Any old time HO model railroaders out there?

[MarkF]

I have a question regarding a DC layout divided into blocks.
How are shorts avoided if a locomotive happens to stop spanning an isolated gap between two blocks?
Short circuiting the rail power drivers.  Assuming the polarity of the two blocks is reversed.



I have a single power supply with polarity (i.e. train direction) of each block done with relays.
The power to each block and block detection is performed by microcontrollers.  So, I have a lot of flexibility. 
But, I'm interested in how is was done before the era of DCC electronics.

[oPossum]

Reversing switches for adjacent blocks must be in the same position when transiting a block.

[SL4P]

The length of the isolation segment must be longer than a chord drawn across the perimeter of the wheel.
Then, the wheel can’t touch both track segments at the same time!

[MarkF]

Reversing switches for adjacent blocks must be in the same position when transiting a block.

Dah.
But mistakes happen.  Do you just rely on the current limiting in each block?
When the track is powered with DPDT switches, there is no current limiting.

In my case, track power to each block is limited to 2 amps to accommodate a consist having more than one locomotive connected together.

The length of the isolation segment must be longer than a chord drawn across the perimeter of the wheel.
Then, the wheel can’t touch both track segments at the same time!

We're not talking about just one wheel.  But, all wheels on the locomotive.

Note:  All the wheels on the left side of the locomotive are connected together and all the wheels on the right side are connected together.
(i.e. Distributed power pick-up on each side of locomotive.)

[CaptDon]

Sorry SL4P but not just 'the wheel' but ALL wheels of the locomotive. As for the next block being reverse polarity, this is goofy logic. If you are an old school H.O. railroader then your locomotive is D.C. powered and as soon as it transitioned into the reversed polarity block assuming it was moving at typical model railroad speeds of 500mph and made it through the short it was briefly creating it would immediately start trying to back up which would be useless but typical of how Norfolk Southern does business. There is one case where we do run into this problem for real, take the typical oval layout, install a pair of right-handed turnouts allowing your train to traverse across the oval and reverse direction. You have just created the perfect shorted circuit layout. You will have to make that crossover section as an 'isolated block' with the plastic insulator track couplers usually at both ends of the crossover. You then need a polarity switch (DPDT) and make the polarity agree when entering the block, then flip the switch and make the polarity agree while exiting the block. Back to the same old problem.....now your train will want to run backwards as it is going around the loop in the opposite direction so you must also flip the polarity of the entire layout!!! You can do this if you use your direction switch to actually operate a 4PDT relay, then everything will switch together. B.T.W., if you want to switch direction around the loop this time you will have to 'back' your train through the crossover.  Have fun, Cheers mate. Just go D.C.C. then old problems go away and hundreds of new ones show up!!!

[MarkF]

Have fun, Cheers mate.
Just go D.C.C. then old problems go away and hundreds of new ones show up!!!

DCC potentially has the same problem.
So, if the layout is powered with DPDT switches, it's the responsibility of the operator to insure the correct polarity of each block?  No safe guards?



However, I started designing computer automation prior to DCC becoming available.  Back then, my problem was that my Apple ][ was not fast enough.  Today, the layout has distributed PIC microcontrollers for automated control with custom wireless hand throttles.


The whole reason against DCC is because I wanted to use a powered Gandy Dancer:

[oPossum]

Reversing switches for adjacent blocks must be in the same position when transiting a block.

Dah.
But mistakes happen. 

Don't make mistakes. If the transformer hums you screwed up. If the transformer smokes you f-k-d up.

[MarkF]

Just a short layout description while I'm here:

Currently, my test track is an inner loop and an output loop connected by a cross-over.  I've the test track operational but foresee some issues for the larger layout.  I'm using nRF24L01+ modules for the wireless throttles and need to resolve conflicts if two throttles try to control the same track block.  Currently, both throttles are locked out until the conflict is resolved (not ideal).  The other issue is this short circuit possibility.  All seems to be okay when it happens but wish I had a better solution.  Worse comes to worse, I can lock it out in software but my blocks are pretty large.

Route planning is still a BIG issue that I need to work out.

I have most of the benchwork finished for the actual layout (but I keep changing it....).  I believe it currently is divided into 17 blocks.  Each square is 6 inches.

[Domagoj T]

Sounds like going digital would solve all your issues.
Seriously DCC is not that expensive. In fact, it may even be cheaper since you can get rid of (almost) all the electronics for blocks.

