Electric Motors for Robotics

Electric Motors for Robotics Munindar Kumar Sunil Choudhary Narendra K. MeenaFactors to choose right kind of motorspeed (RPM), torque, direction, Control and accuracy

Each motor type has several advantages as well as disadvantages depending on a particular robots design.all motors are available in different sizes.

Direction (H-Bridge)

Uni-directional, and Bi-directionalAn H bridge is an electronic circuit that enables a voltage to be applied across a load in either direction. to allow DC motors to run forwards and backwards.In particular, a bipolar stepper motor is almost invariably driven by a motor controller containing two H bridges.Most DC-to-AC converters (power inverters), most AC/AC converters, the DC-to-DC pushpull converter, most motor controllers, and many other kinds of power electronics use H bridges. Torque (Kgcm)stall and operating torque (max and minimum)More voltage, higher the torque.torque ratings can change depending on the voltage applied. So if you need a little more torque to crush that cute kitten, going 20% above the rated motor voltage value is fairly safe (for you, not the kitten). Just remember that this is less efficient, and that you should heat sink your motor.Most efficient at rated voltageTypical DC motors are rated from about 6V-12V. The larger ones are often 24V or more.When buying a motor, there are two current ratings you should pay attention to. The first isoperating current (average current, typical torque). The other is thestall current (max current, limiting torque).

Speed (PWM)Rotations per minute(rpm)try to slow down a motor by reducing its voltage with a variable resistor or other ways will not work well, because it will not only reduce the motor's speed, it will also reduce a motor's strength, while also consuming a lot of electricity as large amounts of heat are generated by the resistor.A far better way is to use a PWM (Pulse-width modulation) device.

How Motor is Controlled ?Direction, SpeedMicrocontroller

Motor Driver Contains H-BridgeMotor

DC Motors(mostly used in robotics)Brushed DC Motors

simply DC motor uses brushes to detect the change in orientation so that it can flip the current to continue the rotors rotation. different sizes and at different speeds. generally useless in robots as they produce the slightest torque. have two wires; ground and power.

Geared DC Motor

DC motors provide good speeds without enough torque.To Overcome this DC motors are often coupled with gears which provide greater torque, but reducing speed. Normally all our robots would require a geared DC motor to pull the weight of our robot and any additional components placed.the rotations per minute of Gear1 is lesser than the motor. Gear2 has even less number of rotations per minute. each gear increases the torque of overall setup.

Brushless DC Motor (BLDC)In a BLDC, the rotor is made of permanent magnet and the stator is made of electromagnet. To detect a change in orientation, brushless motors generally use Hall Effect sensors to detect the rotors magnetic field and consecutively its orientation. Brushless motors are very useful in robots as they are more capable; they provide enough torque, and greater speeds than brushed motors. expensive due to their design complexity and need a controller to control their speed and rotation.

Servo Motors (RC servo motors)DC motors coupled with a feedback control circuitry, a gear system to increase torque and a position sensing device (usually a potentiometer). When a signal (pulse) is sent, it moves the motor shaft to a desired position using the position feedback from a potentiometer. do not exhibit continuous rotation (generally 200 back and forth) and requires modifification for continuous Controlling a servo is done withPulse-width modulation. The length of the pulse is relative to the position the servo will turn to. wide range of applications in robotics, but require a bit of shrewd programming to make it work.have three wires; Ground, Power and Control pulse (control signal). e.g. to move a sensor around, or to move the legs of a robot.

Stepper Motor

brushless motors which divides the rotors rotation into discrete number of steps breaks it into steps per revolution and jumps each step for a certain pulse. Unlike a servo motor, stepper motor does not require any complex position feedback mechanismstepper motors are similar to brushed DC motors with less torque. Based on the arrangement of windings inside a stepper motor, it can be classified as Unipolar or Bipolar step motor.Four wires

Linear DC MotorsNot likely to be used in standard mobile robots, a linear DC motor is a normal DC motor with its stator spread out.

AC MotorsThere are several different types of AC-motors, but their use is limited to high power stationary industrial robots. They are harder to use than DC-motors.won't use AC motors unless your robot is stationaryModifying the AC frequency can alter speed and torqueAC Servomotor, AC Stepper MotorBIBLIOGRAPHYwww.societyofrobots.comhttp://www.robotplatform.com/knowledge/actuators/dc_motors.htmlWikipedia, the free encyclopedia

EE201: ElectroMechanicsSeminar May 30,2015Munindar Kumar B13216Narendra K. Meena B13217Sunil Choudhary B13233

Instructed By: Dr.Bhakti Joshi

Electric Motors for Robotics