Inspired by the LEGO Movie set 70802 - Bad Cop's Pursuit with the collapsing train bridge section. LDD file included!
About this creation
This bridge was inspired by set 70802 - Bad Cop's Pursuit, (link to that set on Bricklink: www.bricklink.com/catalogItem.asp?S=70802-1 ) and the short section of railroad bridge included with that set. When I first saw it, I thought it would make a great play feature for a train bridge that is actually usable by trains!
Anyway, here is the result of all that working and reworking: 12 sections of PF / RC train track (It won't work with 9V, sorry!) with 1 section of old 4.5V straight track plus 2 studs of space to separate the moving from non-moving items and allow the hinge to do it's job.
The design of the bridge is modular so that you can easily disassemble the bridge for transport. It disassembles into 2 lower ramp sections consisting of 4 tracks each, 2 upper ramp sections, and 1 "failure point" module consisting of two identical pieces of moving track hinged into 1 regular non-moving track piece. This last module sits on a 16 x 32 base plate to keep it all connected, as that is the only thing holding both collapsible sections next to each other.
The track leading up to the "failure point" as I call it, is raised ever so gently at an angle of (at most) 1 1/3 bricks high per 1 section of track. (The angle of ascent / descent depends on which part of track you are on, but for the most part it's consistent.)
The bridge when the track is safe to cross: the pins are inserted and it should be stable. Naturally, a very heavy engine will snap the Technic rods in half, breaking the bridge permanently. Thus you can only use this engine with Small engines like my 2-6-0 + it's consist, (AKA the Lone Ranger train) the My Own Train series engines, or something of comparable weight.
I don't think putting a articulated such as a Union Pacific "Big Boy" or even a non articulated Pennsylvania "T1" would look very good on this bridge, as these (among other large types) are longer than the bridge gap itself.
This is how it works:
Their is a hidden Technic rod under the track that should allow trains to pass by safely overhead. Pull the two red Technic connectors (one for each side of the bridge) and your bridge collapses. Move the rod back in to reset the bridge for the next time.