Rotational Field From Two Signals - Confirm

Yes. You need to be able to make a linear combination of phases whose sum i

, but not just sin and cos.

Cheers

Phil Hobbs

I'm not making sense of that

NT

Den tirsdag den 16. januar 2018 kl. 04.41.31 UTC+1 skrev snipped-for-privacy@gmail.com:

os, but not just sin and cos.

it is four quadrants but it is still only two phases

os, but not just sin and cos.

He neglects to show the series coupling capacitors blocking the DC (PC soun d card.)

Also, he says 180deg and 270deg, but his graph doesn't match this.

His first change didn't get the third and fourth quadrants.

the OP is using a sound card, and most have AC coupled outputs,

But non-zero crossing drive you still have a rotating field, just superimposed on a constant field, you can probably drive an aluminium armature but with high losses. a permanent magnet armature would be hard to start, but once started should run

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Peoples brains are exploding because your waveform graphs do not not have zero volts marked like normal graphs do.

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ok, that's clear, but not relevant as far as I can see to whether the 2 quadrant feed could get a motor to turn.

NT

Think about the magnetic North on the ends of the stators. They'll alternate between 0 and 90 degrees (50% each). There is nothing to pull the rotor to 180 or 270 degrees - no rotation.

ith just 2

t least turn.

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

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.

quadrant feed could get a motor to turn.

Rotors move because they see a moving magnetic field. Of course a nice cont inuously moving field is the sane option, but what we are discussing is equ ivalent to bringing an iron magnet close to the rotor, moving it 1/4 turn t hen taking it away. Repeat repeat. Not pretty but with the right motor it s hould result in rotation.

NT

But that's not what's happening (I have a suspicion we have different versions of his contraption in our heads). His field is oscillating back and forth between 0 and 90 degrees. The rotor will do the same. There is nothing pulling it to 180 or 270 and there is no reason for it to go 3/4 revolution when it can go 1/4. In any case, the field is _not_ rotating.

Err... no, as the second sketch indicates, it's doing a full 360-degree sweep.

te:

t with just 2

d at least turn.

s (you need at least 3 phases@120 degrees, but 4@90 works too).

eld rotation. My point was that since you still get patches of moving magne tic field it ought to still move, even if it's not a sensible design.

2 quadrant feed could get a motor to turn.

ontinuously moving field is the sane option, but what we are discussing is equivalent to bringing an iron magnet close to the rotor, moving it 1/4 tur n then taking it away. Repeat repeat. Not pretty but with the right motor i t should result in rotation.

is the drive circuit we're talking about. Note that current is not supplied all the time. The sequence goes: A on B off A on B on A off B on A off B off repeat

That is equivalent to doing what I said with a hand-held magnet, albeit rat her faster. Steps 1,2,3 in the above list are interpreted by the rotor as a moving magnetic field, albeit present only some of the time and only movin g around part of the circle.

How a motor responds to this depends on the motor... but I've been there be fore.

NT

we're discussing the first version the OP posted.

NT

Actually, I don't know what we're discussing anymore. The first version certainly didn't have rotation. I think there are many "second" versions. ;-)

OK, let's look at the motor direction (swap phase and direction at will).

Energy Magnetic vector A on B off = 180 (South) A on B on = 120 (SE) A off B on = 90 (E) A off B off = none repeat A on B off = 180 (S) A on B on = 120 (SE) A off B on = 90 (E) A off B off = none

There is nothing (and not enough time) to pull it through the rest of the circle.

OK, it's a moving field but it is not rotating. It's only moving 90 degrees.

It won't respond well, no matter what the motor.

e:

e:

but with just 2

ould at least turn.

ants (you need at least 3 phases@120 degrees, but 4@90 works too).

field rotation. My point was that since you still get patches of moving ma gnetic field it ought to still move, even if it's not a sensible design.

the 2 quadrant feed could get a motor to turn.

e continuously moving field is the sane option, but what we are discussing is equivalent to bringing an iron magnet close to the rotor, moving it 1/4 turn then taking it away. Repeat repeat. Not pretty but with the right moto r it should result in rotation.

right - the magnetic bit moves 90 degrees

Some rotors don't care. Whether this will work depends on the motor design.

rather faster. Steps 1,2,3 in the above list are interpreted by the rotor a s a moving magnetic field, albeit present only some of the time and only mo ving around part of the circle.

90 degree movement is rotation. If the rotor then freewheels during power o ff and doesn't care where the next moving magnet is, rotation results.

before.

:)

NT

They don't care about the magnetic moment?

You're then relying on momentum for 270degrees of rotation but you only have time for 45 degrees (and it's slowing). That's _not_ going to work. It'll be pushed back after that 45degrees.

In any case the magnetic field is not rotating.

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rote:

rote:

le, but with just 2

t would at least turn.

adrants (you need at least 3 phases@120 degrees, but 4@90 works too).

ous 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.

er the 2 quadrant feed could get a motor to turn.

'll

to

nice continuously moving field is the sane option, but what we are discussi ng is equivalent to bringing an iron magnet close to the rotor, moving it 1 /4 turn then taking it away. Repeat repeat. Not pretty but with the right m otor it should result in rotation.

nt

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r

is

gn.

it rather faster. Steps 1,2,3 in the above list are interpreted by the roto r as a moving magnetic field, albeit present only some of the time and only moving around part of the circle.

r off and doesn't care where the next moving magnet is, rotation results.

I can only conclude we're talking about different motors. You seem to be st uck on ones that will quickly spring back. There's no point in further repetition really.

it's moving 90 degrees round the rotor.

ere before.

NT