Servo motor is a device of small size with output shaft. It works on a code signal. The shaft is designed to be positioned to a particular angular position by sending a code signal. The motor will sustain the position until the coded signal exists on the input line. Servos have practical uses, such as they are used in radio controlled airplanes to place control surfaces such as the rudders and elevators. Some of the common applications of servo also include puppets, radio controlled cars, robots, etc.

Their small size must not be taken as parameter to judge its capabilities. They are extremely powerful for their size. They draw power which is proportional to the mechanical load. Probably, this is the reason why they are widely used in robotics.

As said above the work on the basis of the signal sent to them, Servos are sent a pulse of variable width to control them. There is a control wire that works as medium to send this pulse. Also, there are different parameters for the pulse sent as signal - a minimum pulse, a maximum pulse and a repetition rate. Different servos have different restraints on their rotation, however they all have a neutral position which is always positioned around 1.5 milliseconds (ms). Servo has a bit complex design perhaps this is reason why they are so strong and are popular for various applications. Some of its important advantages and disadvantages are as followed:

Advantages of DC Servo motor:

  1. Comparatively high power output than the motor weight and size.
  2. Encoder sets resolution and accuracy.
  3. Highly efficient. It can reach up to 90% of light loads.
  4. Exuberantly high torque to inertia ratio which leads to quick acceleration of loads.
  5. Reserves power for emergencies and can provide 2-3 times constant power for short time.
  6. Reserves torque and can provide 5-10 times rated torque for short time.
  7. Motor remains cool because the current drawn is proportional to load.
  8. High speed torque is functional as it holds rated torque to 90% of NL RPM
  9. Doesn’t make noise even while running at high speed.
  10. Free of vibration and resonance.

Disadvantages of DC Servo motor:

  1. Needs to be tuned so as to steady feedback loop.
  2. Motor doesn’t work when something breaks, hence safety circuits are needed.
  3. Has complex architecture and requires encoder.
  4. The brush torn out in limited life of 2,000 hrs. Then service is required.
  5. Has peak torque fixed to a 1% duty cycle.
  6. Overload can damage motor.
  7. Complex option of encoders, motors and servo drives.
  8. Required power supply to use peak torque is 10 times average.
  9. Motor generates peak power only at higher speeds and requires frequent gearing.
  10. Inefficient cooling mechanism. If motors are ventilated, they get easily contaminated.
Author's Bio: 

This article is published by Harrie Dadhwal for Harrington Electric Motors. Harrington Electric Motors is leading Australian distributor of Servo Motor who deals in different type of Electric Motors like Single Phase, three phase motors. They are also providing Electric Motor Repairs services in Melbourne as well.