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Hon1nbo

Fri Aug 14 2009, 05:27PM

Registered Member #902 Joined: Sun Jul 15 2007, 08:17PM
Location: Pacific Northwest USA
Posts: 1042

hey, I have an interesting challenge for our homecoming dance: build a secret entrance way for the Senior Lounge (the theme is Super heroes, so it is fitting)
it is going to be opened by flipping up a bust of Shakespeare and pressing a button

my current design, to stress simplicity and safety in case it has to act as an exit for Fire Code, is to have the sliding door spring loaded, using springs that aren't going to slam open the door, to do the opening and have the button simply release a latch that allows the door to open, then it would be closed by hand once on the other side

since the door would stay opened, it would not violate fire code (it would apply as a locked exit door, like the kind with an EXIT button next to it)

however, since it is more than likely not going to take up a required exit, we would like to make it more like a true secret door that would be able to close automatically but we don't want to make it too complicated as myself and possibly one other person on the build are the only ones very knowledgeable about anything like this

preferably it should only have at most one motor, but I do not know how to make that work so if two are required it would not be too much of a problem

any ideas? - it has to be pretty fool proof, and it can't cost us much

thanks, Jimmy

Renesis

Sun Aug 16 2009, 12:24AM

Registered Member #2028 Joined: Mon Mar 16 2009, 08:13PM
Location: Norway
Posts: 319

Heh, sounds like fun.

I have an idea for a simple design. You just attach a bookshelf to a normal hinged door, so that when you open the door, the bookshelf follows with it. Then hide the handle behind some hollowed-out-and-glued-together books. It should be feasible, the question might be wether the hinges can handle the load.

If you want a slightly more fancy system, then may i suggest pneumatics? Pneumatic components are relatively cheap, and pneumatic systems are virtually fool-proof. By using spring returned sylinders and unistable valves it would not violate fire code. Use the spring to open the door, and air to shut it. If you then loose the line pressure or the electricity blacks out, the door would open automagically.

The other great advantage with pneumatics is that you dont really need any electronic control circuitry, the opening switch and closing timer can be fully pneumatic. Here's a quick example of such a control circuit. Adding a 3/2-way valve on the supply line would function as an emergency cut-off, leaving the door open. The two chokes on the line between the valve and the cylinder act as speed control, one for opening and one for closing. The third choke controls the closing time.

Disadvantages are noise, you dont want any loud venting sounds at a dance. This should not be a problem if the valves are located outside, or in a insulated box. And of course, you need that darned noisy compressor.

Edit: If you settle with a motorized system, should there be a sensor that registers if anyone is passing through the door while it is closing? It would be kinda bad if anyone got "bitten"... The first thing that comes to my mind is industrial proximity sensors or optical sensors, or one of those pneumatic bellows used on motorized garage doors.

Hon1nbo

Sun Aug 16 2009, 01:30AM

Registered Member #902 Joined: Sun Jul 15 2007, 08:17PM
Location: Pacific Northwest USA
Posts: 1042

it turns out that the door will not take up a normal exit, one of the planners made a mistake when giving me the details
a pneumatic system would be nice, but it would be noisy and I don't know if I can get the parts to move a bookcase cheaply
I thought about a screw drive system, but main issue is making it move fast enough

as for control, we all want to use the button hidden under the bust of Shakespeare, and it turns out that people are fine closing it by hand afterwards

the spring/counterweight design I originally posted would be perfect, if it weren't for the fact that the bookshelf might be too heavy to make pulling it back easy - maybe with a neutral counterweight, a drill could power a screw system?

Renesis

Sun Aug 16 2009, 02:45AM

Registered Member #2028 Joined: Mon Mar 16 2009, 08:13PM
Location: Norway
Posts: 319

and it turns out that people are fine closing it by hand afterwards

That makes things a lot easier. If you can cook up a clever spring/counterweightsystem, you might not need any motors at all.

Could you place the bookcase on wheels? If the bookcase had hard nylon wheels rolling on some sort of metal rails, then moving it shouldnt be too difficult. If you could motorize those wheels too then problem solved

And as for the latch you were talking about, how about swapping it with an electromagnet? It could be powered directly from the switch under the bust, it doesent get much simpler than that.

Hon1nbo

Sun Aug 16 2009, 04:21AM

Registered Member #902 Joined: Sun Jul 15 2007, 08:17PM
Location: Pacific Northwest USA
Posts: 1042

well, an electromagnet would require power constantly except when the door is opening, and it would have to have a decent strength for the job and i don't want to have to buy one

the latch is simply a solenoid controlled bolt (I say bolt, but I mean more like the bolt in a knob rather than a deadbolt) - it doesn't need much power, and it only is powered when the button is pushed

aonomus

Sun Aug 16 2009, 04:56AM

Registered Member #1497 Joined: Thu May 22 2008, 05:24AM
Location: Toronto, Ontario, Canada
Posts: 801

If you used a conventional electric door strike, some of which had fail-safe/fail-secure option settings, you could put the entire book case on caster wheels and use guides to make sure it stays straight, then use some sort of counter weight just to get the door moving.

If its all decorative, the books can be foam, lightening the entire book case, therefore making the counterweight relatively light. If you lose power, the door strike fails open, and the door would slide open. Note that you would have to rotate the strike to match the direction of door travel.

Hon1nbo

Sun Aug 16 2009, 05:01AM

Registered Member #902 Joined: Sun Jul 15 2007, 08:17PM
Location: Pacific Northwest USA
Posts: 1042

the main issue with the counterweight design is making sure that it is relatively easy to pull back the door by hand - we would have to hollow out real books, and likely text books because some people in the class want to have all of the textbooks we used at our seven years in the school on the shelf, and they aren't cheap to replace!

Bored Chemist

Sun Aug 16 2009, 08:31AM

Registered Member #193 Joined: Fri Feb 17 2006, 07:04AM
Location: sheffield
Posts: 1022

Could you use a suitably creased photo of a bookshelf rather than real books?
Cheaper and lighter.

Hon1nbo

Sun Sept 27 2009, 08:34PM

Registered Member #902 Joined: Sun Jul 15 2007, 08:17PM
Location: Pacific Northwest USA
Posts: 1042

we had our dance last night, and the door was a smashing success! - people lined up just to try the door, they didn't care what was on the other side (of course my class did because our lounge was on the other side lol)
we went with bookcase wallpaper because it was available, and while we could have done a real book case we had to make use of the panels already there and they would have been too flimsy to support it
I use a motor with some basic gears going to a rubber wheel, entire motor assembly was purchased at a surplus store for $7 - it was driven by a 12VDC Wall Wart that was controlled by the bust of Shakespeare. We were going to make our own bust, but someone found one online that uses 120VAC so they bought it to save time. Also, since we had to install this the day of the dance being a thing for only seniors, I ran out of time to make a button that will close the door but the wheel and motor did not stop anyone from closing it by hand

also it looks like the door was not flush with its surroundings in the images, but it really was - these were taken after they started tearing down the dance stuff and the door stopped becoming flush with the wall, likely due to a shift in the adjoining frame

photos:

Proud Mary

Sun Sept 27 2009, 10:27PM

Registered Member #543 Joined: Tue Feb 20 2007, 04:26PM
Location: UK
Posts: 4992

Hey, what fun! Glad that you had a good time!

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