Re: [CAD_CAM_EDM_DRO] Servo amp connections needed. Where should I go from here?

sleyed wrote:

> I have a servo controller that I can't seem to find any information
> on.
>
> It is manufactured by Control Systems Research, Inc. Pittsburgh, PA.
>
> The model is NC121F.
>
> My question is in trying to get control of a servo motor with a
> single or stacked potentiometer.
> The controller has signal and tac inputs. I do not know what it is
> expecting at these inputs. My first guess was 0 to +10v at both
> terminals in relation to the common. I don't really have 0 to -10v so
> I am unaware if a null point could be reached this way.

The tach is a voltage from the motor, indicating speed.
Traditional servos use a +/- 10 V signal for velocity command to
the amp.

>
> My mode of thought here is that the tac may output 6-7vdc/1000 rpm.
> If the inputs were tied together then they would track each other.
> Not so, or at least it did not prove out.
> When I touch either the tac input or the signal input with one wire
> or my fingers. The shaft slows and stutters . Possibly the stray ac
> signal I presume from my overhead lights. Using another power source,
> it was found to reverse the motor direction by connecting the signal
> lead to ground.
> Am I way off base in my mode of thought for bench testing this
> setup?

Do you actually have a tach hooked to the motor? Even if you
hook the two inputs together, the gain of the amp is very high, maybe
30,000 or so, and so minute errors are large enough to drive the
servo into saturation. With a tach connected, grounding the command
input should cause it to move very slowly. If it runs fast, reverse the
tach wires, and see if it moves slowly. Then, you can apply a small
voltage with a AA battery to provide a 15% command, and see what
it does.

Jon