Auto-reverser and DC?

Model Railroader Electronics and DCC
41

So the practical application of this on a walk around style layout is that the direction switch controls “east” and “west”, not forward and reverse.

And it is much easier to keep track of and understand if it becomes a system wide convention on the layout.

Yes, your earlier observation is correct, you will need separate reversing control of each throttle or each block, and depending on the methods and equipment runs the risk of being very confusing to operators and requiring lots of wire and hardware.

That is why I don’t have any reverse loops on the mainline my layout.

I have one reversing section on the mainline - it is a dead end wye - it is semi automated.

I have one reverse loop that is the dead end of the branch line. You have to stop the train, throw the turnout, and change the direction switch on your wireless throttle. Because you went into the loop traveling west, to get out you have to travel east.

These are the only two places on the layout where you can “turn” a whole train from east to west.

The turntable turns locos from east to west, that is semi automated and visually logical as well.

Sheldon

42

ok. i understand that is what you and others do. but i’m not hearing why you do it that way?

doesn’t it make more sense for it to control forward/reverse? this is what’s done with DCC, for example

if reverse loop control is done automatically, are you going to stop your loco, after entering a reverse loop going east and coming out west bound and flick some switches so that your direction switch is now west?

43

Because forward and reverse relative to the locomotive is meaningless. I can change forward in to reverse without reversing polarity by picking up the loco and turning it around.

When I have two F7’s back to back, which way is forward? Unlike DCC I don’t really know, I don’t need to care.

What I need to know is which way they are going to move. The easiest what to know that is label the reversing switch east and west and relate it to my viewing position. On my layout, I set the switch west, the train ALWAYS moves to the left - no matter which way it is facing.

MANY DC layouts have big arrows at the top of the panels indicating “East-West”, especially if the layout design does not follow my convention of always having west to the left of the viewer/operator.

Sheldon

44

Me to but switches belong to people who aren’t as close to Alzheimer’s as I am.
Anyway while Everest expanding this thread I was surfing and This is what I found for auto reverse loops for DC. I don’t understand any of it so, if there are any electronic geniuses out there can you look at the processes and see if they will work. I assume the arduino would allow for most functionality because it involves software But maybe the other processes could be functionally close?

  1. Relay-Based Auto-Reverser

This method utilizes a Double Pole Double Throw (DPDT) relay to automatically switch the polarity of the reversing loop.

Materials Needed:

• DPDT Relay (rated for your track voltage)

• Diodes (e.g., 1N4007)

• Insulated Rail Joiners or Gaps

• Wires and Connectors

Circuit Diagram:

Source: Azatrax - Automatic Model Railroad Reversing Loops

Step-by-Step Instructions:

  1. Isolate the Reversing Loop:

• Use insulated rail joiners or cut gaps in both rails at the entry and exit points of the reversing loop to electrically isolate it from the mainline.

  1. Wire the Relay:

• Connect the mainline power to the common terminals of the DPDT relay.

• Connect the Normally Open (NO) and Normally Closed (NC) terminals to the reversing loop, ensuring that the polarity is set to match the mainline when the relay is in its default state.

  1. Install Diodes:

• Place diodes across the relay coil to protect against voltage spikes and ensure proper operation.

  1. Test the System:

• Run a train into the reversing loop. The relay should activate, switching the polarity to match the train’s direction, allowing smooth passage through the loop.

  1. H-Bridge Auto-Reverser

An H-Bridge circuit allows for electronic control of the track polarity without moving parts.

Materials Needed:

• H-Bridge Motor Driver (e.g., L298N)

• Insulated Rail Joiners or Gaps

• Power Supply

• Wires and Connectors

Circuit Diagram:

Source: Instructables - Automated Train Reverse Loop Using Arduino

Step-by-Step Instructions:

  1. Isolate the Reversing Loop:

• Ensure the reversing loop is electrically isolated from the mainline using insulated rail joiners or gaps.

  1. Connect the H-Bridge:

• Connect the input terminals of the H-Bridge to your DC power supply.

• Connect the output terminals to the reversing loop tracks.

  1. Control Logic:

• Implement control logic (e.g., using sensors or a microcontroller) to detect the train’s position and switch the H-Bridge outputs accordingly to match the required polarity.

  1. Test the System:

• Operate the train through the reversing loop to ensure the H-Bridge switches polarity correctly, allowing uninterrupted travel.

  1. Arduino-Controlled Auto-Reverser

Using an Arduino provides flexibility and precision in controlling the reversing loop.

Materials Needed:

• Arduino Board (e.g., Uno)

• H-Bridge Motor Driver (e.g., L298N)

• Sensors (e.g., Infrared or Reed Switches)

• Insulated Rail Joiners or Gaps

• Wires and Connectors

Circuit Diagram:

Source: Instructables - Automated Train Reverse Loop Using Arduino

Step-by-Step Instructions:

  1. Isolate the Reversing Loop:

• Isolate the loop using insulated rail joiners or gaps at both ends.

