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Author Topic: Why are ACTion Speed Controllers Number of Motor Pole Dependent  (Read 295 times)

Tug Fanatic

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I thought that I basically understood brushed motor controllers. The early one were simple resistance and the later examples turn the power to the motor on & off many times a second. The variable on/off time is the controler but then...........

I have been looking at a new brushed controller and the ACTion controllers are on my list. When I looked I found apparantly similar controllers but with different versions for differing numbers of motor poles. I could understand this with brushless motors but what difference does the number of motor poles make with a brushed controller and why is it an issue with ACTion but ignored by everyone else that I have looked at.

ACTion P79 controller that specifies not suitable for 7 -12 pole motors:https://www.componentshop.co.uk/p79-condor-10-2-autoset-computer-speed-controller.html

ACTion P79S controller for 7-12 pole motors:https://www.componentshop.co.uk/p79s-condor-10-2-autoset-computer-speed-controller-for-7-12-pole-motors.html

 {:-{ {:-{

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raflaunches

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Re: Why are ACTion Speed Controllers Number of Motor Pole Dependent
« Reply #1 on: June 09, 2021, 08:28:53 pm »

Iím no expert on ESCs but when Iíve tried hand turning the con on various brushed motors and the ones with less poles are harder to turn so Iím guessing that more power is required to control a lower number of poles whilst less might be required for more poles. Iím only guessing but thatís my theory- hopefully someone knows the technicality.
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Fred Ellis

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Re: Why are ACTion Speed Controllers Number of Motor Pole Dependent
« Reply #2 on: June 10, 2021, 08:32:02 am »

Hi


Have you asked Component shop ?


I have always found them to be most helpful when I have asked them for help.
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malcolmfrary

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Re: Why are ACTion Speed Controllers Number of Motor Pole Dependent
« Reply #3 on: June 10, 2021, 08:52:25 am »

Guessing, but it is possible that when those ESCs were designed and developed, available hardware determined the operating frequency.  Offering a switching frequency in the wrong band to a motor with a high pole count could result in the on pulses being offered out of sync with the position of the brushes and commutator, resulting in stuttering. 
Since high pole count motors were not common in the model supply world, not a serious problem.  Unless the enterprising modeller decides to use motors from car scrap yards intended for heater blowers, radiator fans, electric windows etc.
When messing with my home made (train) speed controls back in the early '70's I was constrained by the real world and what I had available.  Going for a low frequency, the parts to generate that low pulse rate were unfeasibly large.  Going for higher frequencies, I didn't have easy access to test gear that would allow easy testing.  Like much engineering, the result was a compromise.  The resulting constant 1KHz whistle was sub-optimal, but not too bad in a model diesel loco.
The same problems would have faced any designer 20+ years ago, but rather than the physical size of components, the limit would be processing speed.
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Tug Fanatic

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Re: Why are ACTion Speed Controllers Number of Motor Pole Dependent
« Reply #4 on: June 10, 2021, 09:07:35 am »

How old is the ACTion design?

I have a controller that I made in the early 1980's which still works perfectly well for everything from a Garupner Speed 400 to a car heater motor.

Unfortunately it is rather learge and the main ic's are no longer available.
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malcolmfrary

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Re: Why are ACTion Speed Controllers Number of Motor Pole Dependent
« Reply #5 on: June 11, 2021, 09:21:15 am »

How old is the ACTion design?

I have a controller that I made in the early 1980's which still works perfectly well for everything from a Garupner Speed 400 to a car heater motor.

Unfortunately it is rather learge and the main ic's are no longer available.
Late '90's, early 2000's.
Early ('80's, through '90's) ESCs used the radio frame rate for their timing.  This was 50Hz, and gave that deep hum.  The chip responded to the circuit around it, translating the pulse length from the radio into the required output.
Early PIC designs had their own oscillator allowing the output frequency to be independent of the radio frame rate, and higher was considered better.  Translation is done by the program built in stepping through its sequence.  Because any computer can only handle so many operations per second, the higher the frequency, the fewer steps available to define each output pulse, so control became coarser in that the steps between stop and full speed were fewer, thus bigger.  The compromise settled on worked great on 3 and 5 pole motors, but could get out of step with high pole count motors.
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Tug Fanatic

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Re: Why are ACTion Speed Controllers Number of Motor Pole Dependent
« Reply #6 on: June 11, 2021, 12:21:48 pm »

Malcolm

Thank you for that explanation.

Does the rpm that the motor is running at have any impact here? I guess not as both fast & slow motors run at the same slow speeds if asked to do so.

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HMS Invisible

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Re: Why are ACTion Speed Controllers Number of Motor Pole Dependent
« Reply #7 on: June 11, 2021, 12:45:36 pm »

Malcolm

Thank you for that explanation.

Does the rpm that the motor is running at have any impact here? I guess not as both fast & slow motors run at the same slow speeds if asked to do so.
The bottom line for the esc designer  is to pulse on/off fast enough that the rpm x pole count can't catch up.

 
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malcolmfrary

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Re: Why are ACTion Speed Controllers Number of Motor Pole Dependent
« Reply #8 on: Yesterday at 10:19:00 am »

The bottom line for the esc designer  is to pulse on/off fast enough that the rpm x pole count can't catch up.

 
Yes, and if the constraints of the possible speed of the hardware available at the time did not allow that situation to be avoided, rpm x pole count would catch up.  An on-going problem of finding the right compromise ever since analogue and digital started being converted into each other. 
Using ingenious circuits around a chip was very good at doing the conversion.  Using low powered computers-on-a-chip to do the same job ran straight into the problem area, even more so since expectations of "digital" were, and are, so far in front of reality.  It did cut the component count down enormously, though.
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Re: Why are ACTion Speed Controllers Number of Motor Pole Dependent
« Reply #9 on: Yesterday at 11:02:42 am »

Look again at the hardware and the pdf.
Craig Talbot's legacy had already included PIC processors in the DP relay speed controllers.
I pointedly asked DM, when he had an 11kHz esc on the demo board, why he kept any frame rate (~ 50Hz) controllers at all.
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