Okay, with just the servo, (i.e. no capacitors) it's working just as plugged into the UNO alone. So I'm guessing the problem is either the capacitors or the potentiometer the analog input? my money is the potentiometer. That said, the servo does appear to be able to do the full 180 arc, and that potentiometer is ask 179.
At the moment it does just rotate back and forth, how would I control it to stop at one end or the other - i.e. take an input to move the servo to the far end of it's arc, and then input again to move it back to the other end of the arc?
Do the capacitors / analog input that are now out of the circuit make any real difference?
Agreed, it sounds like power would be a good idea, but baby steps, I'll get this thing working first