I have a situation where a dual track merges at a turnout and I want to create a dead section of track at the turnout if it is thrown against the train entering the turnout. I am using SMAILs (DCC Tortoise) and I know how to control track power where the tracks diverge from the turnout. However, it seems to me that just creating a dead section will cause problems when a 4 engine consist hit the dead section. The lead loco will stop when it hits the dead section but the following loco's will still be on live track and will be trying to continue forward. At some point, the train will come to a stop but the trailing locos will likely still be on the section of live track and will stall out or spin their wheels. I do not want that to occur. I want all loco's to stop as soon as the lead loco hits the dead section. Seems like the best way is to kill power to a section of track that would contain the entire consist as soon as the lead loco hits a trigger point.
What is the simplest or cheapest way to do that?
PS - Everything is DCC with Digitrax and SMAIL components.
Paul D
N scale Washita and Santa Fe RailroadSouthern Oklahoma circa late 70's
IR detector/relay across the rails near the turnout. When lead engine breaks the beam the relay disconnects power to a long section of track. Use the NC relay contacts. Use contacts on the turnout motor to bridge the relay contacts when the turnout is lined correctly.
http://www.scienceprog.com/very-simple-ir-detector-that-controls-relay/
Alan
Freelancing the LK&O Railroad
PED:
Alan beat me to it. IR is the way to go because it will function regardless of how much light is in the room (i.e. for night operations).
If you are not inclined to build one yourself, here is one example of a ready to install detector. Note that you will need a separate relay to handle the track power. Also note that the transmitter/ receiver do not have to be positioned on opposite sides of the track. They can be installed side by side in the roadbed between the rails and the signal will bounce off the bottom of the train.
http://www.azatrax.com/ir-model-train-detector.html
EDIT:
After reading through the Azatrax website, I think you will have to do some research on which relays to use to suit your purpose. As far as I can tell, the relays supplied by Azatrax are timed so that they will turn the track power back on after a short delay. That probably isn't what you want. I'm guessing that you want to manually control when the siding track power goes back on. Maybe send them an e-mail to see what they suggest.
Dave
I'm just a dude with a bad back having a lot of fun with model trains, and finally building a layout!
The plain MRD1 doesn't automatically turn back on after a delay. The drop out they are talking about is the delay after the sensor is no longer blocked. For IR detectors this prevents an inter-car gap from causing the detector to report a clear block as a train slowly rolls past. On a track current type of detector, this delay is used to keep momentary power interruptions from makign the block alternately clear and show occupied - and in both cases also simulates better the big heavy relays that used to be used in track circuits.
The MRD1-T has that automatic restart after a time delay.
There's a link in the description of the MRD1 that shows how to hook up their relay unit to make a stopping section.
--Randy
Modeling the Reading Railroad in the 1950's
Visit my web site at www.readingeastpenn.com for construction updates, DCC Info, and more.
rrinkerThe plain MRD1 doesn't automatically turn back on after a delay.
Thanks for clarifying that Randy.
Thanks for the proposed solution but I think I found a solution which does not require a lot of extra circuitry but it does require some extra wiring, a few DPDT switches and programming to my decoders and command station. This works when using a Digitrax command station in conjunction with loco decoders which allow programing of the momentum CV ( CV03 for acceleration and CV04 for deceleration). I do not know if other brands have this capability.
Per The Digitrax Big Book of DCC, I can hook my programing track outputs to a section of track and use it as a breaking section. Any DCC loco entering that braking section of track will receive a command to decelerate to zero according to the rate programmed into the momentum CV on each mobile decoder. Can be used when approaching a signal, entering a station or anywhere else you want a train to stop or proceed manually or automatically.
To make this work, I would need to do following
1) Change DCS200 command station OpSw47 to “c” (closed). This causes the programing track outputs to operate as a braking section when not serving as a programing track. I would be using a separate command station for programing.
2) Run wire from DCS200 Programming Track outputs to all track sections set up as a braking section
3) Add a DPDT switch at each breaking section so I can choose to operate it as a braking section or as regular DCC track
4) Program all mobile decoders to a suitable deceleration rate that would ensure that all locos have entered the braking section so they will all receive the command to decelerate to zero and stop before the lead loco exits the braking section. I will need to experment with what values work best.
In operation, this means that I would need to set each braking section DPDT switch to feed the track from the programing track outputs when I want it to operate it as a braking section or set the DPDT switch to feed the track from the regular DCC power buss when I want to operate it as continuous running (no automatic braking.
When I am ready to manually release a consist sitting in a braking section, I would change the DPDT switch over to DCC and accelerate the consist to the desired speed. To reactivate the braking section, I would need to flip the DPDT switch back to braking
Lots of ways to use this feature but this simple manual approach works for me.
