[lkasdorf]

My bridgeport clone with an old (dead) bandit CNC controller has DC servo motors, and I'd like to drive from a Gecko 320X. I realize that I'd need to swap out the encoder.

1. Will the 320X reliably drive a motor like this?
stall torque: 400 oz/in
current continuous: 6.0 A
max pulse current: 26.0 A
max volts: 90 v dc
no load speed: 1500 rpm
volt. const. Kv: 59 V/KRPM

2. What type or brand/model encoder would I want to install for use with the 320X? It says that it wants a quadrature encoder with basically TTL outputs. Is there a commonly used & affordable model?


LKasdorf

[Al_The_Man]

My bridgeport clone with an old (dead) bandit CNC controller has DC servo motors, and I'd like to drive from a Gecko 320X. I realize that I'd need to swap out the encoder.
LKasdorf

Why what encoder resolution is on it now?
Al.

[lkasdorf]

Why what encoder resolution is on it now?
Al.

I've heard from several sources that these old servos used with the bandit controller use analog resolvers rather than digital quadrature encoders needed by Gecko.

So, I'm trying to determine a good, cheap encoder that will work.

[morestuff]

The G320X can run these servos reasonably well.

You will need to modify the power supply so that
you do not exceed the 80 VDC rating of the G320X.
I would recommend targeting something like 70 VDC.
This will mean that you will get less top speed, but
for most users this is not significant. The speed
reduction will be linear with voltage reduction.

Most likely your Bandit had relatively low resolution
encoders on it. I would recommend that you look
for encoders that yield about 10 counts per 0.001"
of travel. Too little results in reduced precision,
too much results in problems generating step pulses
fast enough and more sensitive PID tuning.

Many people use programmable resolution encoders
so they can select the best resolution after installation.
One such encoder is the AMT-102 sold by Digikey. See:

http://search.digikey.com/us/en/prod...1307-ND/827015

They include a kit of shaft adapters to fit most shafts.

Don't forget to look at cables for them also.

Regards,
Steve Stallings
www.PMDX.com

[Al_The_Man]

I've heard from several sources that these old servos used with the bandit controller use analog resolvers rather than digital quadrature encoders needed by Gecko.

.

It may be best to actually confirm it, it would be a pity to replace something that you could use?
Al.

[lkasdorf]

The G320X can run these servos reasonably well.

You will need to modify the power supply so that
you do not exceed the 80 VDC rating of the G320X.
I would recommend targeting something like 70 VDC.
This will mean that you will get less top speed, but
for most users this is not significant. The speed
reduction will be linear with voltage reduction.

Most likely your Bandit had relatively low resolution
encoders on it. I would recommend that you look
for encoders that yield about 10 counts per 0.001"
of travel. Too little results in reduced precision,
too much results in problems generating step pulses
fast enough and more sensitive PID tuning.

Many people use programmable resolution encoders
so they can select the best resolution after installation.
One such encoder is the AMT-102 sold by Digikey. See:

Digi-Key - 102-1307-ND (Manufacturer - AMT102-V KIT)

They include a kit of shaft adapters to fit most shafts.

Don't forget to look at cables for them also.

Regards,
Steve Stallings
PMDX.COM - Products for CNC and motion control applications

Thanks for the detailed response, Steve. I have removed the back of one of the motors and observed the tach and resolver, both of which are no longer needed. And, I see where I can install an AMT102 encoder on what looks like a 1/4" shaft. This is all making sense now.

One thing- these servos seem to be direct drive. I read that most servos have gear reduction, but these do not. How odd is that?

I think these servos were quite common on bandit installations- I see them in pics of older machines with bandit controllers quite often.

It is nice to see some sensibly priced components in this area. I spoke with somebody today who was extolling a turnkey fagor retrofit controller for a mere $12k. I couldn't suppress my laughter...