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Building an Ornithopter With No Experience
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- Опубликовано: 5 сен 2021
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I really want to do more flying projects, so since the electric rockets failed so badly I thought I'd try to build another complicated flying machine. An ornithopter is something that flies by flapping its wings. There are various off the shelf kits available but I wanted to start from scratch and work my way through all of the development.
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XROBOTS
Former toy designer, current RUclips maker and general robotics, electrical and mechanical engineer, I’m a fan of doing it yourself and innovation by trial and error. My channel is where I share some of my useful and not-so-useful inventions, designs and maker advice. Iron Man is my go-to cosplay, and 3D printing can solve most issues - broken bolts, missing parts, world hunger, you name it.
XRobots is the community around my content where you can get in touch, share tips and advice, and more build FAQs, schematics and designs are also available.
Bird wings have really interesting features that enable asymmetric force application as they flap. The powered arrangement you have there is applying the same downwards force as upwards so net effect is that it glides probably a similar to distance to an unpowered arrangement. So not only do birds often retract their wings slightly on the return motion but the way the feathers are arranged, the air pressure presses them together when they flap down, creating a seal resulting in an airfoil but on the upflap the air-pressure pushes the feathers apart allowing the air to pass between again limiting the force created by the upwards flap. The retraction motion would be difficult to create but the feather arrangement wouldn't be too difficult to replicate on a macro level (like 3 or 4 large panels emulating feathers) provided it didn't make the whole thing too heavy. I think the wing arrangements in the videos you showed towards the end have those rigid parts on the fabric to allow the wing to deform in a way that achieves the same result, not just to keep the wing rigid.
I was wondering about exactly this. Well said.
Yep. I mentioned this in another comment; The plane of the wing needs to be perpendicular to the ground on the way up and parallel to ground on the way down. Otherwise, just like you said, he's generating equal amounts of force going up and going down.
yes, the wings need carbon spars.. have a look at the ornothopters designed and built by Sean Kinkade back in the day.
@@richkennedy8269 I have a Sean Kinkade ornithopter. Never got it to fly but it looks nice.
This, and the body may be too heavy with those very thick parts, especially if you're using 100% infill. I would recommend a honeycomb infill, and possibly even not making the outer shell solid. Finally you may want to consider a mechanism to either manually or automatically shift the center of balance to control the attitude.
You certainly have the "startled Wood Pigeon" flappy sound down to a tee.
Orinthopter was something that kept me really fascinated with flight projects since school. I've always wanted to make a motorised one. This framework looks promising 😍👌💯
Check out this micro version.. I bought it for cheap and wasn’t expecting much but it exceeded my expectations in every way. Crash resistant, easy to fly and glides well!
ruclips.net/video/HJf2IjJ5BN8/видео.html
Something I haven't seen others try, is this: you don't have to flap the wings, you just have to oscillate a mass, below it. I mean, you can have a glider that's steered with a mass, like a hangglider. Then you bounce the mass. I'd love to see it tried.
Would be interesting but wouldn't that apply the forward force off the center of mass inducing rotation?
Well, after seeing a few contraptions I believe this would be definitely interesting to try. Albeit I guess this would be rather inefficient there's sure a lot to be learnt. Also guessing is often met with surprising results :)
Take a look at the 'Aquaskipper' - it's basically the hydrofoil version of what you're describing.
It doesn't really make sense to describe oscillating the fuselage vs osillating (or flapping) the wings. They're the same thing, just using a different frame of reference.
Really, all you're doing is creating an ornithopter where you flap the whole wing up and down on a linear path, rather than rotating / pivoting a pair of wings. In reality, every ornithopter is also moving the fuselage up and down - it's just that the wings are much lighter, so they move more than the fuselage.
The problem you'd run into is that to get a good amount of displacement (and therefore thrust) from the wing, you would need a potentially complicated or bulky mechanism. Normal ornithopters have an advantage in that you only need a tiny, simple joint (a hinge) to produce a very large displacement at the wing tips.
I reckon the concept is sound, though - it could definitely be made to work.
As others have commented bird wings don't work by just flapping them up and down. Another way to think of it is by comparing it to swimming (breaststroke). You want to maximise drag on the downstroke, and minimise drag when pushing your arms up and forward again. So the wings need to rotate somehow.
