>> Presumably, that rating is for a 100% duty cycle
This is my understanding, too.
Thanks for the responses, everyone. I think I'll stick to brushed motors for
now. Frank's points make a lot of sense to me. One more thing that concerns me
about the outrunners is that most of the housing I've seen are open. That's
good when you're flying a plane and want to use the air flow to cool the motor.
It's bad when there's dust and dirt everywhere and Will is trying to shoot
paint up my tank's ass !
- Doug
-----Original Message-----
From: [email protected] [mailto:[email protected]] On
Behalf Of Frank Pittelli
Sent: Wednesday, July 29, 2015 3:09 PM
To: [email protected]
Subject: Re: [TANKS] Re: brushless motor questions
I haven't looked at brushless motors in detail, but from a couple years of
Physics in college I learned that when you increase voltage/current in a coil,
you increase the strength of the magnetic field generated by the coil. So, I
suspect that the "RPMs per volt" rating for brushless motors tells you how much
voltage needs to be applied to pull the armature hard enough for a given speed.
Presumably, that rating is for a 100% duty cycle (i.e., max speed). Indeed,
the controller pulses the voltage for two purposes (a) to spin the motor one
way or another and
(b) to regulate the speed (i.e., decrease the average voltage seen by the coil).
With regard to torque, for a given duty cycle, if you decrease the input
voltage the torque will also decrease. But, if you maintain the same input
voltage, while decreasing the duty cycle, the torque will remain relatively
stable while the speed decreases. That's why really big earth movers and
locomotives use diesel-electric drive systems ...
maximal torque across a range of RPMs.
On 7/29/2015 12:18 PM, TyngTech wrote:
> Can't say I truly understand the brushless nomenclature (i.e. KVA)
> because nobody ever talks about the controller side. Brushless motors
> are basically steppers and without the controller are inert chunks of
> iron and copper. What I don't get is the KVA ratings (rpm's per volt)
> of these motors. In my mind, the controller dictates rpm by how fast
> it is energizing the phases, not by how much voltage is being applied.
> Voltage would affect acceleration and torque or am I getting this wrong?
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