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Let's build a LEMA!

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Sat Oct 28, 2006 7:09 am PostPost subject: Let's build a LEMA!
babcat
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Who here would like to start the process of building a L.E.M.A?

If one person could get the materials to build one successfully then we could all build one and test them in different configurations attached to rotors with magnets on them.

The only slightly expensive part I see is possibly the magnetic shielding material. Does anyone have an idea where to get some?

So, what do all of you think?
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Sat Oct 28, 2006 8:26 am PostPost subject:
babcat
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This guy has built a LEMA! Check out the thread.

http://www.overunity.com/index.php/topic,1631.new.html#new

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Hey - where did everybody go? Have we got a group of guys that have dates on a Friday, or a group of guys that are all trying to get from the theoretical to the practical stage?

thevorlon, I finally got some co-netic & netic shielding today from http://www.magnetic-shield.com/products/lab-kit.html . I built my first rough LEMA and "tried it by hand". Well, this puppy is going to probably run faster than 600rpm. With two magnets on the rotor that's 1200 LEMA shuttles per minute. Can't tell much when I'm only moving about 30 shuttles per minute. But here's what I did find.

Even if you completely surround the magnet with shielding at least 20% of the field still gets through. The documentation sent by magnetic-shield.com confirms that. This means that a design will need to use repulsion instead of attraction. Here's why....

With attraction the actuator magnet has to be exposed while the rotor magnet approaches because that is when all of the work gets done. But, since magnetic fields dissipate their strength rapidly over distance, 20% is probably all that is going to be available through out the 1/4 arc that the rotor magnet is moving. Once the two magnets are facing each other you then shield the actuator. At that point you still have 20% attraction bleeding through. All you've done is attract the rotor magnet with a small portion of the magnetic force, and you're stuck at that point.

With repulsion the actuator magnet is shielded while the rotor magnet approaches. 20% of the repulsive force is bleeding through to act as a break on the rotational torque. But, when the two magnets are facing each other you remove the shield and 100% of the repulsive force now is applied to the rotational torque as acceleration. As the rotor magnet moves past the actuator the shield is closed - once again 20% bleeds through, but this time the rotor is past dead center so this bleed through accelerates, cancelling the earlier breaking effect.

Also, I think that the sheild has to move ONLY when the two magnets are dead center to each other, not before or after. Take a look at a motor using an electromagnetic actuator. The reed switch closes the circuit that energizes the electromagnet. You can adjust how long the reed switch is closed (and how long the electromagnet is energized) by moving the reed switch closer or further away from the magnet that is closing it. If you increase the length of time, you decrease the speed of the motor. Maximum speed is achieved with the shortest pulse, not the longest. But, if you lengthen the pulse, and also adjust the position of the reed switch so it closes exactly at dead center and remains closed until the rotor magnet has cleared the circumference of the actuator magnet then you can slightly increase speed.

This observation is why I prefer using something like a reed switch to activate the shield shuttle on a LEMA. I don't see how yopu can get that kind of timing using gears or cams. I totally agree with your point that having an external power source involved just totally messes things up for demonstration purposes. But, I have a couple of ideas for doing that with power from the device itself. The device's rotating shaft is a good place to mount a second set of magnets within a coil producing a dynamo-type electric current.

"The most exciting phrase to hear in science, the one that hearlds the most discoveries, is not 'Eureka!' (I found it!) but 'That's funny,,,' " ISSAC ASIMOV (1920-1992)
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