Brushless electrics and headspeed

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Robert Roland - 13 Oct 2007 11:46 GMT

How do the electric helis obtain a constant headspeed?

My Raptor 50 has a governor that adjusts the throttle to keep the
headspeed constant.

I guess you could to exactly the same with an electric, and simply
connect the governor to the motor's speed controller.

But with the brushless motor, the speed controller already "knows" how
fast the motor is spinning, and is able to very directly regulate the
motor speed. This makes me think it should be possible to design a
speed controller that drives the motor at a constant speed, and simply
adjusts torque as needed. Is this how it's done in practice?

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RoRo

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Ron van Sommeren - 13 Oct 2007 14:40 GMT

Goedendag Robert,

A brushless motor by itself already wants to maintain its speed: Rpm =
voltage*Kv. If you keep voltage the same, rpm will not change.
Unfortunately, the motors are not perfect, winding resistance is not zero
and rpm will drop when the motor delivers more torque.

I know nothing about governors, but here's is list of diy brushless
controller designs:
<http://www.rcgroups.com/forums/showthread.php?t=140454>

Maybe ask your question in this excellent diy controller design discussion:
<http://www.rcgroups.com/forums/showthread.php?t=200567>
Or in this group:
http://www.yahoogroups.com/group/osmc

Prettig weekend ;-) Ron van Sommeren
near Nijmegen, the Netherlands
int. E-fly-in http://home.hetnet.nl/~ronvans

> How do the electric helis obtain a constant headspeed?
>
[quoted text clipped - 9 lines]
> speed controller that drives the motor at a constant speed, and simply
> adjusts torque as needed. Is this how it's done in practice?

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Kevin - 13 Oct 2007 19:38 GMT

a lot of speed controllers have it built in already even some of the
cheap ones

http://www.redrockethobbies.com/35_Amp_Brushless_ESC_w_Governor_Mode_5V_BEC_w_EC
3_p/agne35g.htm

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Doug McLaren - 14 Oct 2007 19:19 GMT

| But with the brushless motor, the speed controller already "knows" how
| fast the motor is spinning, and is able to very directly regulate the
| motor speed. This makes me think it should be possible to design a
| speed controller that drives the motor at a constant speed, and simply
| adjusts torque as needed. Is this how it's done in practice?

There's already a number of ESCs out there that can do this out of the
box. And then the Castle Creations ESCs have a mode caleld `Governor
Mode' where the stick position contols the RPMs rather than the
throttle, and so you can easily program your radio to keep the RPMs
pretty much constant just by not moving the throttle channel at all in
normal flight.

As for how it's done in practice, if you drive the motor at a given
speed, you don't have to adjust the torque at all -- the motor itself
will take care of that. The more `behind' the motor gets, the more
current it will draw and so it'll be self-regulating (at least until
it gets so far behind that it falls apart completely.)

Either way, you don't have to build it yourself -- many ESCs can do
this for you already, perhaps with a little programming help in your
TX to help.

Signature

Doug McLaren, dougmc@frenzied.us
That which does not kill me can still really hurt.

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Model Forum / Radio Controlled / Helicopters / October 2007

Brushless electrics and headspeed