Odd Problem

Agent Cobalt

This is probably an odd problem I have, but any help on it would be appreciated.

I am building a decent scale monorail system and need help with one aspect of the control system. The control system has your standard speed, braking, and other functions. Though I've sat and thought about and tried to come up with how to do this next aspect. At certain points on the beamway, there need to be transmitters that send a signal through the track. When a train is on the track, it blocks the signal. These transmitters correspond to locations on the beam called holdpoints. The holdpoints are located at certain numbers. The control panel needs a receiver that can tell how many (holdpoints) it is receiving.

Example: The red monorail is driving behind the blue monorail. If there are four transmitters between the trains, the red train will receive four signals because all of the signals ahead of the blue train are blocked by the blue train's presence. See attached.

So what I need to do is figure a way to send out the signals and a way for the train's control system to know how many are it can "see".
Essentially what this is, is a way to prevent collisions. It acts as a traffic control system.

This system is alot like the MAPO system that Walt Disney World uses for their monorails. (Only there isn't any more information, other than what I explained)

Any help that I can get would be appreciated. I know that this might be challenging because I can't think of anything and I've been pondering for over a week.

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Truth can be dangerous... Trust can be deadly.

Beau Schwabe

This may be a silly question, but are you using a DCC (Digital Command Control) track format?

If not, then perhaps you can design your own so that the trains communicate with each other as well as the control panel. Correct me if I am wrong, but I think the basic idea here is
for the trains to know the distance from one another based on the number of hold points between them.

Each train would take turns transmitting in a "round robin" fashion based on a specific train code. The control panel would basically be in the "round robin" loop as well to transmit
speed, direction, horn, lights, etc. back to the trains. Each hold point could have a unique id that corresponds to a specific segment(s) of track(s). The train passing over each hold
point would be able to obtain the train direction and "log" which hold point it has passed over. If another train runs over a hold point with the same track "segment signature", the logs
between the two (or more) trains could be compared and evaluated for a possible collision (rear end or head on). If a train enters a "new" segment of track, then the previous track
segments log would be cleared since the train would no longer be in that section of track.

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Beau Schwabe

IC Layout Engineer
Parallax, Inc.

Agent Cobalt

The hold points don't have a specific ID (to my knowledge) and all that I need is for the train to know how many holdpoints are it can see. If it sees anything more than 2, than the control system shows a green light. If it sees only 2, then it shows a yellow light and 1 or less and it goes to red and applies emergency brakes. The transmitters send their signal through the power line (DC power NOT AC). So what I need help figuring out is how to transmit through the line, how the train blocks signals, and how to receive (and count) signals.

As for a DCC track format, I've never heard of those before.

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Truth can be dangerous... Trust can be deadly.

Beau Schwabe

Agent Cobalt,

"The hold points don't have a specific ID (to my knowledge)".... No, you would need to do that so they would be unique to one another.

Since you are not using DCC this may actually be to your advantage. Reason I say this is because DCC track does not allow the trains
to communicate back to the controller ...instead, the controller only talks to the trains and other devices.

From your description though... "The transmitters send their signal through the power line (DC power NOT AC). " ...this sounds like DCC.

Try not to focus so much on blocking the signals, this can be done in software. Let me get back to you on this after I think about it some more....

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Beau Schwabe

IC Layout Engineer
Parallax, Inc.

Agent Cobalt

OK. I did a quick read on some DCC systems and it sounds as though the speed is controlled separately. On the monorail trains I'm making, the speed is controlled from the train. But I don't know the full extent of these DCC systems and such as I've never heard of them. So, I can't make any judgements as to whether it is DCC or not. And upon thinking about the holdpoints, you're right in that they must have a unique identifier.

The system is also supposedly called a Moving Blocklight System.

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Truth can be dangerous... Trust can be deadly.

Post Edited (Agent Cobalt) : 8/31/2005 4:50:00 AM GMT

Beau Schwabe

Agent Cobalt,

I need some more information here:

You said...
On the monorail trains I'm making, the speed is controlled from the train

Can you please explain this in more detail?

You said...
I am building a decent scale monorail system

What is "decent" ?
Can you ride in it yourself?
What voltages are involved?
How much current?


Also, what type of sensors are you currently using for the "hold points" ?



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Beau Schwabe

IC Layout Engineer
Parallax, Inc.

