Re: Afordable BLDC drives (was Re: nubie questions)

[Lee Hart <leeahart@earthlink.net>]

Colin Dedman wrote:
> Anyway, here are some BDC motors that will certainly "blow the pants
> off" a brushed motor of the same weight and RPM.
> 
> (a) Unique Mobility DR086S 16-pole BDC
>     4.3 HP cont. @ 5000RPM, 3.9kg, 94% eff
> 
> (b) Kollmorgen RBE-03010-C 12-pole BDC
>     700W cont. @ 2900RPM, 3.4 kg, about 90% eff
> 
> (c) Litton BN42-43AF, 8-pole BDC
>     824W cont. @ 3849RPM, 4.0kg, about 90% eff
> 
> (d) Build your own brushless, ironless NeFeB disk motor.
>     Expect similar power/weight to (b) & (c), but peak eff=95%,
>     and >90% eff over an 8:1 range of power, which is impossible
>     with an iron motor, much less with a brushed motor.

Impressive motors, but I'm not sure they prove your point.

First, when a motor requires a controller, I think you need to include
the size and weight of the mandatory controller. After all, the
commutator in a brushed DC motor is its "controller", and is included.

Second, there is a tendency to leave out controller losses when talking
about such motors. The motor may be 90+% efficient, but the controller
is less than 100% efficient, too.

Third, especially for on-the-road EV sized motors, they leave out the
cooling system losses. All those pumps, radiators, filters, etc. in an
EV-1 drive system consume power. They are powered off the battery pack,
rather than by the motor itself. The corresponding cooling system for a
brushed motor is often an internal fan, whose load automatically
subtracts from HP and counts against it for efficiency calculations.

If you look at a high performance DC brushed motor, like the Lynch or
Lemco, you also see 90+% efficiency and a very high power to weight
ratio. Other examples include Portescap instrument motors (ironless
rotor brushed motors), and R/C model car and airplane motors (neodymium
PM brushed motors with extremely high power-to-weight ratios).

Is there any fundamental reason why you can't take any high-tech
brushless motor construction, and replace the exotic controller with a
commutator and/or slip rings?
-- 
Lee A. Hart                     Ring the bells that you can ring
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leeahart@earthlink.net                  Leonard Cohen