12v dc motor rotate once and then stop

Question

Can anyone suggest the best way to get a 12V DC electric motor (70RPM) to rotate roughly 360 degrees and then stop?

So the process would be;

1. Power switched on.
2. Motor rotates once, then stops.
3. Power switched off.
4. Repeat

Thanks in advance

Answer 1

The most common method of doing what you want is to use a cam that actuates a microswitch at the desired stop point.

To do the sequence that you want, you need to add a tiny bit of smarts. This can be a couple of relays or a microcontroller.

As mentioned in the comments, most automobiles have windshield wiper motors that have such a switch mechanism built in. However, because you want the motor to operate only one full cycle upon power-up, you do need to add the smarts that I mentioned.

Answer 2

The circuit below may be one of the simplest methods, just one micro-switch and one push button.

Pushing the (normally open) push button switch energizes the motor briefly just enough to move the cam lobe off the micro-switch arm, the micro-switch connection then keeps the motor alive. The motor spins until the cam lobe comes back around to the micro-switch and turns the motor off.

You would need to be sure the size of the cam lobe is sufficient to stop the motor when the micro-switch opens, (eg. If the motor takes too long to stop there could be a problem - in which case make the cam wider).

^{simulate this circuit – Schematic created using CircuitLab}

Answer 3

Strap it to a rotary encoder and count the number of pulses generated. Based on the speed of the pulses you should be able to figure out how quickly you need to stop or reverse in order to end up at exactly 360°.