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Author Topic: Using a PWM signal to run an ESC controller for RC outrunner spindle motor  (Read 14541 times)

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Offline zarzul

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Has any had much luck using a PWM signal to run an ESC controller for a RC plane outrunner motor as a spindle.
I am trying to do this but having some difficulties.
The PWM is a little different for the ESC controller. 

This is a description of how they work.
DC ESCs in the broader sense are PWM controllers for electric motors. The ESC generally accepts a nominal 50 Hz PWM servo input signal whose pulse width varies from 1 ms to 2 ms. When supplied with a 1 ms width pulse at 50 Hz, the ESC responds by turning off the DC motor attached to its output. A 1.5 ms pulse-width input signal results in a 50% duty cycle output signal that drives the motor at approximately half-speed. When presented with 2.0 ms input signal, the motor runs at full speed due to the 100% duty cycle (on constantly) output.

I have had some success by doing an odd ball start sequence where I start the spindle and call for 50 rpm which gives me a 1ms pulse width, then a pause to allow the ESC to initialize, then I call for 100 rpm (scale of speed is 1000 rpm) and it will run 2ms pulse for full speed on the motor.
 
I don't think you are doing PWM correctly.  The word here is width.  A fifty hertz rate implies a 20ms time span.  If the pulse is on for 5ms and off for 15ms then the speed should be 25% and conversely if it on for 15ms and off for 5ms then you'd 75% speed.  However I believe that these motors don't have a good turndown (can't go very slow) because they don't have encoder feedback for commutation.  So they rely on the back EMF to determine pole position and that doesn't work well at low speeds.  So while they are very powerful for their size they are probably a poor choice for driving a spindle.  The same motor with a encoder and a controller that could accept an encoder feedback would be a pretty hot setup I would think.

Gary H. Lucas

Offline zarzul

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That is the problem,  the ESC controller takes a hybrid type of PWM. 

Since I am using this for engraving and PCBs the high speed works pretty well.

Thanks for your insight, the info on poor turndown is very useful.   I wonder if these could be run from a different type of controller?  Like a DC servo motor controller with encoder like you suggested?
Hi Zarzul,
I just saw this in Digital Machinist.

http://logicnc.com/home.html

Hope this helps,
Mike
We never have the time or money to do it right the first time, but we somehow manage to do it twice and then spend the money to get it right.

Offline zarzul

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Mike,

Hey thanks a lot,  I will check this out. 

Zarzul

Offline zarzul

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Re: Using a PWM signal to run an ESC controller for RC outrunner spindle motor
« Reply #5 on: November 06, 2015, 06:13:48 PM »
No luck there, he never responded.

I did run into a solution that Tweakie built,  http://www.openbuilds.com/threads/software-speed-control-of-a-brushless-dc-bldc-motor-from-mach3.478/  I will probably build it, it looks pretty easy with all the work Tweakie has done to perfect it.

I think there are probably other good solutions out there,  doing this with an Aurdino would be nice also,  especially if you could connect it on USB and use Modbus communication to pass the parameters for the proper RC servo pulse output.
I would try if I knew anything about programming an Aurdino.

Offline Tweakie.CNC

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Re: Using a PWM signal to run an ESC controller for RC outrunner spindle motor
« Reply #6 on: November 07, 2015, 05:08:03 AM »
Not exactly sure why Logicnc stopped making those controllers - they were cheap enough - still, I always find pleasure in making my own stuff.  :)

Tweakie.
Success consists of going from failure to failure without loss of enthusiasm.  Winston Churchill.

Offline zarzul

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Re: Using a PWM signal to run an ESC controller for RC outrunner spindle motor
« Reply #7 on: November 15, 2015, 09:09:56 PM »
Well, finished my Tweakie designed PWM to RC ESC converter.  Works great, thanks a lot for your design.  I was able to use your g-code for cutting the circuit board also.

Before installing this I had to stand and watch my machine,  as soon as I got a motor start command with the corresponding beep that signaled my ESC was armed then I would crank the speed control pot on my servo tester.  Pain in the ----.

It has prompted me to dig into programming for these chips.  There are so many things you can do with them.

Tweakie, did you do this in assembly level programming or C ?

Arnie

Offline Tweakie.CNC

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Re: Using a PWM signal to run an ESC controller for RC outrunner spindle motor
« Reply #8 on: November 16, 2015, 01:48:47 AM »
Hi Arnie,

I am pleased you have the speed controller built and working.

For MicrochipPIC programming and because it's quick and easy I use the PicBasicPro compiler  http://melabs.com/ (using a compiler does not exactly produce the most efficient code but as said it is quick and easy).

Tweakie.
Success consists of going from failure to failure without loss of enthusiasm.  Winston Churchill.