Here is a simple, low-cost, high quality servo for all your mechatronic needs. Small servo with a standard 3 pin power, control cable, and mounting hardware. This servo is very similar in size and specifications to the Hitec HS-55.
Posted by Adam Ward on 3rd Apr 2011
These servos CAN be modified for unlimited rotation, BUT it might be very fiddly. The plastic mouldings are quite fragile but it should be feasible. Basically it would involve removing the internal potentiometer, breaking the pot open, carefully removing the end-stops and the electrical contacts and then putting it back in (after installing the replacement resistors). The pot is then simply used only in a mechanical capacity as the axle for the final drive gear.
Not easy to do, but should be a fun challenge. :)
For a tear-down, see here...