A small servo motor is an electric motor that has the ability to be controlled, both in speed and in position.
A servomechanism is a mechanical actuator-generally, an engine, although not exclusively-, that possesses enough control elements so that the parameters of its mechanical action, such as its position, speed, torque, etc., can be monitored.
Actually many other types of servos (or servomotors, better) are used in industrial and commercial equipment, from a floppy disk in our computer -or in the home videocassette-, to the storage units and input and output of large data systems. computing (today, more than anything, magnetic disks), and even in elevators in buildings. The motor of an elevator, together with its control equipment and positioning detectors, is neither more nor less than a servomotor. The mechanism that brings out the CD-holder of the CD reader of your computer is a servomotor.
What turns an engine into servomotor? Or rather, why is it considered that some engines are servomotors and others are not? The answer is not too complicated: a servomotor has integrated or attached at least one detector that allows knowing its positioning and/or speed. The position detectors are called "encoders".
From these modeling servos, let's start with the servos that are known as "analog".
Analog servo for model
These servo motors are composed, in essence, of a direct current motor, a set of gears for speed reduction, a potentiometer located on the output shaft (used to know the position) and a circuit board for the control.
If what you want to control is the position of a servomechanism, as in this case, instead of a tachometer (which is to measure speed) we need a position encoder.
If we speak of a servo whose movement is rotating, an encoder (a detector that codes the position) that will give us a different value to its output, depending on its position in degrees, will be necessary.
The servos receive a signal through three cables: power for the motor and the small circuit board of the control (through two cables, positive and negative / ground), and a control signal that determines the position that is required. The power of these servos is normally between 4.8 and 6 volts.
Digital servo for modeling
The digital servos have, like the analog ones, a direct current motor, a set of reduction gears, a potentiometer for position feedback and an embedded control electronics inside the servo. The difference is in the control board, in which they have added a microprocessor that is in charge of analyzing the signal, processing it and controlling the motor.
The biggest difference in performance is in the speed at which the servo reacts to a change in the signal. In the same period, the digital servo can receive five or six times more control pulses than an analog one. As a result, the response of the servo to a change in the position order is much faster. This higher pulse rate also produces improvements in the electromechanical performance of the motor (higher speed and more force).
The advantage of digital is reduced a little when talking about consumption (something very important in, for example, a radio-controlled aircraft, but also in robots), since the consumption of the circuit and more continuous adjustments produce a greater expenditure of energy, and also increased engine wear.
The digital servos are able to memorize programming parameters, which vary according to each manufacturer but in general are:
1 - The direction of rotation can be programmed as "normal" or "inverse".
2 - The speed of response of the servo can be varied.
3 - A different central position (or neutral position) can be programmed, without affecting the rotation.
4 - Different travel stops can be determined for each side.
These values can be set in the servos using devices for programming, which are specific to each brand.