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One of the most fascinating creatures on Earth, the dragonfly has a very ancient stroke. It's an up-and-down stroke instead of a back-and-forth stroke. An airfoil uses aerodynamic lift to carry its weight. But the dragonfly uses a lot of aerodynamic drag to carry its weight. What’s odd is that with airplanes you always think about minimizing drag, you never think about using drag for lift.
The physics of dragonfly flight inspired me to build a mechanical dragonfly based on scientific research by Z. Jane Wang, professor of theoretical and applied mechanics at Cornell University, and Akira Azuma research papers. This design utilizes drag to create flight by using theoretical models including momentum theory and the blade element theory.
The inspiration for this mechanical insect originated from many of the fantasized gadgets of Leonardo da Vinci and other mechanical creations once thought futuristic in times long before our own.
The design of the wings were crucial to figure out how to use drag to create flight.
Dragonflies are insects belonging to the order Odonata, which wings move independently during flight. As the forewing lifts, the hindwing lowers.
They have two pairs of similarly sized long thin membranous wings.
Its fore and hind wings are controlled by separate muscles, and a distinctive feature of the dragonfly’s wing movement is the phase relation between those wings during various maneuvers. Creating oscillating wings at a specific distance apart develops whirls on top of opposing wings which creates lift.
Wings had to be close enough for them to interact hydrodynamically.
The engine that flaps the wings is driven by a twisted rubber band that turns a crank shaft. Mimicking natures design while maintaining a simple design was testing so we defaulted to a proven design. The reason for this decision was influenced by the nature of how a dragonfly uses its muscle.
A dragonfly's muscles flap its wings by flowing blood in its veins which manifest Coriolis forces.
When muscles attached to the dorsal surface of the thorax contract, they pull down on the tergum. As the tergum moves, it draws the wing bases down, and the wings, in turn, lift up. Another set of muscles, which runs horizontally from the front to the back of the thorax, then contract. The thorax again changes shape, the tergum rises, and the wings are drawn down.
Dragonflies perform at low speed flight with ordinary airfoil characteristics, instead of adopting an abnormally large lift coefficient.
The flapping rate of the wings maintain the forces that keep the dragonfly air born. We compromised the wing speed from 30 beats per second to 2 beats per second and added a gliding feature to the design. Dragonflies are also good gliders. Some larger species can glide for 20 m at angle of 10 degrees.
Dragonflies flap and pitch their wings at a rate of about 40 Hz. The blood flowing in veins induces Coriolis forces in the flapping wings.
The body design
When art and science do merge, the result often becomes an elaboration on scientific data through a more artistic medium. The most sturdy and elegant design for the body was to use a "X" shape along the tail and underbelly. The sturdiness of the design allows for greater pressure from the twisting of the rubber band.
I wanted a way to have the students handle all the parts of DNA, so I designed this set in TinkerCAD.
You can construct DNA, copy it, and model RNA transcription with this set.
For this I did put a 0.5 mm tolerance between the tabs. I'd rather the pieces fit loosely then have students smash them together and shoot them over the class.
Everything snaps together
One small thing to glue
Read downloadable PDF instructions with pictures. Part of download files.
- DragonBodyV2 - 15% Infill, raft, supports
- 2x DragonWingsV3 - 100% Infill, no raft, no supports, 1 shell, .4mm thickness, 60 speed
- 2x DragonLegsV1 - 100% Infill, no raft, supports, 60 speed
- Plastic bag from department store (Walmart or similar)
- 2x paperclips
- Rubber band
- Glue stick
- 1/16th drill bit or similar size
Step 1 - Body
The Dragonfly body was made with a sturdy frame that allows you to wind the rubber band tight without worrying about compromising the frame.
The back end of the tail hole should be filed to follow the contour of the X frame.
Tail paperclip - Curl one end and slide other end through tail hole. Bend to correct proportions.
Tip: The Body Crank paperclip should turn effortlessly along the axle. Give it a flick and it should spin freely.
