[Fish4Fun]

I am curious if anyone has thought of using BLDC motors/controllers from the RC airplane hobby world for CNC spindle motors. There are some very healthy motors (up to 8.4kW!) in the 12V to 60V range with matching speed controllers (granted not exactly set up for Mach3 control). The more powerful motors (2kW to 8.4kW) are in roughly 3" diameter housings, and can easily be re-wound to increase RPM or Torque. The stock RPM Range is from 8k to 20k. The concept is pretty simple, the electronics a bit more complex, but the potential for driving a spindle seems pretty good. The RC airplane market is considerably larger than the CNC spindle market, and so mass production prices have less engineering baggage than narrow market products. The 8.4kW motor mentioned (6.4kW continuous) has a price tag of ~$270 w/o controller. Here is a link to one particular motor TowerHobbies.com | GPMG4805 Great Planes Rimfire 65cc Electric Motor it turns ~8.8k RPM @ ~ 55V. Obviously these motors would not be ideal for direct drive of a spindle, but with a belt they could cover the RPM range from 800 to 40k RPM with as few as two "step pulleys" (1:5 5:1). If used to drive a quality spindle the potential appears to be very good at a reasonable price. It is a bit hard for me to grasp "switching" 120A (I consider 120A to be in the "welding" range), but it appears there are existing controllers designed specifically for the task. It seems probable that for extended run times, water cooling might become important, but with the savings over CNC specific designs, this is not an insurmountable expense.

Anyway, I was just wondering if anyone else had looked at these motors wrt building a spindle.

Fish

[atwooddon]

Quite a bit of discussion about using the RC brushless motors to drive spindles in the latter part of this thread.

http://www.cnczone.com/forums/diy-cn...ndle_idea.html

There are also several videos on YouTube showing this approach.

Don

[tskguy]

I have been using a 1kw RC brushless motor for a while now and it works pretty darn well! My motor is 1200kv and I run it at 15volts for about 18000 max rpm with a 1:1 ratio, I also have other ratios to slow it down as needed but mostly I run at faster feeds to deal with the RPM. The biggest problem with the larger KW motors will be supplying it with 55v at 150amps!! That will be one hell of a power supply!! My 15v 80amp supply is pretty beefy and is much smaller than that monster would be. One thing I am currently working on is actually controlling the rpm through Mach3. I’m pretty close but have a few issues that I’m still trying to work out. One major issue will be getting mach3 to initialize the ESC that these motors use. I’m sure a macro in mach3 would work but I haven’t tried that yet either. Any way good luck!

[CarveOne]

I have been using a 1kw RC brushless motor for a while now and it works pretty darn well! My motor is 1200kv and I run it at 15volts for about 18000 max rpm with a 1:1 ratio, I also have other ratios to slow it down as needed but mostly I run at faster feeds to deal with the RPM. The biggest problem with the larger KW motors will be supplying it with 55v at 150amps!! That will be one hell of a power supply!! My 15v 80amp supply is pretty beefy and is much smaller than that monster would be. One thing I am currently working on is actually controlling the rpm through Mach3. I’m pretty close but have a few issues that I’m still trying to work out. One major issue will be getting mach3 to initialize the ESC that these motors use. I’m sure a macro in mach3 would work but I haven’t tried that yet either. Any way good luck!

Deleted reply. Dumb idea I had wouldn't work.

[toughtool]

CarveOne,
Now we won't know what not to try, and why. Isn't that like "There are no such thing as a dumb question". Joe

[toughtool]

Tskguy,
Making a power supply for one of those motors shouldn't be too difficult. I would use the core from an old 2KW variable transformer, like the Variac. By removing the wiper, then insulating and tapeing the wires where the carbon brush traveled; a secondary winding can be wound with little difficulty. That is what I did to get the 15 amp supply for my stepping motors, as well as an additional small 8 volt secondary winding for a 5 volt reg. The AWG wire size of #4 (.204" dia) should handle the 120 amps. While #4 is a lot bigger than the #10 stranded I used for my 24 volt supply. I did make one once (for a solid state KW Amature Radio transmitter) using solid #8. At about .5 volts per turn, doesn't take a lot of turns to make a 15 Volt supply. If the voltage sags a little under load, just add a couple more turns. I don't think these motors care about a highly regulated and filtered supply so a chassis mounted bridge diode assembly and a hefty capacitor should do the trick. Joe

