I think there were some wooden ones shown in ME at one stage.
My motors, a beam engine, and a horizontal open crank , the first was single acting, but after my 9yr old nephew had studied it for a while, he sugested that if I put two coils, and suitable switching, it could be made twice as powerful, so thats what I did with the horizontal one. On my motor the coil is hollow and the armature moves in and out in the manner of a piston, I think the stroke on both motors is 5/8". I'v run them on both AC, and DC. Ian S C