Two rail automatic stop / start for streetcars

[bill937ca]

This is an automatic start and stop system for trams using Tomix tracks.  The Bachmann trolleys are noisy and cheap.

<a href="http://www.youtube.com/v/l2_Aj3GR1xw" target="_blank">http://www.youtube.com/v/l2_Aj3GR1xw</a>

The accompanying article on remote automatic stop and start operation.

[Hobby Dreamer]

Thanks Bill...

Clever!  It would have looked so much better at slow speed! At those speeds I'd rather just buy a Scalextric slot car set

Rick

[IST]

Thanks for the link, although I am quite stupid to understand how is this working. :-(
It would be great to implement something like this in my Unitram roundy-roundy.

[cteno4]

basically you isolate a couple of bits of track separated by a short stretch and the isolated bits are wired together. the first bit is short enough that the car always has a truck in the non isolated track so it can run thru the section. then the second bit of isolated track is long enough that the car loosed power from both trucks and it stops. then when the next tram  tram pulls up behind it and hits the first short bit of isolated track it acts as a bridge (thru the cars two trucks of wheel pickups and the motor) to supply the short isolated bit of track power and thus thru the jumper powers the second isolated bit of track. this then makes the stopped tram run off the bit of second isolated track and behind it the other tram enters the isolated track and stops, waiting for another tram to pull up behind it.

you have to be careful that you have the lengths of isolated track set up just so it will be the one truck powered in the first bit, but long enough to give you power long enough to run the other tram off the second isolated track and the second isolated track long enough to stop the tram but short enough to have the tram get off from the power burst from the first short isolated section. takes some fiddling. might be hard to do this with unitram as you would need to potentially gap the track at non unitram lengths.

also an issue as its an off/on situation so you go from running speed to no power so pretty abrupt stops. also since bits are only one truck powered situations, dirty track can cause more issues, thats why i think he speeded up his trams in the video, momentum will carry you past dirty spots, but you get the insane speeds! in theory this should work at about any speed as the speed should cancel out for the two distances you need to be providing power from the short isolated track to the longer isolated track. in reality the start/stop acceleration/deceleration differences will throw this a bit but should be controllable.

also it does get you a tad of slow acceleration/deceleration as when the bridge occurs now track power is being shared by two motors so you will see a decrease in speed in the one running and the one starting up will be starting up with partial power before going to full power when the second tram behind it stops. would be interesting seeing it at more realistic tram speeds, but the two train at once speed would need to be the minimum to get smooth, non pausing running in the one truck section.

note the distance between the short and the long isolated tracks can be what you want. that way trains can be more separated if you have the room for that.

the main problem with unitram would be isolating the proper lengths of rail. with exposed rail you could just saw a gap where needed with a razor saw or dremel disc cutter. i cant remember can you pull the track out of unitram easily to get clean access to the rail? you could work out your distances (depends on the lengths of trams used) on regular track before tearing into the unitram!

cheers

jeff

[CaptOblivious]

That is amazingly clever. Looks like it could be used with DCC too, if you want smoother starts and stops.

[cteno4]

Capt

How would doing this with dcc make the starts and stops smoother?

Jeff

[KenS]

My first thought was "that's a bad idea".  Generally power loss is something to avoid with a DCC decoder since it can cause them to go through a restart process.  But in this case, that should only happen for the tram that's already stopped, which shouldn't be an issue.  However, doing the same thing with a sound decoder could be another matter, as sound decoders can run through a set of "start up sounds" when power is first applied, which might not be appropriate for a train in a station starting to move.  Still, for a non-sound decoder, I'd think this approach would work okay for a DCC decoder.

I'd guess he's thinking about momentum settings causing the stopped tram to start more gently.  They won't help with the stopping; only a flywheel would help there.  Back EMF might also help keep the train in the trigger section maintain speed as the track voltage changes.  Did I miss anything Capt?

[CaptOblivious]

I think Ken has nailed the pros and cons of using this technique with DCC. Wasn't thinking that of course cutting the power would still bring it to a cold stop, without a flywheel or capacitor in place. Not perfect, but it would work.

[cteno4]

ok thats what i was wondering if the decoder would remember the speed it was set for before loosing power and use its momentum settings to get up to that speed smoothly. the stop i could not see being smooth with dcc as it would loose power just like dc would.

i would be interested to see how this would work with dc going at more trolly speeds to see if the power off would look quite so abrupt and the power on would be a bit gentler as its happening with two trains powered. of course the train in motion at slower speeds might also have a momentary slow down when its bridging the short section to power up the stopped train.

might try to mock this up with some untrak and insulated joiners and see. it is a cheap and cute way to have multiple trams on a single line mini display layout! would work well with a scene that obscures the whole loop some so that you get lots of trams popping in and out and possibly the stops more isolated so you dont realize how one tram is effecting the other.

i just started noodling on how this could be done with a double track station with spring points and reversing the polarity of one of the trams so they would be a single line and pass at the stations. joe price had some interesting ideas with this reversed motor idea and im wondering if the gapped rail might also figure into that in a cool way.

jeff