Rotational Field From Two Signals - Confirm

For proper rotation, the signals have to go both positive and negative, instead of stopping at zero.

And should be sine waves for smooth rotation. Square waves will make jerky motion, like a stepper motor.

in practice they would be, but do they have to be?

jerky motion is more like jerky when eaten.

NT

If the wiring convention of the symbols is what it seems to be, the color paired coils produce same-sense poles (two N poles, then half cycle later, two S poles). That's exactly backward, you want something that will , control a compass as a rotor, so one N and one S pole pointed inward is wanted.

Square waves (like for a stepper motor) are relatively inefficient, power-wise, and (as others have noted) pulsed DC isn't desirable. Four drive signals (forward current winding next to reverse current winding) rather than two is the norm for synchronous/stepper motors driven from single DC power supply.

How do you get the other two quadrants? You're just alternating between 0degrees and 90degrees. The typical way of driving this sort of thing is with a full bridge (four switches), so the current can go both directions to get the third and fourth quadrant.

I have redrawn based upon my understanding of the comments received. Is this now correct?

I want to use only two signals so they can be output via a sound card into a bipolar driver.

Steve Morris

Yep, that looks like a normal two-phase motor wiring. Torque should be nearly constant at all angles, and (with a permanent magnet rotor) the rotation should be synchronous. It'll be nearly synchronous with a soft-iron rotor (slightly slower, depending on load).

The other 2 quadrants would certainly be nice & sensible, but with just 2 you've still got a moving magnetic field, so I think it would at least turn.

NT

To get continuous _field_ rotation you need all four quadrants (you need at least 3 phases@120 degrees, but 4@90 works too).

Cheers

Phil Hobbs

It's moving but it's not rotating. The motor will not go all the way around. It'll go 1/4 turn one way, then 1/4 turn the other.

Of course what was initially proposed doesn't get continuous field rotation. My point was that since you still get patches of moving magnetic field it ought to still move, even if it's not a sensible design.

NT

the magnetic field doesn't do that.

In simple terms,

1. no magnetic attraction anywhere
2. Magnetised area builds up at A
3. Magnetised area effectively moves from A to B, causing rotor movement
4. Magnetised area disappears, leaving rotor unattracted. Rotor keeps moving on inertia

NT

Please refer to corrected diagram below as per my second post.

Steve Morris

People already have

NT

But he wanted rotation. His changes didn't get it.

What????

The magnetically rotated machines tend to have magnetic detents when there is no current in the coils. The detenting stops the rotatiion when there is no current. To verify, pick the nearest stepper motor and turn the shaft.

The unipolar drive will wiggle the rotor between two positions back and forth.

com:

urn.

at least 3 phases@120 degrees, but 4@90 works too).

you would count I/Q as four phases?

But whit3rd stated.

"Yep, that looks like a normal two-phase motor wiring. Torque should be nearly constant at all angles, and (with a permanent magnet rotor) the rotation should be synchronous. It'll be nearly synchronous with a soft-iron rotor (slightly slower, depending on load)."

Now I am confused. Does the configuration linked above, with the changes, exhibit continuous rotation or not?

Steve Morris