I am going to steal #10’s ESU DCC decoder for #622; it’s not doing any good sitting in the tender while #10 awaits shopping. This decoder wants four magnets and a Hall sensor to synchronize the exhaust chuff sound.
Now, there is not much space on the axle between the gear box and the wheel bearing – not quite 2mm. I’ve found sources for 1mm and 1/16″ magnets, but I don’t have them in hand yet to test them with a Hall sensor. So, after five or six tries, I made a ring with four 5/64″ holes spaced around the exterior. This should work, and if not, I have a whole 2mm on the other end of the axle to play with!
Incidentally, the days of fabricating such a part are numbered. The next engine, assuming a magnetic cam is still required, will probably have a printed magnet by the likes of Polymagnet.