The basic working principal of all servos remain the same. They have a three wire connector. While one of the three wires supply five to six volts of positive charge (DC), the second wire is used to serve as the voltage ground and the third wire as the signal wire. The receiver of the RC motor respond to the servo with the on/off signals passed on through the signal wire. Digital servos have a microprocessor that evaluates the signals received and processes them in to pulses of very high frequency. The motor receives these high frequency voltage pulses to produce a torque. In case of the normal analogue around fifty pulses are sent to the servo motor through the signal wire.
The use of the microprocessor in a digital servo increases this pulse rate to around three hundred pulses per second served to the digital servo motor. This decreases the length of the pulses making them shorter but with an increase in the number of pulses the speed of the motor increases considerably producing torques at a quicker and constant rate. This is the reason why a digital servo produces a somewhat musical beat when a light weight is placed on them as the short high frequency voltages are acting on the motor of the servo.
The use of the microprocessor itself makes the digital servo faster and quicker with a smaller deadband and smoother acceleration. The microprocessor giving out large number of processed pulse beats also increase the holding power of the servo motor. This increases the efficiency of the motor. This can be noticed when comparing the working of a digital and an analogue servo at the same time.
The servo wheel of an analogue servo can be displaced only to a small extent before the servo motor starts to resist the force. In case of a digital servo, the servo motor responds fast and holds on better to the signals supplied. The microchip present in the digital servo controls the initial power supplied to the motor of the servo. This reduces the deadband of the digital servomotor and in turn generates high resolution and increased holding power. The only disadvantage in this is that with so much of energy being supplied to the digital servo at a frequent rate the power consumption is very high.
This problem of the digital servo can however be solved with the use of batteries. Installing a large capacity battery that can be allowed will prove to be energy efficient and solve the problem of power consumption.
Read more about motor control.