Hi, please bear with me as I’m new to HO Model Railroading and DCC electronics. And any assistance would be most appreciated. Basically, my current mainline is a continuous loop with switches to a secondary track and another switch to a yard. I’d like to be able to turn trains around so I put in 2 switches to go from the east side to the west side of the secondary track (or west to east depending if the train is going north or south). I believe this will give me a reverse loop. To take care of the short circuit created, I want to get a Digitrax Auto Reverser AR1. My question is do I only need one auto reverser connected to the track between the 2 new switches? I’m attaching an image of the current layout in progress so you can see how I connected this crossover track. Sent from my iPad using Tapatalk
You CAN wire this with only a single auto-reverser, but more planning is needed to decide if that is the correct solution for you. How long are the trains you run, and can they fit completely in the cross-over section? Or, more accurately, do you have metal wheels on your cars, or lighted cars, or do you run helpers in the middle / rear of train, that would then extend longer than the cross over section? If the answer to that question is YES, then you will need to reversers. The trick is you need to ensure you aren't tripping both ends of the electrically reversing section at the same time. The way I would do it, is to place an auto-reverser on the long single track on the left, between the two switches, and another one on the track running next to small building, from the switch just in front of the building, to whatever switch is in the far back.
Thanks RB. Definitely some great advice there. Initially I don’t plan on running trains longer than that cross section. When that time comes (a couple years or so) I’ll be expanding the setup and making major changes that would include the cross section. So at the moment, I don’t have to be concerned with trains longer than the cross section. Since trains will be traveling into the cross section from both directions, would I need an auto reverser for the cross section as well as the sections of track leaving the cross section? Now I’m wondering if I might need 3 auto reversers. Maybe I’m over thinking this? LOL Sent from my iPad using Tapatalk
Nope, if you can fit completely in the cross over section, then all you need is a single auto-reverser, feeding the tracks between the two switches. Remember to isolate the tracks, and only feed from the reverser.
Excellent! That actually does make sense. I was overthinking the solution. Thanks again. Sent from my iPad using Tapatalk
Even if your trains don't fit into the diagonal between the 'teardrops', all you have to do is double-gap with staggered gaps separated by a couple of mm more than the longest metal--wheeled truck on your rolling stock. Digital Specialties explains this in detail in their instruction for the PSX-AR, or whatever its replacement is. What you must remember is that the most important, or critical, component is the decoder. You want both to protect the decoder from hard shorts and to prevent the locomotive from stalling, figuring out it's okay, and then restarting again. That's the reverser's job...to detect a short before the circuit in the base system does and before the decoder can react to the mismatch. All those cars trailing the engine don't matter. Just their metal tires when they bridge two gaps simultaneously, which is what will cause that short. Hence the instruction about two sets of gaps at each end of the reversed section. Also, theoretically, the reverser could reverse the phase under the locomotive every second and the locomotive wouldn't know what, or if, there was anything to do about it. The decoder won't care. As long as it's not a short, it doesn't care what phase is running under itself. Let the reverser determine what, if anything, it should do when a metal tire bridges two rails anywhere it controls the current. The problem there is that those gaps provide a dead zone between them, and that dead zone may set problems for the pickup wheelbase length of the locomotive. If you're having trouble with this, let's do a thought experiment: Your locomotive crosses over the gaps at one end and the current is conflicted between the rails on either side of the gap. The reverser smells it instantly and reverses the phase to match the tracks the locomotive is leaving. Your train continues to enter the reversed section, now the same phase as the tracks being left behind, and the locomotive encounters the next set of gaps, crosses them, and ...shucks, it's conflicted again!! The reverser under it reverts the phase back to the previous orientation, and the loco decoder is once again quite content to trundle across the gaps as if they weren't even there. No conflict. The cars trailing the locomotive don't care. They don't have decoders in them. As the last car enters the turnout, the locomotive is now back on the other main, other loop, and it's just fine, continuing to run as it did before. Can you see that the last car, now crossing the first set of gaps and entering the reversing section, won't matter? At all? To summarize, it's all about the decoder and not frying it. Or the system shutting down, and then having to wait for the decoder to start up again and to move across those gaps. Secondly, it is metal tires bridging rails in conflict phase. That's why you stagger them. If you have passenger car trucks picking up power from the rails for lighting.............................................that's why you gap twice at each end, with gaps separated just over the length of the longest trucks supporting your cars with pickups.
Crandell, you need to rethink your example. If the reverser flips while a loco is bridging between the reversing section and a non reversing section to opposite polarity, you may very well fry your decoder. It isn't just the pickup of one wheel set, but, for most locos, all of them. This is not good, as the reverser may declare it a "dead short", since it cannot match the polarity at both ends of the section (and you could blow the decoder, if it doesn't do it fast enough). What if you have a train with helper locos further back. All you need to short everything is for a lead loco and a helper loco to be bridging both ends of the section.