[MarkF]

Sounds like going digital would solve all your issues.
Seriously DCC is not that expensive. In fact, it may even be cheaper since you can get rid of (almost) all the electronics for blocks.

Did you miss this statement?   
   "The whole reason against DCC is because I wanted to use a powered Gandy Dancer"

I'll change when you can get a DCC decoder in one of these:

   


Plus the majority of all the DCC hand throttles are wired.  A big deal breaker for me.
I want to be able to walk around the layout and not be dragging a wire around.

[CaptDon]

One interesting thing with the Bachman D.C.C. stuff is the ability to run older analog D.C. locomotives on the same layout at the same time as your D.C.C. stuff. I have some old original AHM New Haven Fairbanks Morse C-Liners, A's and B's which I run along with my CSX GP-35 D.C.C. stuff. Not in the same consist, but on the same track at the same time in different blocks of course. Those AHM's sound a bit angry with the variable duty cycle A.C. across the motors but the motors have enough self inductance to not burn up and they actually do run smooth when set in motion. Also the cool thing about that A.C. on the track is that the lights stay on in the New Haven passenger cars even if the C-Liners are sitting still. B.T.W., the voice on the Bachman DVD's is radio personality Dennis John Cahill whom I worked with in York Pa. years ago. Nice guy, total trainiac!!

[MarkF]

Each one of my blocks has its power generated from its own DAC. So I can have any waveform I like. For startup and slow speed, I'm generating a 80Hz PWM waveform with 128 steps. For higher speeds, I output a constant DC voltage.

Then, each block power driver has a relay for direction, does current limiting to 2A and performs block detection which is returned to the master host computer.

By the way CaptDon, I'm originally from central PA myself. Been through York many times.

[Kleinstein]

My model-railway experience is with a center rail system, so I never had these odd problems.

To avoid the problem with the possible short when a locomotive goes from 1 block to the next one could have the block in front on the locomotive floating and only connect when the locomotive brings the power in. This may need more and smaller blocks and more than just simple reversing relays as the blocks have an additional off state. As a side effect this should reduce the chance to get a collision.

[MarkF]

My model-railway experience is with a center rail system, so I never had these odd problems.

To avoid the problem with the possible short when a locomotive goes from 1 block to the next one could have the block in front on the locomotive floating and only connect when the locomotive brings the power in. This may need more and smaller blocks and more than just simple reversing relays as the blocks have an additional off state. As a side effect this should reduce the chance to get a collision.

Some of my thoughts exactly.  (i.e. Block signals on real railroads.)  Reducing the block sizes is something I haven't give a lot of thought to.  The current hardware design can support up to 30 blocks.  Through software, I can enforce the block in front and the block in back of the currently active one to be off.

I'm gathering from the conversation that for DC layouts with blocks, the possibility of short circuits was just ignored.  Relying totally on the operator.  I've never had a HO power pack and don't know if they even have current limiting built-in.  When I was a kid, we had a 3 rail Lionel train set and enjoyed seeing the locomotives flying off the tracks in the curves.  Go Gomez Addams and the Adams Family!   

[CaptDon]

That's why I made the comment "Typical model railroad speeds of 500mph". Most of my friends and I started putting side boards on the train tables to keep expensive rolling stock from targeting the floor. WSBA AM910 and WARM 103.3 FM. 13 years originally Susquehanna Pfaltzgraf Corporation but later Susquehanna Broadcasting Company. Now owned by Cume-ing-Less!!!! They suck royally. Got rid of all the really great people and replaced them with satellite feeds!! Spouting the same forgettable dribble nationwide. They took ZZ-Top literally, We're Bad, We're nationwide, that about sums up Cumulus offerings.

[Domagoj T]

Did you miss this statement?   
   "The whole reason against DCC is because I wanted to use a powered Gandy Dancer"

I'll change when you can get a DCC decoder in one of these:

   


Plus the majority of all the DCC hand throttles are wired.  A big deal breaker for me.
I want to be able to walk around the layout and not be dragging a wire around.

Some of these look like they would fit.
https://www.coastaldcc.co.uk/products/decoders/z-gauge/

As for controllers, there are wireless ones. For example, this one from Roco:
https://www.roco.cc/en/product/235722-wlan-0-0-0-0-0-004001-0/products.html

But since you're not shying away from custom DIY controllers, there're are plenty of resources for Raspberry Pi and Arduino based controllers, which can of course be wireless.
https://dccwiki.com/Do_It_Yourself

[MarkF]

Current wireless throttle design operating the test track: