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Name: andrew m childs
Status: N/A
Age: N/A
Location: N/A
Country: N/A
Date: Around 1993


Question:
I am setting up a device that needs to run a motor at variable speeds, controlled by a knob or slider. How should I do this? I have tried a large number of combinations of motors, deferent voltage batteries, and various potentiometers, connected in series or parallel with the motor, but nothing gives me a wide range of control. What should I do?



Replies:
It really depends upon how closely you want to control the speed of the motor. The most precise way is by "closing the loop", or creating a servo system. If you can come by a tachometer (really a very precise DC genera- tor, you can monitor the speed of the motor by coupling the two together. By adding a reference voltage (say +/- 10v), and summing that with the tachometer voltage, you can build an amplifier that will give you quite precise speed control. For DC motors SCR's can work, although good PWM amplifiers are better (and considerably more expensive). Several books from your local library can give you many common circuits for closed loop speed control, depending upon the size and type of motor you are planning on using. If you want to use a 3 phase motor, you need to build a phase invertor that literally changes the frequency of the 3 phase current. A DC stepper motor would require a phase sequencing circuit with drivers. There are simpler ways to get rough, less precise speed control from a variety of motors.

dipper


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