[RomanLini]

My aplogies Tskguy, I may be a little out of date as if has been maybe 5 or 6 years since I had a good look at these small brushless flight motors. I guess the technology might have matured a lot since then!

RomanLini
I would have to disagree with a couple of your points. Regarding efficiency, most of these motors have measurable efficiency numbers closer to 85%.
I have personally measured this.
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85% efficiency? At what amps? I'll still argue a bit with that, you might get 85% eff at lowish loads (say under 20 amps) but at 100 amps (as people have discussed) the resistance of the copper stator winding is significant and eff% will drop way low...

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Another assumption you have in regards to runtime is way off. RC Helicopters have very large power requirements and have run times over 10 min. I have also seen these motors last for hundreds of hours of flight time. They never wear out! And have very easily replaced bearings.

Thank you! I will stand corrected on this. The motors I originally inspected were rather flimsy with tiny blonze plain bearings, and the guy in the RC shop gave me the "500 flights" life figure. Like I said that was years back and I'm probably just out of date.

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All that being said I do agree with making sure you get a motor that fits your needs. I personally want to cut aluminum with high speeds and feeds and my machine is small. So the size vs. power was attractive to me. No downer here! I am a fan of these motors and think you should truly consider interfacing them to your product!!!!
Eric

Ok, no product promises but I will look into the idea. Please bear in mind that (like I originally said) the kW stats advertised for these motors are still quite exaggerated, but that does not mean they won't make good spindles. I cut aluminium with my router using around 200 to 300 real watts, ie 0.2 to 0.3kW. So they will have enough power. I'll go back into the RC shop and have a good look at some new motors.

It's not trivial designing an industrial quality (ie made to last) 100 amp 3 phase controller! What about the option of a SuperPID like device to do the PID controlling, but using a standard motor controller to drive the motor?? I guess it comes down to "How much is a decent motor controller?" and "Will a Taiwanese flight controller be reliable for continuous use on an industrial machine?".

I'm open to suggestions.

[atwooddon]

You are correct that the RC brushless motors have come a long way in the past couple years. I have flown large brushless motors in my competition pattern plane for about 4 years now. My first motor had over 850 flights on it before it got replaced with a more powerful, lighter model. Most outrunner motor designs now use 3 ball bearings to support the shaft and as long as you don't crash or get dirt in them, they last a very long time. They take a lot of radial load abuse during high G maneuvers like snap rolls, etc.

Your idea of using a SuperPid like device to drive a motor controller (ESC) should work fine and you wouldn't have to re-engineer the logic in the ESC. The cheaper ESCs from China would probably work fine. I use them in my sport planes all the time with no issues. My competition ESC is much more expensive but the demands on it are much greater.

Don

[tskguy]

I agree with atwooddon It would much easier to control an ESC rather than integrating it in to the super PID. These ESC's use a 1 to 2 ms pulse at I think 80hz or so. One issue you may run in to is that these ESC have an arming mechinism for saftey. Most have you give full throttle and then low before it arms. Please reach out if you need any help with resources regarding this RC stuff. Im sure Im not the only one but I dont mind helping if needed.
Eric

[RomanLini]

I agree with atwooddon It would much easier to control an ESC rather than integrating it in to the super PID. These ESC's use a 1 to 2 ms pulse at I think 80hz or so. One issue you may run in to is that these ESC have an arming mechinism for saftey. Most have you give full throttle and then low before it arms. Please reach out if you need any help with resources regarding this RC stuff. Im sure Im not the only one but I dont mind helping if needed.
Eric

Thanks Eric I appreciate your knowlege and the offer to help! I won't have a lot of time for checking this out this week but I did look over some motor and driver stuff online today. There are some impressive motors out there!

I understand the RC pulse system quite well as I have worked with hobby robotics in the past using RC servos under computer control. It would be good to know more about this "arming" feature. Is it as simple as turning on all the power then applying a short period (a second?) of HI (2mS pulse)? Does the motor spin up when arming?

Also other info that would be useful is RPM curves vs input pulse. I'm not sure how sophisticated the ESC drivers are, mainly; do they keep the motor at a constant RPM for a constant pulse control? Or does the motor speed "sag" under load similar to DC traction motor? There could be awkward issues with PID control with 2 controllers in the closed loop...

