Recommend me a servo amplifier / driver / h-bridge

Hi,

I'm retrofitting a small cnc lathe (Hercus PC200).
I'm using steppers for X and Z
I have a servo to use for the spindle. I want full speed control, and ultimately would like to use the spindle as a C axis also.

For the spindle I have a DC brush servo:
Global Motion Technology SM34840 DC Servo Motor
Constant Torque 170 oz/in – 1.2 N.M
Peak Torque 840 oz/in – 6.0 N.M
Continuous Current 7.8 Amp
Peak Current 40 Amp
Maximum Speed 4500 RPM ±10 % AT 72V, 2750 RPM ±10 % AT 50V

I have a 70V powersupply.

Motion controller: 7i43 + 7i76

I have been trying to get it going with an old G320x (Rev6, the first released version) but I cannot get the G320x tuned to get the servo over ~300rpm. I just get faults. The servo runs at expected 4500rpm with full 70V supplied directly. I changed from a Renco 8192 count encoder to a AMT102-V which improved things from very low rpm achievable to low rpm achievable. I don't have an oscilloscope.

I'm looking for a replacement servo amplifier / driver / h-bridge. I can't waste more time on this.
My preference would be to close the loop within Linuxcnc, which I believe has a number of advantages.

Options:
New G320x - not appealing
Machdrives BRB Servo driver - I contacted them and their drives are not suitable for spindle use as "the position variable is stored in a signed 32 bit integer so if you "move" continuously in one direction for more than approx 2 billion steps the counter will overflow causing instant axis reversal at full speed. While this is a huge distance for a CNC axis it will quickly be reached on a spindle application."
I'm worried all the step/dir drives will suffer a similar limitation
Pico PWM Servo Amplifier - $125 plus shipping, which is often $50 USD to Australia
Mesa Servo amps - all appear to be for multiple motors and more $$$ as a consequence.
CNC Drive DG4S-08020 - step/dir. Looks like a nice drive, but will it work for spindle use?

Thoughts / help is appreciated.

Or do I give up and buy a cheap speed controller?

www.banggood.com/6V-90V-15A-Control-PWM-...Switch-p-917304.html

Here is a cheap used drive that would work (but is a little over kill.)
www.ebay.com/itm/Advanced-Motion-Control...047675.c100009.m1982

Todd,

That AMC drive has tach input and also adjustments for gain. Is the tach input needed? Is it a 'dumb' drive (I.e. I can do all the pid tuning in lonixcnc)

Thanks

Yes it is just a dumb drive.

The tach input is optional. Of course it would have more linear and less load dependent control with tach feedback. But these AMC drives usually have the option of reading the voltage (and back EMF) from the motor to "fake" tach feed back. and this usually works ok, especially if it is closed loop with the control.

Fantastic, Thanks for your help.

I was struggling to find which AMC model would be suitable.

AMC's product line has moved away from basic brushed motor amps. I am not sure there is still anything much that would be suitable in their current product line. Up until about a year ago AMC's web site was very nice for researching the specs for their old and discontinued product. While most of the info is still there, it is now much harder to mine it. You kind of have to have an idea what you are looking for first. Not real helpful if you are looking for ideas.

Based on Todd's pointer, I've found a range of drives that may work, and use +/-10V, allowing me to close the loop in linuxcnc.

Copley 422 (or 412, or 423).
AMC 25A8, 30A8, 50A8, 120A10
Galil 25A8E-GAL (aka SA-12-80)

The galil and AMC drives appear to be the same.

I've attached some PDFs in case they come in handy for someone in the future.

I've bought a second hand Copley 422 on ebay - will see how it goes.

Thanks for your help Todd

So I got a Copley 422.

Just realised that the 7i76 spindle output is 0-10v, not +/-10v...

Not sure where to from here...
I do not want to buy a full Mesa Servo card (like 7i48) just to drive one +/-10v servo amp.