Does anyone have any ideas how to implement a Vex IQ Servo?

I wanted to be able to scan back and forth when I was using the ultrasonic ranger, so I mounted the ranger on a motor. It works, but the problem I have is that I have to manually position the ranger at the zero position every time I use it. What I really want is a servo that always comes up at a known position.

I tried adding a stop, and spinning the motor until it hit the stop. It did stop the motor from spinning, but there is so much play in the gears that trying to use this as a calibration point did not work.

Here are some pix of the bot and the ranger scanning mechanism.

IMG_2338 IMG_2339

You’ll always have to reset the encoder at a known reference. Unfortunately there isn’t a potentiometer in IQ so nothing with a fixed reference.