RE: [CAD_CAM_EDM_DRO] Brushless Motor Spindle with CNC desktop machine

Hi Richard,
Cc Dave,

The RF format follows the "servo" format used in the R/C world. A PWM
signal designed to control an R/C servo. The pulse width varies around a
center of 1.5 mS (.5 - 2mS), and the pulse is repeated at a 20 mS rate.
There are PIC controllers to run R/C servos that can do this. The robot
guys use 'em all the time.

It would be difficult to control this R/C servo with Gcode, unless it was
the only thing the controller did! A special PWM signal (which would have
to run continuous) would be needed.

A PIC controller could be devised to take step/dir signals and ramp up/down
a continuous PWM signal (1 "slot" in about 10). In this case, the CNC
controller would generate an "up" direction and a few pulses to set the
speed to the desired level.

I like the idea of the high speed R/C spindle, just what I need for PCB
work. I take it I can look for an "AXi 2826/10" motor at my local hobby
store? How much?

"continuous pulses" That's an oxymoron! The pulses are no doubt TTL (.5V
low, 4.5V hi) signals of sorts, it's the generation of them that is a little
more complex. And this stream of pulses doesn't start/stop like the axis
moves do. The "1 in 10" may be thought of as "time slots", if one were
running 10 channels of servos (!), then the time allotted to one servo would
be similar to what's being described.

Chuck, an old friend of mine from the "Homebrew Robotics club" (Silicon
Valley, circa '86) has a good write up.

http://www.mcmanis.com/chuck/robotics/projects/servo.html

Humm... That's a good circuit for an H-bridge, if the FETs are big enough,
(or half an H-bridge) ...could drive your motor. And the PIC code could
be modified to take an occasional step/dir command to set the spindle
speed. COOL!

Alan KM6VV

> Subject: [CAD_CAM_EDM_DRO] Brushless Motor Spindle with CNC desktop
> machine
>
> hey everyone,
> I am building a small desktop 3D milling machine and needed a
> brushless motor for the main spindle. I got sick up and fed of
> changing brushes on the prototype I built, and a brushless motor will
> also be much quieter for indoor use and last a whole lot longer.
> I purchased a model aeroplane motor - AXi 2826/10 motor (rotating
> outer housing for better torque and the rotor doesn't throw off it's
> windings) with an "easy 25" 25amp controller and I need to know how
> the controller signals are sent from the RF module to the controler
> and the type of pulses. In the "easy 25" instructions it lists
> positive pulses at 1.5 ms with a period of 10 - 30 ms. What voltage
> would these be. "3v - 5v"? and are they continuous pulses. If this is
> the case then I think it would (maybe)be a case of programming the
> software to use the 4th axis as the speed controller and inputing the
> appropriate commands into the G-Code
> These motors spin around the 10K-20K revs at 12V(and faster) and pull
> up to 40 amps so the power is there for a small Miller but I am not
> sure how they would react to a filtered DC power supply with the BEC
> (Battery Economiser Circuit).
> The best case scenario would be to just have a switch to turn the
> thing on and off and if anyone out there has a way of doing this
> (small circuit board with a pulse module?) then that would be great if
> they could contact me about doing this or better still post here.
> If anyone else has any ideas Idea about controlling a brushless motor
> with a CNC spindle then I will be forever, eternally greatful if you
> could let me know how you can do this.
> I haven't found anyone else doing this sort of thing with radio
> controlled stuff on CNC machines so maybe this will be a first and if
> it works the we can tell all the other CNC people out there how to do
> it and I know they will be greatful as brushed motors just aren't
> cutting it when it comes to running a CNC/engraving job for 9 hours at
> a time. The brushes wear out after a very short period of time and
> usually halfway through a job and I know you can all sympathise with this.
> Please help.
> Warm regards
> Richard.
>