On Sat, 2009-11-14 at 16:37 +0000, Ian W. Wright wrote:
> Hi, I'm wanting to change the spindle motor on my little
> mill to one which I can speed control and which has a bit
> more speed than the synchronous motor I'm using at present.
> I have a 24volt 5amp motor which I think will do the job OK
> but I'm uncertain as to how to control it from EMC2. I will
> build my own drive electronics - plenty of components,
> plenty of time, little cash !!;-{. So, what system should I
> use to control it .... 0-10v, PWM, analogue opto or what..
> Can you point me towards relevant literature / examples or
> maybe suggest a suitable circuit? Thanks
>
> Ian
Off the top of my head, If I had a little mill with a small budget, I
would consider shopping for a KBIC controller,
http://www.wallacecompany.com/machine_shop/kbic/
http://cgi.ebay.com/KB-ELECTRONICS-KBIC-120-DC-MOTOR-CONTROL-REMANNED_W0QQitemZ250527988998QQcmdZViewItemQQptZLH_DefaultDomain_0?hash=item3a54a1bd06
(Short URL) http://preview.alturl.com/sfrw
scrounge a free 110 VAC universal motor and use a PWM signal from EMC2
from a parallel port pin. Small mills need high speed motors to spin up
small end mills and engraving bits. There should be plenty of vacuum
cleaner, blender or similar brushed motors available for free. You may
need to fit higher quality bearings if you use the motor directly as a
spindle. I suspect you would like the experience of building your own
motor driver, but the KBIC would probably be cheaper than the parts for
a home-brew driver and has a design that has evolved for many years.
Higher power drive circuits need protection features and controls that
are not trivial to design. If you really need to DIY, get the KBIC, then
DIY another drive while you are having fun _using_ your mill. The EMC2's
software PWM from is not very fast, so one needs to balance PWM
frequency and step resolution. My recollection is that with sixteen
levels, a 2kHz frequency can be had. One problem I have not figured out
yet, is how to get from a PWM to an analog voltage for the KBIC. Some
people have run the PWM into an RC filter but the time constant leads to
a _very_ sluggish control. I made a serial DAC for this purpose,
http://www.wallacecompany.com/machine_shop/EMC2/serial_dac/
but some might consider it too complicated for the application.
The down side to the above is that it is mostly speculation and I
haven't actually put any of this to practice on a small mill.
--
Kirk Wallace
http://www.wallacecompany.com/machine_shop/
http://www.wallacecompany.com/E45/index.html
California, USA
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