Re: [femm] Re: Incorrect force direction

["Greg Watson" <gowatson@xxxxxxxxxxxxxxxxx>]

----- Original Message -----
From: "Rob Tickle" <tickle@xxxxxxxxxxx>
To: <femm@xxxxxxxxxxx>
Sent: Thursday, January 04, 2001 3:21 PM
Subject: [femm] Re: Incorrect force direction


> I tend to trust this result, but I would be interested in seeing some pics
> of Greg's actual setup and magnets. I know the NdFeB magnets are highly
> anisotropic and very strong; one possible source of stray force to look out
> for would be if the magnetization direction of the magnet were not
> completely perpendicular to the bar surfaces. Does the actual setup show a
> true centring force in the center of the bar; i.e. does the force direction
> switch signs as you roll past the middle?
>
Hi Rob,

I'll see what I can do over the weekend.

One of the basics of my "seat of the pants" approach to estimating ferromagnetic
force direction is that a MMF source will be drawn toward a area of lower
magnetic reluctance.

The area of the rails and volume of the air to the right of the magnet should
show lower magnetic reluctance than that to the left of the magnet due to the
larger amount of inward facing rail surface and larger air volume between the
parallel rails and thus the magnet should be drawn into a equal & balanced
magnetic reluctance neutral point in the horizontal centre of the parallel bars.

It's not rocket science, just common sense ferromagnetic stuff.

Greg.