Content

1. Motor

2. Working of a Motor

3. Types of motor

4. Actuators

5. Types of actuators

6. Difference between motor and actuator

Motors

What is a motor?

  • A motor is a machine that converts electrical energy to mechanical energy.
  • The word ‘motor’ is rooted from a classic Latin word ‘movere’ which means ‘to move’.

Working of a motor

  • A motor works on the principle of electromagnetism.
  • A current carrying conductor creates a magnetic field. But when this conductor is placed in a magnetic field, it generates force proportional to the current. But when two field magnets of different poles are placed on either side of the conductor, it creates forces of equal magnitude but opposite in direction thus constituting a Couple. This is responsible for the rotation of a shaft of the motor.
  • The conductor is usually referred to as the Rotor and the field magnets constitute the Stator.

Types of motors generally used in Robotics

  • Geared DC  motors
  • Brushless DC  motors
  • Servo Motors
  • Stepper Motors

Let us discuss each of them briefly

Geared DC motor

  • These are general purpose motors.
  • They provide good RPM (Rounds per minute)
  • But provide less torque.
  • They are generally used for the locomotion of the robots.
  • Different  gear ratios in the gear train provides different RPM’s

Brushless DC motor

  • In this type of motor the rotor is a circular permanent magnet. It is situated outside the stator.
  • Three coil pairs are placed on the stator. When one of the coil pair gets energized the repulsion or attraction between the magnetic fields of rotor and stator to cause the rotor to rotate.
  • Used in high speed and high torque applications.

Servo Motor

Unlike a normal DC motor, A Servo motor is used in  control systems where precision is required.

A Servo rotates for an angle that is provided by the user.

A Servo can rotate up to an angle of 180 or 360 degrees and thus  plays no role in locomotion of a robot. Used in high torque applications.

Stepper Motor

  • Imagine a circle divided into ‘n’ equal segments. When this ‘n’ is given as an input to the stepper motor it covers these segments in the form of ‘steps’ with equal intervals of time to cover each segment. (Like a clock)
  • Used in high torque low-speed applications

Actuators

  • An Actuator can be referred to as a type of motor than converts energy to run or control the motion of a mechanism.
  • It receives energy (either electrical or fluid pressure : both  hydraulic and pneumatic) and converts this energy to motion.

Types of Actuators

  • Linear Actuators
  • Hydraulic Actuators
  • Pneumatic Actuators
  • Piezoelectric Actuators

Now let us discuss in brief about each

Linear Actuators

  • Linear actuators create motion in straight line, with respect to the motion of an electric motor.
  • Widely used Linear Actuators:
    • Screw Thread Mechanism
    • Wheel and Axle Mechanism

Screw Thread Mechanism

  • A Screw Threaded shaft is connected to a motor (or any external rotary force).
  • A nut is interlocked with the shaft such that rotary motion of the nut is restricted.
  • Eg: Removing a screw-nut combination using a screwdriver.

Wheel and Axle Mechanism

  • A Wheel is connected to a motor.
  • This is connected to a cable, rack or chain to produce linear motion.
  • Eg: Rack and Pinion mechanism

Pneumatic Actuators

  • Pneumatic: Pressurized Gas
  • Pneumatic Actuator: Actuator that uses the pressure of the gas fluid to create motion is said to a Pneumatic Actuator.
  • Applications: pneumatic braking systems.
  • Cheaper than Hydraulic Actuators

Hydraulic Actuators

  • Hydraulic Actuator works on the same principle as that of a Pneumatic Actuator.
  • The difference between these two is the different kinds of fluids that are  used
  • Hydraulic Actuators use the liquid medium.

Piezoelectric Actuator

  • Piezo-Electric Effect: The ability of certain materials to generate electric charge in response to applied mechanical stress.
  • ‘Piezo’ is a Greek word which means ‘Push’
  • Piezoelectric actuator creates motion under the application of  electric current. (works under the principle of inverse  Piezoelectric Effect.)
  • Eg: Alarms

Difference between motor and actuator

A motor provides rotational movement while an actuator provides linear motion.

A Motor is designed for continuous rotations, can have high rotations speed. But an actuator is designed for precise positioning and not for Continuous rotations, doesn’t have a high rotation speed.

A Motor shaft can rotate 360°, by an actuator is limited to 90°.