Mini-Ornithopter Prototypes

Somewhere around 1996 I got caught up in that Magic: the Gathering card game that was going around like the flu. One of the cards, the Ornithopter, had a picture of a set of wings made from sticks and cloth that I found facisnating. I haven't played the game in years, but that card got stuck in the back of my memory, probably because its name is fun to say.

I've had a resurgence of interest in these devices thanks to the growing popularity of micro air vehicles (MAV), like palm sized helicopters and quadcopters, and suddenly had the need to try build my own ornithopter. This Instructable documents my recent attempts at crafting my own micro-orithopter from inexpensive components. This is really more of an Instructadon't, as none of these prototypes actually fly. I'm close to having a working version in the air, when that happens l will also create new Instructado using a more conventional format.

Project Goals

1. Design and fabricate a palm sized flying machine using 3D printed parts
2. Non-3D printed pieces, such as structural material and electrical components, must be cheap and easily to find.
3. Printed parts should total no more than $10 when being made from ABS plastic or similar.
4. Total cost should not exceed $40, including RC.
5. Design and fabricate a Infra-red receiver and transceiver for remote control
6. Small is the name of the game! I'm shooting for a wingspan of less than six inches.

Materials Used

1. Spring Steel, aka Music Wire. hobbylinc.com
2. Guitar Wire
3. Miniature Motor, common pager style solarbotics.com
4. 40mAh Lipo Battery sparkfun.com
5. Tissue Paper
6. Plastic Film, various thicknesses
7. Sewing Pins
8. Gorilla Glue

Design Software and Tools

Objet Printer
Up3D Printer
123D beta9, Autodesk Inventor Fusion
Dremel, scissors, wire cutters, micro drills

3D Files for my prototype are attached to this instructable and can also be found on thingaverse:

https://www.thingiverse.com/thing:2393413

Step 1: Initial Design and Material Testing

While building the first design I had three main objectives: to make a working mechanism, to test different materials for strength and flexibility and, most importantly, to make it look cool. I know next to nothing about the science of flight, so I wasn't all that surprised when the first prototype nose dived. The important thing was that I learned why it was failing and how I might correct it.

In the pictures you can see parts of the ornithopter printed from different materials.  These were all printed on Objet 500 UV cure 3D printers that are able to mix a rigid material with a flexible material while printing. To test these materials  I made several separate prints using different ratios of rigid and flexible at different thickness. The parts were then assembled to a semi-functional state and stress-tested to determine what combination made for the best ornithopter.

The type of material that comes out of these photopolymerization printers is very similar to plastic, but it's not quite the same. Thin pieces tended to be floppy, and thicker parts were prone to snapping. These materials were not intended to be made into mechanical parts. As far as durability was concerned, I was having much better luck with pieces made from ABS plastic printed by an Up3D. ABS is plastic, and I think that will be strong, flexible, and light enough to be used in the final version.

I learned a lot from this first test model. For one, the small gear ratio didn't provide enough  torqueto flap the heavy wings. More importantly, I started to realize that slapping on ad hoc paper wings and expecting the craft to actually fly was a bit optimistic. I did find a suitable material, the gears and linkages were working, but the wings were flat and lifeless. I went back to my virtual drawing board and started on the revisions.

Step 2: Version Two - Less Yap More Flap

Having gotten the mechanics working, it was time to move on to the secrets of flight. In the first model I felt that the wings weren't flapping fast enough and that they were not large enough. To shore up these problems in the second version I used a 64 tooth gear instead of a 32, giving the wings much for flapping power. They also attach further back than before to create more area and to produce a more curved wing.

I'd bought a bag of ice and decided that the plastic the bag was made of would work well for wings. I very, very, carefully applied glue to the wire struts, folded the edges of the plastic wing over, and then applied generous pressure to squeeze the glue down the full length of the seam.

Sadly, after all my hard work and perseverance, this version also failed to fly. When thrown it did glide in a far less vertical fashion than the first, and the ABS did stand up to crashes, but I really didn't get the impression that any lift was being generated. After this defeat I realized that it was time for some research.

Step 3: Going Further

Up to this point the only real research I had done on how ornithopters achieve flight amounted to nothing more than a few google image and youtube searches. I had assumed that one simply makes a mechanism that goes up and down, slaps some wings on it, and the machine couldn't help but fly. It looks so easy in the videos after all. This is where I'm at right now with the project, two prototypes made but not much flying going on. I finally did do another search and took the time to read the results.

As it turns out, there is a lot I don't know about flight! Things like "wing stroke amplitude" and "lift distribution" which, to the uninitiated like myself, sound like they may be kind of important factors to consider in the next design. I eventually found a few websites that go into every little detail of how ornithopters fly, including different designs for the wings. Most of the technical jargon is a good meter over my head, but I think I've gotten the jist of it from the pictures.
www.ornithopter.de, www.ornithopter.org (Ornithopter Zone)

As I understand it, an ornithopter's wings need to twist during flight so that they generate both lift and thrust. This curvature creates an airfoil that, at some points along its length, produces lift during both the up strokes and down strokes. Thrust is provided by wizards...

I still don't fully understand it, but I'm going to forge a head anyway under the banner of "flex good, no flex bad!" I plan to tweak the design more, use guitar wire for the struts, try a few different hinge designs, and see if I can get one of these bricks in the air. At that point all I'll need to do is design and fabricate an IR receiver / transmitter pair to control it, a project that is a little more within my realm of expertise.

Thanks for checking out my progress so far and learning what you shouldn't do when making tiny flying machines. On the final step you'll find a video collection of actual working models made by people who know what they're doing :p

If you or someone you love has experience building these and would be willing to point out what I'm doing wrong, please do leave a comment!

Huge thanks goes out to Jake and Steve over at Instructables for their help in working out the bugs and with the video. You guys rock!

Step 4: Inspiration

People have attempting to build ornithopters for a very long time, even before Da Vinci did his famous sketches. Unlike my prototypes, there has been much success in getting them to actually flutter about, they are even available as toys. Universities are working on ways to make them smaller and smaller and the Air-force dreams of swarms of microthopter spies.

Shapeways 3D printed Ornithopter
Rubberband Ornithopter Instructable
www.ornithopter.org
www.ornithopter.de

These are videos of some of the more interesting models that ultimately gave me ornithopter fever.

Butterfly Mimic
Hiroto Tanaka of Harvard University and Isao Shimoyama of the University of Tokyo

Cornell's 3D Printed Hovering Ornithopter

Flapping Wing Micro Air Vehicle (Micro Ornithopter) - 2.17 grams



Harvard Monolithic Bee
I'm not sure if this one actually flies, but the fabrication is really neat. The unit is created as though it were a circuit board, and then popped up and soldered into a mechanical structure.
 

Hummer / Da Vinci RC Ornithopter 10cm wingspan 1.1g
Winner of MAV-07, developed by Petter Muren. It was later made into a toy, but was never mass distributed.

Robo Hummingbird