The Ossie motor

[Jimboot]

a quick update. Work has kept me busier than a one legged river dancer playing football. Been messing about with coils Based on Augen & Gyula. Ended up with stacked end to end in series. No theory just mucking about. Pardon my ignorance but in the scope shot attached the spikes represent the pulse across the coil? The wave is the mags passing the coils. That is what I have deduced from what I see. If I spin the rotor without the battery I get the wave. So from my noobie thinking I need a coil arrangement that is efficient pu as well as able to turn the mags. I realise I probably sound about as clever as a box of hammers but atm the motor has been running for three days no change in voltage. The stacked coils are in series, voltage at 1.4 amps bouncing between under 0 and 0 rpms @360.The key to me is the timing & type of coils.

[gyulasun]

....

HHHH or    H   +   H   +   H   +   H
HHHH       H        H        H        H
HHHH       H        H        H        H
HHHH       H        H        H        H
HHHH       H        H        H        H

Using the formula for B, the 4 thinner coils together should be 4 times stronger then the 1 thicker.

Explanation: The sum of the length is the same (100m) so the DC resistance and the current is the same.

Thicker coil:
   Number of turns: 4 times more then the thinner, so 4N
   Thickness: 4 times more then the thinner, so 4l

   B=u*4N*I/4l=u*N*I/l

Thinner coil:
   Number of turns: N
   Thickness: l

   B=u*N*I/l, but you have 4 of it, so B=4*u*N*I/l

What do you think?

Thanks Augen

Hi Augen,

Well I think the magnetic field, B can indeed be increased by 'sandwiching' several thin coils of the same thickness as a single thicker coil has, made of the same wire length. However I think you have to make the ID of the thin coils as small as practicable because only this way can you fill out the space in the radial direction all the way to the OD. I think this is important, and by choosing a higher ID you eventually lose on the benefits of the smaller ID (radially you introduce more air space if your ID is higher). I think of ID values as small as 5-6mm.

I think the B field increase effect is similar to the one when you attach two identical permanent magnets to each other, NSNS, and B becomes higher in the axial direction, flux lines will be more oval-like than for the same one single magnet.  I am not sure the B doubles in this case but may approach the double value.

Also, I am not sure the 4 thin coils together will increase the magnetic field, B by four times as the formula may predict (you have to consider the air gap between the 4 layers, and possibly some other factors).

rgds,  Gyula

[gyulasun]

a quick update. Work has kept me busier than a one legged river dancer playing football. Been messing about with coils Based on Augen & Gyula. Ended up with stacked end to end in series. No theory just mucking about. Pardon my ignorance but in the scope shot attached the spikes represent the pulse across the coil? The wave is the mags passing the coils. That is what I have deduced from what I see. If I spin the rotor without the battery I get the wave. So from my noobie thinking I need a coil arrangement that is efficient pu as well as able to turn the mags. I realise I probably sound about as clever as a box of hammers but atm the motor has been running for three days no change in voltage. The stacked coils are in series, voltage at 1.4 amps bouncing between under 0 and 0 rpms @360.The key to me is the timing & type of coils.

Hi Jimboot,

I think you have found a good coil setup by stacking two coils of different ODs and placing the smaller one nearer to the rotor magnets. Because I think the smaller coil is able to guide most of the bigger coil's flux towards the rotor magnets, and it can do it better than you would place the big coil as near to the magnets as the smaller coil.  The reason is I think that the big coil's flux obviously 'jumps' towards the small coil's flux (they appear almost in the same time) and vice versa BUT then the permanent magnet flux is also there and 'sees' and interacts with the guided and focused flux of the coils.  Can you use 2 more coil pairs like those? and connect them in series, this way current could go below 1 Amper?

Yes I think those spikes are from the coils but then you have now two coils interacting by their flux and maybe the small time difference between the two spikes represent the difference in their inductance? IF you remove the smaller coil you can see only one spike as usual, I think?  (Maybe I goof here.)

Thanks,  Gyula

[Augen]

Hi Gyula,

Last time when I wrote about the 4 thinner coils, I didn't mean to use them as a sandwich, but to put them to 4 different places, like the 4 magnets on Jimboot's rotor so you have 4 magnet-coil pairs. This way, you use all the 4 magnets at the same time, not just 1 at the time. I guess, it is like the original Jimboot replica of the Ossie motor (4 magnets, with 4 coils around them). The problem is, if you have a geometrically good coil (like my blue coil seems to be, which has special geometrical rate), cutting it to pieces and use them in series make it worse, because in that way, you ruin the good geometrical rate. The thinner coils will be too thin comparing to their OD-ID rate. I will explain it later. But if you have a geometrically good coil, using 4 of it will decrease their strength because the 4 coils have a 4 times greater resistance, so each coil will get 4 times less current comparing to the setup, when you use only 1 coil. That's why Jimboot got a higher rpm using 1 coil instead of 4, but using that setup, you using greater current. Is that clear? Because it is harder to explain things by writing them instead of telling them.  "See coils.png"

I'm not sure that the sandwich type is better. The outer coil is too far from the magnets. Check this out: http://www.magneticsolutions.com.au/cgi-bin/flux-graphs?page=fluxgraphs
On that graph you can see magnetic flux, and how it decreases by increasing the distance.
The sandwich type is just a longer coil, but it has an air gape between the 2 coils it is made of. If the sandwich type has a better geometrical rate, it can be stronger, I guess.

Returning to my previous problem:
- Gyula, I guess you were right about the smaller ID, but this means when you calculate the force between the magnet and the coil, the 'A' is not the ID, but the OD. But why? I always belived that the effective area of a coil is the inner area, not area of the coil itself. Maybe I was wrong.

- Calculating B, I got that the Green coil should be about twice as strong as the Blue. But, when I tested them by connecting them is series, the result showed me that the Blue coil is stronger then the Green. So I guess, there must be some sort if geometrical rate, when the calculated 'B' is correct. The length of the wire in the 2 coils is almost the same.

- Next I'm going to make a new coil, with a much smaller ID (about 5mm), using the same geometrical rate as the Blue has: (OD-ID)/2 = l

I posted some pics, so you can compare the 2 coils I used, and you can see my setup of the Ossie motor.

Regards Augen.

[Augen]

I forgot about my setup.