I’m still in love with airfoils and wing-related things, so I thought I’d try to make a horizontal axis wind turbine for my office. There is really nothing practical about this, but it sure looks cool. I’m learning some programming, so I thought it would eventually be nice to control it somehow.
Anyway, I started off making 18″ long blades out of cardboard sheets. I then cut out two more sheets to sandwich around the middle sheet. When viewed from the end, the sheets fit inside the boundary of a NACA 0012 airfoil. The intention was to eventually wrap this core with sheets of pop-cans to create a strong, weatherproof coating. I haven’t gotten that far yet, because it’s really not necessary for this proof of concept.
I then made a triangular hub from 3 sheets of cardboard offset 1″ from each other and rotated 120 degrees to even out the grain. I then wrapped a single sheet around these 3 parallel triangles to give me a triangular prism that was 3″ on a side and 2.5″ high.
Next, I glued the blade roots to the hub at a 30 degree angle, just because that seemed about right for the speeds I expected. A hole was then drilled in the center of the hub and a wood dowel was glued in for a shaft.The mast was made from two interlocking segments that taper toward the top and lean forward about 10 degrees. The mast base and top cap are diamond shape to match the main interlocking supports.
I placed the shaft into the cardboard near the top and took it into the hallway one morning to go for a run. Here’s a video of it working in a wind of about 8 mph. (Coming Soon)
My office doesn’t get strong drafts so I decided to motorize it. I used an oscillator motor that I pulled out of a space heater. It’s geared to spin at 4 rpm. That’s not much, but when a turbine that’s 3′ across spins once every 15 seconds, it looks like a large one sitting out in a field somewhere. It’s just fast/slow enough to intrigue and relax someone.
I ended up needing that motor for Alex’s mobile mobile. I had to settle on something else. I decided to use my stepper motor that came with my Arduino kit from Oddwires. I would also be able to add some control capability this way!
With the motor gone, I wanted to see how much air this thing could move, because a coworker suggested I turn it into a temperature-controlled fan. A new challenge, GREAT! I hooked the shaft to my drill and spun it up. I had someone stand across the room about 16′ away to see if anything could be felt. I’m not sure how fast I had that thing going, but it looked about 4 rps, so 240 rpm. I could feel its push against me. I added just a bit more juice…. THUNK THUNK THUNK! One blade separated and slammed into one wall, one hit the ceiling, and the last one hit the floor in a fraction of a second. Hmmm… So it was actually pretty strong, and I never intended to rev it that high when in office fan mode.
All the pieces were intact, so I just made a new hub to fit the NEMA 17 stepper motor and was quickly back in business. This time, I joined 3 steel wires inside the hub and ran each down the inside corrugations of each blade, and over the end, and back into the hub. All 6 wire ends were joined inside the hollow hub, so there was no way the blades were flying off again.
I had to make a new mount on top of the mast to hold the stepper, and it required even more counter weight at the base.
I programmed a simple Arduino control that allows me to spin between 0 – 120 rpm. A regular potentiometer controls the speed, and the RPM is displayed on the computer. Unfortunately, the stepper motor is not ideal for this type of application, but it works. The system is really loud because the wires inside the blades vibrate against the cardboard, and the stepper motor seems to chatter a bit because the inertia of the whole thing is too high. I will work on a new motor soon.