Andy Burns wrote:
Dave Liquorice wrote:

On Fri, 31 Aug 2012 21:29:28 +0100, Andy Burns wrote:

http://dyson.co.uk/Vacuumcleaners/DDM.aspx

Bollox after marketing have got at it. Looks as if they are stepper
motors to me.

I think you'd need more than 2 poles to guarantee they rotated in one
direction, rather than just vibrate back and forth at 1.7kHz

probably has a sensor on the armature - you energise the pole that will
'kick' the armature in the right direction and then once spinning the
two pole motor will keep going in the right way.

Its the same as model aircraft 'brushless' motors. Although those are
three phase normally.

I liked this

"They are incredibly efficient too €“ due in part to high tolerances. For
example, the impeller spins at over 600mph with only 0.3mm clearance
between the blade tip and the impeller housing"

1/. the "for example" gives absolutely no description of efficiency at
all. In fact...

2/. Things don't spin at 600mph. That's linear velocity and if that
refers to the tip speed of the impeller...

3/. Mach 0.9 for an impeller is not only extraordinarily inefficient its
inefficiency manifests as MASSIVE noise, too. You WILL get transonic
airflow over parts of the blade.

(http://www.youtube.com/watch?v=Y6vWa...eature=related)

Actually the efficiency will be down to having that neodymium magnet and
plenty of copper so the winding resistance is low. Even hand wound
motors can get up to the high 70s or more, and careful choice of
laminations magnets and bearings can net you over 90%. Its not hard.
Just expensive. I doubt Dyson have that sort of efficiency though - its
marginal gains for a lot of expense.

The model aircraft boys are chasing the ultimate power to weight, and
heat is a problem so they do go to extremes. Essentially 90% efficiency
to 95% means double the power for the same heat rise. However that in
itself becomes a useless exercise as battery weight totally dominates
past a certain point.

All of which confirms the suspicion that Dyson are long on bull**** and
short on engineering.

Their technology is not selected to last, be tough, or be efficient: Its
selected for the maximum ability to brand-differentiate from their
rivals and construct an appealing narrative about the product.

Or as we used to say about Microsoft

"Designed to sell, working is a secondary issue"



--
Ineptocracy

(in-ep-toc-ra-cy) €“ a system of government where the least capable to
lead are elected by the least capable of producing, and where the
members of society least likely to sustain themselves or succeed, are
rewarded with goods and services paid for by the confiscated wealth of a
diminishing number of producers.