How to Calculate the Torque in a Servo Motor

Written by grayson charles
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How to Calculate the Torque in a Servo Motor
Servo motors are often used in motorised toys. (aeroplane image by Goran Bogicevic from

A servo is a small device with a shaft that can be turned to specific angles with electronic signals. Servo motors are used to create robot movements and to control the rudders of model aeroplanes and helicopters. The torque rating of a motor measures the force of rotation created by the motor shaft. Torque is measured in foot-pounds in the English system of measurement and as newton-meters in the metric system.

Skill level:

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Things you need

  • Servo motor
  • Power supply for the motor
  • Thread
  • Set of small incremental weights
  • Table
  • Ruler

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  1. 1

    Secure the motor on a table with the shaft overhanging the edge of a table.

  2. 2

    Attach the lightest weight to the end of the thread.

  3. 3

    Attach the other end of the thread to the motor shaft. The thread should wind around the motor shaft when the motor turns.

  4. 4

    Apply power to the motor and observe the shaft as it turns freely and winds the thread.

  5. 5

    Replace the weight with a slightly heavier weight and repeat the experiment if the motor turns freely.

  6. 6

    Determine the smallest weight that causes the motor to stall. Your torque rating calculation will be more accurate the smaller the weight increment used.

  7. 7

    Measure the radius of the motor shaft.

  8. 8

    Multiply the mass of the weight causing the stall by the radius of the shaft. This is the torque rating of the motor.

Tips and warnings

  • Torque measuring equipment is sold for precision applications required in science and manufacturing.

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