Thread: Fingers crossed it'll cut ally
I think the only way to hold revs if to have some sort of direct feedback (optical or something) of the motor RPM, and get mach3 to control the RPM as I detailed earlier.
I should really buy the ER25 collet for my massive brushless motor....it's occured to me that I can still get the 100mm one and make it longer. Drill an 8mm hole in one end, and whack a piece of 12mm with one end turned down to 8mm and knurled into the hole. The annoying thing is the motor only does 6000prm, which isn't so good as a router...but nice for machining aluminium.
Oval holes: same here, the worrying thing is I *did* use the CNC mill for the holes! I didn't make them oval though, just drilled the 8mm holes out to 9mm
your right jonathan, i meant a helli ESC in govenor mode... iv switched it off, i read somwhere that it would hold revs under diffrent loads, sadly, no joy on that one, its just a slow wind up to speed to stop all the power stripping gears betwean the motor and the main helicopter rotor... maybe it will hold revs when it is flat out?
on the brighter side, my motor has enough power to drill 10mm holes through 40mm of alli without getting particularly hot :) the ESC gets a bit warm though but nothing to drastic... fingers crossed
that motor you have would be wasted as a router !! it may even be over kill for milling alli on your 3 axis... id stick that one on a bike and start doing wheelies up and down your street and use a similar size as mine to mill alli, i really cant see my 3 axis out performing a 2000w spindle
ps: you get extra points for getting your holes wrong on a CNC :) yeeeee Haaaaaawww !!!
A long time ago in this thread I mentioned a method of controlling the ESC from mach3 using the spindle PWM output....so I thought I'd give it a go.
Basically I connected the ESC up to my normal radio system on the model car and used multimeter to measure the duty cycle, and frequency, of the signal at neutral, full reverse and full throttle. I measured 45.6Hz and 5%-6.7%-8.5%. That's a bit annoying as it's only using a small range, but nevermind.
So then in mach3 I ticked 'PWM control', 'Use spindle motor control output' and set 'PWMBase frequ.' to 46hz, and finally set 'Minimum PWM' to 5% (i.e. full reverse).
Then on the motor outputs tab I enabled the spindle and just set the step pin to the one I wanted (in this case pin 2).
Then I went to Config-->Spindle pulleys and set the max rpm to 1000 and left the rest. (more on why I chose 1000 rpm later)
Next I connected multimeter to the parallel port pin to check it was outputting the right frequency, and that the max voltage didn't exceed 5v since more would damage the ESC. Both were fine (I'm using laptop to test, which probably explains the port being 5v) so typed in 'S100 M3' to set the spindle moving at 100rpm. That way if I use the override slider 100rpm corresponds to 10% duty cycle, or more usefully 67rpm is 6.7% ... i.e. neutral.
Now I set it to 67rpm connected one of the parallel port ground pins to the black (ground) wire on the ESC signal connector, and pin 2 to the signal wire (the other side of the 3 pin connector). Esc initialised fine, so I upped the spindle speed a little with the override thing in mach3 and the car promplty shot off the desk :exclaim: and drew briefly half a kilowatt from the battery.
Connected it back up, and yes it works fine.
There's one issue though, at the moment 67rpm is motor stopped, and 85rpm is full speed - in this test 85,000rpm!
I think in my case I'm not going to be too worried about sending the motor backwards, so clearly I can use the forwards only setting on the ESC which makes things a bit simpler. You'll find the duty cycle values for your ESC will be slightly different - use my neutral (6.7%) as a starting point and you can do the normal calibration thing on the ESC to set the endpoints.
I'm sure with a bit of fiddling I should be able to get the RPM values in mach 3 to correspond to actual motor RPM, I'll have a think on that one and let you know.
Hope that helps, ask me if something isn't clear...
PS It took me a grand total of two bits of wire stuck in the parallel port to do this - you MUST check that the parallel port doesn't output more than 5V (5.1 in my case but that's close enough). If it's more then use a couple of resistors as a voltage divider to reduce it. Either way I strongly advise optically isolating the thing.
The Following User Says Thank You to Jonathan For This Useful Post:
07-11-2010 #75Is that without a pilot hole? i.e. removing a 10mm diameter cylinder? If so that requires roughly 310W (at 'reccomended' rpm). What rpm did you use?
if i push the motor hard the pc power supply trips out... iv got a 12v 30a supply and two 12v 45a power supplies but iv not got around to sorting them out and as im getting by with the one im using iv percivered with it... the large motor dosnt get warm at all... the ESP worries me now and again, its a turnigy 85a so im thinking the heat is normal
Yeah, I bought it to put on my bike, but that's not happened. I'm thinking of replacing the pathetic motor on my sieg C3 lathe with it. I still think it'd be good on my router for aluminium
Some nice research there Jonathan!!!!!!!! im going to have to pick your brain when iv absorbed what you have up to now... sounds like your nearly there, it would be a winner if it can be sorted... im still on the mechanical side of things at the moment but another week or so and i should be mounting my steppers and wiring the whole thing up
iv built a low profile pc out of my scrap box that im fitting into the base, im just hoping the hard drive can handle a bit of vibration
07-11-2010 #76What rpm did you use?
Last edited by Jonathan; 08-11-2010 at 12:10 AM.
I remember trying 12mm drill with 5mm pilot hole in steel on my mill ... at 2150rpm as I couldn't be bothered to change it. That was fun, but right at the limit of the motor.
Anyway I've concluded that there's no way to get mach3 to read the actual motor rpm with this method, so instead you're going to have to use the following formula I just worked out to convert.
Spindle rpm = (u*x-v*Kv*L)/(u-L)
Or rearranged for x:
u=max duty cycle, so in my case 8.5.
L=neutral duty cycle, 6.7 for me.
v=voltage to motor
x=rpm mach 3 reads out
rpm=actual spindle rpm
(formula simplifies nicely once you've got the values, tell me what they are and I'll do it for you in Excel if you like)
For that formula to work you need to set the 'Max speed' in 'Spindle Pulleys' dialogue to:
So for instance with the 7700kv motor I was testing with earlier, on 11.1v ... that's 11.1*7700*100/8.5 = just over a million rpm. Putting that value in means that if you put the correct max rpm of your motor in the spindle speed, then the motor will spin at that speed. It's only true for the max speed though, for other speeds you need to use the other formula.
More to follow, my posts are getting long...
08-11-2010 #797700kv motor
its a shame its so complex... (it is to me)
im sure i read somewere that the servo tester pot might possably be removed and driven by mach but no more was said about it... any chance of you casting your skills on that one jonathan?? :)
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