RE: e-tek speed ratings

[Roger Stockton <rstockton@delta-q.com>]

On Tuesday, January 29, 2002 10:12 PM, Dylan Pfeifer 
[SMTP:dcpfeifer@earthlink.net] wrote:
> While the E-tek motor is in on the table, I was wondering if I 
could
> drop in a question that maybe other buyers have...
>
> Suppose I've got an 810 rev/mile tire, and I'm designing it to
> cruise at 60mph with the E-tek.  Single gear trans.
>
> Well, the E-tek says "min nonload speed"=3,200rpm, and "max nonload
> speed"=3,600rpm.  Not knowing any better, suppose I think this 
means
> "can't run slower than 3,200 rpm and can't run faster than 3,600
> rpm."

Just a guess, but I think what this means is that the no-load speed 
is spec'ed to be in the range of 3200-3600RPM.  Put another way, they 
are stating that the RPM/volt constant of the motor is in the range 
67-75RPM/volt (assuming a 48V pack).

> So say I gear the E-tek with chain and sproket 0.23:1 ( 60mph with
> 810rpm @ tire and 3,500rpm @ motor).
>
> Well, but if I go 30 mph.  Then the E-tek is going 3,500 * 0.5 rpm,
> below it's minimum speed rating.
>
> So what happens... does the motor overheat... blow up.. what. 
  What
> happens also if you exceed 3,600 rpm, say going downhill.

You are fine going slower, although if you go too slow, the motor may 
have insufficient cooling and overheat.  If you exceed 3600RPM, the 
motor will fail, though possibly not until 4000RPM or so.

Gearing for a top speed of 60MPH with a motor that can only sustain 
about 8HP for any length of time seems a bit ambitious; but the real 
problem may end up being at the lower speeds.  Because of the tall 
gearing you will need a fair bit of torque to accelerate or climb 
hills, but the motor cannot take very high current, and not for very 
long.  The vehicle will need to be very light and aerodynamic.