Brushless DC CNC Spindle

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Re: Brushless DC CNC Spindle

Postby Enraged » Fri Feb 24, 2012 7:22 pm

out of curiosity, can you drive the ESC unit with a servo tester like this: http://www.hobbypartz.com/ek2-0907.html
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Re: Brushless DC CNC Spindle

Postby bdring » Fri Feb 24, 2012 7:28 pm

I am pretty sure that would work. I almost mentioned that in a previous post, but I was hoping no one would take the lazy way and actually do the code.
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Re: Brushless DC CNC Spindle

Postby Enraged » Fri Feb 24, 2012 8:26 pm

lazy way haha

Pololu had a great blog post about controlling a servo: http://www.pololu.com/blog/18/simple-ha ... ng-a-servo

The most important graphic on the post:

Image

I'd still love to have something Pololu-compatible, so what about using the Ardiuno to read an M3 gcode spindle on, and then use that to activate a transistor and "turns on" the circuit above? Ideally, you would have a potentiometer either on the little Pololu-compatible board, or have it connected via the standard stepper output connection. After all, you would have 4 wires to work with on that connection, so servo power, servo signal, servo/pot ground, and pot resistance for the circuit.

Thoughts? Sorry if this post is rather haphazard, I'm reading/searching during odd free time.
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Speed Control

Postby bdring » Fri Feb 24, 2012 9:54 pm

With a single pin you could control the motor on off and the speed via the Arduino with no external components.

It is actually very simple. GRBL, Sprinter, Marlin, etc use a timer interrupt to do all the work. When you get a speed change command or on/off command you you calculate two numbers "on time" and "off time" for the pulse pin. A counter in the interrupt counts to each time and flips the pin. Those time values are simply what would give you the duty cycle at the update rate you want based on the interrupt frequency. It is all incrementing integers inside the interrupt so it would not effect performance.
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Re: Brushless DC CNC Spindle

Postby edward.ford » Tue Feb 28, 2012 5:59 pm

Quick update on the RC Spindle:

I got around to cutting a proper UHMW mount plate on Saturday, then did some test fitting. Everything seemed to line up nicely and the mount looks like it's going to work pretty well in terms of rigidity and support.

So... there we have it. Everything needed is in hand and the spindle has been mounted to my test rig. If all goes well, I'll have the video up tonight!
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Re: Brushless DC CNC Spindle

Postby iGull » Thu Mar 01, 2012 11:00 am

Hi All

Just a note, I get the R2hobbies newsletter, and in today's February 2012 #2 issue, they have a new 1800kv water cooled brushless inrunner boat motor ...

http://www.r2hobbies.com/

This may or may not be useful to you.

Cheers

Neil
EMOs are a sign of weakness ...
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Big On ORD

Postby bdring » Thu Mar 01, 2012 1:55 pm

Just for fun I mounted it on the Quantum (virtually). It looks pretty big, but it does fit with only drilling 4 holes. One of the goals of the original spindle was minimal distance of the spindle shaft from the mounting surface to reduce stress on the machine. I think that helps, but I don't think this design is appropriate for the ORD. It is too big. I think for PCB milling you want a higher speed than this geared down version. The water cooling would be a pain.

ord_with_spindle.jpg
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Re: Big On ORD

Postby frob » Thu Mar 01, 2012 4:00 pm

bdring wrote:...I think for PCB milling you want a higher speed than this geared down version. The water cooling would be a pain.


I like it!
i will definitely want to add that as an option to my Hadron build. I was thinking about this before - you're right about PCB drilling- high speed but low torque is ok , and considering how inexpensive RC brushless motors have become, i would prefer to have 2 separate mounts , one geared down for machining light metal and plastic, and another just holding the high-speed motor with a 1/8" collet chuck substituted for the motor shaft itself and better bearings installed.
I also agree about water cooling - its efficient but not too practical on such an elegantly simple & portable platform - so "heli" style motor with integral cooling fan would be the way to go i think.

What may be more of a problem though is the Z-axis feed rates; for drilling PCB's they need to be quite fast (it explains why the refer to holes as drill "hits") otherwise you burn the board and ruin the bits pretty fast.
I was just thinking about that earlier this morning - there's 2 options i think to increasing the Z- speed:
1 - change the leadscrew system for something else, maybe timing belt again ?
2 - add a secondary, short throw but fast Z- axis, on the spindle itself.
I'm not sure which is easier or better. Option #1 requires significant re-engineering of the ORDbot platform, so not so easy.
But it would be nice i think to make all linear motion based on a common system (timing belt) like the X and Y.
Option #2 is probably easier as an add-on, but still a little tricky to keep it light and thin enough so you don't end up with the spindle axis cantilevered too far out in front - even a little flex when drilling 10 thou holes will either make the hole miss its mark or more likely snap the bit.
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Re: Brushless DC CNC Spindle

Postby Enraged » Sun Mar 04, 2012 7:57 pm

if you are considering changing the Z screws, look at ACME threaded rod. You can pick up a set of appropriate size, with a nut and bearings, for around $20 on eBay.
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Re: Brushless DC CNC Spindle

Postby daveczrn » Wed Apr 11, 2012 12:27 am

How were you powering the brushless motor? Maybe it was said and i just missed it but isnt it expensive to supply enough power for a motor like this without using batteries?
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