My best guess was an inverse-square law. Maybe an inverse cube...
When the magnets get really close, there's no further increase in flux, hence I believe the curve flattens out close to the y-axis. Steven Fahey
I am guessing they were 0.5" or so. G-[ Parent ]
This was from the axial I built a year ago, RIP. It had 1/4" thick magnets, each 1" diameter. The two rotors had 16 poles, and the stator was 3/8" thick. I only tested down to 1/2" air gap, where things could start scraping together. I was doing the test to correlate what I could see in FEMM.
If you want to know more, I can dig up details about the coil, RPM, etc., or you can find it in my diaries and postings from about 2006. Steven Fahey[ Parent ]
Beyond gaps greater than total magnet length you will likely see increased leakage and with close magnet spacing you may see leakage effects with gaps at magnet length.
The linear approximation I gave is not really applicable with large changes in gap but works well enough if you don't stray too far from the magnets best operating point.
Flux[ Parent ]
