Depends how the rotor is built, there is significant stress on it, not
just the bearings. My previous EV had a Hughes induction (AC) motor with
a 9,000 RPM redline and I believe that at that speed, the rotor surface
is going
about 300 km/h (200 MPH) in a thight 1/2 ft circle, so the centrifugal
forces on that rotor surface are enormous, at some point it will
litterally be pulled apart by the force that wants to let it fly in a
straight line instead of turning a 1/2 ft circle at a third of the speed
of sound.

Cor van de Water
Chief Scientist
Proxim Wireless Corporation
Email: Private:
Skype: cor_van_de_water Tel: +1 408 383 7626

-----Original Message-----
From: EV [] On Behalf Of Dennis Miles
via EV
Sent: Tuesday, August 05, 2014 7:58 PM
To: Lee Hart; Electric Vehicle Discussion List
Subject: Re: [EVDL] Hybrid Mustang: motorcycle drivetrain?

Lee, I must be too young to have seen those, or else I did not have one
fail because they were stronger. The other question is how does it
the AC motor to over speed and why does a speed limiter in the
controller/inverter cause damage as was indicated in the discussion? The
motor doesn't have a commutator, or windings on the rotor so what is the
harm in driving the motor to more than 8,000 rpm? All I can conceive are
bearing stresses.

Dennis Lee Miles

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On Tue, Aug 5, 2014 at 7:43 PM, Lee Hart via EV <>

> Dennis Miles via EV wrote:
>> David, and others, the most fragile part, of a series DC motor, is
>> commutator. And that is, because the copper segments are glued to an
>> insulating core. When the current is flowing, the segments heat up
>> soften the glue, then they are subjecting to "lifting," away from
>> insulating core, and causing problems with the brushes, resulting a
>> for an extensive repair. But, with no (or very low) current, the glue
>> maintains its strength, and the motor can be spun to a higher RPM,
>> damage.
> Relatively new DC motors are built with commutator bars that are glued
> place. Older and heavy-duty motors instead have "steel" commutators
> don't depend on glue to to hold the bars. Instead, there are steel
rings at
> each end hold in the bars. They use mica or other materials to
insulate the
> bars. This type of commutator is much stronger, and better able to
> withstand high temperatures and high RPMs.
> Here's one image I could quickly find:
> --
> We cannot waste time. We can only waste ourselves.
>         -- George Matthew Adams
> --
> Lee Hart's EV projects are at
> _______________________________________________
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