How good is governer mode on an ESC? - RC Groups
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Jan 23, 2002, 08:21 PM
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How good is governer mode on an ESC?

If you set your throttle to, say, 80% at zero pitch. How much variation do you have when pitch is changed for the non-governer mode vs. the governer mode.
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Jan 23, 2002, 09:11 PM
Registered User
When you step on the gas in your car how fast does it accellerate? It depends...

80% is usually about the highest you can go for really good governing if everything else is right - assuming you radio's 80% is the 80% I have in mind from mine .

Is the motor big enough and low enough resistance to maintain the load? Is your max pitch appropriate for the power system? Have you chosen a pinion size which matches the torque of the motor to tha maximum load? All these affect whether the headspeed will hold or not.

Assuming everything is roughly correct then it holds the speed quite well, you can hear a change in sound but unless you get a guy with one of those spinning disk tacho things to actually measure the inflight RPM it is pretty hard to tell. When you push in the pitch the gear noises chage and the blades noises change. The RPM may chage somewhat but if everything is right it isn't much IMHO. But, I could be prooved wrong with one of those tachs .

You cold potentially get a better match with a throttle curve I suppose but that would take a lot of iterations...
Jan 23, 2002, 09:31 PM
Registered User
I totally agree with Chris... it depends on the setup. The more power headroom you have, the better it will govern... and there still might be some incompatibilities between the motor and ESC and the heli as a system. That's worth a pretty long research paper in itself.

Still, when it's working well, it is great!

Greg in Minneapolis
Jan 23, 2002, 10:31 PM
Registered User
Chris: I'm not talking about comparing it an ESC in governer mode to a computer TX with throttle curves.

Electric motors try to maintain the rpm for the voltage they are fed over a wide range of power settings. That's why they have a voltage constant. They are essentially a constant speed device, meaning that they are self governing. It would seem to me within reason that any old ESC could supply the motor a constant voltage and that it could govern itself assuming it had enough power to do the job.

What are the governer ESC's actually doing?
Jan 23, 2002, 10:57 PM
Registered User
While electric motors try to stay at a constant speed, because of imperfections in their generating mechanisms (mostly resistiive loss), they don't. Active speed governance can be much more effective at maintaining a constant speed than the motor's intrinsic perpensity to maintain rpm.

Much of what causes this is the tremendous difference in power requirement between on-the-ground spool-up and hover and full-pitch climbs... big current diff between these states.

It's like taking a typical motor, say an Astro 05, and running it through prop sizes from a 5x5 to a 9x6... from almost no load to overload. That will cause a significant rpm diff at a constant voltage... having it idling at 80% (spool-up) and having the controller responding to speed variations by varying the voltage will allow some constancy of speed.

Greg in Minneapolis
Jan 23, 2002, 11:00 PM
Registered User
Ahh, OK. No, that won't work too well. If you had a really strong low resistance motor you would get a 5-10% speed sag at a guess. The problem is that such a motor makes a miserable heli motor, it would be great for F5B though! A really strong low resistance motor has it max efficiency at high currents - say 40+ amps. In a heli the hover point will be between 11 and maybe 22 at most for a less efficient desing or one running a low cell count in relation to its weight. If you look at the efficiency curve for a strong motor at less than 20 amps you would be way down - in the 60-70% area rather than 80. Duration will be poor. A good heli motor which is most efficent at say 15 amps will sag much more when operated with no speed or power regulation.

Not saying you can't fly that way, it would work but the headspeed will not be constant.
Jan 23, 2002, 11:04 PM
Registered User
Another piece of data... typical prop setups have a motor running at 80% to 60% of no-load rpm for a given voltage input to do reasonable work... in other words, my AFI 05 from above on 7 cells might turn 18000 RPM... but with a useful prop like a 7x6, it will be turning at around 13000 RPM.

That same AFI 05 in a heli, if you were running it on the same pack at full throttle, at spool-up, might be running at a load equivalent to about 17000 RPM... so not quite no-load, but a very light load. Then when you hover, it might be running at a load equivalent to about 15500 RPM. Then when you punched full pitch, it might run at a load equivalent to about 9000 RPM... and be pulling way more amps than at spool-up.

Does this help?

Greg in Minneapolis
Last edited by gstew; Jan 23, 2002 at 11:16 PM.
Jan 23, 2002, 11:15 PM
Registered User
I think Chris and I are saying the same thing in different ways... I think he's saying that a strong motor with a high Kv and low resistance would give you the least variation in head speed from spool-up to full pitch when run at a single throttle setting, and would be very inefficient when used as a heli motor.

What I'm trying to say that a more typical heli motor, a less-strong motor with a more well-matched Kv (which means higher resistance) would show more variation in head speed from spool-up to full pitch when run at a single throttle setting, even though it is probably a better choice as a heli motor.

Chris, did I get this right?

Jan 24, 2002, 02:37 PM
Registered User
I think you're all saying that the motor would lose too many rpms. I think an interesting experiment would be to take a VoyagerE with a stock motor and 9-10 cells and replace the the ESC with an off/on switch. (I think the motor is brushed.)

Set the transmitter at zero pitch, gingerly switch the motor on, stand back and fly!

How would it work?
Jan 24, 2002, 02:46 PM
Registered User
Pretty much, except Kv isn't necessarily the factor changing. You could go from a high wind little motor to a medium wind mid size motor and a low wind big motor without changing the Kv, the resistance would drop a lot though which is what counts as far as ability to maintain RPM under load. Less resistance means less voltage loss inside the motor which is what causes it to slow down according to Ohm's law...

Speed maintenace depends on snot . Bigger motors have more snot!
Jan 24, 2002, 02:48 PM
Our Daddy and Heli Junkie
Fred Bronk's Avatar
No! An on/off switch would give you short flightimes, cook the motor and batteries and be very hard on the gears!

If you notice the motor is almost never setup to "run" at full power, but the ESC will use full power to maintain the HS you want. Hense a smoother flying heli with a constant HS.

When the HS goes down under load (you hear the motor bog) the recovery time is very fast if the setup is correct. It is like flying an IC heli with a good throttle curve so the motor is always in the "sweet spot".

Just like on a car. You have a throttle to keep the engine in the torque curve to make it driver friendly. Otherswise you could just wire the throttle wide open and slip the clutch!
Jan 24, 2002, 04:35 PM
Registered User
Fred, I wasn't seriously suggesting an off/on switch!

If you can get the motor up to speed, I was suggesting that the ESC (and governor mode) wasn't really necessary to operate a CP heli.

Of course, for brushless motors, an ESC is essential since it performs the commutation function as well as the throttle function.
Jan 24, 2002, 06:49 PM
Our Daddy and Heli Junkie
Fred Bronk's Avatar

It just threw me too see that, although it used to be the norm!