STEORN DEMO LIVE & STREAM in Dublin, December 15th, 10 AM

[captainpecan]

Just a few practical hints for winding toroids. Assuming you know how many turns you need . First take a short piece of wire , and wind 10 turns. Unwind it , and measure its length. You now can calculate total wire length needed . Add say 10% to be safe , more if the winding is to be multi layered. Find the middle of the wire . Wind the coil in 2 halves , start at say 6 o'clock and wind through 9 o'clock to 12 o'clock. Start again at 6 , wind through 3 to twelve o'clock . You may find that if the wire is long , a shuttle is useful . Take piece of 10 mm dowel about60 cms long , and cut a slot about 2 cms deep into each end [ like the slot in an arrow. Bind the dowel with thread to stop the slots splitting . wind wire end over end onto the shuttle , and keep threading it thru the toroid like a needle . Unwind wire from shuttle as and when necessary . Hope this helps someone.

Thanks for the info, it will most likely help save some alot of headaches.  I use pretty close to the same method, but there's a couple tips I can use.

[PaulLowrance]

@PaulLowrance,

Do you have a used computer fan? Some super glue? Some magnets?

Then you can make a super low friction rotor in no time. Just carefully take
apart the fan, remove the fan blades, glue magnets onto rotor hub, remove
the fan electronic. Now you have a low friction rotor with magnets on.

Groundloop.

Hi,

I just got back from the garage where I was tearing apart an old computer, and managed to get the hard drive disc out. It was a 130 MB (not 130GB) drive. And I found a screw that fits it just right, so it's now mounted on a piece of wood (not eddy currents). It spins okay, but I took another HD apart, newer HD, and this thing spins forever, but I can't find any screws to mount it, so I'll just use the old 130MB HD. If this does not work that well, then I'll try the PC fan like you suggested. Thanks for help though! I did not read your message until just now.

Here's a very short video of it so far,

http://www.youtube.com/watch?v=OnxipzeLvD4

Regards,
Paul

[Omega_0]

Following everyones results, it seems that all that is required is to disrupt the domains in the core, to break the magnetic attraction.  So we should keep in mind that complete saturation may not truly be the goal here anyway. 

That is a matter of experimentation. If you can get the same torque while staying below saturation, its a bonus !
However, you don't want the rotor to get attracted in reverse direction, when it flies by the core. So you can compensate that by keeping the coil on for some more time, which means increased duty cycle and input power. Sure there is a trade-off.

Some more thoughts on input optimization:

Building some arrangement to vary the duty cycle manually will be best. Goal is to keep it minimum. When the rotor magnet is well past the core, there is no point in keeping it on.
Say if there are 4 magnets (or 4 pairs), its not good to keep it on after 45 deg. Seeing that the motor will work with as little as 25% duty cycle, its better to keep it as low as possible given that torque remains constant. If the core is driven into saturation, the viscosity (if there is such a thing ), will let the rotor not see it even if there is no current in it.

Collecting the induced emf (bemf or cemf or whatever) is a good thing, and it will lower the input even more, but I don't see how a battery would be able to keep up at high rpms, a cap will be needed if you plan to collect the emf.

That should cover the input side, IMO, and reduce some amount of hit-n-trial or rebuilds. Any more ideas are most welcome. Its very difficult to come up with design parameters at this time (and steorn is not telling any), but I will try to find something for output side also. And probably a decent method of measuring mechanical energy at the rotor, without which there is little point in building this stuff

[captainpecan]

@ PL,
Yeah, I like using the hard drive parts also.  That's what I am using currently. What I like to do though is cut 2 circles from plywood, use a hole saw to cut out the center of them both.  Then pinch the disk between them using brass or aluminum screws, just outside the outer perimeter of the platinum disk.  I use brass and aluminum screws on the rotor, so as to not effect your magnets flux you are planing to install.  Aluminum screws work good on the rotor, but if the magnets are moving past the aluminum, it's not a good idea.  So I would steer clear of aluminum on the stator unless it's out of range of the flux.

But pinching the disk between two pieces of wood, makes it really easy to switch out your rotors if you need to make a couple different variations.  Hope some of this info may help. At least this is how I do it.

[PaulLowrance]

captainpecan,

That's a great idea to cut round pieces of wood. I only have one size round cutter for the drill press, and it's too small though. What's nice about that idea is arrow dynamics. Unfortunetly I might end up cutting two pieces of wood, one for each side of the disc, and epoxying those to the disc and of course the magnets will be epoxied to the wood, but that will have some wind drag. BTW, does anyone think that epoxy can hold the wood & magnets at say 2000 rpm?