Agent Cobalt

When I am done with the monorail I will be able to ride in it myself. Not sure how much voltage and current I will be using because I still am debating about the motors I'm going to use for propulsion on the train. About the speed control, essentially what I'm going to have is a throttle with four or five different speed settings. I don't know what else to say about the speed control that you might need to know. Just for some information, I have started building the train but not the controls yet. The holdpoint trasmitters are always transmitting and they are doing so through the power line on the track. I asked a question about what they used at WDW and the response I got was as follows:

On the beamway at certain points there are transmitters. These MAPO transmitters send an electrical signal through the track. When a train is on the track, it blocks that signal. These transmitters correspond to locations on the beam called Holdpoints. The holdpoints are located at certain numbers, which must all be committed to memory (your memory, not the train's). Each train has a receiver that can tell how many of these signals it is receiveing. Say Monorail Red is driving behind Monorail Blue. If there are four transmitters between the trains, Red will only get four signals, because all the signals ahead of Blue are blocked by that train's presense. The MAPO system is also called the MBS (Moving Blocklight System).

I don't know if any of this helps and I do understand how hard it can be to take the sometimes minimal information you get and try to come up with a solution and I'd like to say thank you for taking your time to help me out here. I'm trying to give you the information you need to help me and just let me know if something else needs clarified or such. I'll do the best I can with what I've decided upon (for what to do about the train's propulsion) or from what I've read. Again, thanks.

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Truth can be dangerous... Trust can be deadly.

Post Edited (Agent Cobalt) : 8/31/2005 4:23:11 PM GMT

Beau Schwabe

You said...
The holdpoint trasmitters are always transmitting and they are doing so through the power line on the track

Do you have any specifics on these transmitters as far as how they are expected to operate?



Also, will·the track be a continuous loop or an end-of-line then switch direction format?



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Beau Schwabe

IC Layout Engineer
Parallax, Inc.

Don Buczynski

I am not familiar with the MAPO system that helps control the monorail at WDW. When I first started reading this thread I though about how this might be done using some type of transceiver·at the hold points and monorails in a distributed system. It is an interesting problem and I'll think about it some more.

Another way to do this is to use·a centralized block occupancy detection system. Referring to your diagram, the power being applied to each section of track between the hold points is isolated (in model railroads the rails are gapped) to prevent current flow into adjacent track sections. In this way,·a track·section receives power for the monorail only from·its main power feed. A·current detector circuit is wired in series with the section power feed.·When a monorail is present in a section, it is detected by the current it draws from the power feed and asserts a logic level. These logic levels can be·read as·Basic Stamp program inputs. Since each block of the track is well defined with respect to the others, the distance relationship between monorails is easily computed. From this result,·indicator lights, message transmission,·or power·control could be initiated·by the Basic Stamp code.

A Google search using "block occupancy detector" will return a number of links to off-the-shelf products that work with AC or DC track power.·The circuits may need to be scaled for the power levels you will be using. There are a number of good circuits at http://home.cogeco.ca/~rpaisley4/CircuitIndex.html#Current. Have a look at·my model railroad page "Block Signal" at the link below for some other ideas.

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Don Buczynski

http://www.buczynski.com

Post Edited (Don Buczynski) : 9/1/2005 2:19:20 PM GMT

Beau Schwabe

Agent Cobalt,

What I was thinking was that if you knew what the "protocol" was for the transmitters, you could mimic the same protocol and equip each train with the ability to "send" information down the track.

That said, you could modify the existing transmitter positions with RFID tags instead. As each train passes over the RFID tags, the trains can determine where they are and send that information
via the current transmitter technology down the track to the controller AND other trains. Knowing where each tag is in relation to the train, you can easily determine the number of tags between
each train.

I'm not sure what the range of Parallax's RFID tags are (speed of the train will also be a consideration) but you could apply the same principles to a larger RFID design if necessary.


You could even use something like a "barcode" that the train passes over instead of the RFID.·· ...There are several ways to get the track·position information to the train

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Beau Schwabe

IC Layout Engineer
Parallax, Inc.

Post Edited (Beau Schwabe (Parallax)) : 9/1/2005 2:40:27 PM GMT

Paul Baker

Beau Schwabe (Parallax) said...

I'm not sure what the range of Parallax's RFID tags are (speed of the train will also be a consideration) but you could apply the same principles to a larger RFID design if necessary.

I am concerned that RFID will not be able to react fast enough, since most RFID tags are parasitically powered by the electric field generated by the reader, by the time the chip is powered, it will be beyond the sensing range.

Instead, why not use a hall effect sensor on the train, then at each station have a series of (electro)magnets, the number of magnets and thier spacing will follow a huffman coding scheme in which all palendromic pairs are eliminated, (a code when read forwards matches another code when read backwards).·This should provide a more robust (and cheaper) solution to providing an ID to each hold point.·


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