I am anticipating changing the control system on a 1985 Servo Mini mill that finally broke and I can't get parts.
It is a 4 axis milling machine with Pittman Motors, Harowe size 11 resolvers and size 11 tachs. The machine has ample power supply 24 Volts. There are two ways to deal with this upgrade, either buy new motors with encoders (Pittman 14204S006) and abandon the resolvers and tachs or Upgrade the resolvers to QD-110 size 11 encoders and abandon the tachs.
I plan to use your MPU11 and the GPIO4D board, I will use the outputs to fire contactors on my machine for oil, spindle power, light, and aux1 thru aux3. I plan to use the Servo Brand Drives that are in the machine that are capable of 40 Amps. I am not certain they support +-10VDC signaling yet but I will consider ELMO Drives if these won't work. Please suggest a drive if you can, The motors are 30.3V and they can consume 23Amps stalled.
I intend to implement one of your operators control panels as well, and use a regular PC display rather than a touch screen.
My Motor to lead screw ratio is 4 motor turns for each lead screw turn, the lead screw moves the slide .200 inch per rotation. The encoder rotation to lead screw rotation ratio is 5.67 so I was thinking that 500 steps would be enough. By the way the tach has the same ratio as the encoder if it would be valuable to leave it in.
What is your experience with the QD-110 encoders, and what would you suggest for Drives if mine fail? Is my sizing on the encoder acceptable?
See attached pictures for details:
Thanks
**RESOLVED** Upgrading Servo Brand Mini Mill
Moderator: cnckeith
**RESOLVED** Upgrading Servo Brand Mini Mill
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diycncscott
Re: Upgrading Servo Brand Mini Mill
Hello Juan,
Though we spoke on the phone, I thought I would post answers here for the benefit of others.
The QD (Quantum Devices) encoder you list will work fine. Although the 500 line count encoder is fine on a machine with your ratios, I suggest using the 2000 line encoder because they are the same price. In general more resolution is always better than less resolution. And though there are times when a user may have to worry about bandwidth, unless your going above 32,768 counts per rev at more than 6000rpm it's a non-issue. A simple rule of thumb for minimum encoder resolution is that you need at least 20,000 counts per inch of travel.
If you're looking for replacement drives, I'd suggest looking at AMC drives on EBAY. You can typically find them used in the $50-$75 range for that size motor.
Though I know that you chose to purchase the GPIO4D because it offers 4axes of control, you might also have considered using the DC3IOB kit which includes a 3 axes servo drive and then adding our DC1 single axis dc brush drive for DC Single ($395). The DC3IOB and DC1 will run those Pittman motors very well.
Thank you for your business.
Regards
Scott
Though we spoke on the phone, I thought I would post answers here for the benefit of others.
The QD (Quantum Devices) encoder you list will work fine. Although the 500 line count encoder is fine on a machine with your ratios, I suggest using the 2000 line encoder because they are the same price. In general more resolution is always better than less resolution. And though there are times when a user may have to worry about bandwidth, unless your going above 32,768 counts per rev at more than 6000rpm it's a non-issue. A simple rule of thumb for minimum encoder resolution is that you need at least 20,000 counts per inch of travel.
If you're looking for replacement drives, I'd suggest looking at AMC drives on EBAY. You can typically find them used in the $50-$75 range for that size motor.
Though I know that you chose to purchase the GPIO4D because it offers 4axes of control, you might also have considered using the DC3IOB kit which includes a 3 axes servo drive and then adding our DC1 single axis dc brush drive for DC Single ($395). The DC3IOB and DC1 will run those Pittman motors very well.
Thank you for your business.
Regards
Scott