Seems like a lot of interest.
Greg - I wanted to levitate it vertically not just "hang" it off a magnet - but that will do (I actually want to build two, one horizontal and one vertical - possibly combined - just swop the rotor.
Stan - that's an excellent link and anyone interested should look it up. I agree with their magnet configuration - with like poles facing out so it doens't matter which way around you place the rotor.
Andrew, Jerry - you can have any number of poles but 4 is the easiest - odd numbers requre connection in star or delta.
Now for a bit of practical info:
Firstly none of this is complicated or requires any exacting fabrication - almost anything can be made to work.
I scrounged the solar cells off some dead Chinese pathway illuminators (garden lights) - these cheapies tend to die within a year and are then discarded - so keep your eyes open.
The actual cell is a QHDQ-08A - which is a 50mm x 50mm x 2mm thick solar cell - probably the most commonly used cell on this type of application.
They're rated at 100mA @ 3V - In direct sunlight in Cape Town the best I could get was 68mA @ 2.7V - so I'm guessing that rating applies at the equator with the sun directly overhead.
You need high current / low voltage for this application - higher voltages will require more turns of thinner wire.
I connect each cell pair in paralell - you could do it in series - but you'd just be making work for yourself. Opposite pairs are connected together in reverse and on to the coil - simple.
The magnets I bought - just look up a magnet supplier - they are not terribly expensive.
I used a 25 Diameter x 7 Diameter x 6 thick. (Neodium, Iron, Boron) - this is a standard size - obviously the hole in the middle simplifies mounting - also since these things are sintered - the sizes are quite precise.
Be careful these things are powerful enough to inflict a nasty pinch and can fly together so violently they shatter (in pairs) I've broken two and my grandson 4.
(I use some 50x50x15 magnets on industrial applications and they are seriously dangerous.)
My rotor hub is made from 6mm MDF and tongue depressors - somewhat incongruous machining a lollipop stick in a mill but WTH.
I placed the bits of wood in the MDF grooves and secured by pressing drill shanks into the slot to hold in place - then applied superglue to all the joints to secure (being careful not to glue the drill shanks in place) - after winding, a coat of Glyptal secures the winding and everything else together.
The shaft is a diameter 7 x diameter 5 carbon fibre tube from a hobby shop and the spacers are Dia 10 x Dia. 7 aluminium tube.
Winding wire is 36 swg (0.18mm) ± 150 turns = 40m.
Again I "scrounge" my winding wire from rewinders and transformer manufacturers who consistently throw away near empty spools - still plenty of wire on them but not enough to bother with the next "run".
So if you are interested - you might start looking for scroungable materials.
The height at which the rotor levitates is obviously determined by the position of the magnets and the mass of the rotor - hence my lash up - the final centre height will only be determined once the rotor is finished.
Ballance is an issue - static ballance is dead easy - but it really needs to be dynamically ballanced as well - without using sensors etc. I am doing mine (not finished yet) by sticking lumps of modelling clay to the rotor - static - then with a piece of tape wrapped to the rotor shaft I bring a magic marker to make a mark at the high point of the "wobble" - add a small clay mass (a guess) to counter it (removing the piece from the static lump) - once I get that right I will replace the clay with bits of copper wire bonded into the winding grooves. Final touch up ballancing will be by adding epoxy or laquer.
The other reason ballance is a bit fiddly is the "centre" is the magnetic centre - so bond the end magnets in place before final ballance tuning (if you move them angularly after ballancing you can throw the ballance out slightly).
I did the winding in my 4 jaw (turning by hand - gearbox in neutral - a PITB) with alternate layers going to opposite sides of the shaft - I used glass tape over the shaft spacers and between crossover layers for added insulation (given the low voltage this is probably overkill but WTH). I wound half of each winding then changed to the other to ensure a more even crossover.
The crossover obviously ends up with a lot of voids which I filled with a hard (very quick setting) polyurethane resin - but any quickset epoxy or polyester would do the trick.
Hope to get more done over the weekend.
I'm going to make the base and support structure out of perspex (to enhance the open appearance). I'm going to replace the brass acorn nuts with perspex end extensions with a steel ball in the end - this will run against a glass plate - I might put a small magnet behind the glass to secure against collywobbles from imperfect dynamic ballancing / higher revolutions.
I intend to put supports at both ends to gaurd aginst rubberneckkers knocking it off.
The rotor should just float on the magnets with a slight bias towards the support end (only one) with two it will move to one or the other end (who cares).
I have made a few glass disks with a 30mm diameter diamond tube drill - but the edges look like they were made by a neolithic flint knapper - does anyone have tips on how to do this splinter free ?
Ken
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