Motors and Actuators -by vvk lalithej

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 shaft of motor. The conductor is usually referred to as the Rotor and the field magnets constitute the Stator.

Working of a motor

Types of motors generally used in Robotics Geared DC motors Brushless DC motors Servo Motors Stepper Motors

Geared DC motor General Purpose motors Provides good RPM but low Torque Generally used in locomotion of robots Different Gear Ratios in the gear train of the motor provides different RPMs

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 a 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 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

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 screw driver.

Screw Thread Mechanism

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 gas fluid to create motion is said to a Pneumatic Actuator. Applications : pneumatic braking systems. Cheaper than Hydraulic Actuators

Pneumatic Actuators

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

Hydraulic Actuators

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