[Fish4Fun]

atwooddon,

I had only read through about page 10 of the spindle thread when I made this post, like always I should have kept reading prior to posting, but sometimes I think I have thought of something new and just can't resist posting :-) Thank you.

toughtool,

I have NOT played with any of these motors, or any power supply designed to pump out more than 20A at any voltage (except welders), but it seems to me a welder might be a good place to start, lol. It's a shame so many of the old "buzz boxes" have been scrapped for their copper, but perhaps a cheap modern welder could be retrofitted to act as a power supply for these high current motors? Something like:

Northern Industrial Arc 200 230 Volt, 200 Amp Arc Welder, Model AC4180 | Arc Welders | Northern Tool + Equipment

@ $149 might be worth investigating. Most stick welders have an Open Voltage ~80V, but the Voltage drops quickly under load. A fairly rugged rectifier could be fashioned from industrial SCRs in anti-parallel and the output VA could be controlled by a combination of the welder's settings and phase firing of the SCRs. I would think for < $500 one might be able to achieve a fairly reliable 50-100A supply in the 20V to 50V range. Filtering the 60hz chopped output could require a large capacitor bank if output ripple is a consideration.

This is just mind-candy for me right now, I have not looked seriously at these motors or building a suitable supply for them. There are probably several threads that deal specifically with building/sourcing high power spindle supplies that I just haven't read yet, lol. So much to read, so little time....

Fish

[CarveOne]

CarveOne,
Now we won't know what not to try, and why. Isn't that like "There are no such thing as a dumb question". Joe

If I told you what it was, and everyone started laughing at me for thinking of it, I might feel obligated to lay on the CNC table and V carve "DUMB A--" into my forehead. We can't have that, now can we? :nono: (Kidding of course.)

CarveOne

[toughtool]

I did laugh while reading your response CarveOne. Sometimes we can't help but embarrass one's self. i.e. using "are" instead of "is", in a quote. Especially since I have happily lived with an English teacher for 44 years.

Fish4Fun, The welder would be a viable candidate. I have thought about getting one of those 250 amp bridges and making my 30 year old Lincoln 220 into a DC welder, but after looking at the prices of those things, I just go over and use my brothers new MIG wire feeder welder. I think the voltage of my old Lincoln is about 25 volts. Joe

[CarveOne]

I was thinking along the lines of using a high current ESC connected to an R/C servo tester and figuring out how to get Mach3 to control the servo tester, but there has to be a more direct and lower cost way to to it.

In my demented little mind I'm seeing images of Romanlini busily cobbling up a prototype of the next big PID board product for brushless motor spindles with a on his face. Someone send him some sample motors as encouragement.

CarveOne

[tskguy]

I actually thought of that as well. It would be very cool if the next Super PID had the ability to interface with an RC brushless motor! I have a feeling it would be pretty hard though. Most of ESC's for these motors are little computers, in fact the one I’m using now has a usb interface. I’m in no way an expert though. Maybe he could do it.
What I am doing now is pretty close to working. I have a circuit that is basically an rc servo tester but instead of a potentiometer it excepts 0-10v dc in. I am using Mach and my g540 to use pwm signal to create the control voltage but it’s backwards!! When I tell mach to output the highest rpm my ESC is set t its lowest setting. I am sure I can get it working I just have been using my machine to upgrade the z axis and it’s not as high of a priority. It would be cool to use an rpm sensor to feed Mach3 and use it’s built in PID to help keep RPM steady.
And toughtool I would love for you to build me one of those transformers!! I could always use more volts and amps!!!!

[RomanLini]

...
In my demented little mind I'm seeing images of Romanlini busily cobbling up a prototype of the next big PID board product for brushless motor spindles with a on his face. Someone send him some sample motors as encouragement.

CarveOne

Ha ha I heard that!

Here's my take on it.
1. Don't believe anywhere near the hype of the claimed "kW" of those little motors. I was originally trained in the early 80's as an electrical technician in heavy industry and working with electrical motors was a big part of it. Those motors only run about 65% efficient at best, and if they actually produced 8.4kW shaft power they would consume about 13kW total and give off 4.5kW waste heat, about as much heat as a large hot water system for your house. The kW figures are pure bunkum used to sell motors with shiny kW stickers. Consider that your largest Colt router like a 7518 runs at up to 15A 120v = 1.8kW at about 70% efficiency so thats about 1.2kW shaft power only WHEN it's cutting REALLY hard which most people will never reach. Actual routing in real watts in the real world is maybe 400 to 800 watts.

