20880-1511