At the most basic terms, a servo is a small powered motor that moves in the direction as instructed by the transmitter stick.
There are two types of servo, analogue and digital.
The older analogue servo receives a supply of electricity whose voltage decreases to zero as it reaches the required position. Should it go too far it will receive a reverse voltage which sends it back towards the centre position. If the supply of electricity is supplied too quickly either side of the centre position the servo is likely to ‘overshoot’ the centre position because of the inertia of the motor, It will then head back towards the centre position and if too much push given it will overshoot on the other side.
Digital servos are constructed identically to normal servos except they use a microprocessor to control the electricity flowing to the motor. Instead of gradually reducing the voltage supplied to the motor as it approaches the centre point, a digital servo supplies a series of pulses of the full 5V to the motor but varies the width of the pulse i.e. making them narrower as the centre position is approached. This means the motor will always be able to supply its maximum torque right up to the centre point because each pulse is the full 5V. The microprocessor allows the servo to gauge more accurately how it approaches the centre point and reduces the width of the pulses accordingly.
The result is a servo which is far more precise in its positioning with a smaller dead band. The rudder then will more precisely point in the direction indicated by the transmitter stick. In addition because its motion is controlled by a microprocessor, the digital servo can be ‘programmed’. The amount of dead band, total travel angle, centre position are some of the factors which can be varied.
To be able to give one or two clicks to the rudder trim on the transmitter and see a corresponding response to the motion of the boat.
This is just a basic guide to servos, and I would recommend further research as to which is the best type for your model boat.
