Jagman:
It would slide lengthwise along the under side of the tonearm.
Ah.
I've been looking at Mini linear motors on eBay. So far they are all stepper motors. I know the arduino can drive them. Perhaps I will buy one and experiment. There are some very tiny ones that have only about .25 inch of travel. That's about perfect.
Okay, scratch crazy idea #1, that’s one serious turntable!
Maybe use a micro “linear servo” that via a piece of insulated solid wire maybe #10, the servo would be able capture the arm at the pivot point and lift it up. They usually are good for couple grams of lift which is likely all you need. Add a uplooking TOF sensor that can see when the arm swings over it which then the arduino raises the servo.
A cut down piece of command adhesive to hold the assembly down as that stuff works really well on concrete and is removeable.
Defainately wouldnt want to perm-install anything on that.