When I was a teenager, it was very simple to prototypically run multiple locomotives in a train because Athearn Blue Box always put out dummy versions of its locomotives. But now, outside of Athearn’s RTR F unit series, no one seems to be putting out dummies. So with that fact, how do you run multiple locomotives? If you run them elephant style, you have both engines lit up. I see Model Railroader layouts running multiple locomotives, coupled rear-end to rear-end. How are they doing this? Do you have to gut out a running locomotive and make it a dummy? Or if you run them elephant style, are you going in and manipulating the lighting so the front end does not light up?
With DC you have to find a way to reverse the motor leads so you can run them back to back. With DCC you can run them any way you like, and control the lights exactly as you want.
–Randy
Randy, I believe you’re mistaken. Surely, when you turn the locomotive around you are reversing the effective polarity at the same time. As for the lights, if they are polarity-sensitive this will also be taken care of automatically. If not, either ignore it (my vote), or install diode control.
Modern non-DCC units have “directional lighting” installed. The lights are wired with diodes so they are only on if the engine is going in that direction. This works because, as rails5 said, you are reversing the polarity inside the engine when you turn it around.
DCC allows you to turn lights on and off if you’d like. The simple decoders will automatically turn on the light which points in the direction of travel.
Does MU-ing know which is the “lead” locomotive so it can figure out which headlight to turn on?
Right! When you reverse (physically) the engine you reverse the polarity. As for the lights, I’ve always rigged my lights w/ diode constant lighting where 1.5 V. is tapped off of 2 diodes w/ a third diode to prevent the 1.5 B. bulb from lighting when the current is reversed. By using 3 diodes w/ the opposite polarity in the same circut, I keep the same voltage forward and backwards to the motor but the headlight only goes on when the engine is moving forward. Of course, if you run “elephant fashion”, you have all the engines that are facing the same direction running w/ headlights on, but then, that’s why we have B units.
I’m DC & run my P1K- F3’s either way, AABB or ABBA. One consideration that generally works is same loco manufacturer rather than mixing an Atlas with a P2K. However there are exceptions within the same manufacturer, such as the P2k SD 45 & 60.
For the DC side of the question, NMRA Standard S-9, paragraph II answers this. That’s been a standard as long as I can remember. Regardless of which way the locomotives are facing, if they’re wired correctly, they will run the same direction
II. CONTROL
A. Direction control by polarity reversing shall be provided. Positive potential applied to the right hand rail shall produce forward motion. (3)
The full collection of Standards and Recommended Practices can be viewed for free (no membership required) on the NMRA website www.nmra.org