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Variable Speed Control For A Dc Motor


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I am a 3rd year mechanical engineering student at Ryerson University. I am currently working on a design project in my design course. I am designing a DC power assisted light duty snow blower. My professor would like our design to incorporate varying motor speeds depending on the weight of snow that is being moved through the auger and out the discharge tube. My understanding is that the higher the weight, the more power is required by the motor to move the snow, thus prompting motor to move faster and possibly causing failure. Thus reducing motor speed would eliminate this problem.

I would appreciate ideas on how i can change motor speed depending on the weight of snow in the snow blower. Help will be greatly appreciated.

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Hello nainster


You can vary the speed using a DC controller, and you could use a nmber of options for detemining the weight of the snow.

One possible option, wold be to determine the load on the motor and compare this with a known look up table.

A DC motor is not a very good speed regulator unless there is a closed loop, so it will slow down with increasing load. To get the motor to operate at a fixed speed, you will need to adjust the excitation to compensate for the shaft torque required. This is normally done automatically using some form of feedback which can be a shaft encoder, tachogenerator, or a voltage feedback from the motor windings.

If you compare the level of excitation against the speed reference at any given speed in a closed loop system, you will get a measure of the load on the motor.

Create a look up table of running speed against load and adjust your reference accordingly.


Best regards,

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