Regarding the comment about the "pull"  of the electromagnet increasing
as the armature closed with the coil pole-piece:  Telelectric started
out with the traditional electromagnet form, but by the time the system
was in production the magnet was a clever rotary configuration that
provided an even pull over the entire travel.  The armature was shaped
sort of like a rounded "Z", with the pivot in the center.  The "arms"
of the Z tapered to a point.  As the armature rotated into the pole
pieces, the amount of new magnetic material per unit of travel decreased.
Proper shaping of the arms thus provided constant rotary force as the
armature "closed".

I know I keep rattling on about the Telelectric, but it was a quite
well-developed system.

Bob Billings