# Force in a magnetic coupling

1. May 26, 2012

### Jonny6001

Hello,

I trying to create a magnetic coupling on the end of a shaft but I need to work out the size of the magnets that are needed.
The torque on one shaft needs to be transferred to the other through the magnetic interaction. The magnets on the outer shaft will be opposite polarity to it's aligned counterpart on the internal shaft, thus creating an attraction. The adjacent magnet will be of the same polarity therefore producing a repulsion force, this force will increase as the level of "slip" between the two shafts increases.

I understand that if you bring the N and S poles of two magnets close on a planar surface the magnetic field will more or less be perpendicular to the faces and therefore the force. What would happen if you were to move one magnet below the other with a small gap but keeping the attracting poles together:
N-------S
S-------N

I feel that the fields would then curl around similar to this

They would obviously be arranged in a circular array around each coupling.

What I'm really getting at is, is there a relatively easy was of calculating what the magnetic force will be between the magnets and how much torque could be transmitted through the coupling?
Or is this something that would need to be solved using FE methods or experiments?

Thanks very much for your time.