In message , Roger L
rogerlov@ix.netcom.com> writes
>
>
>Yes, sputtering ferrite dust with a printer probably wouldn't work to make
>lams for today's high B field magnets......I agree that the laminations really
>do need to be continuous metal along the flux path. Otherwise we end up
>simply summing a lot of little gaps.
>But I can't help noticing that the guys who make flexible circuits of copper
>laid on mylar film seem to have solved that problem for current flow. Could
>something similar work for magnetic flow in the lams?
>Along that same line of thought, just how thin we could go with high
>permeability lamination layers? I wonder if they could they be made of foil?
>What determines the limit? I've not done any work on that at all.
>
>Yes, it was ferrous silt, sludge, or debris that I was referring to. It certainly
>builds up in the working gap. But when does it become a problem? Or
>does it? Has anyone seen it be a problem? A certain amount might even
>be an advantage since one of the effects there is to narrow the gap where
>the work is done.
>On the other side of the ledger, we also see that ferrous sludge or
>particles build up anywhere that flux is leaking. That type of buildup has to
>be a detriment as it makes the path for flux leakage become fractionally
>more permeable. Might be a very small effect, though.
>
>Magnetic sludge is one of those things to look into "someday". Fun to
>think about - and it wouldn't be difficult to test for effect and get some
>numbers - but so far I've not seen it be enough of a problem to spend time
>on.
> Roger L.
Hi Roger.
After reading yours and Craig's inputs, I can see we do have the
technical knowledge here to design a low-speed BLDC motor that can
operate efficiently at the desired prop rpm without needing gearing
down. The axial-flux construction gives a motor design that could be
constructed by the skilled amateur, and by making the motor a 3-phase
design (using Hall-effect sensors for the position sensing) would allow
the use of one of the Chinese BLDC motor controllers that are readily
available.
For medium to larger sized monohulls, this sort of motor, coupled via a
conventional prop-shaft to a high efficiency ducted or integrally
shrouded prop would be a cost-effective and high-performance system.
For my specialist canal boat requirement, and also for ocean going
catamarans with an open bridge deck at the stern, an integrated ring
motor/ducted-prop would be even more useful. I have given my canal boat
reasons in another email, but for the cat, an integrated unit that could
sit in a central well in the bridge deck, on a vertically travelling
carrier would allow the assembly to be raised completely out of the
water for sailing, in a safe single-handed manner. A tilting carrier on
a transom would also be possible, but look more ungainly.
Such a thruster would probably require a radial-flux BLDC motor (ring
stator and inner ring rotor, carrying the multi-blade prop inside the
rotor ring), as this is best suited to fit the hydrodynamic shape
required by the duct holding the stator assembly.
The motor would require two low-friction seals, attached to each end of
the duct, allowing the rotor to turn, without letting water into the
rotor/stator gap. Many years ago I saw electric thrusters on a
remote-controlled inspection submersible that had the motors oil filled,
but kept pressure balanced by a simple flexible oil-filled bag at the
water pressure at whatever depth the RPV was working.
I still think that there is a fair-sized market for such a device,
perhaps in the 3kW to 4kW range. I guess from the fact that no-one has
mentioned any such unit being on sale means that at the moment, they
don't exist (or not at any sensible price)? Anyone else reading this
who might be able to point at a real supplier to the end user?
A Google search for 'Electric Ring Thruster' comes up with lots of
prototype devices, some very expensive units for deep-sea RPVs, and a
few Masters degree and D-Phil dissertations (mainly from India and the
Far-East), so somebody is working on these somewhere!
--
Chris Morriss
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