At 08:19 PM 21/10/2003 +0200, you wrote: >What 'magnetic dipoles' ? You can use F=B*I*l (Laplace magnetic force) >where B/H=Mu for isotropic media (i.e. air coils and no armature). >H=I/(2*PI*d) at a distance d from an infinitely long wire carrying a >current I, and H=2*I/r in the center of a single turn coil of radius r, >H=N*I/l inside a long and narrow solenoid (the last formula is empirical >afaik - the exact version is very hairy). If the coil(s) have cores with >Mu different from air then B will be non-linear and probably change with >the inverse square of the distance if the distance between the poles is >reasonably large (larger than the diameter of the pole pieces) so >alignment errors do not play a major role. So F ~= N*I*B/(l*r*d^2) for d > >= 2r where B is the induction from a nearby magnet or other coil. Try a >book near you ? The very first thing I did was look in my old physics text book. It didn't seem to be any help, which is why I came here. Perhaps I should have tried a little harder to develop my own equation, I don't know. This all looks very helpful, but let me make sure I've got the variables right. (sure would throw a wrench in the works if I had that wrong) F: Force N: number of turns in the coil i: current in the coil B: you stated L: length of the coil r: radius of the coil d: radius of separation between the coil and the other source of magnetic field. Now all I have to do is try to apply the Mu of a ferrous material (like a steel bolt) to this equation. Well, anyway, for a better idea of what I'm trying to accomplish, have a look at http://members.shaw.ca/annirak/index.htm, and have a look at the "[EE]: Active maglev with permanent magnets & solenoids" thread Thanks for the help, that's pretty well does it. --Brendan -- http://www.piclist.com#nomail Going offline? Don't AutoReply us! email listserv@mitvma.mit.edu with SET PICList DIGEST in the body