Has anyone tried using the track as a points switch. I reckon if around an inch on one rail were insulated from the rest and connected to the points motor, and a slightly longer section connected to the common switch motor supply the points could be switched by an approaching train. Obviously needs there to be a decent wheel base, but wondering if it is possible?

Isn't there an issue with point motors normally being AC and the track DC quest:

Or have I got the wrong end of the stick.

Ed

I think one can overlay the other so long as they are different circuits.

David

No - it won't work.  Assuming it's DC then the amount of power fed to the rails will be small - enough to drive the engine at the selected speed.  Quite simply this won't fire the point motor, and even if it did it would take all the power and cause the loco to stop immediately with its wheels still in the gap.  The point motor will thus remain powered continuously until you intervene - probably with a fire extinguisher!

Reed switch might work though.

Ed

You could try a flange operated microswitch to switch the point, and then another on the switched line to turn it back again after the train has passed. The problem would be that all the wheels of the train would operate the point. As Ed suggested, a reed switch operated by a magnet in the last vehicle of the train would do the trick, and that could also be used to return the point to normal afterwards. Another advantage of trying that is that if you want the train to change the points you put a magnet on the end, if you don't leave it off.

I tend to use point motors - does that make me a Luddite ...........? :roll::roll:

It can be done but takes two isolated sections of rail, far enough apart for the longest train that would be run but requires ideally a CDU and the use of common return. To do common return, one must know that each power supply used has to be an independent supply.
You could use IRDOTs in place of isolated sections of rails , that overcomes common return concerns, but I am not sure if the IRDOT relays would like the heavy load of solenoid coils - usually 3-4 amps whether DC or AC.

Thanks for the comments. It will be the new year before I have time to experiment. I must admit the more I think about it the less sure I think using the loco chassis as a switch will work - but still intend having a go.

David

I think you could neon to something. I'm not sure what yet but I am thinking the loco's wheels bridging a gap just prior to the point. This triggers some kind of switch which in turn changes the point over.

The switch that is triggered would have some kind of time delay to stop it being activated by subsequent sets of wheels from the same loco. A couple of seconds would be enough to let the loco clear the points.

This may work on routes where loco's only travel in one direction like a dedicated up line or down line. There again, I may be waffling complete rubbish.

Might be something to work on if you have the head for electronic gizmos.

Maybe not .

Cheers

Toto.

But how would you stop the wheels of each piece of rolling stock its pulling also switching the points? assuming the stock all has metal wheels

Some kind of time delay. It would have to be capable of allowing the initial switching to take place but prevent another activation for say 5 seconds or as long as it takes the train to clear the points. Or……..and this may be complete pie in the sky but if you could have some kind of gizzmo on the very last axle of your train, perhaps this could switch over again by somehow operating on some kind of reversed polarity basis.

Tell me if I'm one slate short of a tiled roof.

Toto

This may do the trick
redirect to IRDOT-3D
    To change polarity    
   Useful for allowing trains to run non stop around DCC reverse loop

Aha,

I've not lost the plot after all. I would still need to get my head round it totally but the actual theory is there.

That's a step forward.

Cheers

Toto

Just had a nostalgia attack and it may be totally irrelevant, but anyone remember that old Triang (or maybe Hornby) train set where a helicopter took of from a flatbed well truck when it passed some sort of trackside switch quest:

I did have the old operating mail coach which I seem to remember had to have a couple of trackside levers/switches which had to be placed a certain distance from the pickup/drop off points, but the details are lost in the mists of time.

We're all thinking electronics and was just wondering if this could be done with some sort of trackside switch just operating a point motor as Petermac said.

I'm thinking from David's OP we're talking trams and not long trains.


Ed

I thought the challenge was for auto point operation,the idea being a switch less system using the loco as the switch.

Might be wrong, back to the original post me thinks.

Toto

Could not the IRDOT 3D (see Sol's link) be used to switch points the same way it can switch two aspect signals ?? If the IRDOT can be powered by 16v, that is enough power to switch Peco solenoid point motors. Maybe a set-up of two IRDOTs could be used, one to detect the train and bring it to a halt for say 24 seconds and the second to switch the points for a period of say 18 seconds, allowing a train to pass before resetting the points, just before the timer on the first IRDOT has lapsed, sending the stationary train back on its way. Just a thought…

Cheers, Gary.

Going back to the reed switch idea have a look at these:

http://www.maplin.co.uk/p/assemtech-miniature-reed-switch-no-cl38r

These could be buried in the track bed and operated by a magnet on the train/tram or whatever.

Hi,

I've never used reed switches before so would have to get my head around the principle of how they actual work/ operate. I think between that and the IRDOT gizzmo that Sol highlighted, there would be a solution and a reliable one at that.

I need to do a bit more reading on both to see which would be easiest.;-:hmm

Cheers

Toto

A reed switch is just a switch operated by a magnetic field, so you would have a small magnet on the loco which would (via some system) switch the points and then another switch a distance after the point could switch it back.

I picked up a simple diesel horn system where you put reed switches at positions around the layout and when the loco with the magnet passes the switch it triggers the system to sound a horn.