Wye vs. Delta

[BrianG]

I wouldn't bet on the feedback being a "sine-wave". Don't forget that we are feeding square waves to a coil. The inductive kickback is usually a large spike - the amplitude dependant on the inductance value, how quickly the field collapses, and voltage.

[zeropointbug]

Yes, but there would also be a natural sine wave present/super imposed in the signal as well.

[What's_nitro?]

The BEMF pulses are what tells the ESC where the rotor is relative to the stator coils. When one pole of the rotor passes under a coil, it sends a pulse back to the ESC. The ESC then "knows" that this particular pole (N or S) is 60 degrees from the next coil, and can determine when it should fire the next coil. Have you ever wondered why sensorless motors "cog" only at low speeds, or very high gearing? It's because the rotor's speed is to low to send accurate pulses to the ESC, and in turn the ESC can't accurately calculate timing.

OK, there you guys go again, turning a nice pleasant exchange into a lesson in electrical engineering. All of which went right over my head.

[zeropointbug]

Originally Posted by What's_nitro?

The BEMF pulses are what tells the ESC where the rotor is relative to the stator coils. When one pole of the rotor passes under a coil, it sends a pulse back to the ESC. The ESC then "knows" that this particular pole (N or S) is 60 degrees from the next coil, and can determine when it should fire the next coil. Have you ever wondered why sensorless motors "cog" only at low speeds, or very high gearing? It's because the rotor's speed is to low to send accurate pulses to the ESC, and in turn the ESC can't accurately calculate timing.

Hence, sine wave...

[What's_nitro?]

Originally Posted by AAngel

OK, there you guys go again, turning a nice pleasant exchange into a lesson in electrical engineering. All of which went right over my head.

Sorry about the techno-babble AAngel. I can't help it. And yes ZPBug, the pulses are in fact a perfect 3-phase AC sine wave. Assuming a 2-pole motor.

[BrianG]

I still don't think the feedback pulses are perfect sine waves. You are applying a high current square wave signal to a coil. When the field collapses, it will generate a back-EMF spike. However, since this is happening kinda fast, the spikes aren't as bad as they normally would be. It probably looks more like a semi-sinusoidal pulse with a little decay before the next pulse from the ESC comes in.

Now, if we were talking about variable frequency sine-wave drives, then yes, the feedback would be a perfect sine wave. Man, I wish I still had access to a o-scope to check this!

[silentbob343]

Originally Posted by AAngel

OK, there you guys go again, turning a nice pleasant exchange into a lesson in electrical engineering. All of which went right over my head.

If you think that's bad listen to this:
http://video.google.com/videoplay?do...ell+automation

[What's_nitro?]

Thank you silentbob343. That, was awesome. I understood every word out of his mouth. It's sad, because half of them are made up; sinusoidal deplanaration, capacitive deractance, etc.

[What's_nitro?]

Originally Posted by BrianG

I still don't think the feedback pulses are perfect sine waves. You are applying a high current square wave signal to a coil. When the field collapses, it will generate a back-EMF spike. However, since this is happening kinda fast, the spikes aren't as bad as they normally would be. It probably looks more like a semi-sinusoidal pulse with a little decay before the next pulse from the ESC comes in.

Now, if we were talking about variable frequency sine-wave drives, then yes, the feedback would be a perfect sine wave. Man, I wish I still had access to a o-scope to check this!

Yes we are giving the coils square wave drive pulses, and the BEMF would also be a primarily square wave. But, the BEMF pulse is influenced by the present magnetic field to the effect of a sinusoidal wave being factored in as the rotor passes each coil. The same is true for wye winds or delta winds. So if you filter out the inverse of the drive pulse, timing included, you'll be left with a sinewave.

[zeropointbug]

Originally Posted by What's_nitro?

Yes we are giving the coils square wave drive pulses, and the BEMF would also be a primarily square wave. But, the BEMF pulse is influenced by the present magnetic field to the effect of a sinusoidal wave being factored in as the rotor passes each coil. The same is true for wye winds or delta winds. So if you filter out the inverse of the drive pulse, timing included, you'll be left with a sinewave.

I was just about to post that exactly. Well said.

Oh, seen the video before, love it.:005:

[What's_nitro?]

Ha! I win! But seriously I would prefer the wye/star wound motors because of their increased torque output. That's basically what it comes down to when your talking electric power. You will always be able to gear up more than you can gear down. Plus, running higher voltage and lower current for the same power equals higher efficiency.

[silentbob343]

Originally Posted by zeropointbug

I was just about to post that exactly. Well said.

Oh, seen the video before, love it.:005:

yeah it has been floating around the internet for quite some time, but never gets old.

O.K., Technobabble aside, I thought ALL BL timing was in the controller too, however the more I read the more it seems there is some 'timing' built into the can as well, (and wye is very sensitive to it (I'm assuming)).
The only thing I could think of as 'directional' (or 'timing') in any way would be the direction of the current in the stators, (the direction of the 'wind' in conjuction with the width of the stators...) Wouldnt it be 'timed' to work better one way. (maybee Delta cancelles this out and wye makes it more pronounced...(gaining a bit of efficiency in the favored direction...)
However, NEU's (and most BL I think) are made for planes, so counter-clockwise should be the 'right' direction. (this would be of no help to AAngel's problem, you were going CC anyway right?...)

[Serum]

Don't quite remember who posted this;

saying a Y is always sqrt 3 stronger than a delta;

not true; if they have the same windings, with the same amount of wire used, then yes, if they are matched on KV, then this is not the case.

So it's not a fact a Y is by definition 1.72 times stronger in terms of torque than a delta.