RC SERVOS

                                 Difference between Analog and Digital Servos


SERVO FUNCTIONS

Note: First thing to remember there is no physical or main component difference between an analog or digital servo. The difference is the way they perform or do their job. 

Futaba  Servo

Analog
RC Servos were all analog originally, and are still widely used today in sport flying applications. To drive the motors in the servos standard transistors ( PNP and NPN) were utilized.
When inputs were initiated by the operator via the transmitter, voltage to the servo motor would be transferred and the motor would start turning.  The downside to this control system was that a certain quantity of dead band was present on smaller control inputs, because a couple of volts had to go across the motor before it reacted and started to move, usually slowly with a limited amount of torque.
As the movement ended the voltage tapered down as the servo moved to its new position and never quite got to its final destination.
Before digital servos came along operators and pilots never really noticed or understood it at the time and learned to compensate for it.

Digital 

Servos mounted in Fuselage of Plane

FET transistors are used in digital rc servos like ESC's or speed controllers.
Transistors deliver full voltage in a pulse like modulated fashion, instead of ramping up the voltage to the motor the same way a speed controller does with a brushless motor.
Operating in this manner, the motor can deliver maximum torque right from the start, for moderate control inputs, and can precisely match the position of the stick for higher resolution and centering control.
They also provide the power to the servo at a significantly higher rate, about 400 Hz as compared to 50Hz for a standard analog servo. Consequently the servos respond quicker to control inputs and gives an instant feel to the control element.
When the application requires precise accuracy and speed, digital rc servos can deliver it and make a substantial difference.
Because of the updated faster rate,.digital servos often whine or buzz some around the neutral position

Downside - the downside to digital rc servos, they definitely pull more current than the standard analog servo. With that in mind, you will need to make sure to use a battery large enough to power them.

 Servo with covers removed

Hopefully this simple informative page on servos helped explain the common differences between analog and digital rc servos.
Many models on the market today utilize both of the applications presented here, you can check out many of the models on our website airarmorrc.com