Servo motor basic theory pdf

From the gear box, the output of the motor is delivered via servo spline to the servo arm. The potentiometer changes position corresponding to the current position of the motor. So the change in resistance produces an equivalent change in voltage from the potentiometer. A pulse width modulated signal is fed through the control wire. The pulse width is converted into an equivalent voltage that is compared with that of signal from the potentiometer in an error amplifier.

The difference signal is amplified and provided to the DC motor. So the signal applied to the DC servo motor is a damping wave which diminishes as the desired position is attained by the motor. When the difference between the desired position as indicated by the pulse train and current position is large, motor moves fast.

When the same difference is less, the motor moves slow. The required pulse train for controlling the servo motor can be generated by a timer IC such as or a microcontroller can be programmed to generate the required waveform.

Power supply for Servo. The servo requires a DC supply of 4. For a specific servo, its voltage rating is given as one of its specification by the manufacturer. The DC supply can be given through a battery or a regulator. The battery voltage must be closer to the operating voltage of the servo. This will reduce the wastage of power as thermal radiation.

A switched regulator can be used as the supply for better power efficiency. Learn more about working of a servo motor through exclusive images at the Insight about servo motor. Selection of a Servo. The typical specifications of servo motors are torque, speed, weight, dimensions, motor type and bearing type. The motor type can be of 3 poles or 5 poles.

The pole refers to the permanent magnets that are attached with the electromagnets. The servos are manufactured with different torque and speed ratings. The torque is the force applied by the motor to drive the servo arm.

Speed is the measure that gives the estimate that how fast the servo attains a position. A manufacturer may compromise torque over speed or speed over torque in different models. The servos with better torque must be preferred. The weight and dimensions are directly proportional to the torque. Obviously, the servo having more torque will also have larger dimensions and weight.

The selection of a servo can be made according to the torque and speed requirements of the application. The weight and dimension may also play a vital role in optimizing the selection such as when a servo is needed for making an RC airplane or helicopter. The website of the manufacturers can be seen to obtain details about different models of the servos. Also their product catalogue can be referred to. Some manufacturers like Futaba also provide online calculator for the selection of a servo.

Interference and Noise Signal. The PWM signal is given to the servo by the control wire. The noise or interference signals from the surrounding electronics or other servos can cause positional errors. To eliminate this problem the control signals are supplied after amplification. This will suppress the noise and interference signals. Servo Modification for full Rotation. One may want to use the servo for his robot applications and desire to move the servo continually.

This is possible by a little modification. The servo gear box has a mechanical stop which avoids the servo to make full rotation. File off the mechanical stop s so that the gear box is free to make a complete rotation.

But this is not the only sufficient thing. The servo works on a feedback mechanism. So the pot of the servo must be first moved to the centre position. This can be done by sending medium pulses to the servo by a microcontroller. Then fix the gears attached to the pot shaft with glue. This will keep an impression to the control electronics of the servo that the current position is the middle point.

Here the device is controlled by a feedback signal generated by comparing output signal and reference input signal. Here reference input signal is compared to the reference output signal and the third signal is produced by the feedback system. And this third signal acts as an input signal to the control the device. This signal is present as long as the feedback signal is generated or there is a difference between the reference input signal and reference output signal.

So the main task of servomechanism is to maintain the output of a system at the desired value at presence of noises. First of all, we use gear assembly to reduce RPM and to increase torque of the motor. Say at initial position of servo motor shaft, the position of the potentiometer knob is such that there is no electrical signal generated at the output port of the potentiometer. Now an electrical signal is given to another input terminal of the error detector amplifier.

Now the difference between these two signals, one comes from the potentiometer and another comes from other sources, will be processed in a feedback mechanism and output will be provided in terms of error signal. This error signal acts as the input for motor and motor starts rotating. Now motor shaft is connected with the potentiometer and as the motor rotates so the potentiometer and it will generate a signal. After sometime the position of potentiometer reaches at a position that the output of potentiometer is same as external signal provided.

At this condition, there will be no output signal from the amplifier to the motor input as there is no difference between external applied signal and the signal generated at potentiometer, and in this situation motor stops rotating. Interfacing hobby Servo motors like s90 servo motor with MCU is very easy.

Servos have three wires coming out of them. Out of which two will be used for Supply positive and negative and one will be used for the signal that is to be sent from the MCU. The picture of MG is shown below:. The color coding of your servo motor might differ hence check for your respective datasheet.

All motors have three wires coming out of them. There is a minimum pulse, a maximum pulse and a repetition rate. Servo motor can turn 90 degree from either direction form its neutral position.

The servo motor expects to see a pulse every 20 milliseconds ms and the length of the pulse will determine how far the motor turns. For example, a 1. Servo motor works on PWM Pulse width modulation principle, means its angle of rotation is controlled by the duration of applied pulse to its Control PIN.

Basically servo motor is made up of DC motor which is controlled by a variable resistor potentiometer and some gears. High speed force of DC motor is converted into torque by Gears.

The potentiometer is connected to the output shaft of the Servo, to calculate the angle and stop the DC motor on the required angle. Servo motor can be rotated from 0 to degrees, but it can go up to degrees, depending on the manufacturing.