Can a DC motor be used with positional feedback as a servo?

[fle33.com]

Hi,
I am amasing parts for my first CNC router table. I have managed to lay my hands on a fantastic unit that is a motorized lead screw mounted to a linear slide giving about 5" of travel It's from the 80's and has a 20 turn potentiometer mounted to an integral rack and pinion system. So the pot provides feedback.

This is earmarked for my z axis drive..

It wouldnt be difficult to swap the geared DC motor with a servo but I just wanted to ask if it'd be feasible to use this as it somehow or will I need to use a stepper motor?

[Al_The_Man]

High quality DC servo's are constructed slightly different from ordinary DC motors, but it may be possible to add an encoder and use it as a servo, if it was used for precise positioning before, there is a chance it may have the potential for a servo axis.
Al.

[fle33.com]

Yeah this is from a piece of medical equipment, I had a closer look and its a maxon gearhead dc motor but there are 4 wires coming out the end of it.. I need to investigate further. It doesnt look like a servo , it might have built in encoder..

thanks for the info anyway..

[keebler303]

I would guess 2 wires are for the motor and two are for a thermal switch, could be wrong though. If there are only 4 wires, it does not have an internal encoder. You might also consider the amount of backlash in the gearhead, whether it is acceptable or not.

Matt

[asuratman]

Hello,
I have ametek motors that I bought from surplus, do you think that this motor is dc servo motor or its just dc motor. The motors, some have 2 shaft, long (1.5 inch) in front and short (.25" in) in the back. I also have bought CUI encoder for this motor. Do you recommend to use this motor with this encoder? What about performance based on your experience will be? Thanks.

[BobWarfield]

Sure, it can be done. There are some cogging issues that will impact performance relative to purpose-built servos, but you can make a servo out of a DC motor.

Here is a good resource:

http://www.truetex.com/servomod.htm

Best,

BW

[Al_The_Man]

Originally Posted by fle33.com Yeah this is from a piece of medical equipment, I had a closer look and its a maxon gearhead dc motor but there are 4 wires coming out the end of it.. I need to investigate further. It doesnt look like a servo , it might have built in encoder.. thanks for the info anyway..

It could be a tach, spin the motor while measuring the voltage on each pair, if both generate a voltage, one will be the motor armature and the other the tach,
The tach is usually the rear most mounted.
If it has a tach, it is an indication it is servo grade.
Al.

[fle33.com]

Hi All,
Yes the unit on the end is a DC-Tach. The gearhead is 5:1 and at 12v the unit travels the 5 or so inches in about 10 seconds. The lead screw is a high quality system.. so I think I've picked up a real piece of good luck here.
The tach might have to swap for an encoder..

Thanks for the link Bob, that info is perfect.