can large accessory doors be opened automatically

Radio control airplanes, boats, etc. use small activators that could easily be adapted to the activity you describe. Seems to me that there would be adequate room in the "attic" of structures to install the needed drives, rods and bell cranks.

Check it out at your local RC shop - I'd bet they have some used equipment that would be reasonable in cost, plus the knowledge, bits and pieces to help you get where you want to go.

If you have the room should be able rig a servo motor and a linkage.  Servo's aren't microscopic but they are used all the time in the model aircraft hobby to control the flaps so there not that big either.  If you local hobby shop does planes as well as trains ask them to show some.

I used an RC servo in my Tie-Jector TMCC conversion to activate the mechanical tie dropping mechanism.  You could do a similar thing to move all sorts of stuff for accessories.  The servos are surprisingly powerful, even in small sizes.

I remember seeing an article in CTT a couple of years ago where someone rigged a bell crank and linkage to open 2 gates in a fence. It was very simple to build and install.

Chris

LVHR

I seem to remember a G gauge engine shed that was spring loaded open, when you pulled an engine into the shed the engine would push on a bar and pull the doors closed behind it. 

For inspiration, you might wish to look at some of the HO engine sheds by companies such as Faller. Many of these have built-in door opening mechanisms. Some are purely mechanical using rods and springs (As mentioned by Clem K above.), others use motors and contact switches, and some use servos and electronic controllers. It may even be worth buying such a kit, purely for the door mechanism of your choice. 

On Lionel's Lionelville Firehouse accessory, the doors automatically open when activated. The last time I looked underneath, it appeared that there was at least a motor and gear box set up that opened and closed the doors.

As DaveP and others have stated there are building you can buy that have opening doors - one of these might do, modified, for your needs.  Two other options are:

1) Many people have some old remote control turnouts (switches).  These have a solenoid or other actuator that switches the turnout.  You could remove that and use it to power an actuator arm built onto the door to open and close it.

2) The photo below is of an Autochron Automatic Light Switch Timer.  Unlike most light timers, this mounts onto an existing light switch and actually flips the switch - it has a motor driven mechanism inside powered by batteries that generates enough forcd to flip a standard wall-mount light switch. While it has a timer, that can be turned off and the unit operated by the On and Off buttons shown.  It would be easy to remove the motor driven mecchanism from inside it and use thatto open or close a doorfrom inside your building, while running wires to the rest of the unit at your control position so you can use theswitches - the advantage the autochron has is much more power than the solenoid in a typical turnout -- it would oepn quite a large/stubborn door.

Here's what I use: Futaba S3115 High Torque Micro Servo

You can also get neat sheathed cables to allow mounting the servo remotely.  There are larger ones as well which offer greater travel and even more torque.

One sticking point with these servos is you need to generate the PWM stream to position them.  No problem for the electronically inclined, but that may be a problem for some.

There was recently (within the last couple issues) an issue of Model Railroader with an article about adding a device to open and close a fence gate like one would find on a gated roadway or switch siding for an industry. I can't remember if it was manual or automated but if nothing else it will assist you in designing the linkage to the servo or whatever device you use.

GRJ  what is a PWM ??

PWM = Pulse Width Modulate = A modified square wave is needed to run servo motors where the width of the 'square' determines the angle of the servo. My definition maybe too simplistic, but you need a little electronics background to run one of these. They won't work off of straight DC.

Regards,

It requires a little electronics, but not too much.  I needed two positions in my previous project, so I just did it with a 555 timer chip with the change triggered by the smoke output of an ERR MiniCommander that was also running the unit.  Probably for any future ones I'd do them with one of the small Arduino processors, very simple program and just a few wires.