Thanks mr al, actually interesting about CD focus, didnt know that.
Yeah I was thinking maybe a opto interrupter type affair for a home position sensor.
The thing that hangs me up is how linear motors are driven, if there was a spring return that'd make things simpler, but there isnt, I'm wondering if the controller in the drive just gives the voice coil a bump one polarity to go one way and the other polarity to go the other.
Even the flexible pcb that carries the signals for the coil and the heads pulls on the arm assy, making me thing theres a technique to making the motor hold position.
I made a basic solar tracker, just uses a servo and a couple of norp12 photoresistors, I was gonna build a r/c compatible servo using a wiper motor to swing a bigger panel but never got round to it, the pid system put me off.