This is the same building project as my DPDT switch from earlier for which I got great help.
I need to buy a servo to move an arm. There seem to be a wide variety of servos out there from 5$ to $500 dollar.
It will run off a 3 V supply. The mass it is moving is negligible. The slower the speed the better.
What specs am I looking for?
Most of these want 4.8v or more, but 3 may work, and be slower than spec to boot.
Maybe give them a call.
I agree that RC servos are just what you need, but you can shop at other places.
Hobby King is likely to have better prices. But yeah, they run off of ~5 v.
RC servos can be a little tricky to drive–they require a very specific PWM signal. Depending on the circuit, it may be possible to use a servo tester to drive one.
How much current can your 3 volt supply handle? It may be cheapest/easiest to get a 3V to 5V converter and use that to power the servo. That would allow you to use much more common (and inexpensive) servos like the RC types that have been mentioned in this thread.