Servos

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I decided recently that I would design my mechanism similar to the guy over at themagicclock.com, so I ordered 5 of the GWS S125 1T 2BB servos online. They arrived on Friday so I hooked one up to my Arduino with an external power supply, loaded the sample servo sweep sketch, and watched in horror as the servo spun continuously clockwise.
I browsed all over the web looking for the source of the problem. I read that some people had servos where the pinion gear that drives the potentiometer inside the servo was not firmly attached to the driveshaft and a little lock-tite was the solution. I tried that but had no luck. I think it actually stripped out the little plastic gear attached to the potentiometer. Metal pinion gear vs. plastic potentiometer gear is not a good recipe for success.
I tried using different pins on the Arduino. No good. I tried running the servo off the Arduino power. It made the Arduino croak due to the load. I tried manually setting the PWM frequency of the servo output, but without an oscilloscope, I couldn't see what it was actually doing. Same as before.
After nearly pulling my hair out and abandoning servos for steppers (not sure how I was going to do that since most Arduino projects are limited to 2 or 3 steppers, not 5), it struck me this morning that I was powering the servo off an external 5V supply, and powering the Arduino off the USB port on my Mac. There was nothing tying the ground of the power supply to the ground of the Arduino, and this might be the cause of my problems.
It was! After connecting the power supply to the external power pins on the Arduino, my servo happily returned to center. I did have to take apart one of the other servos to get it off the end of the potentiometer travel that was stripped out, but it's functional.
Also, using a frequency range from 0.9 ms to 2.1 ms gave me about 400+ degrees travel from end to end. I only need one full turn, so this is great. I suspect that this servo is capable of more total travel, but I don't want to push it anymore in case I hit the ends where the gear is stripped out.
I've modeled the servo in Sketchup, so I should be able to plan out pretty accurately how to mount these things. I don't have any extremely precise cutting tools, but my scroll saw and bench press should be up to the task.

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