brakes

Model Railroader General Discussion (Model Railroader)
1

please explain dynamic braking on real locomotives and how it applies to HO size locomotives.

2

http://en.wikipedia.org/wiki/Dynamic_brake

3

In relation to model trains, you could say that a dynamic brake is simply stopping the locomotive. This of course considering our lack of trainline brakes…

4

Since the drives on model locomotives don’t allow the wheels to turn the motor, there’s no practical way to apply dynamic brakes to any scale model you can run on a table.

Brake dynamics for a model are utterly different from those for prototype trains, because the laws of physics aren’t linear. If you start with a small-scale model, every time you halve the scale the mass increases by a factor of 8 (2 cubed) and the total energy at the same scale speed by a factor of 32! And that’s just from HO to O scale. From O scale, the mass of a full-size `model’ is 48 cubed and the energy is (48 cubed)(48 squared) of the model’s mass at the same scale speed. OTOH, the wheel-on-rail contact goes up by a linear factor, so the effective brake power per braked wheel is only 48 times as much as that of an O scale model. That’s why model freight cars don’t need brakes, and prototype freight cars do.

Chuck (Modeling Central Japan in September, 1964)

5

Freight trains have tree different brakes sets.

  1. The independent or engine brake applies brakes to the locomotive wheels only.

  2. Dynamic Brakes (if used) reverse the motors into generators, whose power is dissipated as heat through a bank of resistors and fans. It could also be used to charge the batteries were the locomotive a Gen-Set unit. In the model world his is represented by the cooling warts on the locomotives and nothing more.

  3. The train line brakes reduce the air pressure on the brake line applying brakes (at about the speed of sound) from one end of the train to the other. With modern FREDS the trainline could be opened from the rear of the train, string the consist out rather than allowing it to bunch up. If so that would be a fourth brake handle that the engineer could play with.

  4. With “Distributed Power” he could also play with the independent or dynamic brakes of the pushing locomotives.

ROAR

6

Dynamic brakes on a model loco don’t really exist. If your loco has sound, there is usually a button that will turn on the Dynamic brake SOUND. It is sound only for simulating Dynamic brakes.

It makes operating and running trains more fun when you have a bunch of buttons to play with.[swg]