Pulse motor self start on a certain direction?

[neazoi]

Hi I have seen this video on youtube (I do not know how else to attach this here)

Which shows a so called "pulse motor" with self-starting capability. The schematic is shown inside the video.
I think what the schematic does is to somehow set the current applied to the coil into plus or minus alternatively, until the motor starts.
However the motor starts at a random direction based on the rotor stationary position.

I wonder if you have any ideas to make the motor start at a certain direction only?

Interference is a thing I want to tackle, so this motor seems to produce no serious RF interference?

 

[BradtheRad]

Motors for radio-controlled craft often are called 3-turn, 5-turn, etc. With an odd number (not just 1 or 2) of coils, it ensures proper spin direction.

 

[betwixt]

Agreed, just reversing polarity gives equal pull in opposite directions so unless you give momentum it would just sit there or could even flip back and forth. Adding another force 'off axis' give the phase shift needed to provide a rotating rather than alternating magnetic field.

Something to try: start a microwave oven a few times and see which direction the food rotates.

Brian.

 

[neazoi]

How about placing the coil a bit off center? And flip polarity on the begining?

 

[betwixt]

The field runs through the coil core so it doesn't matter if you move it off center, by misaligning them you just reduce the pull it gives the rotor. You can do it easily if you add a second coil at some angle to the original and pulse them out of phase and it also gives you greater torque.

Brian.

 

[neazoi]

You can do it easily if you add a second coil at some angle to the original and pulse them out of phase and it also gives you greater torque.

That's very interesting.
I wonder though if you can really start always in one direction with this. I mean, doesn't the starting direction depend on the resting point of the magnet in this case as well?

I would love to see a simple discrete circuit on this phase pulsating for 2 coils. Maybe a two series transistors amplifiers, one triggering the other but some kind of small capacitor in the base of the second one, to somehow delay the second pulse?