Re: Incorrect force direction

["Greg Watson" <gowatson@xxxxxxxxxxxxxxx>]

--- In femm@xxxxxxxxxxx, "Rob " <rtickle@xxxx> wrote:
> Also noticed that if you take away the bottom steel bar, the force
> is correctly calculated to be positive rightward, so it's something 
> about the 2nd bar being there...

Hi Rob,

Removing one of the parallel bars eliminates the return flux path 
between the bars. This return flux direction between the bars is 
such that the magnet's own return flux will be in the same direction 
and thus in opposition. This is where the negative force (to the 
left) comes from. This force is correct and is present but is not 
the whole picture.

The problem, as I see it, is that FEMM doesn't take into 
consideration how the magnet's flux distribution will be effected by 
the different working points encountered in the parallel bars. I 
think it assumes a symmetrical distribution where it should be skewed 
to the right. This should generate a positive (to the right) force, 
which should be must greated than the much weaker negative (to the 
left) repulsive force generated above.

I'm sure David will work it out.

Greg