Magnetic Coupling for Steering - V3

The magnetic coupling used to transmit the steering servo's torque to the rudder through a waterproof barrier has been quite successful.

But the design has evolved over the years, and it is time revisit the topic to explain the latest design.

I had previously used an array of a 8 magnets, 10mm x 3mm, per disk.

Magnetic Coupling Version 2 - new Magnet Layout

This worked fine on the smaller 1.2m vessel, but the larger 1.8m Voyager 3 was experiencing steering interruptions when the magnetic coupling would be overcome, and break free.

More torque was required in the magnetic coupling for the larger vessel.

Review of the V2 magnetic coupler

These images show the version 2 coupler that was used extensively on the smaller 1.2m sailing drone. 

When used on the larger 1.8m sailing drone, Voyager 3, it proved to provide inadequate torque.

When the relative torque was measured using a spring scale, it broke free at around 200g.

Version 2 Magnetic Coupler - 8 magnets 56mm diameter - magnet side.

Version 2 Magnetic Coupler - 8 magnets - other side.

V2 Magnetic Coupler - 12 Magnet

To increase the torque that could be transmitted by the coupler I tried adding an additional set of magnets, totalling 12 magnets per disk, and increased diameter of 76mm.

This worked ok, but in practice the increased diameter of the disk was going to require more clear space in the equipment bay, which would require shifting other components, and became too difficult.

When the relative torque was measured using a spring scale, it broke free at around 320g.

Version 2 Magnetic Coupler - 12 magnets 76mm diameter - magnet side

Version 2 Magnetic Coupler - 12 magnets - other side.

V3 Magnetic Coupler - 2 Magnets 

The next step was to employ larger magnets, 20mm x 4mm, on the same size disk of 56mm diameter.

This configuration yielded a significant increase in the torque that could be transmitted, within the same space. 

When the relative torque was measured using a spring scale, it broke free at around 525g.

This increase in performance yielded a practical result for the Voyager 3.

I have now retrofitted the smaller Voyager 2 with the same design of Magnetic Coupler. 

Version 3 Magnetic Coupler - 2 magnets 56mm diameter - magnet side

Version 3 Magnetic Coupler - 2 magnets - other side

View of 2-Magnet Coupler in the Voyager 3 Equipment Housing

View of 2-Magnet Coupler in the Voyager 3 Equipment Housing

View of 2-Magnet Coupler in the Voyager 3 Equipment Housing

The new coupler design has proven so good, it has been retrofitted the smaller Voyager 2.

View of 2-Magnet Coupler retrofitted to Voyager 2, shown partially installed

Compass Interference

Of course stronger magnetic fields on a small sailing drone create problems for the magnetic compass.

The only solution is to increase physical separation until the magnetic interference with the compass reduces to a tolerable level.

The following images shows a simple test set up to observe the effects of the new Magnetic Coupler on the magnet compass located within the equipment housing.

It showed the interference dropped to reasonable levels once separation was increased by around 100mm to 200mm.

Testing for Compass Interference

 This was handled in Voyager 3 by adding an additional compass on the deck well forward of the equipment housing, but not too close to the magnetic disk used for the wing angle measurement, as shown in the following image:

New compass mounted away from magnets to reduce interference.