Why is a cubic arrangement of coils considered a good idea?
Geometrically, the dual shape, a regular tetrahedral 'diamond' seems much better, for the following reasons ( I am assuming current circulates in one direction in the circular coils, around the larger diameter):
1) with a cubic arrangement, the flow in the top and bottom coils alternately opposes and coincides with the flow in the side coils, assuming the side coils are set up to always co-incide in flow direction where they meet. In other words, with a cubic arrangement, there are always points where the adjacent flow is opposed. This must cause weak points in the induced magnetic field.
2) with a cubic arrangement, there are 6 face cusps, and eight corner cusps. With a tetrahedral arrangement, there are 8 face cusps and 6 corner cusps. The corner cusps in a cubic arrangement are formed from the flows from three coils. Either the flows in the coils do not coincide where they meet, or the 'flow' around the sides of the corner cusp consists of both clockwise and anticlockwise components, necessarily asymmetrically because there must be two in one direction and one in another.
With a tetrahedral arrangement, all faces can be made identical modulo coil orientation (mag field lines in or out at centre), ditto all corner cusps, which become symmetrical. The arrangement also seems to be able to be 'wound', that is one can trace a single wire in at one point and out at the same point which will create the current flow round all the faces.
The attached diagram shows what I mean. The arrows show current flow and the numbers show how it can be wound. You probably need to wind twice from different points to create a sturdy structure at the corner cusps.
Again, the question is why is the cubic arrangement of coils better?
- Tetrahedral Wind Drawing.png (15.45 KiB) Viewed 11433 times