Re: [CAD_CAM_EDM_DRO] Servo drivers

Nic van der Walt wrote:

> Hi
>
> I'm rather new to the CNC scene, and after a lot of searching around
> and reading about what is going on the biggest thing that strikes me
> is that there is almost nothing for free when it comes to servo or
> stepper
> drivers. This is a sad situation.
>
> What is the current status of the hardware and drivers for EMC? Has his
> design been tested?
>
> I need a 3/4 axis servo controller with EMC and I'm willing to
> do the following:
>
> 1) Change interface from ISA to Printer port. I have done this
> previously,
> and it should be possible to run four sets of DAC's and counters on the
> printer port. I can also add some IO for limit switches and relays.

I have already done this. I have a board set which has 4 encoder counters
on one board, 4 16-bit DACs that produce +/- 10 V for servo amp
velocity command on another board, and another board with 16 opto-isolated
digital inputs, plus an e-stop circuit, and place for 8 solid state relays.
I also have a backplane for this that holds up to 8 of these cards.
See http://pico-systems.com/PPMC.html for more details. This
connects to a PC parallel port.

I am now working to integrate drivers for this and my 4-axis stepper control
board into the BDI CD, but it already works with EMC, and I can supply
you with ready to run executables until then.

> One thing I will need advice on is the best way to drive the servo's.
> The simple
> bridge in the circuit seems ideal, going for PWM is going to add
> mountains
> of complexity and maybe even resonance problems in the motors. The only
> downside I see in linear drive is dissipation, and if the driver is not
> inside the PC that does not matter.

Linear drives are insane! You will end up building a room heater
that uses THOUSANDS of $ of power transistors.

> I will keep this a TTL chip and standard transitor design, so that
> anyone anywhere
> can build it. I want something cheap, simple and not to nasty.

Series 4000 CMOS runs on 12 V, and works a lot better in noisy
environments.

> My expertise is digital electronics and PCB design. If the circuit is
> sound, and the
> driver not to complex I can do this very quickly.
>
> If someone offers to help with the driver this will go much faster. I
> will post preliminary
> schematics in a couple of days.

I have designed my own PWM servo amp, good for 100 V and 10 A.
I have been running them in my milling machine for over 3 years.
I had PC boards made, but decided to not go commercial with it
because Copley Controls and others sell complete, tested amps
for less than I can buy all the parts for mine. (Of course, they
get better volume discounts than I do.) My amp also has a
lot of high-end features, such as fully differential command and
tach inputs, fault relay and output filters to keep the 100 KHz
PWM carrier off the motor lines. If you really want to roll your own,
I still sell the blank boards with info for $60. See
http://pico-systems.com/servo.html for more info on that.

Jon