The most important thing after makeing the wings more rigid, is that there is a flow from front to back.
As the wings flap they need to twist in just the right way or you will generate the same amount of lift down as you do up. Having them flex spanwise will help with that.
Using aluminum can be easier than carbon fiber as its easier to get it to flex without breaking over such a short distance.
Yes, he seems to be generating the same amount of lift down as he does up, The flapping is too symmetrical.
dog days
@@MrDarkbluewater yes
Its not so much about the flex as its about the twist. Its not lile a bird wing, more like an insect's one
@@Personnenenparle thus why I said it needs to twist in just the right way, problem is in order to keep it simple an do minimal engineering that will require span wise flex to accomplish.
So yes your correct.
It definitely looks tail-heavy in your tests.
You need it to be slightly nose-heavy, with the horizontal stabiliser being tilted upwards (as yours is). The nose weight and the deflection of the tail produce opposing moments which cause the aircraft to pitch up when flying fast, and pitch down when too slow - this negative feedback is essential unless you have active stabilisation.
Rather than sharply curving the trailing edge of the tail, a gentle camber with the entire tail having a negative angle of attack will be more efficient. It's just a wing, upside down.
I would suggest spending a bit more time doing some glide tests to ensure it is stable and trimmed - making the tail's angle of incidence adjustable will be very helpful for tuning it. I'm not sure exactly where the CG should sit on an ornithopter, but about 1/3 of the way from the leading edge is about right for a normal, straight wing. It'll need to be further forward on yours due to the fact there is less wing area the further you go back. I'd guesstimate about 10-20% of the way from the leading edge.
It would be a good idea to print a very simple, 1:1 scale model using the same wings and tail, but no moving parts. You could make this very lightweight and use it to figure out the correct CG and horizontal stabiliser angles, and it would prove the aerodynamics are sound. If yours doesn't fly but the model does, you know it's just a matter of weight and thrust, not stability.
On the topic of weight, I think you'll have greater success making EVERYTHING lighter. Smaller battery, smaller motor, thinner carbon, and smaller, thinner prints with cutouts where possible. As someone who has made and flown a few model aircraft, looking at your current design had me screaming "WOW, that looks heavy!". It's always possible to compensate with more thrust, but this usually produces a worse aircraft.
Minimising weight should be your #1 priority, and it should guide every single design decision.
This is the comment I was looking for. I completely agree the CG is way too aft.
@@Tritone_b5 ruclips.net/channel/UCAanjlVj-9dI6-Akwd1f5EQ
Looks like James could build a robot mower/strimmer for the garden. Kill two birds with one stone, project for the channel and laid back lawn care.
It’s certainly be a very useful project more of us could potentially want to replicate
Looks very promising!
Very similar profile picture to this guy!
The main problem here, as other have pointer out, is the equal thrust generation up as down. How about making the wing skeleton linked, so it's rigid one way, but flexible the other, like a cable drag chain carrier, or those flexible couch trays they have at IKEA.
A tip: I have a flying cow on a string as a toy, but there is one difference: the sicks, which hold the wings, are curved back at the tip, so that they stabilize the wings at the tip further back
Try having segmented wings joined with a gear, prevents equal force upwards
Oh ! This is a fun one! Looking forward to watching this one evolve!
7:22 Think your next project should be a robot lawn mower my guy...(!)
Your next project should be a robotic lawn mower and pruning machine 😊
An old adage about CofG says something like "nose heavy flies ok, tail heavy flies once"
There is no better designer, builder & flyer of ornithopters than Kazuhiko Kakuta. His youtube channel is full of beautiful flying birds.
This seems like a good opportunity for a colab with Tom Stanton
I LOVE Tom Stanton! 🌈
Hey James, looks extremely heavy to me relative to other flapping, flying machines. I would try to skeletonize literally everything You can get away with it, especially the drive pulleys. Maybe you could go to a stiffer filament material so you can get away with less material on the frame and pulleys.
Same thought after 2 minutes of the video or so.
As I'm preparing my own robot pigeon for my thesis since last year I'm glad you joined the club. I was a huge fan of a T shaped gearbox for bilateral symmetry but I'm using a reciprocity drive (mech. mov. 276) with wirework as musculature .
