Mendocino Motor Under Construction

[steamboatmodel]

A couple of questions;
1. Will it run without the end stop?
2. Have you tried with magnets at the sides of the unit?
Regards,
Gerald.

 

[Ken I]

No it will not run without the endstop - the rotor is "perched" on repelling fields - since this is frictionless it will fall off to the left or the right - the stop is just off so its effectively just trying to fall towards the stop all the time.

Have I tried - yes - every damn trick in the book - the more I experimented the more it became obvious that it wasn't possible - you can get stable levitation in one plane only.

The obvious aproach is repelling magnets at opposite ends of the shaft to hold it in the middle - but that throws out the vertical stability and the rotor climbs out of its magnetic vertical support.

So I did some research (sure that's doing it the wrong way around) and discovered Earnshaw's theorum which proves via Maxwell's equations that stable static magnetic levitation is not possible.

It is possible using electronics, sensors etc. to control the position but not by any simple arangement of magnets.

Earnshaw's theorum leaves a few loopholes such as gyroscopic (non-static) action and the interpositioning of diamagnetic materials but neither are practical on this motor.

I still want to find a way and intend experimenting with diamagnetic Bismuth but I don't hold out a lot of hope.

I am also going to build a vertical version but the vertical suspension will almost certainly be electronically controlled as the diamagnet approach can only support very small masses in insanely powerful magnetic fields.

Diamagnets are materials that repel regardless of polarity - almost all non-magnetic substances exhibit diamagnetic properties even water and hence your body could theoretically be levitated in a very powerful field (thus far only small frogs have been suspended in the most powerful fields we are capable of generating).
Some materials such as Bismuth and Pyrolytic Carbon have much higher diamagnetic properties - but still weak compared to paramagnetics.

Confused enough already - I know I am.

Ken

 

[Blogwitch]

George,

Use epoxy for your adhesive.

Rubber cements (those containing spirits) and most superglues will attack pink foam, destroying it's cellular structure, epoxy is inert to almost everything except human tissue, that means wear gloves.

I think blue foam is safe with most adhesives.


John

 

[George_Race]

I have tried getting it to levitate in two planes as well, just can't be done! I find that Earnshaw's theorem wins out every time.

On the rubber cement on the pink foam, I tried it on a piece of the foam, and no matter how thick and wet I put it on, it does not effect the foam. It just dries hard and sticky. Pressed two pieces together and it really does hold.

This build is a prototype, just to see if it was a practical idea, possibly leading to the putting together of a kit that others could assemble. I think the idea of foam for the armature core is OK, but would like to make something a bit more solid. Today I picked up some 2 inch thick plastic material, believe it is nylon and will be designing a new armature built around the same dimensions of the foam prototype. It probably will be considerably heavier, by a few ounces, and I may have to go back to a narrower spacing of the "flotation" magnets. So, another design is in the works. Will keep you all up to date on the build as it moves along.

In the mean time, this first one is just humming along, and it does hum when running in sunlight. Well, maybe more of a hiss than a hum!

Someone over the weekend suggested I put some kind of fins on the end and it could be used a a free power desk fan! Someone else suggested that if it contained flute type openings on the ends, it probably wold produce different tones at different speeds. Boy, wouldn't that drive you crazy!

Really don't think I will consider doing either!
George

 

[steamboatmodel]

Thanks Ken and George,
At one time (Forty years back) I did run into Earnshaw's theorem, and Maxwell's equations. They gave me headaches then so I don't think I will try to understand them. I will just sit back and watch these threads, and look around for some magnets, wire and solar cells.
Regards,
Gerald.

 

[boatmadman]

Thanks guys for the plans etc.

Here is my effort, 0.5v 125ma panels, 50 turns of .22 wire and acrylic structure.

It seems to need a good amount of light to run, think the next one needs to have higher voltage cells.

Ian

 

[Ken I]

Way to go Ian - nicely done.

Try putting your cells in series to up the volts - if you are already in series, try parallel to up the Amps - I know both method cannot be right but WTH its worth a try.

Ken

 

[boatmadman]

Ken,

I cant change the cell configuration on this, they are in series and there are only 4 cells. Maybe if I do another I'll use higher output cells for better slow running.

Another option would be to reduce the number of turns to increase the current flow.This one currently has 50 turns on each coil.

Ian

 

[Ken I]

My guess would be more turns not less - I'm guessing your coil is already too low a resistance and you are probably sinking more of the available energy in the cells.

