Brushless DC Motors Sohaib Hasan

Motor Basics What is a motor Where did it come from Converts electrical energy into kinetic energy Where did it come from Identification of rotating magnetic field principle by Nicola Tesla in 1882 Introduction of Electric Motor by Nicola Tesla in December 1889 (U.S. Patent 0416194)

Parts of a Motor End Bell Fastners Shaft Key & Keyways Bearing & Brushings End Ball Flanges Identification Plates Wire Warnish Commutators Brush Holders Laminations Conduit Connection Box Magnets (Ferrites) Brushless Motor Components Armature or Rotor Commutator or Brushes Lamination stack Windings Shaft Bearings Brush Type Motor Components Images courtesy of Hernon Adhesives & Sealents (http://www.hernonmfg.com/electricmotor.htm)

Parts of a Motor Images courtesy of How Stuff Works (http://electronics.howstuffworks.com/motor3.htm)

How It Works When electric current passes through a coil in a magnetic field, the magnetic force produces a torque which turns the motor. Force in Motor: F=ILB F = Force B = Magnetic Field L = Length of Conductor I = Current in Conductor Torque in Motor: T = IBA sin θ A = LW L = Length of Winding W = Width of Winding A simple DC electric motor. When the coil is powered, a magnetic field is generated around the armature. The left side of the armature is pushed away from the left magnet and drawn toward the right, causing rotation. The armature continues to rotate. When the armature becomes horizontally aligned, the commutator reverses the direction of current through the coil, reversing the magnetic field. The process then repeats. Images courtesy of Wikipedia (http://en.wikipedia.org/wiki/Electric_motor)

Motor Types

Brushless DC Motor No Commutators Position of Coils with respect to the magnetic field is sensed electronically. Current is commutated through electronic switches to appropriate phases.

How it Works Halls Sensors sense the position of the coils The Decoder Circuit turns appropriate switches on and off The voltage through the specific coils turns the motor Images courtesy of Servo Magnetics (http://www.servomag.com/flash/2-pole/2pole-bldc-motor.html)

Advantages Increased Reliablilty & Efficiency Longer Life Elimination of Sparks from Commutator Reduced Friction Faster Rate of Voltage & Current Precision Voltage & Current Applied to Field Coils

Applications Low Power High Power Consumer Electronics Medical Field Industrial Machinery Vehicles Airplanes Consumer: Hard Drives, CD/DVD Drives, PC Cooling Fans, toys, RC airplanes, air conditioners Medical: Drills, Operating equipment Industrial: servo drives Vehicles: electronic power steering Airplanes: Antares 20E, an electric self-launching sailplane, flies with a 42kW DC/DC brushless motor and Li-Ion batteries and can climb up to 3000m with fully charged cells

Disadvantages Requires Complex Drive Circuitry Requires additional Sensors Higher Cost Some designs require manual labor (Hand wound Stator Coils)

Useful Links http://en.wikipedia.org/wiki/Electric_motor http://electronics.howstuffworks.com/motor3.htm http://www.hernonmfg.com/electricmotor.htm http://hyperphysics.phy-astr.gsu.edu/hbase/hframe.html http://www.servomag.com/flash/2-pole/2pole-bldc-motor.html http://www.engineersedge.com/motors/brushless_dc_motor.htm http://www.freescale.com/webapp/sps/site/application.jsp?nodeId=02nQXGrrlPY7r803B5