I"m sure there's a simple reason but why can't auto reversing be built into decoder?
Because it's the power to the track that shorts out when the feeds are out of phase.
--Randy
Modeling the Reading Railroad in the 1950's
Visit my web site at www.readingeastpenn.com for construction updates, DCC Info, and more.
In other words, you want the decoder to recognize reverse polarity and automatically reset to avoid a short? Interesting.
Randy, is there no way around it? I mean, other than the traditional methods - - flip a switch, use an auto-reverse unit, etc.
Speaking of which, what would work besides flipping a switch or using an auto-reverse unit?
Rich
Alton Junction
The main problem is that the front power truck is the same polarity as the rear power truck. So lets say you solved that problem. Now the problem is the front wheels of the power truck are at the same polarity as the rear wheels of that same power truck.
Now, some G scale folks have the right idea by carrying a battery that powers the train, and radio control is used for control.
So, if you don't want to fool with wiring the track, consider G scale and radio control.
Elmer.
The above is my opinion, from an active and experienced Model Railroader in N scale and HO since 1961.
(Modeling Freelance, Eastern US, HO scale, in 1962, with NCE DCC for locomotive control and a stand alone LocoNet for block detection and signals.) http://waynes-trains.com/ at home, and N scale at the Club.
As noted, the problem isn't with the decoder, but the track. When a loco crosses a reverse section the first thing that happens is the wheels short out. This causes the reverser to trip. Otherwise the secton shorts out and everything dies. The other thing to take into consideration is that there are pick-ups on the front and rear trucks. Once the front crosses over the reverse section, if the track didn't reverse, the front and rear trucks would be opposite polarity of each other which is once again a short. This is also true with lighted passenger cars.
Springfield PA
No possible way around that, as long as power comes throught he track and you use 2-rail track. Follow the lines around a reverse loop and you will see that the outside rail eventually touches the inside rail. Put insulated joienrs there, and there is no short - until something crosses that gap with metal wheels, or a motor or lights in it. You now have a short. Nothign you can 'reverse' past the wheels would correct that.
Three rail track doesn;t have this issue, because the inside and outside rails are the same polarity. The center only contacts the center.
To do this in the loco would require some alternate power source - on board batteries for example, in which case the entire loop could be left unpowered so there is no issue. Adn ideal dream system for the future would have batteries that can be charged via power picked up fromt he rails, so you wouldn;t have to remove the locos to charge them, and you wouldn;t have to power all of your rails, just places like the engine terminal to recharge each loco. Or maybe at each water tower for steam locos - fail to recharge often enough and there's a simulated boiler explosion due to low water.
So, what would work to reverse polarity besides flipping a switch or using an auto-reverse unit?
Or, are those the only two methods?
Those are the ONE only method - an auto-reverser is simply an automated DPDT switch. If you always go the same way in the loop, you can use a relay connected to the switch machine contacts, you can use a block detector to trigger the switch device in the middle of the loop instead of waiting for the short, you could mount a magnet ont he locos and use a reed switch to trigger a relay - lots of ways to trigger it, but they are all doing the same thing, reversing the polarity (really phase since it's a square wave) under the moving train, which has no effect on the decoder. Exactly opposte of DC, where once the train is int he reverse loop you flip the polarity of the main to match, since polarity determines direction. You can do the same thing in DCC< but it's become convention to reverse just the loop section rather than the entire rest of the layout - on a larger layout it's just not practical to switch the entire layout's current load just to reverse one loco.