That set up is good for creating a good low reluctance magnetic circuit (reluctance to magnetic flux is like resistance to electric current). The more steel the lower the flux density and so less chance of saturating the magnetic circuit at any point, which would choke off and waste the flux generated by the coil. Steel is cheap, copper expensive, maybe they wanted to shift the balance to more steel/less copper and still get the same amount of flux to the moving core, therefore same force. Anyway, on paper it's a better magnetic design, but more expensive and more parts to go wrong.

Don C.

I was just commenting on the magnetic circuit design, one vs. the other. Maybe Sonic copied their design ideas from multiple sources, I don't know. Many moons ago when flippers were invented the magnetic circuit design chosen was simple, used a small number of parts but was a bit inefficient (wasteful of the flux the coil generated). Fewer steel parts but a bit more copper in the coil to get an equivalent strength. An optimal design depends on the costs of steel, copper and labor at any one time. I think the simpler design with fewer parts that we are all familiar with was and still is the right way to go.

Don C.