As long as there is enough momentum on the lead locos - they would hit the braking section first, and begin to slow down, while trailing units are on the regular main. Then the second unit hits, and starts slowing down, so now you have slow, slowing and still going last speed (assuming a 3 unit consist). Once all 3 hit the brake section, the lead unit will be mostly stopped, the second unit partly stopped, and the third unit just beginning to slow. Somebody's going to have spinning wheels. It's better for the train than just killing the power, but it doesn;t solve the spinning wheels as one unit stops and the other hasn't yet.
However - if you combine the IR detector with the brake zone idea, using a relay activated by the detector to toggle between brake zone or main (or use something like the DCC BitSwitch braking generator, instead of your command station's program track - they're only $30 https://tonystrains.com/product/dcc-bitswitch-brake-signal-generator-analog-dc/ ), then you get the best of both worlds. None of the consist will begin slowing until the detector is tripped, which should be positioned such that it trips only after all units are past the gaps between the main and the braking zone. THEN they will ALL begon slowing at the same time, rather than one by one, so the train will come to a smooth halt (due to the momentum setting) but there will be no issues with one unit still going faster and trying to push the ones that have slowed more.
Randy....sounds like the BitSwitch performs similiar to another Digitrax approach to create a brakeing section via using a detector to determine when an engine hits a trigger point and then it switches the track power from DCC to DC in a selected section of track. With decoder VC29 (analog mode conversion) turned off, the locos will not operate on DC thus they will come to a stop. You would position the detector such that the entire consist would be in the track section changed to DC when the lead loco hits the detector. This would cause the entire consist to slow to a stop at the same rate.
The Digitrax example uses a relay for switching based on how a signal is set (stop/go) but the relay can be triggered manually to revert to DCC if desired.
There is another method I can use but I avoided it initially due to cost. I may need to go back and reconsider this other method as follows. I am using the Circuitron DCC SMAIL for my turnouts. The SMAIL has an "auto align" feature which can make it change position when a loco hits a trigger point (tiny section of grounded rail). I can use this feature to align a turnout position if desired. However, in my application, I can use the internal SMAIL switches to control a relay which would change the rail from normal DCC to programing track (aka my brakeing section) when the lead loco hits the trigger point. The braking section would need to be large enough to include the entire consist when it changes to the programing track mode so they all stop at same time at the same rate. The SMAIL would be used as a smart switch rather than controling a turnout. If you buy the SMAIL in bulk (12 packs) as I have been doing, they cost about $27 each. That makes them about the same as a bitswitch.
The bitswitch broadcasts (address 00) a SET SPEED TO 0 command - In addition to address 00 being used by Digitrax to run a non-decoder loco, address 00 is also a broadcast address that all decoders are supposed to respond to, both for control and for programming. When you use address 00 on a Digitrax throttle to run a DC lco, it's not sending DCC address 00 packets at all, it's modifying the waveform in the command station. The only address 00 DCC packets you cna send with a Digitrax command station are when you use Ops Mode programming and select address 00 - that sends an address 00 programming packet which will reprogram every loco on the rails. The Bitswitch actually generates a DCC packet, not just puts DC on the rails. Not all decoders support brake on DC, some will just stop running instnatly, regardless of momentum settings, when encountering a DC section of track with CV29 set to turn analog off. All decoders that are NMRA compliant must respond to address 00 though, it acts like you dial up the loco's actual address and set the throttle to 0.
Some newer decoders also respond to asymmetrical DCC, basically putting a diode in the track power line to chop off half of the DCC waveform. That too is something not every decoder will work with.
rrinkerThe bitswitch broadcasts (address 00) a SET SPEED TO 0 command ...The Bitswitch actually generates a DCC packet, not just puts DC on the rails.
Actually, the device you linked to does not produce DCC packets, it simply uses a bridge rectifier to create DC from the DCC bus. Here's the Bitswitch Set Speed Zero packet generator($90): https://tonystrains.com/product/dcc-bitswitch-set-speed-zero-packet-generator/
I like the DCC stop packet solution myself - it should be more predictable and, I am not certain but I do believe that if you use the program track outputs to generate the brake signal you still have control over the functions of the stopped loco. The biggest drawback to the DCC stop packet, whether using the program track ouputs or the Bitswitch, is you have to feed the signal through a separate booster(this would be a good application of Tam Valley Depot's $55 booster). You also need 12 volt light bulbs wired between the booster and the brake section to prevent shorts between the main bus booster and the brake section booster when trains cross the insulated joints between the sections.
I think I will try out my SMAIL switch solution first rather than invest in the other solutions. The Digitrax programming track also sends out a "set speed to zero" to the 00 address which will affect any loco on the braking section. Toggeling the track between a regular DCC or braking section would be determined by the switch position of the SMAIL (plus a 12V DPDT relay) controling that section. With this approach, I can use the routes feature to correctly align all turnouts involved plus move the SMAIL switch to the correct DCC/brakeing track position.
To reiterate what I said before - if you use the program track outputs as a braking section you'll have to feed them through a booster.
CSX Robert To reiterate what I said before - if you use the program track outputs as a braking section you'll have to feed them through a booster.
