giving a motor a set number of revolutions then stop


Old 01-11-08, 10:10 PM
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giving a motor a set number of revolutions then stop

so basic question (i'm new to engineering)...

i have a music box, and i want it to to be so that when a button is pressed (or unpressed), the motor begins spinning and when the song is over it stops, aka...

how can i get a motor that will spin for a set number of revolutions, and then stop (without using a computer chip or something because that's over my head)?

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Old 01-12-08, 08:08 AM
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It's difficult to get a regular motor to spin a set number of revolutions because though the motor is specified as xxx revolutions per minute (RPM), it's just an approximation. So running it for y seconds, doesn't really get you what you want.

You could time the music and just set up a timer to run the motor for however many seconds then stop (look for 555 timer schematics).

The other method would be to use a stepper motor. The motors are more complex in terms of how they are manufactured, but the benefit is that you can tell the motor to rotate 15 degrees, then another 15 degrees, etc, so therefore they are quite precise. You would need a stepper motor controller and a timer to go with it. Again, some electronics design, but nothing that hasn't been done before and available somewhere on the net.

Either of these solutions sound interesting?
Old 01-12-08, 10:31 AM
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yes, stepper motor

A cheap setup will not use any encoding, and for pretty cheap, you can get a stepper motor controller that will send out a certain number of pulses, then quit.
If you are more mechanically inclined, then consider a ball screw with a limit switch on the ends to kill the power at end of travel.
Old 01-12-08, 03:42 PM
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The music box uses a motor and plays only one song, correct?

Use a timed relay. Your momentary switch activates the relay, which starts the motor. After a set period of time, the relay shuts off the motor and waits for another push of the switch.

They aren't cheap, though, and you'll be dealing with wiring both low and high voltages.
Old 01-13-08, 02:46 PM
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Modify the music box mechanism to actuate a switch to stop the motor when the song is over.

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