2. Those little motors do produce quite a bit of power FOR THEIR SIZE AND WEIGHT. But everything else is sacrificed to do it. Their shaft is skinny, they have tiny windings (that get hot) small flimsy frames and tiny bearings etc. Even life is sacrificed as they run very hot and destructively and are meant to run at most a couple of minutes each time. Most have plain bearings, with a very short life span of maybe 50 flights of a minute each flight being typical.

As high-tech and pretty as they are, I just don't see that these little motors are a good choice for a cutting machine. If you need larger cutting forces (ie routing wood) then a router is highly optimised for good power and life span.

If you need a high-RPM low-power spindle for engraving, this only requires 10 to 40 watts. Not kilowatts! Pretty much any small motor will work well here.You still need a spindle with good bearings (no matter what motor) but because you have a spindle (and a drive ratio) the motor RPM is not so critical as you can use a long life reliable small DC motor and just gear it up from 10000RPM to 30000RPM. You don't need a high-tech super lightweight 20000 or 30000 RPM motor that has a very short life. I'm open to the idea of making a controller for engraving use but it would be aimed towards proven DC brushed motor technology rather than expensive super lightweight brushless motors.

Sorry to be a downer guys, but I have to call it the way I see it.

[tskguy]

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. 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. Plus this one pulls way over 100amps at 30-50 volts!! Here is a video.

[nomedia="http://www.youtube.com/watch?v=kxLGiHF17uU"]YouTube - ‪Bert Kammerer - T-Rex 700 Electric sneak peek video‬‏[/nomedia]

It really just seems that you haven’t looked very deep in to what these motors are capable of. My 1kw spindle far exceeds the cutting capabilities and the stiffness of my machine. The bit snaps way before the motor bogs!! I don’t doubt your technical knowledge regarding motor design but I can personally attest to the power and longevity of these motors if chosen correctly! It far exceeds the cutting power my router provided. (Without the Super PID by the way )
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

[blighty]

i would agree with tskguy.

a lot of the facts and figures in the above,above post are in correct. the motor in the above video is kicking out more power than the IC engine that is normally put in a 90 size machine and that IC engine will deliver 3.6hp. so electric motors are capable of spitting out a lot of gg's.

as to "they only last 50 odd flights" ........i have been flying a trex500 "hard!!" 4 flights every Sunday and the odd flight or two in the week. i have been doing this for over 2 years and the motor is still as good as it was on day one.

the only problem that i can see with running RC brushless motors of this power are the amount of amps you need to supply to it. you could go for a high volt set up and drop your amps, but your still talking about 80 odd amps. but saying that do you really need an 8Kw motor for your bench top router? my RF 45 only has a 750watt motor and that's works fine.

cooling...... as far as i know all high power (.90 IC) electric motors come with built in cooling fans.

[tskguy]

just for fun...check this heli out. it has a motor running 45v at 155amps!!!
yep 7kw claimed to be over 7hp!!! This thing is actally pretty scary.
[nomedia="http://www.youtube.com/watch?v=l7TBxFEPttI&feature=related"]YouTube - ‪Trex 700E "The Beast" - Tim Jones insane power‬‏[/nomedia]

[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.
...

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...

...
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.

...
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

[Fish4Fun]

RomanLini,

The Thread Title of 8.4kW was chosen for shock value, not out of any need for an 8.4kW spindle. I have been "watching" these motors evolve for a number of years, and they seem to have matured very nicely in the last few with prices dropping and performance/reliability increasing. The primary advantage I see to them is the very large, competitive consumer market they are aimed at, much like the Bosch Colt is aimed at a much larger market than CNC router spindles; this large market greatly increases the performance to cost ratio. I feel like the 1kW to 2kW BLDC motors have reached a place in the cost/performance curve that we as CNC hobbyist/professionals should be looking at them seriously for spindle motors. While power to weight ratio is NOT a primary concern for most spindle motors, less mass can have advantages.

Thank you for offering to take a serious look at them.

To everyone who has responded,

Thanks! The thread is going exactly the direction I had hoped it would!

Fish

[CarveOne]

Some of these motors also have water cooled versions for the R/C boat guys. I don't know much about them and they may or may not be useful as a CNC spindle. I have installed some Hacker C50 geared motors in an Osprey wind tunnel model we built during the Osprey crash investigations, so I know that something like that is available for lower speed higher torque needs.

CarveOne