Servo controller

["Nic van der Walt" <nic-at-unibell.co.za>]

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.

I have download and looked at Garrett's servo controller schematics.
I have tried to send him email, but the address in the readme bounced.

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.

2) Do a PCB layout and put it in the public domain.

3) Do some modifications of an existing driver to change from driving
and ISA card to a parallel port based card. I don't want to get to
caught
up in lots of coding though. Starting a driver from scratch is not
really an option.

Maybe modifying the servo-to-go driver is a better idea.

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.

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.

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.

Regards,
Nic van der Walt