Subway track spark simulation

From the looks of it, might be one leg of an LED attached to ground, and the other leg close to the center rail (or connected to a wire going to the arm of a microswitch) where it can be momentarily pressed down by wheel flanges or pickup rollers, thus sending a brief burst of current to each LED.

---PCJ

What they are simulating is the third rail shoe coming off the third rail under load.  It is nicely done.  It appears that the flash occurs by a truck and only one per truck.  It is well thought out.  I do not know how this is being done, but it could be a minor truck mod to provide a contact to ground the LED once per truck.  If the trucks had sliding accessory shoes, these could be grounded to produce this effect.  

Based on his comment in the video, I think he is doing the following:

He notches the outer rail (two examples shown above) making tiny "islands".  When a truck rolls by, the metal wheels and axle conduct to complete the circuit to the LED(s).  The LED power supply could be just a recycled DC wall adapter, cellphone charger, or whatever.  Or track power could be used with a dollar or so of assorted parts like diodes and resistors.  I'd think 3mm LED would work fine...on eBay they run about 10 for $1 with free shipping.

If I understand your question, the notch in the track allows each wheel axle to become the "lever" (by analogy to a typical electrical switch) which completes the circuit to the LED.  It's hard to see from the video where he physically mounted the LEDs and he may have placed them in or under the gap created by a notch.  You might try asking him on youtube.

To your point, by notching the track you are breaking the electrical connection in the outer rail.  But the two outer rails are electrically connected elsewhere on your layout - probably in multiple places, at lock-ons, etc..  From the video, he says he did this on one 10" section of track as opposed to on his entire layout.  So IF the notches materially affected the performance he could have added wires (shown in purple) underneath his bed to provide outer rail continuity to the broken lower rail.  As suggested above, there are other methods which don't require notching - I'm simply taking your original question at face value and speculating on how the youtube version works (and quite well I think!).

What kind of track do you have?  One nice thing about 3mm LEDs is a 1/8" drill bit might be all you need to make mounting holes.

As for using track power, it can be as simple as the following.

The diode converts the AC to DC since LEDs run on DC.  The resistors limit the current to the LEDs.  The value of the resistor depends on what kind of track power you use (command, conventional).  If you use conventional the brightness of each LED will be proportional to track voltage which is probably not a big deal...or with some additional circuitry such as a voltage regulator you can take care of that too.  In any event, I'd think all the electrical parts would fit in the cavities underneath one track section if you use, say, MTH Realtrax.

I think the biggest hurdle is to take the mental leap of faith that this can be done!  I think it might take a few tries requiring some sacrificial track sections and there are some additional electrical details that need clarification but that's what the OGR forum is about!  There are several guys on the Electrical Forum who would also have ideas if you do choose to proceed.

Hi, Some time ago someone posted a similar sparking action I believe using a disposable camera flash.  The LED's are a lot simpler.  Real nice effect.    

You will get good results not using an LED, but a piezo-electric crystal, such as is used for igniting a gas range. This produces an actual spark.

I commented to the YouTube poster about the block occupancy design.  I think these are blinking LEDs.  The only problem is that the LEDs will blink continuously if the train stops in the block.

The youtube guy says he uses "flashing" LEDs.  You can get them for about 2-3x the price of regular non-flashing LEDs on eBay.  Hopefully he will provide additional info but I think he does this to somewhat randomize the simulated sparks so they don't all look the same.  That is, for a train going at some fixed speed each wheel will hover over an "island" for roughly the same amount of time meaning the flash will last the same.  Techniques such as different-sized islands, flashing LEDs, non-constant LED supply voltage, etc.. seem like possible candidates to vary each flash.  With a few more electrical parts, each LED could be made to flash just once when the wheel enters an island so there would be only one flash even if the axle stopped on the island.

The job in that video was very well done

cheers

Sorry for the late reply, I didn't know the link was to one of my videos. There are a lot of ways to do this I did the easy route. I use MTH realtrak but it can be done on any track system. Some experimenting will need to be done to get the effect you want. The LED's that I used cool white 1.8mm from Evans Designs. They are alittle prices but all of the wires, resistors, diodes, etc.. are already build in so that eliminates a lot of wiring plus they work with ac or dc power supply. I used a 10in track section MTH model #40-1029. http://www.mthtrains.com/content/40-1029

You can use any track you want but this one requires no cutting of the rail.

The track comes in two 5in sections that are cut down the middle to give you 4 sections at 2.5in in length which is about the size of one subway wheel truck. Removing the wire on the bottom of one of the outside rails will isolate that section of track from the rest of the system. That is where one wire from the led goes, the other is connected to the hot or center rail.

In this pic the top rail is isolated for the LED to flash when the train rolls over this section. Also more step may need to be taken to prevent the LED from lighting up at the wrong time or staying lit when the train has passed. In this case the copper clips that connect the track together are removed (only on the isolated rail and not the copper clips holding the white wire in the 2nd pic) and use small pieces of plastic or postcard to slide in between the rails to prevent contact. If you like real close you can see the plastic in between the joints. The LED is a 1.8mm flashing light and should fit in between the top and bottom of the rail. I moved the led out so you can see it. There are two downsides to this.

1. If you have other thing going on your layout, crossing gates, signal lights, a lot of switches and double crossovers. Adding some of these could mess with you DCS signal

if you are using DCS to run your trains.

2. If you stop the train and one of the wheels/truck is on the isolated track the LED will keep flashing. There are ways to prevent this but I didn't go through all the trouble because my trains only stop at stations.

Any track system can be used, You will either have to cut the rails or buy smaller track sections and isolate one rail on that section. I used this method on a O-31 1/2 curve.

I don't have the short track sections he used so after initially trying to cut an outer rail with a hacksaw, I gave up and used a bandsaw to cut from the edge to make two outer-rail isolated islands - I figure some putty and gray paint could touch up the bed if need be.  3mm cool-white LEDs are installed from the bottom through 1/8" holes.  With a diode attached to center-rail and 1 resistor per LED taking track power as previously diagrammed, here's a short video with a streetcar which is closest thing I have to a subway.

Have you "sparks" guys seen the Ace Trains "third rail" British electric loco with the built in 'spark' unit ?  See the video posted on 3/5/13. 

SZ

What does the value of the resistor have to be for the LED? idk what amount to get or how to figure out the right resistor

I feel a new project coming on!

Genius guys.  Awesome!

I've seen that one, it is a very neat effect.  It looks like they also used LEDS.

I couldn't find the 3/15/13 video mentioned above (does anyone have a link?) but I found the following which shows the Ace Trains E/17 "sparking".  The sparking starts midway at about 1:49 as shown on the video time-stamp in the photo below.

http://www.youtube.com/watch?v=BR90rJXt8yk

I pasted in a photo from the Ace Trains website showing the sparking unit on the underside of the trucks.  From the video, comparing the sparking "color" to the headlight color it looks like they used blue LEDs. 

If blue is your preferred color, "3mm blue LED" are the same cost (10 for $1) as white on eBay.  Same circuit.  Or a dab of clear-transparent blue paint could be applied over a white LED to add some blue to the flashes.  Animated garage-workshop dioramas often use a mix of LED colors (white, blue, orange) to simulate the welding sparking.