General > General Technical Chat
How Does the Dyson Motor Work?
rob77:
that would make it start always in one direction and eliminate the need for detection of direction and reversal of rotation during the startup - would save few lines of code in the micro ;)
but i have no clue how i would achieve that , my imagination has it's limits :D i would say the rotor needs to be magnetically symmetric and that would rest always centered - so no clue how i would bias it towards one of the poles.
Zero999:
--- Quote from: mikeselectricstuff on October 22, 2016, 09:43:02 pm ---I'd imagine that at high speeds, a strong permanent magnet might cause eddy current losses.
With only 2 connections I'm curious as to how they make sure it starts in the right direction.
--- End quote ---
Shaded pole?
I don't see how it could be done any other way.
rob77:
--- Quote from: Hero999 on October 22, 2016, 10:44:29 pm ---
--- Quote from: mikeselectricstuff on October 22, 2016, 09:43:02 pm ---I'd imagine that at high speeds, a strong permanent magnet might cause eddy current losses.
With only 2 connections I'm curious as to how they make sure it starts in the right direction.
--- End quote ---
Shaded pole?
I don't see how it could be done any other way.
--- End quote ---
wouldn't that create a significant drag at such a high RPM ?
T3sl4co1l:
Weak magnetic field because back EMF is proportional to field intensity.
If you have a parallel wound DC motor with separate rotor and stator connections, you make it go faster by reducing the current in the stator winding.
Likewise, series wound motors have metric shitloads* of torque, because at low RPM, back EMF is low, so the equivalent resistance of the motor is very low, current draw is very high, and stator field is very high. Series-wound motors do not have a constant torque to current ratio, but rather a parabolic curve because the rotor current is multiplied by the field current. (Squaring a negative value also makes a positive number, which is why series motors cannot be ran in reverse: they are also known as 'universal' motors, because they run on AC.)
*A technical term.
Tim
amyk:
--- Quote from: Hero999 on October 22, 2016, 10:44:29 pm ---
--- Quote from: mikeselectricstuff on October 22, 2016, 09:43:02 pm ---I'd imagine that at high speeds, a strong permanent magnet might cause eddy current losses.
With only 2 connections I'm curious as to how they make sure it starts in the right direction.
--- End quote ---
Shaded pole?
I don't see how it could be done any other way.
--- End quote ---
Shaded or otherwise only very slightly asymmetrical would be enough to ensure the motor spins in the right direction.
Too bad he didn't try driving it with a waveform of his own...
And that sort of power density isn't so surprising, the RC world has had 100W brushless motors of around that dimension for a long time: http://www.maxxprod.com/pdf/HC2808-xxxx.pdf
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