  1. Set Up Sensors:

• Place sensors at the entry and exit points of the reversing loop to detect the train’s presence.

  1. Wire the Arduino and H-Bridge:

• Connect the sensors to the Arduino’s input pins.

• Connect the H-Bridge to the Arduino’s output pins and to the reversing loop tracks.

  1. Program the Arduino:

• Write a program that reads the sensor inputs and controls the H-Bridge to switch the track polarity based on the train’s position.

  1. Test the System:

• Upload the program to the Arduino and run the train through the reversing loop to ensure proper operation.

Additional Resources:

• Automated Model Railroad Layout With Reverse Loops

• Automatic Reverse Controller-Single (AR1) - Digitrax

• How to wire a reversing DC loop - World Of Railways

45

This is the whole problem with automating this. When I come out of the loop after the automatic polarity change of the mainline, the effective action of all the manual reversing switches will be opposite what it was going in.

Trust me, that will become confusing because nearly all DC operators are using fixed or tethered throttles, not wireless throttles.

Even my wireless throttles - they do not have a single button for direction - they have a button to go left, and a separate button to go right. Power packs and tethered throttles have slide switches or toggles.

Sheldon

46

Take a loco that is running forward on DC. Pick it up, turn it around, and place it back down in the same place. Now it is running in reverse, although the direction switch didn’t change, so no, forward/reverse doesn’t make more sense.

47

ok. that clear;

48

Let me explain this from a different perspective.

When you walk up to a train on a DCC layout, dial in the address, and start to move the train you know which way it will go because you told it to go forward.

But when I walk up to a DC train on a layout, I need a polarity reference to know which way the train is going to move. Traditionally that reference is the position of the reversing switch, typically labeled “east-west” or simply slid/flipped left or right to show which way the train will move.

Until I apply power to the track to move the train, there is no polarity to measure. So there is no way to light indicators, etc.

With my wireless throttles, I know that if I push the left button, the train will go left, because the whole layout is set up that way. It never changes. But it would change if there was an auto reverse loop setup that had changed the mainline polarity separately from the buttons on my throttle.

This would not be desirable.

I was typing this during your last reply…

Sheldon

49

so a DC-AR make no sense for you

50

Not for me.

As a viewer or operator of my layout you are always standing on the south side of the tracks, left is WEST, right is EAST.

The wye - how I turn trains on the mainline when desired. Two legs of the wye are the mainline, the third leg dead ends into a 24’ long 10 track staging yard. Let’s say you are moving west toward the wye, and you take the diverging route into the wye. You have entered the wye at its East end. The stub end track of the wye is automatically connected to your route with the correct west bound polarity.

You drive the train in.

Now, if you want to turn the train, you select the block on the west end of the wye and push the button to align that turnout route. The polarity of the stub track you pulled onto changes automatically. Your train will be moving in reverse now, but it will still be west bound as it relates to the mainline. You power up your train, it backs out of the wye, still moving west.

Once you clear the wye, you stop your train, reselect the mainline route thru the wye, change your direction to east bound and now you will go back the way you came.

The whole time the direction selector on your throttle has been set to your movement relative to west or east on the mainline with no regard for forward or reverse.

AC-Layout-15a 400 DPI
AC-Layout-15a 400 DPI1920×1830 324 KB

Sheldon

1 Like
51

One other note, even if I was using DCC, I would build my layout with the same “east - west” convention. It is so confusing on some layouts when you really don’t have a good reference as to where you are going or coming from.

Sheldon

52

u

it’s seems odd that to direction of the loco reversed by selecting a route

can you explain how this would work with a reversing loop where the loco always moves forward by changes direction east/west?

53

Only odd because you are use to DCC.

OK, my little WESTERN MARYLAND branch line has a hidden reverse loop. It works like this. You can set the incoming turnout either way, the polarity of the loop is automatically matched to the mainline. You proceed into the loop. Once the train is completely in the loop, you stop the train, throw the turnout, reverse the direction switch on the throttle. Now you can proceed out of the loop. You went in westbound, you came out eastbound. While you were stopped you changed the throttle direction from west to east - the track wiring did the rest thru the turnout position.

Sheldon

54

ok. thanks.
again odd that you need to stop the train and flick a direction switch. (i understand why)

i believe this is why people say in DC you drive the track while in DCC you drive the loco.

Proto throttles attempt provide more realistic control of the locomotive

55

Greg, DCC is very oriented to the idea of being the engineer, being in the “cab”.

But this is not the primary goal of everyone with a model train. I like operation, but reliving the details of being the engineer is pretty low on my radar. This has a lot to do with why DCC is not a necessity for me.