The coil should be the same or higher than the cells in your case that works out to 32 Ohms or more - I'm guessing your 50 turns is lower than this.

Ken

 

[boatmadman]

I originally started with 100 turns on each coil, that gave a measured resistance of 15 ohms and the motor wouldn't run at all.

I reduced to 50 turns ( 7 ohms measured), and it runs, reduced further to 40 turns and it runs in slightly lower light levels.

If you have too high resistance, current will not flow through the coil and so the magnet will not produce a turning force. Ohms law, V=IR, I=V/R, so, as resistance increases to V, then current reduces and eventually goes to zero. See Flemings left hand rule, if there is no current, there cant be any force.

There is a trade off here however, if you drop the resistance too far the current will be too much for the wire and burn it out.

At least, thats how I understand it, but what do I know!

Ian

 

[George_Race]

Nice job Ian, very nice looking frame and armature.
I had just about the opposite experience, as far as windings go. My first armature had 120 turns in each coil. It would run but took a lot of light. My second has 150 turns and runs right along with just the ceiling lights in the shop.
My cells are .55 VDC at .250 mills from a 1 X 3 inch cell.
These things are sure fun to play with.
George

 

[boatmadman]

George,

What size wire did you use on your second motor? Also, do you know what the resistance per meter is?

The wire I used is 0.35ohm per m.

I think my mk 2 will have cells similar to yours, I want one to run at lower light levels than my mk 1.

Ian

 

[George_Race]

Hi Ian:
I used 150 turns of #30 wire, per coil.
Each turn is about 9 inches That makes each winding about 112 feet long. The AWG wire table shows #30 wire is 100 ohms per 1000 feet so that would make the coil resistance about 15-17 ohms. I did not measure the actual resistance, but that should be close.

I did measure the voltage across a fully illuminated cell, connected to the coil and it showed .45 volts DC.

Hope this helps,
George

 

[Ken I]

Ian,
Attatched an *.xls spreadsheet that will do the calculations for you from 14 to 47 swg.

Just insert your target resistance and average length of wire per turn and it will calculate the number of turns and give you an approximate mass and cross sectional area of the wind.

Ken

View attachment SWGWIRE.xls

 

[John S]

Thinking aloud here but what about using machining wax instead of foam ?
You could get some good detail in wax.

John S.

 

[George_Race]

Hi John, I would expect that would probably work just fine. Would be heavier than foam but all you would need to do is find the right magnet spacing for levitation.

I am not going to continue building them out of foam, that was a sort of proof of concept piece. My next will be a more solid material, plastic, nylon, etc...

George

 

[boatmadman]

I have managed to get my motor to run at about 60rpm in dull daylight. This was achieved by careful balancing of the rotor. Its surprising how much difference it makes.

Ian

 

[Ken I]

Yes the finer the ballance the better it runs in low light conditions. In particular its ability to self start.

I also posted another caveat in my thread - if you didn't pick up on it, I've repeated it below.

As I metioned previously, ballance is about the magnetic suspended centre rather than the mechanical centre. They should be the same but in an imperfect world they won't be.

If you leave the motor stopped (in the dark) and magnetically suspended, when you next try to run it its slightly out of ballance again and will not self-start in low light conditions.

My speculation here is that the magnetic field of the rotor magnets becomes displaced slightly from standing in one position. The resutlant shift the the magnetic centreline throws its fine ballance out of whack.

Running the motor for 30 minutes to an hour at moderate rpm's resets the field back to normal and ballance and low light running is restored.

Lessons :-

1) Store the rotor off its cradle when not running.

2) If it has been standing don't attempt a high speed "sunlight" run straight away - it will likely wobble itself off and away.
"Run it in" first.

Ken

 

[George_Race]

Ian, great, nice that it now runs. Yes, balance is very critical to having it run in low light. Now you have it running, you can tune and tweak to make it better.

Ken I, that is a very interesting supposition. I would expect you could prove that by knowing where it stopped, last time in the dark, and then after running it and getting it back in balance, stop it 90 degrees off of where it was and let it sit in the dark again. If that position is then heavy, you are right on the money with your theory.
George

 

[Ken I]

George,
That is pretty much what I am seeing hence the theory.

It is a very small out of ballance to be sure (but these things are sensetive to milligrams) and the fact that it clears up on further running seems to prove the point.

However I'll only know for certain once I get my acrylic armature finished - the wooden arm could be the cause.

Watch this space......

Ken