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World Record LEGO Train Layout in Seattle
The Dev writes "The Pacific Northwest LEGO train club is attempting to break the world record for the longest LEGO train layout. They are setting up in the Seattle center right now, so you if you are in the area you might want to check it out.
There are of course some Pictures on Brickshelf and a live webcam at the PNLTC website.
The original announcement is here on Lugnet"
Finally something I can comment on with some degree of expertise! :)
Someone mentioned Mindstorms control of the layout. First off, Lego 9V train systems run off of a single power source controlled by what appears to be a crude stepped power supply (the 4548 Regulator). DC is fed into the entire track, and the Train Motor pack picks up that DC and drives its wheels. You can put as many packs as you like on the same track, but they'll all go forward and backwards at the same time because the entire track is electrified.
A Mindstorms RCX 1.0 could be used to power up these tracks in place of the 4548 and execute control on one of its motor ports. The other two ports could be used to drive cranes, scenery, gates etc or another isolated track system. That's kinda boring though.
The first option is to use what's called cab/block control. Fans of model trains (HO etc) will recognize this as powering on sections of track from a cab, or one power supply/regulator. So any given section of track could be fed separately by Cab A or Cab B, effectively meaning two motor packs are independently. As a train approachs a section of track, you power it up with the given Cab you are controlling, and unpower the section you're coming off of. But this means only one motor pack can be travelling within that section.
If you wanted to use Mindstorms to automate here, there's probably some cool application of using one motor to do the switching of block sections, and one output to power the track.
Another option is to isolate the motor pack from the track and power it solely using an onboard RCX. This has been tried by Matthew Bates and others. However, the draw of the motor pack soon drains the 1.0/1.5 RCX's six AA's. This would be one way to have a "ghost train" drive by itself without any connection to the 4548 powered track. You need to hack the motor to remove the pickups from the metal wheels.
A third, and much more elegant option is inband signalling, or DCC . Model train fans have long enjoyed the NMRA DCC (Digital Cab Control) standard, which sends a coded pulsewidth modulation signal along a powered common track. DCC motorpacks pick up power and pick up the control signal. When they get a command intended for itself, it powers the wheels. In effect, the track becomes a common bus where power and signal come from but the operation of the motors is dependent on the commands issued in the signal. What's also cool is that switches, scenery, etc can be latched into the track bus and controlled with automation or remotely.
Attempts have been made to put DCC into Lego trains-some experiments to isolate the track pickups/motors, then solder in a DCC decoder/controller into the pack have been successful. However, problems with voltage (9V vs normal 12V model train power) have hampered this. The cost is also hard to deal with-you're looking at least $400USD, when most people have tons of spare 4548's from trainsets.
There's also a lot of other cool stuff you can do with Mindstorms-using the IR, you can have a proximity to set something off (like gates on a road) and play a warning bell when a train nears. It's a $110USD track crossing, but... :)
--Calum