Road Bridge

Would you take a work in progress? One span of the Cambridge Creek bridge model I'm in the process of scratch building for the RFC train garden, with the street lights and red navigation lights newly installed:

 

Here's the prototype, for comparison:

Already built in, George.

I have NC contact switches in the power feeds to the geared motor (you can *barely* hear them click at the limits in the video), one in each direction. Each is spanned by a diode that temporarily restores the feed when the direction switch reverses the polarity of the feed, until movement releases the open limit switch.

The net effect is that power will be cut whenever the bridge span is either fully down or fully up, and the motor will not be powered until the opposite direction is pressed on the control switch, in which case the diode on the 'open' limit switch will allow power to temporarily bypass the open contacts and reach the motor until the NC switch contacts make contact.

Instead of the momentary-contact DPDT control switch I used (a car window control replacement part), I considered (and could have used) a snap toggle instead, but I wanted the system at rest to default to "off", and be activated only when an observer was present and desiring to activate and control the animation.

The *real* fun will come when I fabricate the traffic control modules at each end of the bridge. I sourced some overhead traffic lights, and a pair of HO scale (to better match those on the prototype) slow-motion gate kits. The gate kits are a clever design, using two coils to snap a control rod back and forth, mediated by a damper that slows the actual speed transmitted to the gate's arm. It appears the kits are designed for momentary power applied to one coil or the other to initiate a change to the control arm position. This of course is not the same as the lights, which require continuous power to red or green.

My tentative plan is to use a delay module (similar to the one I earlier used for a trolley stop animation) to limit the time power is applied to the gate's coils, even when power is continuously applied to the lights. I'm still debating whether (or if!) I can integrate the traffic control modules with the bridge span animation. At this point, I'm leaning toward separate switches, leaving the coordination between traffic control animation (initiated first, and turned off after the bridge is closed) and the position of the bridge spans to the observer/operator -- hey, that's truer to the prototype! 

Thanks! Sorry, I do tend to go on a bit, especially when I'm in the middle of a project and still muddling through on the design (and re-design, and re-re-design . . . ).

Well, in the spirit of *almost* road bridges, how about "almost a bridge" -- a pier into a fishing pond?:



I scratch built this out of wood coffee stirrers purloined from the local coffee shop, and some small dowels, and modeled it (in shortened form) after our prototype pier out into Cattail Creek:

No road bridges or bridges at all for that matter on my layout. Some excellent examples shown on this thread. Good stuff!