1. What is the servo ?

In a robot mechanic-electrical control system, servo control effect is one of the important factors affecting the performance. Servo can be used as a basic output in MEMS ( micro electro mechanical system ) and model aircraft actuator, servo simple control and output make it very easy to interface with the SCM system .

Servo is a kind of position(angel) servo drive, applies to those control systems, which can remain stable when the angel changing. At present,  remote control robot has been widely used in the high-end remote toys field , such as model airplane, including model airplane and submarine model.In fact,  servo is a kind of servo motor.

2.Working principle：

The control signal into the signal modulation chip by the receiver channel, get the DC bias voltage.It has an internal reference circuit, the cycle is 20ms, the width of  reference signal is 1.5ms. Compare DC bias voltage with the  potentiometer voltage, get output voltage difference.Finally, the positive and negative output voltage difference to the motor driver chip motor positive decision.When the motor speed must, through the reduction gear drive cascading rotary potentiometers, the voltage difference is 0, motor to stop rotating. Of course, we don’t need to understand the working principle, know the control principle is ok!As we use transistors, just know  it can be the switch tube or tube amplifier, we  don’t have to consider how tube electrons specific flow .

3. Servo control:

Control servo usually needs one time-base pulse about 20ms, its high level portion is generally in the range of 0.5ms ~2.5ms angle controlpulse part.Take 180 degree angle servo as an example,  the corresponding control relationship is as follows:

0.5ms————–0 degree

1.0ms————45 degree

1.5ms————90 degree

2.0ms———–135 degree

2.5ms———–180 degree

This is only a reference value, the specific parameters, please see the technical parameters of servo.The working voltage of small serco is  4.8V or 6V, speed is not very fast,usually 0.22/60 or 0.18/60 degree. Some serco has 1024 position levels. If the valid angle range of serco is 180 degree, the control precision can reach 180/1024 degree is about 0.18 degrees. From the time, PWM control accuracy is 2000/1024us about 2us. when you have a serco, the control accuracy is less than 1 degree, and we see the serco shaking.In this case, as long as the serco voltage don’t jitter, the jitter is your control pulse.