Roger:
Thanks for the treatise on magnetism and new software regarding magnet design. It's good to think that some new motors for electric boats might be becoming out of some experimenters garage and not always out of a manufacturing plant. More choices is always good.
Capt. Mike
http://biankablog.blogspot.com
From: Roger L <rogerlov@ix.netcom.com>
To: electricboats@yahoogroups.com
Sent: Tuesday, January 1, 2013 9:18 AM
Subject: [Electric Boats] Magnetic Circuits & The Prototype Motors
The discussion of the Gemini Motor makes a good sounding board for some magnetic discussion. I've followed some good electrical discussion on this forum, but there's been little on magnetic side.
Looking at the Gemini site, part of Gemini electric motor prototype seems to work around the idea of incorporating extra magnets into the magnetic field circuit.
On the face of it, the idea makes sense. Common sense says that adding magnets to a magnetic circuit might will work in much the same way as adding batteries to an electric circuit. And we already know from experience that adding more batteries increases the ability to do work.
But magnetics doesn't work quite the same way. It turns out that adding batteries works to advantage for a couple of reasons that aren't true of magnets. When a battery is added, the battery's own internal resistance needs to be low - and it's conductivity high - compared with the rest of the circuit. While that happy situation is true for charged batteries, the analogous situation is not true in magnetic circuits. In fact, all of the magnetic material we have available so far has a rather poor ability to serve as a conductor of magnetic energy or "flux". The materials are said to have "low permeability".
Low permeability in a magnetic circuit has a double impact because of another difference from electrical circuits. Not only is the total magnetic "flux" reduced in sort of the same way that resistance reduces current....but the flow path itself can change to become less efficient.
Looking at electrical circuits, electrical current is mostly predictable in the direction that it goes. It prefers to flow only along conductive surfaces and is blocked by insulators. And if the flow of current is resisted, the result is simply that less current flows and some heat is generated. Restricting the path made electrical paths are restricted which makes calculations and predictions simple. Even before computers, a guy with a pencil, paper, and a slide rule could do a pretty good job designing electrical circuits.
The flow of magnetic energy - often called "flux" - is way different. Magnetic flow is NOT constrained by a conductive or permeable path. When the permeability of some portion of a magnetic circuit is lessened, the magnetic energy flows in alternate paths and loses energy by doing so. Magnetic energy can leave the designed path, flow out through space, and then re-enter the circuit at many different places with different values. Calculations of magnetic circuits in the days before computers was a miserable task - and technically formidable. But that's in the past. Now that there is software to help with the math, we are free to model magnetic circuits even more simply than electrical ones.
This magnetic modeling software has already led to better motors, and the field is yet young. There are now a free programs available that is fantastically powerful. Today the self-taught magnetic amateur has the ability to design magnetic motor circuits far more sophisticated than anyone in the world could do only a few years ago.
Consider this: Big motors are expensive, but all of the components of electric motors are commonly available online at reasonable prices. A nice feature of electric motors is that prototyping is so easy. An electric motor isn't an explosive high temperature, high pressure, high dollar engine full of monkey motion and custom hardened parts. Every part in an electric motor can be obtained online and assembled by hand. The only movement is rotation about a single axis. Basically there is a shaft with bearings, a shell with mounts, and the guts which consist of an electrical path interacting with a magnetic path. Instead of welding and machining, we have bolted, glued, and hand-wound parts. Using the free magnetic software completely eliminates the need for expensive custom shapes. The software also predicts quite accurately what the results will be even before the motor is built.
There is lots that can be done. Magnetic design is wide open for innovation and could make for a pretty good career, too.
But mostly it would be neat to see more folks design their own motors.
Enjoy!
Roger Loving
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