Also any more info on the typical RPM range from a ESC controller, from 1mS to 2mS pulse control?

And what kW range do people really want? Considering a 1kW 50 amp DC supply will be very expensive in itself, plus motor plus ESC controller that's going to get pricey. Maybe something around 500W brings the prices right down and even 250W is still way overkill for engravers.

Groswald- That's an impressive 22lb plane! I can see why these motors are popular with their good torque at all revs, the comparable 2-stroke motor would have a very peaky powerband.

Thanks Fish4fun and everyone who provided motor info. I'm still soaking this up...

[atwooddon]

Maybe I can answer some of your questions.

It would be good to know more about this "arming" feature. Is it as simple as turning on all the power then applying a short period (a second?) of HI (2mS pulse)?

Arming works a little differently in various controllers. But, basically, with most of the 'standard' controllers, the controller will not arm until it sees a pulse width of less than 1ms. After it arms, the control range is 1.0 - 1.8 ms unless you program the controller with different end points. Some controllers can be programmed, some can't. Some smaller, less expensive controllers expect to see full throttle, then low throttle to arm but that isn't how most work.

Does the motor spin up when arming?

No, not on normal controllers, it is a built in safety feature preventing 'runaways'.

Also other info that would be useful is RPM curves vs input pulse. I'm not sure how sophisticated the ESC drivers are, mainly; do they keep the motor at a constant RPM for a constant pulse control? Or does the motor speed "sag" under load similar to DC traction motor?

Some controllers have a 'governor mode' but it is not very flexible, it is more of a fixed constant speed, typically used for helicopter for 3D aerobatics. The motor would 'sag' as additional load is applied. For RC airplane use the load is pretty constant since we are not changing the pitch. For helicopters, the load changes significantly. I would think the load from a milling bit (except for large bits in metal] would be pretty constant based on a constant feed rate, but I could be wrong in my assumption.

Also any more info on the typical RPM range from a ESC controller, from 1mS to 2mS pulse control?

The rpm range will be determined by the kV rating of the motor and the voltage of the power supply. For a motor with a kV of 1000 and using a 12V supply, the max rpm would theoretically be 12,000 rpm.

And what kW range do people really want? Considering a 1kW 50 amp DC supply will be very expensive in itself, plus motor plus ESC controller that's going to get pricey. Maybe something around 500W brings the prices right down and even 250W is still way overkill for engravers.

Since 12V or 24V supplies are readily available, even in larger max amp supplies using server power supplies which are very cheap to by on ebay, we would probably need motors in the 600-900 kV which would yeild 0-20K rpm approx.

Hope this helps with your questions.

Don

[groswald]

RomanLini,

Thanks. It was quite a project, and my first electric. I have to say that I am quite impressed with the capability of such a small powerplant. Now, if the batteries would just come down in price!

Regards,

Randy

[tskguy]

Hi all,

Here are a few of my thoughts to Romans questions. First off let me explain what difficultys I have with my current setup and also how I think the super PID will help. Currently I have a Castle Creations 100amp controller its not a High Volt one so the max volts is maybe 16v. Anyway the way Im currently using the controller is by using the built in gov mode for helis. I am doing this to try and keep the cutting rpm constant. It actually does a great job but doesnt kick in until after 50% throttle. So my RPM choices are very limited. Im also never sure of what the rpm is so speeds and feeds are tuff to get right.

What I envision for the super PID is setting the controller to airplane mode which is basically a linear rpm curve. It would also allow the use of cheaper ESC's. Then use a tach feedback like the super PID to hold spcific rpms.
Would that work? Oh I forgot to mention, I actually gear down my motor to the spindle, Similar to a mill head. I assume the gear ratio would also be a key component. I may be in the minority for that requirement, my machine is designed for milling aluminum and brass. Thought I would throw that out there.

Here is a link to my spindle, it has some pics of my first motor. I have replaced it with a larger outrunner sence then.
Eric
http://www.cnczone.com/forums/diy-cn..._complete.html