[EVDL] How hard is it to turn a DC motor counter/clockwise? - DIY Electric Car Forums
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Old 07-05-2012, 02:56 PM
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Default [EVDL] How hard is it to turn a DC motor counter/clockwise?

Little question for the DC motor experts here:
When my EV is off, the motor is essentially unloaded
as I removed the power steering belt and also the
automatic transmission has no pressure so it will
rotate freely (this is noticeable when I place the
gear in Park and turn off the car, the motor will
spool down from "idle" (which is about 200-300 RPM)
until standstill in several minutes with a distinct
screeching sound that I attribute to the brushes
moving across the commutator.

Now, when I grab the pulley at the tail shaft, I can
easily rotate the motor, but I notice that the resistance
in the normal driving direction is much larger (and is
accompanied by the soft screeching sound from the brushes)
while rotating the shaft counter-clockwise (seen at the
tail shaft pulley) will run much lighter.
Something in me says that the normal rotation direction
should result in the smoother and easier turning, but I
can also reason that pushing the brushes backwards will
lift their surface from the comm and result in lower
friction. In reverse I do not hear the soft screeching
from brushes.
I wanted to check with the experts here that these are
correct observations, as I am still hunting for the
reason of the bad efficiency of my DC conversion with
automatic transmission.

BTW, yesterday I drained the transmission fluid, it was
indeed overfilled as normal it should have 3-4 quarts
and I could not get all oil in a gallon milk jug, so
it was probably 4.5 quarts in there. I put 3 quarts
back in, I did not notice much improvement though.

Cor van de Water
Chief Scientist
Proxim Wireless Corporation http://www.proxim.com
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