Just as a bit of a progress update, we have redesigned the elevator trim to provide 4 turns, utilising the same spiral principal as per the original.
In the original, the smaller diameter section of the base contained a cog in order to move the chain which in turn pulled the elevator trim cables to and fro. This section is empty in our implementation.
The interesting bit is the larger diameter section of the base. The original had a spiral with a follower which moved the cable to the indicator on the instrument panel, thus providing a mechanical means of showing the elevator trim position. The follower also limits the movement at either end of the spiral, resulting in 4 turns without being able to stress the elevator trim system beyond its limits.
We have taken this principal but instead of the follower moving a cable, in our case it rotates a spur gear which has a magnet attached to it. The movement of the magnet then gets interpreted by a rotary hall sensor mounted on the rear base cover.