ERR chuff switch sync question..

The only accurate chuff switch measures driver rotation. The ERR switch is capable of that if you place in on a driver with 4 magnets. Any technique that measures motor rotation is only an approximation. Close but still not 100%. For most its close enough.

Pete

 Gunrunner Johns, Chuff Generator from Hennings Trains is the hot ticket. You will need some soldering skills. But much easier than playing with magnets and a reed switch.

The Chuff-Generator above syncs to the flywheel, which is obviously geared to the drivers.  After you program the chuffs, it will have exactly the number of chuffs desired for each driver rev.  Most folks are going for the prototypical 4-chuffs/rev.

Realizing that some folks find it challenging to do the soldering and spacing of the sensor, I also offer a service to mount the Chuff-Generator on the motor with wires and the sensor correctly spaced.  It's tested in place, so all you have to do when you get it back is connect up the included wires and calibrate it to the specific locomotive it's installed in.