SERVO MOTORS

• A Servo is a small device that has an output shaft. This shaft can be positioned to specific angular positions by sending the servo a coded signal.

• A servomotor is a rotary actuator or linear actuator that allows for precise control of angular or linear position, velocity and acceleration. It consists of a suitable motor coupled to a sensor for position feedback.

What’s a Servomotor?

Parts of a Servomotor1.Motor2.Gears3.Shaft4.Position Sensor5.Control Circuit6.Supply7. Control Wire

Principle of Operation

How it is controlled?Servos are controlled by sending an electrical pulse of variable width, or pulse width modulation (PWM), through the control wire. There is a minimum pulse, a maximum pulse, and a repetition rate. A servo motor can usually only turn 90 degrees in either direction for a total of 180 degree movement. The motor's neutral position is defined as the position where the servo has the same amount of potential rotation in the both the clockwise or counter-clockwise direction.

The maximum amount of force the servo can exert is called the torque rating of the servo. Servos will not hold their position forever though; the position pulse must be repeated to instruct the servo to stay in position. 

Servo Motor ControllersA servo motor controller is a circuit

that is used to control the position of a servo motor. It is also called as a servo motor driver. A servo motor controller consists of a controller, the servo motor and the power supply unit.

MICROCONTROLLER

1. PWM Generator/Modules2. Timer (Usually using PIC

Controllers)

 AT89S51The AT89S51 is a low-power, high-performance CMOS 8-bit microcontroller with 4K bytes of In-System Programmable Flash memory. The Atmel AT89S51 is a powerful microcontroller which provides a highly-flexible and cost-effective solution to many embedded control applications.

PIC18F

ARDUINO

Characteristics of Servo MotorsPower Supply Voltage and Current :The common RC servo motors powered from supplies in the range of 4 – 6 V and 100 mA - 2 A . 

Operating Speed :Common servos have operating speeds in the range of 0,05 to 0,2 s/60 degree.

Torque :Typical values of torques of servo motors are in the range of 0,5 to 10 kg/cm. 

Control Pulse :Two main types of control pulses used in RC applications: center position in 1-2 ms and 1,25-1,75 ms. 

Resolution :Typical servo motors have resolutions in the range from 1 degree to 10 degree. 

Size and Weight :Typical RC servo motors have a weight range between 15 and 200g.

TYPES OF SERVO MOTORS1.Positional rotation servo2. Continuous rotation servo3. Linear servo

ADVANTAGES AND

DISADVANTAGES

Advantages:oIf a heavy load is placed on the motor, the driver will increase the current to the motor coil as it attempts to rotate the motor. Basically, there is no out-of-step condition.

oHigh-speed operation is possible.

Disadvantages:oSince the servomotor tries to rotate according to the command pulses, but lags behind, it is not suitable for precision control of rotation.

oHigher cost.oWhen stopped, the motor’s rotor continues to move back and forth one pulse, so that it is not suitable if you need to prevent vibration

Applications:•In Industries they are used in machine tools, packaging, factory automation, material handling, printing converting, assembly lines, and many other demanding applications robotics, CNC machinery or automated manufacturing.•They are also used in radio controlled airplanes to control the positioning and movement of elevators.•They are used in robots because of their smooth switching on and off and accurate positioning.

• They are also used by aerospace industry to maintain hydraulic fluid in their hydraulic systems.

• They are used in many radio controlled toys.

• They are used in electronic devices such as DVDs or Blue ray Disc players to extend or replay the disc trays.

• They are also being used in automobiles to maintain the speed of vehicles.