Star Trek Doors

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My sister and brother-in-law have an unusual house. Its layout includes a living area, and then a series of unheated areas, an attached garage, a workshop, and finally a heated studio space. You literally have to open, walk through, and then close, a dozen doors to get from one end of the place to the other, which is not easy to do with your hands full.

As a big Star Trek fan, my brother-in-law always thought it would be pretty cool to have fast automatic doors, just like on the star ship ENTERPRISE. The ideal location for this would be between the garage and the workshop. Not only would they be hands-free, but the automatic closing feature would be good to keep the heat in the workshop in the cold Wisconsin winters.

So, we started putting together the materials and skills needed to build fully automatic Star Trek style doors.

We found a pair of 24″ dual-acting air cylinders for $25 each at a surplus store. Air power seems like the best choice for fast doors, and the sound they make is very similar to what was always on the television show. To go with the cylinders, I mail ordered a 5-port air valve that runs 12V DC power. By connecting air to this valve, and its two outputs to both ends of the air cylinders, the cylinders can be driven either open or closed using 12V and a switch.

Next, I started playing around with sensors. What I really wanted was for a relay to open or close based on some sort of electric eye. I originally thought that perhaps a repurposed  safety sensor from an automatic garage door opener might work, but when I did some research, it turns out that those things are actually surprisingly complicated. (They send both power and signal over just two wires!)
Instead, I found that a person could buy cheap relay boards with sensors already on them for $5-$10 (Tons of these neat gadgets on Amazon and e-Bay.)

Knowing that I would want the doors to automatically open AND THEN STAY OPEN FOR A FEW SECONDS, I ordered a light-sensor relay AND a time delay relay. By wiring them together and then to the air valve, I had a way to open the air cylinder, wait a few moments, then automatically close it. By putting the light sensor inside a tube or cover, I could shine a laser-pointer at it and have it only activate when the laser beam was broken – say, by somebody walking up to the door.

I’ve also just started learning about Arduinos. Not knowing how to use them has made me feel “left in the dust” compared to other Makers. So, I bought myself a kit, which included an Arduino Uno, a breadboard, a pile of assorted electronic bits, and a manual. So far, I’ve gone through all the tutorials and now know how to make LEDs blink, and understand the basics of inputs and outputs.

So, just tonight (2015.2.5) I put together the tutorial on photoresistors and the tutorial on relays for a setup that would let me activate the air cylinder by shadowing the light sensor with my hand.

The nice alternative of this setup is that I can reverse it to sense whether or not a laser beam is shining on the sensor. (I have a bag of laser diodes and power supplies coming to me in the mail right now.)

I also just received a pair of combination muffler/throttle valves. These are put on the “exhaust” end of 12V air valve and allow for fine-tuning the speed of the air cylinder. For example, the valve needs at least 20 PSI to work properly, but that’s pretty fast (and a hard stop!) for this air-cylinder under no load. Throttling down the exhaust slows the travel of the plunger, and means I can also adjust the speed of opening and closing separately. This is great to make the Star Trek doors open very fast, but close at a slower speed.

As much as I’d love to just copy somebody else’s design, I have NOT YET FOUND a DIY door which fully documents using air power AND a hands-free design. Probably the most well known similar project right now is this one, but it requires PRESSING A BUTTON to open the door. One of the few doors I could find that DID use a motion sensor seemed as though the motion sensing could be improved upon.

Of course, there are also unfinished projects –

And ones that are AMAZING, but with ZERO documentation! –

Reading through comments on the YouTube videos and build blogs, I see several themes, the main one usually being safety. Some of the projects had NO mention of safety, while others mention an air release or other feature, but no details on it. Of course, the devil is in the details. Another common concern was the door working properly in an emergency, such as a fire, or during a blackout.

Since nearly all the components so far on our project are 12V DC, I don’t see why we shouldn’t just run the whole system from a small 12V battery, topped off with a simple charger. In essence, it’s half of a UPS, just no need for conversion back to AC power. In event of a blackout, the door system would still work fine. When the power did come back on, the trickle charger would top the battery off once again from whatever was used. Air already stored in the compressor tank would be able to open and close the door a number of times. Alternatively, a small 12VDC air pump could be used instead of a compressor, and also run from the 12V system.

There’s still lots more to design and think about as we go. Whether the final version is powered by an Arduino, or just something as simple as a couple of relays, is far from decided yet.

If you have some great ideas or advice let us know!

I’ll keep you updated as the project progresses.

-Ben N.

Feb 7, 2015. I did some work more or less building a mock wall out of 2×4s. I found an old closet door – it’s less than a typical door size, which is nice because I can make my entire mock-up small enough to move in and out through another entryway. I hung the closet door using standard sliding door hardware and connected it to the air cylinder. The door is very heavy, which slows the start of movement AND makes a big banging when the door closes. I also hooked up the light-sensing-relay and timer relay so that it would activate the door when the laser beam shining on the sensor is broken. Proof of concept seems to be working well so far. Now it’s a matter of figuring out all the details.

Feb 13, 2015
I got a pair of surplus Bimba 18″ throw 1&1/16″ bore air cylinders with built in position sensors. I was able to get information from the sensors and send it to an analog in pin on an Arduino. LINK for details.

Feb. 26, 2015
I hooked up the second air valve for a better way to open and close the doors.. We purchased some scratch n dent doors and started cutting them. LINK for details

Dec. 2, 2015.
Been a busy summer of working on things OTHER than this project. Back to it, I wired up a control panel with an Arduino controlling relays to run the air valve and got the Arduino software working the way I want. Meanwhile, Fred started building the false wall for the shop side of the doors and a really nice looking decorative frame for the garage side.
See details at this blog entry.

{ 3 trackbacks }

Air Cylinder Position Sensors
February 14, 2015 at 11:18 am
PIRs and Scratch-n-Dent Doors
February 27, 2015 at 11:00 am
Star Trek Doors: Progress and Project Overview
December 3, 2015 at 10:41 am

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