It is why my CTC panel is simplified and does not look like the real thing. It is why my signal aspects are “streamlined”. It is why I have deep scenery with a low percentage of track to benchwork surface.

It’s not just about the trains, it’s about the whole little world that justifies the existence of the trains.

From a spectators standpoint, the trains move from left to right, from right to left, they travel thru the scene and disappear. So East and West makes perfect sense.

I commented on some of this years ago when I first posted some info about my layout plan. If I was happy just being the engineer, I would not want a 1400 sq ft layout that can run six 50 car trains at once and store 30 of them.

I’m the president of the railroad, riding in a fancy business car.

Sheldon

56

Sorry if I seem dense. Trying to more completely understand how DC layouts are operated. (the club and my home layout are DCC)

I assume there are 3 types of reversing switches on a layout with reverse loops: throttle, mainline, rev-sect, and that there are separate mainline reversing switches for each throttle. Am I correct in saying that the mainline (not throttle) reversine switch is primarily used for controlling the direction of the loco?

Is the mainline reversing switch typically mounted horizontally so that it indicates the direction of the loco: west/left and east/right?

If so, when a loco is powered, are the mainline and throttle reversing switches typically set such that the mainline reversing switch indicates the forward direction of the loco?

if there is some trackage (a loop) that reverses the direction a train is traveling, would the mainline and throttle reversing switches be toggled so that the mainline reversing switch matches the direction of the loco?

if this is the desired use of the mainline reversing switch, won’t the it continue to indicate the direction of the loco after it passes thru a reversing section and the mainline reversing switch is toggled?

57

Typically yes, but not always. It can depend on the type of throttle.

In the best case on a layout with a linear track plan, yes.

It indicates direction of travel, the loco may be backing up.

If you change both the mainline and throttle direction switches the polarity will not be reversed, so if you have a separate throttle reversing switch you ignore it or only use it for reverse moves that do not involve the reverse loop.

YES, exactly. That is why you often ignore the direction switch on a fixed power pack, so the orientation of the mainline direction switch remains consistent with direction of travel but not with the “forward” end of the loco.

Keep in mind - what is “best practice” and what many modelers did years ago are two completely different things. Hence my comment often that a great many modelers, especially today, have never seen or operated on a well planned DC control system.

Finally learning how this forum software works…

Sheldon

58

There are many ways to wire and control a DC layout, depending on layout complexity, number of operators, number of trains and personal preference, so there really is no standard.

Of course the simplest is one big block and one reversing switch (and anytime a say reversing switch, that could be a relay which could be controlled from multiple locations).

If you want more than one train on the layout at a time, then you have to split it into blocks. If you only need one train running at a time, then those blocks might only be on/off blocks, and again, only one reversing switch. If you want to individually control more than one train at a time, there are a couple of options: block control and cab control. Block control has a separate throttle connected to each block and you control whatever train is in a block with the throttle for that block. That method is not as common and I won’t go into further detail with it unless requested. Cab control means each block can be connected to one of two or more “cabs” (throttles), and the cab controls whatever trains are in whatever blocks are connected to it. In cab control, reversing switches can be connected to the throttle or the block, depending on the users preference. If you have a lot of blocks, but not any reversing blocks, it probably makes more sense to have the reversing switch connected to the throttle - fewer switches (one per throttle instead of one per block) and since the train can’t be turned the throttle direction switch will always match the loco direction switch, and there are no chances of shorts from miss-matched polarity (unless you try to run into a block controlled by another throttle).

When you start adding reversing blocks, you have to add at a minimum one additional reversing switch. If you have more than one reversing block they could all be controlled with one reversing switch, but that would probably be extremely rare. You can still choose to not have reversing switches on the non-reversing blocks (and have them on the throttles), but that would require you to stop within the reversing block to change both the reversing block and throttle directions before leaving.

If you have reversing switches on the non-reversing blocks, then you do not have to stop within the reversing block because you only change the non-reversing block you are travelling into when leaving the reversing block. The general recommendation when you have reversing switches on the non-reversing blocks is to not use throttle reversing switches and only rely on the physical direction according to the block reversing switches. You can, however, still use throttle reversing switches if you so choose. In this case, the block reversing switch will indicate only the direction the train is facing, while the throttle direction switch will indicate forward or reverse.

59

When you get into the details of a specific DC layout, control panel designs and locations, fixed throttles or tethered throttles, type of block selection, number of cabs available to each block, all of these things effects the detailed wiring of reverse loops.

On my layout, my throttles are the only “direction switch”. It is not possible for me to tap the track power ahead of the reversing switch inside the throttle to power a reverse loop thru a separate reverse switch.

So I handle them as I have described.

I have eight throttles available to most of the control blocks on the layout. They are totally discrete from each other, each having its own 5 amp power supply.

Sheldon

60

I will add that what is “best practice” varies greatly from layout to layout depending on layout design and operator preference.