Wish me luck with the jury by month's end, your vids surely helped me more than my uni ever did so thank you 4 everything
10:09 Next up you should build a lawn-mover. :)
even if your project was unsuccessful, my esteem and my respect for you remains strong
Would changing the flap "top" and "bottom" angles (so the top of the flap is around 45 degrees and the bottom only -15) contribute in any meaningful way? Other examples seem to have this going for then as well
yea dihedral adds roll stability, so that when its tilted to the right, the right wing has more lift so it cancels out
Start by making a test bench where it measures the amount of lift, and the amount of forward pull. Attach your ornithopter to the bench, and start collecting data.
This type of testing is made for prototypes. When you can get a substantial amount of satisfactory data, then you can move to field tests.
It's sort of the same thing with the 'RoboDog' harness that prevents it from falling and damaging itself.
P.S other people are more qualified than I, but put a bend in the wing somewhere, so that you catch more lift. You are probably getting equal amounts of lift, and pushing itself towards the ground. The reason why it stays up so long is the 'gliding' aspect of your design.
Oh, I simply _adore_ ornithopters! I assembled a balsa kit pair of them back in middle school.
Great to see the ornithopter building video. Always glad to see it flying high in the sky.:)
Another really cool project! It'd be cool if you could mount the ornithoptor and use some smoke to visualize air flow, maybe with a weak fan to keep air/smoke moving and not just a cloudy mess. This would allow you to visualize the efficacy of the wings, similar to wind tunnel testing. Good luck!
Most successful ornithopters I've seen, aside from the little plastic bird kites we could get as kids in the 80s, involve a rotating joint to the wing that better mimics nature.
You could easily adapt to that by putting a ball into each wheel attached to a rod that runs through an offset bearing before becoming the wing.
It feels here like you're trying to make a glider, and then make it flap.
I admire how, that in the face of previous failure, you decide to build something infinitely more complicated, than your last project.. baaahaa!!!!
I admire your enthusiasm and tenacity..
Good luck! I really like this project. I wonder what the birds in your neighborhood will think about it.
the reason why most ornithopters work is because when the wings flap the create a wave starting from the leading edge of the wing going down to the back to help push air downward with a slight bit of air going backward pushing the ornithopter forward
I am happy to see that you gonna try one more time...
I really want to see this flying...
I'm not sure how you could make this content more up my alley
I think the biggest improvement you could make would be to build a better horizontal stabilizer (The first tail section that you put on). The card paper one you showed in the video was folding on itself as it flew, so it couldn't do anything to stabilize the ornithopter. Once you have a working horizontal stab, you can tyune the incidence angle (How much it's tilted relative to the wing) and the center of mass. Getting those two right is absolutely critical to making it fly, far more so than having an ideal wing design.
Looks like your backyard could use a robot lawnmower ;)
Its always a good day when its james post day
Use 4mm carbon rods for flexing in front and 2mm for the middle wing to tail "spar"...
Build it lighter, use lighter batteries too...
RIP Sean Kinkade, master of the ornithopters. Watch also YT Kazuhiko, the other master of ornithopter.
If you had two carbon fiber flat sheets held together like this |) with one side further apart than the other, it could bend one way but not the other. Attach the wing fabric to the one that’s bent and face the flat one down and when the wing gets pulled up, the flat one will bend and the wings will pull in slightly. When it flaps down, the straight one goes taut and the wings spread out without bending up
That looks so ridiculously heavy. You really need to get the right motor and ESC so you can eliminate that huge gearing system.
james - i thing the redesign of the wings should include some posebility to "fold/collaps" on the up motion and expand on the down. i feel like the reds on this one just push the hopper up and down in the same amount of air. if you collaps a bit on the up motion, it will "shovel" more air on the down motion and you get lift. nice job as allways!
You were definitely making progress, stick with it
I love the descriptive thumbnail! "Flap flap"
Oh my! Looks, for now, like an exhausted bird desperately flying away from you, only to fall unconscious to the floor. 🤭
On a more serious note, hats off!
It seems like the
- wing should be curved like a parachute.
- wing down motion should be faster than wing up
to generate better lift.
Most of the birds and insects have curved wing motion. If you look at their wings sagittally during a flap, the motion is like an S curve with hysteresis. Controlling the separation between two S curves can be use to steer the robot.
To enable it to flap its wings a lot faster (without murdering the motor)...
