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pozzo d'uscita --> output shaft

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Note added at 12 min (2012-01-10 14:55:40 GMT)
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Servos are constructed from three basic pieces, a motor, a feedback device, and a control board. In hobbyist environments the feedback device is typically a potentiometer (variable resistor). The motor, through a series of gears, turns the output shaft and the potentiometer simultaneously. The potentiometer is fed into the servo control circuit and when the control circuit detects that the position is correct, it stops the motor.
http://www.pc-control.co.uk/servo_control.htm

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Note added at 13 min (2012-01-10 14:56:56 GMT)
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The output shaft is supported with a rolling-element bearing pressed into the housing. The output shaft is connected to the potentiometer with a torsionally rigid flex-coupling. This coupling compensates for minor offset and/or angular misalignment, thereby reducing lateral loading on the potentiometer.
http://www.stiweb.com/proddata/cmcpVALVE.htm


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Note added at 19 min (2012-01-10 15:02:52 GMT)
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The other basic step in modifying a servo for continuous rotation is decoupling the potentiometer from the final output shaft. This can also be arbitrarily difficult, especially if the potentiometer shaft mechanically supports the output shaft (servos with ball bearings are more likely to mechanically work well without a potentiometer in place). The servo control circuit board still needs to be given a fake position feedback, so you must keep the potentiometer in the circuit, with the shaft in the middle of its range, or replace the potentiometer with a pair of equal resistors.
http://www.pololu.com/blog/24/continuous-rotation-servos-and...

Servos are electromechanical devices that respond to a control signal, which instructs them to move their output shaft to a certain position. A servo is normally plugged in with a three pin connector: power, ground and signal. The signal wire carries a PWM (Pulse-Width Modulation) signal - a pulse that tells the servo to move its output shaft. A potentiometer (pot) is a three-terminal resistor with a sliding contact that forms an adjustable voltage divider. Potentiometers are used to adjust the level of analog signals (e.g. volume controls on a radio or a dimmer on a lamp), and as control inputs for electronic circuits.
http://www.smartsurfaces.net/servo