Step 2 - Legs
We wanted to mimic the iconic shape of the Dragonfly so we paid extra attention to the legs. They are more of an aesthetic but they do cushion the landing while not adding significant weight.
Grab the legs with 3 fingers and with the thumb by pressing on the top/middle of the leg. If you press your thumb down the legs go up and the bracket arms on the legs open.
Slide in one bracket around the X frame and open the bracket slightly to slide in the other end. It should be a very tight fit.
Tip: Consider printing an additional pair of legs. They are brittle and maybe damaged after some time.
Step 3 - Wings
Sit back and enjoy the process of building this enchanted design. Take your time with the wings.
We wanted to get the design of the wings with function and visuals considered. The reaction of the first print was amazing, everyone loved it and we were even more ecstatic when it flew if only for a few times. The wings are brittle but with the addition of the plastic bag film they get a lot stronger.
File out the excess plastic residue in the wing shafts.
Get a flimsy plastic bag from your local department store. We prefer the bags from Wal-Mart.
Cut one side of the bag out and tape it onto the bracket provided in the instructions.
Cut 4 wings out
Using a glue stick place glue starting from the center to 2/3rds of the under wing.
Apply the wings onto the underside of the wings. The glue should hold nicely.
Special wings - To create forward acceleration try bending the wings in a wave shape.
Test wings - When the glue is dry grab the center of the wings and rapidly turn back and forth like in a flying motion. The ends of the wings should flap up and down. When the wings move upward they allow air to pass through the frame. When they swing downward the plastic film flaps up onto the frame to catch the air. This repeated motion allows the wings to sustain flight.
Using the 3 finger hold squeeze your thumb down a little to open the cavity in the center of the wings. Snap in both wings onto the body. Place the crank arms in between the wing forks.
Rubber band - Wrap one end around both hooks.
Congratulations you have completed the build
How to fly
I can feel your anticipation similar to how we felt. If you got everything right get ready for a thrill, there's no going back from this point. Well ... you can still make adjustments ;)
With your fore finger and thumb hold the crank and wing forks. Crank the tail paperclip as much as you can. The rubber band should wrap over itself. You are trying to achieve 2 beats per second.
Get ready! Throw...
Objectives: Students will learn about fractal generation and iteration while creating a unique mosaic art piece. Students will need to use technical skills and critical thinking to construct a well-centered, and straight mosaic.
Audiences: This project is suitable for grades 5 and up. If the student is able to fold paper, they can learn this concept.
Preparation: Choose which design iteration you want to build and print out the appropriate number of pieces. The higher the iteration the more pieces you will need. Get a melamine board or wall for mounting and some locktite GO2 glue. You will need some drafting tools to get everything square. Recommended tools are: mechanical pencil, T-square, large triangle.
This idea introduces students to the concept of fractals. I would recommend using existing video media like ViHart and Numberphile videos on youtube as a supplement. Giving students paper strips to form the first few iterations of the design is great for younger students. Older students that have access to CAD software can easily be shown to draw a curve, copy, paste, and rotate 90degrees and generate higher order curves.
Printing all the pieces doesnt take very long and will give all students a chance to get some face time with their schools printer. Finally students can be in charge of their row of tiles and use technical drawing tools to construct the mosaic, or each can construct their own low order part. Moreover, since these patterns tessellate every year students can add to previous years mosaic with a different color until the pattern is completed!
To summarize, the general flow for completion is as follows:
Introduce core concept with video media and paper/CAD demonstration
Print tiles and assemble inserts
Assemble a dry fit to establish correct placement
Apply tape to each tile row so that rows can be moved and stored while glueing.
Glue center row using T-square. Allow 24 hours to cure. All rows should then square up to center row.
Finish other rows using a triangle and make sure path lines up on all tiles.
Results: The result will be an interesting piece of art with a fantastic mathematical back story. Grade students on correct placement, comprehension of core concepts, and participation.