Glad you made this comment. The Digitrax tech notes are inconsistent on this point but I think you are correct. Digitrax tech note KB193 (from May 2012) does not mention an extra booster and that is the design I have been refering to up to this point. However, due to your comment, I dug deeper and found tech note KB331 (June 2016) which has a design that does show the extra booster. I have an inquirey to Digitrax to determine if KB193 is obsolete.
Looks like I need another booster dedicated to the brakeing sections.
It absolutely requires an extra booster, the program track outputs do not have any sort of drivers on them that could provide enough power to actually run a loco. All that setting the command station up for the brake zone does is have the output of the program track generate the broadcast stop commands, the electronics of the program track are still the same low power electronics it always had. The original tech note may have mentioned this in the fine print, or assumes this was common knowledge, the newer one is likely a product of the effort to update all of their documentation to address shortcomings that people have noted.
The small Tam Valley booster would be perfect for this. You would toggle its input between the neighboring main (for normal running) and the program track termiansl of the command station (when braking is in effect).
rrinker It absolutely requires an extra booster, the program track outputs do not have any sort of drivers on them that could provide enough power to actually run a loco. All that setting the command station up for the brake zone does is have the output of the program track generate the broadcast stop commands, the electronics of the program track are still the same low power electronics it always had. The original tech note may have mentioned this in the fine print, or assumes this was common knowledge, the newer one is likely a product of the effort to update all of their documentation to address shortcomings that people have noted. --Rand
--Rand
I received a response from Digitrax concerning the two different tech notes and they said either one would work but the booster version is prefered.
I am not familiar with the Tam Valley booster you refer to but will check it out. Since a consist would only be slowing down (not running at speed) during its time in a breaking section, any booster should work. My largest consist (N scale) would be 4 loco's, a breaking section would be low load during braking. In theory, I could have two consists (total of 8 loco's) hitting two different brakeing sections at the same instant but that would be the max. All my other boosters (Digitrax DB200+) are 8A boosters (overkill for a brakeing section) but I will probably use another DB200+ so all my boosters are the same in case one goes bad.
Please tell me you have circuit breakers between those DB200's and the track. And still I wonder at multiple DB200's for an N scale layout. The slight price difference over a DB150 is almost a false economy - sure, 3 more amps for a few bucks more, but the power supplies for 8 amps are not common. 5 amp supplies are cheap as chips because they are common laptop power supplies. What are you using to power the DB200's?
Ah... So! YOU have discovered the problem!
LION connects such locomotives with drawbars, and him hard wires all of the engines together. The power only cuts out when the LAST truck crosses the gap.
LION now runs SUBWAY TRAINS. Trains run terminal to loop to terminal. See the train will run with either end forward. In order for gaps and automation to work, the ENTIRE (six car) train is joined by Rail Joiners, AND are wired from end to end. I use four conductors, one pair for the traction motors, and the other pair for the car lighting.
If you use DCC you would only need one decoder for the whole train regardless of how much power you have in the consist.
Yes, LION knows that it is difficult to pick up a single four foot long -- six car consist.
Him builded some foam cradles 4' long for lifting, turning and moving the consist.
ROAR
The Route of the Broadway Lion The Largest Subway Layout in North Dakota.
Here there be cats. LIONS with CAMERAS
You'd need one giant decoder that probably wouldn;t fit to use a single decoder for a 6 car set of those subway cars, as I suspect the current draw of 6 of them exceeds the typical 1 amp limit for HO size decoders. You could still hook all the pickups together and use individual decoders and it would work the same way your DC wired together cars do.
ANd a decoder larger than a typical N scale one, to power 4-5 locos in an N scale consist, that fits in one powered loco? Not likely.. Stick one dummy in the middle and you might do it. But again, no need, jumper them all together the same way and they all will run until the last one crosses the final gaps.
rrinker Please tell me you have circuit breakers between those DB200's and the track. And still I wonder at multiple DB200's for an N scale layout. The slight price difference over a DB150 is almost a false economy - sure, 3 more amps for a few bucks more, but the power supplies for 8 amps are not common. 5 amp supplies are cheap as chips because they are common laptop power supplies. What are you using to power the DB200's? --Randy
Randy....all is well. I have a seperate Digitrax PS2012 power supply driving my command station as well as one for each of my boosters (DB200+). Track is fed thru multipl Digitrax PM42 (auto circuit breaker protection for each district) such that I have 12 power districts. One district is dedicated to driving the 90 SMAIL's I am using, two for reversing loops and the rest to drive the track. Any one district could have 8 - 10 loco's running at the same time in that district. Collectively, the 90 SMAIL (aka Tortoise) will draw about 1.5A. Also, if I did not have extra boosters in my layout, I would be faced with power buss runs over 30 feet and I did not want that added complication. Now none of my power busses exceed 20 feet.
In general, the 8A power is probably overkill but I prefer it that way.