I just had one of my 4am brain waves, and came up with an idea for working Dynamic Brakes for Model Loco’s. I doubt it would be of any use in N, as there would be neither the room for the circuit, nor sufficient inertia in the model to warrant brakes. However in larger scales it could be usefull, or at least something interesting to toy with. Anyway the circuit is shown below.
This would probably work fine with the simpler DCC decoders, in locomotives with spur gear drive trains, but generally not worm gears. On the higher end decoders, especially the ones with BEMF, the decoder would get very upset when the motor was disconnected, possibly to the point of letting the smoke out.
This is similar to an idea I had a long time ago. Use a spur gear drive, very free-rolling, so that perhaps even the loco could roll down a grade with no power. I also thought of having some sort of drive in a caboose, not enough to hold back the loco under power, but enough to add drag. Thus you’d have an independent brake int he loco and a train brake represented byt he caboose (since fitting it to ALL cars would be crazy). This might require a scale larger than HO though.
The problem with putting a load across the motor is even with a very large value resitros, it would stop way too fast. As good as my Stewart DS4-4-1000 could coast on DC power (generating enough power to keep the headlight LED illuminated!), it still coasted far less than a real loco. And shorting the track after removing the power, while it was coasting, brought it to an instant halt.
I think such things are better left to software simulation int he decoder - hit a function and the ‘dynamics’ activate and the loco gradually slows, regardless of throttle setting. This is in the newer QSI decoders, such as in the Atlas Trainmaster, and works great. You hear the dynamic brake sound, and the loco slows. Cut off the brakes and it resumes speed.
–Randy