[ausev] hub motor noodling

[Chris Robison]

On Mon, June 12, 2006 7:42 am, MLAB said:
> I just got my renewed EAA membership card, so I think I will write this
> post that has been on my mind for a while.
>
> I deal with hub motors a lot since my EV work involves bicycles and
> tricycles (for myself or for clients).  I know that hub motors are used
> on electric cars as well, such as that ugly-as-sin but ridiculously fast
> Japanese 8-wheeler that graced the cover of a recent EAA newsletter.

Arguably the most important function of a suspension is not to provide
comfort for the occupants but to A) force a wheel that's hit a bump back
down onto the road as quickly as possible and B) make it stay there (not
keep bouncing). Add mass to the wheel (eg. by adding a heavy motor to it)
and you've made that job a lot harder. A wheel hanging in the air after a
bump provides no traction or grip for cornering. This problem increases
rapidly with speed, and wouldn't be much of an issue with bikes or small
scooters.

I'm guessing the eight wheels on the Kaz and Eliica concepts most likely
reduce the problem caused by any one wheel being momentarily airborne
after a bump.  Or perhaps I'm wrong and that's why you only see these cars
zooming around smooth oval tracks.  :o)



> So every time I see a Geo Metro (or the like) sputter past, I imagine
> stripping out the motor and drivetrain and attaching hub motors on all
> four wheels.  The front two motors would be identical, with low and
> medium-low speed windings, and the rear motors would be similar with
> medium fast and fast windings in each.  All four motors could engage at
> low speed for extra torque when needed, but normally only the front
> wheels would drive from a start.  This would give the car 4 speeds, and
> save room on the chassis for batteries.  Some sort of differential would
> connect between the steering sensor and the throttle system.

Maybe there's something I'm not thinking about here, but I'd say any time
you have a motor with more than one winding where the windings are used
individually and/or optionally, you've got certain operating modes where
some of that copper amounts to nothing more than dead mass. Probably
better to have all the windings in use at all times, but wired in a way
that gives you different gearing (similar to what I'll be doing with my
truck). Take advantage of the fact that you have four motors; make all of
them simple and identical. Wire them in parallel for high speed and in
series for high torque. Four motors would give you 3 basic speeds (all
series, two series sets of two in parallel, and four parallel). Simpler to
manufacture when all the motors are the same, simpler to repair, far
broader performance envelope as long as the motors can handle the current
and voltage extremes.

  --chris