- Planetary IVT (Starts with extreme torque to get things going before it speeds up)
- Compliant Centrifugal Clutch (for reasons)
- Compliant Overrun Clutch (Freewheel)
- Variable Inertia Flywheel (expands through centrifugal force as it gains speed, increasing its rotational inertia)
- Elliptical Crank Sprockets/Pulleys...? (Perhaps)
- Mating the battery to a bank of supercapacitors. (LAUNCH!)
I remember a wind up toy I had as a kid which was very similar except for the wing shape. I would try some wings that don't stretch all the way back down the body more bird/plane shaped than glider/kite. Looking forward to a follow up.
I'm just gonna name-drop Kazuhiko Kakuta. That man knows ornithopters and he's quite prolific with his creations. Maybe that's what James is referring to when he mentioned "some videos on RUclips".
I really like the sound that it made while it was flapping, it sounded almost like a living creature.
Good start!
However, a 2d-movement (up-down) is just like flapping your arms in the water, you're going to move a lot of fluid, but won't move an inch in any direction. The force against air when the wing is going down is immediately countered by the exact same amount of force when the wing is going up: you're moving air, but that's pretty much it.
From what I read in several papers about bird-flight (based on lift, insect-flight is totally different), the movement at the base of the wing is circular, not linear, just like when you swim. You want to reduce the friction to a minimum when the wing is going against the movement, and maximize it when pushing on the medium, just like a breast-stroke.
Cheers!
it isnt lifting at the front, it is falling and air resistance is nosing it up. those wings would never work because you are just flapping the same up and down applying the same energy to the air both above and below the wing. working ornithopters always have some sort of articulation to create and maintain the classic high pressure below and low pressure above that traditional wing and props take advantage of.
Why not try making a wing out of kite fabric that has one way air valves.
On the upstroke the air can pass through but on the way down it closes up and sends the air downward.
Aero 101: CG ahead of AC; requires a download on the tail
...maybe try a one way locking hinge joint on the wing 3/4 to the tip; reduce drag going up/ max lift down
- roll control (in lieu of ailerons) a leading edge actuator (pivot off carbon tube) with fabric to increase lift on one wing vs the other - a downward LE would increase camber on one wing (ie lift) and cause the bird to roll right or left
- automate tail positioning to compensate for Cd alpha
You always make amazing things, I never would of known you can do that type of stuff with 3-D printing!!!
Ok this one's exciting. I've got most of these components sitting around and a printer to do the rest.
I think going from ground-based robot to flying robots is quite a big jump! You should do static testing to work out where the center of mass is: the kits are all narrow with very light wing to keep the COM stable. Your wing supports are way too heavy and they make balancing the robot impossible as they shift the COM too much. Then you should determine where the center of lift is: it should be above your COM so in a static test (think wind tunnels) it should move upward without tilting too much. A V shaped very light wing would help with that. Your floppy wing varies from positive to negative dihedron (spelling?), to the ratio between your COM an COL varies wildly. Try playing on the ratio between the upstroke and the downstroke: your COL should stay above your COM so your robot will be dinamically stable. As others have already pointed out, your wings should also flex to reduce air resistance in the upward stroke. . Easy peasy..... :)
Everyone has already said it, moving a sheet up and down doesn't make lift. You need to have more force generated as you move the wing down, as it makes as the wing moves back up, so the net force is able to push the craft upwards. Right now it seems you just have flapping tarps, with a net force more or less 0 or center.
V.1 you need a tail. V.2 YOU NEED A HORIZONTAL TAIL. V.3 you need a vertical tail. V.4 horizontal tail needs adjustment.
Battens. YES. Battens are good, but pay close attention to how flexible they are! They will dictate the shape of your wing. Slow motion footage can help you figure out where the flapping wing is acting weird.
2:56 I literally cramped my jaw cringing at the angry motor noises 😅
Your garden looks super fun to roll around in. Also this is awesome, definitely looked like it wanted to take off a few times, I can’t wait for part 2
I suppose everyone will have mechanical opinions, so do whatever you think will work. But here are my particular mechanical opinions, for consideration:
1. Center of mass lower with respect to (and directly under) center of wing area. This provides stability and balance.
2. Rigid carbon rods replaced with something flexible like delrin or fiberglass. Ideally in tension curving backward along the leading edges of the wings. This in combination with item 1 provides lift (because wings can flex to different tension/stiffness on the upstroke vs. the downstroke) and forward thrust (because wings can twist to different angles on the upstroke vs. the downstroke).
