User:Brian P. Josey/Notebook/2011/02/01

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FEMM Model of My Lego Electromagnet

On Thursday I finished the building portion of my electromagnet, and took some measurements of its dimensions. Today, I want to collect all of this information together into a model in FEMM, to calculate the magnetic field within the electromagnet. Because of the unique design of my electromagnet, I have to make some changes and assumptions to model it in FEMM.

Most of the changes I have to do deal with converting a real three dimensional object into a simplified axisymmetric object. The first assumption that I made is that I could average out the distances between two parallel sides on the Lego piece to get an average diameter. This comes from the wires having a roughly rectangular shape in my magnet, and FEMM only working in cylindrical shapes. The next assumption is that the plastic, and its complex shape, will have no effect on the magnet. I feel that it is safe to assume this, so the plastic will be simplified greatly, leaving only a small strip.

Putting these assumptions to work, I created a model in FEMM. Unfortunately, I ran into some errors with triangle, the program that draws the grid that is used to solve the magnetics problem. I started off with a fairly large, but still precise grid size, and it crashed. After increasing the grid size, which lowers the precision, twice, it continued to crash each time. It could be that I am using Windows 7 on my personal computer, while in the lab I used Windows XP, because I know that FEMM has changed between the two operating systems. But this seems unlikely. I saved the information to a USB drive, and I will attempt it on the lab's computers as soon as I get a chance. I am a little upset that I kept running into this problem.

Andy Maloney 01:11, 2 February 2011 (EST): That sucks. You can using the XP compatibility mode in 7 but I'm not sure how it works.