Servo Dynamics brushed dc servo (sd1525) tuning

I started a linuxcnc conversion on my Bridgeport and have never completed it so its about time to finish! I've updated to 2.7 and am following John's pid tuning tutorial: gnipsel.com/linuxcnc/tuning/servo.html

But first I need to tune my servo drives. You know you've got old equipment when the instruction manual was typed on a typewriter! So page 16 describes the "Simplified System Setup" process but right off the bat I've hit a snag: in the "preset the pots as follows" section it says to turn the pots fully ccw. This doesn't make sense as these pots don't have a "stop" in either direction: I can turn the pots ccw and cw till the cows come home.

Can someone who has tuned an SD1525 before provide some insight?

drembedded wrote: This doesn't make sense as these pots don't have a "stop" in either direction: I can turn the pots ccw and cw till the cows come home.

Multi turn pots generally start to make a very faint clicking noise when a the end of travel.

However, I have not seen pots with any more than 25 turns, so you can be pretty sure that after 25 turns they are all the way CCW.

Had my hopes that this was the case but for both the Servo Dynamics SD1525 and the Fenner SDF1525 cards there wasn't any ticking or clicking. Even with a stethoscope, no joy.

While I was checking I noticed that the drive cards are mounted to a metal card. The backside of the drive cards are covered by the metal card except for the area right underneath the potentiometers/trimmers. That got me thinking that maybe I can turn the pots while using an ohm meter (with the power turn off) to find out when I'm at a "stop".

Since a potentiometer is a length of coiled wire with a "wiper" that travels across the coiled wire (pins 1 and 3 are connected to each end of the wire and pin 2 is connected to the wiper): by rotating the pot CCW the resistive reading between pins 1 and 2 or 2 and 3 should go to 0. When it does I know that the pot is in the fully CCW position.

Shouldn't take long to test this theory out....

Success!

If you turn the potentiometer CW the ohm reading increases between pins 1 and 2 and decreases between pins 2 and 3. Turn it CCW and the ohm reading decreases between pins 1 and 2 and increases between 2 and 3.

The picture shows the pin numbering for the top potentiometer (AUX ).

Here's several of the pages showing the potentiometer description and tuning process