Rick, the decoder will only ever get a match of phase because the PSX-AR will switch to match the phase before the detection circuitry OR the decoder can squawk and begin to shut down. If there is a conflict under any one of the pickup wheels, including drivers, the reverser flips the phase. It will match what the locomotive is moving toward. There is one, maybe two MU'd locomotives that have already crossed the reversed section. The first one crosses the gaps and encounters a conflict. Immediately, the reverser switches phase so that what the locomotive has under it, and under the trailing locomotive still within the reversed section of rails, is now in phase and the decoders carry on as before. What they don't want is a conflict. The reverse corrects it inside of three or four milliseconds. It corrects the fault by making the rails it controls in phase with the phase the lead locomotive is moving into. Neither decoder cares about which phase it is, just as long as it isn't a short. So, the locomotive decoders still in the reversible section, including those on a trailing locomotive, will simply adopt the switched phase and carry on as before. So, when you say, "... ..you have a non-issue. The reverser's job is to correct one end of its controlled length of rails at a time. Whichever end it is, when the first metal tire bridges and causes a conflict, the reverser instantly matches phase and nullifies the short. Inside the locomotives, the decoders won't detect the switch of phase. Trust me on this.
Digital Specialties Reverse Section Notes (instructions for the PSX-AR ): 1) Make sure isolating rail gaps are offset by 0.75” [21mm] and the AR Zone is longer than your longest train 2) If your train is longer than your reverse block and has metal wheels: a) You may need to cut additional gaps in the REVERSE SECTION. b) Simply cut another set of gaps at BOTH ENDS of the reverse sections inside of the original gaps. c) The distance between new gaps and original gaps should be longer than the wheelbase of any metal truck. ========================================= I see where they also recommend staggering the gaps on the two rails at each end of the reversing section by about 3/4" or 21mm. I hadn't seen that before. Most diagrams show the gaps across from each other. I'll do it this way I guess although I'm using a different auto-reverser. So if you double gap with staggered gaps and the second gap is further from the other one by a distance longer than the longest wheel base of a truck with metal wheels do you have to provide any power to that short section from the auto-reverser or is it dead. Also confused about the second set of gaps and the distance from one to the other one. Since the cuts are staggered does the distance have to be such that neither axle/wheel set crosses a gap in that short section between gaps (confusing?? I could insert a diagram if needed for what I'm asking.). Thanks, Sumner
Unfortunately, that section is dead. We're talking about maybe 2", so it shouldn't be a show-stopper. For a small SW switcher or a 0-4-0 tank engine steamer, yeah, you'll likely be hooped. However, you asked a good question. Theoretically, you COULD power a substantial dead zone at each end of a short reversing loop ('cuz that's as long a loop or diagonal as you can shoehorn into your layout space) with a second PSX-AR. Why not? It, too will instantly deal with an conflicts, and it'll otherwise power those zones to boot. As for the arrangement of the two gaps on each rail at each end of the reversible section of track: === ========= === == ========= ==== Where the pair in each rail is separated by the same distance as the pair opposite, but staggered by literally 1/8", or maybe 3 whole mm. However, if your longest power collecting passenger car truck, or your longest set of metal tires in any truck, are maybe 1.5" long (that is, from bottom-dead-center of Axle #1 to bottom-dead-center of Axle #3 on a heavyweight passenger truck), then each pair of gaps would be separated by 1.6-ish" on each rail.
I think I have it. So if you have a truck or engine with 2 or 3 or more axle sets with metal wheels the dead track between the staggered gaps should be longer than the wheelbase of those axles and they should fit in that section of track as shown above??? Sumner
Exactly, but so as not to make a long dead spot, measure precisely the outside bottom-dead-centers of the two outer axles of a three-axle truck...if you have one...and then literally add maybe two whole mm, or about 1/16" to that to place your gaps. How do you intend to manufacturer the gaps? Some use a small Dremel tool with a cut-off disk. Be very careful and those disks, at very high RPM, will sometimes snag one rail and literally rip it out of the small spikehead details. A razor saw might be good. Or, if you had a jeweler's saw, even better. Whatever it will be, keep the gaps as small as you can so they don't make wheels bobble or cars waddle.
At the moment I don't see a need to do this myself with what I have planned. The reversing sections I have drawn up are plenty long enough for my situation but was asking in case it comes up and for general knowledge and to maybe help the OP of this thread. Thanks for the explanation, Sumner
Thank you all for the great advice. It’s definitely a lot to take in. As it turned out, I set up the auto reverser and it worked perfectly. At a later date, I’ll be adding more track and more trains and I’ll have more to worry about then for sure. But for now, things are running well and it’s on to the next set of projects (adding switch motors, painting and scenery). Sent from my iPad using Tapatalk
