Well I couldn't help my self
Found this idea in an old Physics text book and had a go .Now for the life of me I can't find the book but this was basically what it showed .Excuse the hand drawn sketch.
Schematic.jpg
Basically its an aluminium tube , about 40-50mm in diameter and about 60 mm long that rotates when the two coils are held near it .
The trick is that one coil is feed via a capacitor that causes the current to be 90deg ( or pretty close to it ) ahead of the current in the coil that is connected directly to the 12 AC .
By placing the coils at an angle to each other , a rotating magnetic field is created which is induced into the aluminium tube and by the process similar to the prac I mentioned earlier where a magnet rotates around an aluminium disc causing it to follow , the tube rotates to follow the moving magnetic field .
To see if it would work , my first lash up was an old plastic bottle ( of similar dimensions ) with some aluminium sheet wrapped and sellotaped to it .
( incidentally I tried aluminium foil and it did not work ....but thin sheet works , so does a tube )
It rotated on an old magnetic compass stand I found in the draws . ( a plastic base with a brass stand about 80mm long with a point on it )
The coils were pinched off an old horseshoe electromagnet and the capacitors were pinched from a pile of old circa 1950's power supplies that were decommissioned and hiding in a back cupboard .
So at no materials cost to the establishment I proved it worked
.....unlike a lot of theoretical sketches in physics book that seem not to
Then I got carried away and made a more permanent version
Basic Induction motor.jpg
I fixed one coil to the base and made the other so it can be moved around the aluminium tube . The teacher can show when the coil is opposite the fixed one , it does not work . when it is rotated round 180 deg , the aluminium tube rotates the other way . When the coils are near each other the field is the strongest and teachers can explain how multiple coils (poles) in a motor can increase the torque ...if they want to go that far .
They can also use this as a basis for 3 phase motor theory ...Imagine the coils at 120 deg and driven 120 deg phase shifted
So this is it up and running .
I put binder posts so a CRO can be connected ......seeing is everything and the students can clearly see that the voltage supplied to each coil are 90 deg phase shifted .Sorry about the CRO not being a full screen full ...my phone camera "took the photo" quicker than the CRO displayed the trace .
But you get the idea
Induction motor setup.jpg
Now that big Green capacitor is 4 electrolytic capacitors snatched from our old power supplies , squished into a piece of PVC pipe . Wrapped in a laminated printed paper and has some old rubber I found near the bins shoved in the ends .
About that Capacitor .
It is a Bi-polar type which as shown in the Schematic can be cobbled up using standard polarized electrolytic types.
I tried a 400uF bipolar capacitor from Jaycar at $29.00 by the way ( personal expense ) and it just didn't cut the mustard .....it worked but nothing like the 4 electros version .
It has nothing to do with the 400uF verses 500 uF but more to do with the current that can flow in PHYSICALLY BIG CAPACITORS .....so the person that worked this out is a legend. .....and should you be interested in trying this , then do spend some time trying various combinations here as it makes a huge difference to the way it works
Also ....just to add , I spent 10 minutes here and there over a few months and a bit of time at home making this ...But ...If you talk to your electronics or TAS guys , I'm sure they will be more than willing to help . At two schools I have worked at , the TAS guys were both mad keen on this sort of stuff and its right up their ally ...They are looking for a project like this ...and you get to keep it .
Show it to your Physics teacher ,if they like it , show it to the TAS guys.
But then again some chinabot has already probably started mass production