Thanks for all your thoughts about my kooky idea of the diode separation of the motor leads to deal with an aspect of track polarity. I currently use mag reed switches with thin wires to trigger signals at the tunnel entrances where the train passes from the library to the living room or vice versa depending on track polarity, of course. Although I'm not fond of these wires, they are hidden under the ties and only run 2' out into the room. All the signal wiring and relays are permanent and hidden in the bookcases and the short lengths of wires just get coiled back up and put away after the 'season' ends I'm using security alarm reed switches and they don't reliably trip the relays even with a super magnet glued under the loco. I'd love to know some of the sources that you use as well as your favorite mini pin plugs. Recently fried my cab control as a result of a hidden short in a 1/8' radio shack phono jack that was defective when bought. Later checked and found several others that were bad right out of the package.
To give you an idea of how my poor brain seems to have the need to come up with solutions and thus create problems where none exist without my intervention, let me digress. Inside the tunnel off the library is a short hard rock mining spur, lighted with yellow christmas tree LEDs and taking track power from that point which then runs through a diode rectifier bridge so the miners (three lil fellas with pic, jackhammer and shovel) can keep on working regardless of the train direction. The spur is only 10" long and has some code 210 track laid with 1 3/16ths inch gage at the tunnel mouth to a 7/8ths inch gage at the back to heighten the perspective illusion. My mine car will run back and forth on this track with a timer to keep the grandkids entertained. The wheels are brass knurled 10-31 knob/nuts with a turned groove that gives me a wheel with a flange on both sides of the rail. The mine manager told me that the cars came from an abandoned claim nearby where the cars ran on timber as it was a low budget operation run by some dudes that had previously hauled logs in Virginia back in the '80's. Anyhoo, the variable gage issue required brass tube and rod so that the axels can 'grow' and they come forward or 'shrink' as they retreat back for another load of ore. This part works great so far, but haven't devised the back and forth power mechanism yet. I'm open to suggestions.
It was soldering up the diodes for the mine lights that triggered the engine wiring idea. When I build my GG 1, I'll try this out just for giggles and see what happens. As Herb already suggested, I had planned on making two saw cuts through the track 6.35 mm apart (you know who you are out there) to avoid the dead short as the train ran across. With a small DTDT slide switch hidden in the ties, I would have the ability to restore power across the gap in case this section of track needed to be used in some other location later on.
P.S.--Thanks for the mike cable idea Si, I'll make sure to check that out. I'm also thinking of getting the tools to add plugs and jacks to US telephone wire for low power triggering as it's flat flexible, brown and small.
Thanks, but the cellar door misses the back if the mine shaft by 2 1/2" (or 63.5 of those 'other' measurements for you who deal with such things). You're right that a rod would be nice as with guides, it could keep the car body centered over the wheels. I need about 10" of movement and so the rod is out. A heavily weathered and greasy wheel between the tracks with a cable drawing the car out of the mine shaft could accomplish the same effect. Other pulleys could route the cable to an area where the lines could be attached to a lever (a segment, so to speak, of a wheel). The advantage could be slower startups and slowdowns at each end which would have a nice prototype action. The lever, or wheel (a grooved wheel or pulley with ends attached at opposite points on the wheel) could trip a micro switch stopping rotation and a timer would restart rotation for the return trip. The problem with a lever is the changing length of the cable. The good news is that you don't need to reverse rotation to reverse the direction of the car. One half pi D to get a 10" movement gives us a wheel diameter of 6 3/8" which would be doable space wise, but it means reversing motor direction which is no biggie for a Circuitron AC 2, but at $50 makes a lever with a 555 timer more attractive.
Thoughts plz, guys and should we move this to a minimg thread?