The Ossie motor

[woopy]

Hi all

For my weekend thinking

What is the best arrangement of coils and magnet.?

I will go from the fact that the best impulse station is as it is described on the attached picture.

So what is best    a round coil with round magnets    or rectangular coil and magnets to get a longer torque to width ratio?

Another thing it seems to be more powerfull when i hook a soft steel plate to connect the magnets    what do you thgink ?

thanks for reply

good night at all

Laurent

[gyulasun]

Hi Laurent,

I think Tesla Coil for electromagnets patent may be a good answer for you first question.  It includes a huge benefit: if one could build such coils with a resonant frequency near to the one that comes from the rotor RPM then the input current to these coils would not find any inductive impedance, only the copper wire resistance would limit the current. (By winding the two parallel wire the way Tesla drew and connecting the ends as he showed, there will be a resonance circuit developed from the coils and the distributed capacitcnce created by the closeness of the two wires,  and behaving as a series resonant circuit.  Problem is that for normal RPMs like a few thousand, the resonant frequency is around some ten Hertz, it seems impossible to find a high dielectric material which would insure high enough capacitance for the limited number of coil turns to reach the low resonant frequency.
But I vote for flat and thin round coils anyway.  Thickness seems important because a thin coil demands for a small airgap between the facing magnets, and this involves higher flux density hence higher torque.  And I also think that using many such small flat coils as stators, distributed evenly around the rotor circumference, would enhance torque manyfold because it would involve many magnets hence much more flux to deal with.

Your second question connects to also the question of how flux density could be increased, using soft iron back plates is a good solution for this effect.  (Door magnets utilize such back plates to increase their attract force.)

rgds, Gyula

PS here is link: http://www.tfcbooks.com/patents/512340.htm to Tesla electromagnet coil if someone wants to read it.

[neptune]

@Gyulasun . re Tesla coils .Why not lower the resonant frequency by adding capacitance in the form of a capacitor?

[gyulasun]

Hi Neptune,

Yes, I have thought of that already, thanks for bringing it up and it may work in the same way as if it were the distributed capacitance.  It surely needs testing, I have not built such flat coils that thickness is constituted by the wire diameter only.

I have attached a drawing how the addition of a normal capacitor ought to be connected to get the same effect. 

To get close to the needed resonant frequency, say your motor's RPM is 1200  then you divide it by 60 to get it in 1/seconds i.e. in Hertz. (1200/60=20 Hertz)

This is a very low audio frequency and if you can make ,say, a 1mH bifilar flat coil as Tesla shown, it would need a 63325uF non electrolytic capacitor.  (I used this link: http://www.whatcircuits.com/lc-resonance-frequency-calculator/ )

I chose 1mH because for flat coils like these with a single wire thickness you cannot make much higher inductance coil, rather only less.
See this link: http://deepfriedneon.com/tesla_frame6.html 
If I choose D_I=3mm   N=60   W=0.1mm  S=0.1mm (this turn spacing will come from the second 0.1mm parallel wire), then the inductance comes as 41.5uH, obviously for a non bifilar case, and when you connect the second wire in series as shown by Tesla, the inductance roughly becomes 3.7-4 times as many i.e. 3.7*41.5=153uH And for this coil the outer diameter already comes out as 27mm!
For such a low inductance the resonant capacitor for 20Hz is 413,894uF!
A rather difficult value in practice.

Of course to test this all, you may start out with conventional bifilar coils wound on normal bobbins because that way you can really get bifilar coils (connected the two parallel wires in series as Tesla showed) several tens of mH inductance hence the capacitor value gets more practical, though still in 1000-2000uF range.

When you have wound a bifilar coil and connected the ends as Tesla showed, then you may use an inductance meter to get the resultant inductance between the two ends indicated in the patent drawing. Then you can figure out the needed capacitance to come near to resonance.

rgds,  Gyula

[woopy]

@ Gyula

thanks a lot for the very interesting link and infos

So this afternoon i wounded a Tesla coil. It is not flat but as i understood from the Tesla patent it does not need to be  flat. He draws it flat for better comprehension for the patent. Is it correct?

So i made an almost flat coil  (to get as you proposed the most flux ) and wounded it with 50 turns bifilar 0.3 mm copper and connected it a la Tesla.

the resistance is 1.7 Ohm  and the inductance is 0.28 mh.

I enclose some picture of the set up and scope traces the last one is the pure flyback trace after the schottky rectifier plus one  shottky diode to get total separation  from battery (see my shematic some post ago)

And the result is with only one coil the motor spins at about 900 rpm for 25 ma on my old battery which deliver now 3.9 volts

Have you a proposition for a capacitor value to test with those values ? and is it possible to get resonnance or what would be the cset up to get it ?

good luck at all      and  by the way where are you in your progress  Ossie ,JB ,CP ,Frenky and all ??

regards

Laurent