When Five Ton Crane was commissioned to build an art car version of The Nautilus, the classic submarine from 2000 Leagues Under The Sea, I knew there were going to apertures involved, I could have never guessed it would be this big. As we started talking about the project a few things started to become clear.
First, this was a great opportunity to wholly revise my original aperture designs to make them more durable and more precise. I’d learned a few nifty techniques since I built my first set of apertures in 2007. Second, not only were we going to use apertures in the windows, but we also wanted to incorporate a big one into the door, which we were estimating would need to be about 4′ in diameter. Third, since incorporating a huge aperture into the door was going to be a major challenge all the other elements if the door would need to be designed around it, so it only made sense that I would build the entire door. Fourth, I would need to add some new elements to the project to keep it interesting for myself so I decided that I’d not only custom machine the hinges, but I’d also motorise the aperture in the door, and use a RFID system to control the locking mechanism. Oh, and I’d need to build two of these doors, one for each side of the sub (only one aperture though).
The four small aperture windows went together easily, and as gorgeous and cool as they are, honestly, they are so deep in the shadow of the 4′ door aperture that they are hardly noticed.
I was really amazed at how well the 4′ aperture worked, in fact, this large one is mechanical smoother then the small ones. See each of the blades needs to overlap several other blades. If you image the blades being very thin and flexible then you can see that when they are all stacked up atop each-other the stack is very thin and there is not a lot of torsion on the blades. Now since these are made of brass, the material can only get so thin before it lacks the strength to be constantly twisted without deforming. Usually I use a brass in the 0.03″ range. This thickness works well when they are small but works even better when it’s large, because the important metric is not the material thickness but the ratio between the thickness and size of the blade. I also found a new much stronger method to attach the pins to the blades (this is the hardest part of the design).
The motorization of the large aperture was surprisingly easy. I used two small DC motors with spur gears and nice torque mounted on either side of the cam ring. I then welded chain around the cam ring turning it into a giant gear. It worked the first time I tried it. I controlled the two motors with an Arduino and a motor shield, two limit switches and a few lines of code. I then modified an old positioner and inserted a set of buttons, so that when you pull the handle of the positioner it trips the buttons and turns the motors.
The RFID was super easy. I got a D12 RFID reader, hooked it up to another Arduino, and used it to flip a 40A relay attached to a 30 lbs pull automotive solenoid. The solenoid was coupled to a super beefy industrial latch. The latch keeps the door closed until is sprung by the solenoid, when to door is closed it pushes the spring latch back into its locking position. Just like the trunk on your car. I love the result. The door is rock solid closed with no visible way to open it. Then you wave your fob by the reader and the door literally pops open. When you close the door there is solid, satisfying snap as it latches in place.
The hinges are one of my favorite parts. Not only did they come out really nicely but they are so smooth and stable, and add just enough friction to give opening the door some nice tactile feedback. I modeled them on old harpoon heads and went to great lengths to hide all the welds. I love when I catch people staring at them and wondering out loud how they are put together.
- 2 doors
- each ~300lbs ~4′ x 8″
- 4′ diameter, 12 blade, motorized brass aperture
- RFID locking mechanism
- custom hinges