Best DIY Brushless ESC Kit? - RC Groups
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Aug 22, 2004, 01:18 PM

Best DIY Brushless ESC Kit?

Hi, I've been reading the threads here on brushless ESCs, and am interested in experimenting with one. I'm mainly a software guy, and have some ideas I want to try out.

What is the best brushless ESC kit that allows repogramming? I know about the Speedy-BL kit, but are there others? Ideally, I want one with the most processing power possible. If there is a pre-soldered option, that would be great.

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Aug 23, 2004, 04:42 AM
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Mr DIY's Avatar
I want one with the most processing power possible.
How much power? What you trying to do?

Aug 23, 2004, 08:33 PM
That's my secret, until I know it works or not. But I will share results once my experiments are complete, either way.

I'd like to have at least a few hundred clock cycles between PWM updates even at the highest RPMs. I run EDFs well above 40k RPM typically.

e.g. a DSP processor would be better than a PIC, at the same clock rates. 16-bits better than 8-bits, etc.
Aug 24, 2004, 01:42 AM
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Mr DIY's Avatar
Ok .. so you want to play

The only reason I asked is because I designed and built my own that is now capable of over 40K RPM. It is not using any fast micros (a Mega 8 running 8 MHz) and an external chip that handles the PWM (being clocked at 25MHz). The speed will be way too slow to handle doing any Fourier or other DSP type algos between PWM updates. It is not needed anyway. I run highish PWM frequencies that will not help your situation as well.

Nobody here is doing anything that I am aware of, with more powerful controllers. It all about cost and small size it seems.

Aug 24, 2004, 02:12 AM
I'm a little short a free time, being flying season. Is your available as a kit?

I'm not playing , just not wanting to sound foolish before I naively run some experiments. But, venturing ridicule from experts: basically, I want to play with finding another 5-10% efficiency from my motors by doing smarter/adaptive pulse shapes of the 3-phase instead of the normal square waves. I expect an overall loss of top end power, but that can be solved by just motoring up a little. Another aspect I want to explore is that of creating a true 3 phase AC signal through dynamic PWM - my EE classes from years ago tought me that a true 3-phase AC motor has constant power - which means no per-phase acceleration/decelerations and their losses - smoother power, maybe more efficiency?
Aug 24, 2004, 02:27 AM
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Mr DIY's Avatar
Hi gfcermark

No, mine is not available as a kit ... mainly because of the complexity of programming the logic device. I suppose I could presolder the device and program it though. Have not given it too much thought, as mine is more complex than most.

I donít think you would be able to do what you want to do with mine though. I can see more or less what you are trying to do. I pretty sure my logic device does not have the capacity to handle the PWM manipulation. A bigger logic device would most certainly be able to this though. Would make for an interesting project though.

Aug 24, 2004, 02:53 AM
Also, the PWMs would probably need to be an internal peripheral to the proc so it only takes a clock cycle to update the new duty.

For the true-sine AC, processing-wise, it would not take much to determine the new duty, just some addition on the ring-counter variable for table lookup with the step size changing with RPM. Even 8 updates per phase at 50k RPM would better approximate a sine wave for true AC.

Now, the adpative algorithms would require a bit more work (sample, calculate, update PWM) multiple times per phase. Don't ask me what I'll be sampling, yet - I still need to hook up a scope and start tinkering.

Years ago, I worked on a laser guage that rotated a mirror hit by a laser that could measure the shadow of a wire. When calibrated, it could determine the wire diameter (on one axis) down to 0.1 micron with a 100MHz counter. The prototype used a hard-disk motor driven much the same way as our BL motors (3 phase square wave). Inititally, it had the nasty problem of not being able to be calibrated properly across the full range of wires (up to 1/2 inch). It turns out the phase to phase accelleration was causing the error! We solved it cheaply with a large flywheel.

DSP processors are getting quite cheap these days.
Aug 24, 2004, 05:21 AM
"Simplify, then add lightness"
It seems to me that with all three windings being constantly driven with true 3-phase sine waves you would have a hard time sensing the back emf, since you would never have an undriven winding.
Aug 24, 2004, 11:16 AM
Jeff, I think there may be opportunities to sense back EMF levels in between PWM pulses.
Aug 24, 2004, 06:06 PM
"Simplify, then add lightness"
You will probably have to use a DSP to sense the back EMF inbetween the pulses, and it won't be easy. Most of the available controllers filter out the pwm pulses with an rc filter on the back EMF signal, because of the noise induced when the pwm switches. TI and Motorola have some app notes for doing BLDC controllers using their DSP chips. They may have development boards that you could use to prove out your concept.

Motorola even has an app note for a controller with 3-phase sine wave output, but it uses hall sensors.
Aug 25, 2004, 02:23 AM
Thanks for the links Jeff.

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