A) Refer to the diagram on “Speed Control of a Shunt Wound DCMotor.
Suppose the no load voltage V = 90V, Ra +R1 = 4 ohms, Rsh + RF = 130 ohms,and the motor runs at a rated speed of 1000 RPM when IL= 4 amps. What is the back EMF VB in volts when themotor runs at IL = 6 amps?
Note: Type a 1-decimal number, rounded off to the nearest0.1
B) How do you know that the compound motor provides good speedcontrol at the no-load condition?
1) The torque speed curve is flat nearzero torque. This means that small changes in load do notappreciably change the speed.
2) The torque speed curve is flat nearzero torque. This means that large changes in load do notappreciably change the speed.
3) The torque speed curve has a largeslope near zero torque. This means that large changes in load leadto very small changes in speed.
4) The compound motor runs at slowspeeds when heavily loaded.
5) Items (1) and (4)
C) You are designing a new emergency brake mechanism for anautomobile featuring one of the following DC motors. Which onewould you choose?
1) Permanent magnet motor
2) Brushless motor
3) Servomotor
4) Compound wound motor
5) Torque motor
(D) Suppose you are building amachine where the timing sequence of two drive axes requires thatthey operate at precisely the same speed. What type of motor wouldyou select: AC or DC and why?
1) You select identical DC motorsbecause controlling frequency input gives simple and precise speedcontrol
2) You select identical AC motorsbecause highly accurate and reliable AC speed controllers can bebought for very cheap prices
3) You select identical DC motorsbecause controlling voltage input gives simple and precise speedcontrol
4) You select identical AC motorsbecause the variance of torque and speed specs on NEMA specifiedmotors is very small
5) It doesn’t matter whether youselect an AC or a DC motor. The cost of supplying accurate speedcontrol for either type of motor is the same.
