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ENGINEERING Electric Motors Engineering MVRT 10-21-2006 WHAT IS A MOTOR? A motor generates rotational motion. Conventional motors use chemical or electromagnetic and electric PE. ie: Car engines (motors) burn gasoline to turn wheels. THE ELECTRIC MOTOR An electric motor uses electric Electromagnets energy. Magnet Magnet Armature Once A The simple armature it has DCreached motor. continues Current theto zero flow generates rotate. position, the ancurrent EMF around is reversed the armature. and the process repeats. ROTATIONAL MOTION Rotational motion has two components. TORQUE SPEED Torque is the force of the rotation. Speed is the rate of rotation. POWER Power describes energy over time in Watts (W). There are two power equations that deal with electric motors: ELECTRIC ROTATIONAL P=IV P=TV Power = Current times Voltage Power = Torque times Speed ELECTRIC POWER Power = Current times Voltage P=IV V Voltage is difference in charge, or potential. Volts V I Current is the quantity of electrons moving over time. Amps A ROTATIONAL POWER Power = Torque times Speed P=TV T Torque is the force of the rotation. Newton-meters Nm Speed is the rotations per V unit of time. Rotations per Minute RPM MOTOR CHARACTERISTICS Electric motors behave with certain characteristics. P T V V P As the armature of the motor With The Thus, Even At these graph no maximum the as load you high faster of put and the power the load in relationship constant a motor and huge inputs, turns, most the maximum speed of Here At To We This The And find low those take is torque speed find is always speed, the points, our when at graph best at real halfway this this you their power you torque point of point either power have product between output is is vs. have called called either vs. isof Ideally, any the point, the maximum graph graph the of product should speed torque look versus of at T However, At this point, in reality, the motor the is power most is turns, it generates backward This is called the free load rpm. voltage, constant between the amount of the greater energy of motors voltage, torque power, its isresistance converted output and the the rpm motor graph a to certain looks to This is called the stall torque. the motor at this voltage. speed. low a speed greatest. motor... two max power torque graph... extremes. power or or high high torque. rpm. power. torque. this like and power. voltage. this. V is the same. not efficient. constant. current. rpm.this.to outputs like current begins heat. flow. a flatten certainout. torque. THE CIM Power Output: 343 Watts Free RPM: 5310 Stall Torque: 343.4 oz-in Ideal for long running times. THE FISHER PRICE Power Output: 387.5 Watts Free RPM: 126 Stall Torque: 51.79 Nm Hi power, but suited for medium loads due to plastic gears. THE WINDOW Power Output: 22 Watts Free RPM: 84 Stall Torque: 10.6 Nm Useful for preventing backdrive. THE GLOBE Power Output: 55 Watts Free RPM: 81 Stall Torque: 150 in-lb Low power motor for low-medium load applications. THE MABUCHI Power Output: 16.8 Watts Free RPM: 4700 Stall Torque: 60.8 mNm Counterclockwise rotation with additional spur gear. Sadly, the Mabuchi was not around when motor photos were being taken. Nobody missed it. ENGINEERING Electric Motors By Humphrey Hu Photographs from Wikipedia, USFIRST You may not modify this Powerpoint without permission