3. IMO It would help if you started with a shape that can glide at least a little, like a kite.
Can't wait for your follow up video! I love watching your problem solving process
James, try putting a gyro along the spine that triggers the wings to flap in order to maintain attitude, rather than a perfect wave function. You might also have luck with composite golf club shafts; some are quite flexible, especially women's clubs
Here's a suggestion: Add an extra joint at the base of each wing, allowing them to pivot back and forth. This should allow slightly vectored thrust/lift, and give control over pitch and roll without using the tail.
Nifty ! Perhaps like a cam mechanism to change/flex the wings shape/angle during the up stroke, you got this.
I suggest a solar powered gardener Robot as your next project.
Looking forward too a successful flight!
The most honest title to a video I've ever seen!! Well done James!!
You could put a way smaller lipo battery on it. Maybe like a 500mah lipo. Should still give you plenty of flight time. And save a lot of weight.
Looking forward to part 2 now.
Your wings need to be more insect like! In order for the wind to allow it up for a new grasp of air.. they need to close fully on the upstroke and close on the down stroke. This will create stability.
The best config would be to vary the angle of attack, as the wings go up, the angle of attack should be more parallel with the motion of the wings and on the down flap, the wings should have a more perpendicular angle of attack to the motion of the wings. Even if a 90 degree rotation is impractical, a 30 degree rotation of that angle of attack would produce enough thrust asymmetry you probably could get flight. Lift would be cos(AoA) so at 30° it would be 86% of the thrust produced on the up flap.
If the flexible types don't work, you could always cut a tube in half, and use the 2 halves separately, see if that helps
If you're still having problems with the center of balance, you can attach a weight, like the battery, to a something that can slide front and back, then program something to keep it level or up like 5% or something, then adjust the weight with a pulley or a piston, something you can dial in.
Can’t wait to see next week! I’d recommend getting it to fully glide and be stable with the wings in the up position first. If it isn’t stable move the CG forward and increase the incidence (downward angle) on the tail
I used to build chopstick ornithopters like 20 years ago, it's a concept I still love.
In retro spec, the "electric rocket" was a good idea: the fastests quadcopters (i.e. the one made by Redbull to film F1 races) are basically like featured here.
Great project... although when I saw the performance characteristics of that first motor I was expecting you to be building an aggressive wasp 😀
I admire your ability to stay in there over time with "fail" after "fail".🙏👍 ( I don't have that)
I wonder.. if you had ..lets say a wire coming down from a crane or a high point.. if you you could test fly it in circles while being attached in the balancing point
nice work! I would add "legs": a hanging mass that you can pivot automatically sensing the angle of the robot, like an automatic swing hanging in the bottom
maybe even mixing the code from the self balancing robot
In the late 80's or early 90's I remember getting some plastic toys that looked like birds and flew in a similar fashion.
I think a lot of the technical comments will center on your Ornithopter theory. I think either you need to provide asymmetric lift, as suggested by the bird wing, or enough forward thrust so that your 'thopter moves forward fast enough to create the dynamics of a manta ray moving through water.
Try perhaps another controllable degree on the attack angle of the wings?
Simpler? Perhaps a sprung elbow on the wing strut to add the asymmetry?
I think your biggest issue is your weight to wing ratio, the more weight you have the bigger the wing you need. The best test for this is to get it to glide before an input, it should be able to glide gently to the ground, and only then do you have a chance of lift.
Hey, make a small DIY wind turbine. Ask "Engineering with Rosie" RUclips
channel which general design to choose for a small turbine for your
rooftop, and common caveats and what to avoid. It would be great to see
something like this being built from scratch.
Interesting, useful, environmentally friendly!
even Butterflies compensate the lift by changing the angel of the wings. Birds add changing the complete wing-geometry.
We need to imitate that ? Segmenting the wings ... outer segments overlap the inner segments below ?
Love the project! I build (somewhat:) conventional RC planes and I think you were right about it being nose heavy in the beginning. I think for the next one you should definitely have the rudder and elevator be controllable which will really help the flight characteristics (I recommend depron with a hot glue heng). Anyway: Nice video and I look forward to seeing the next one!
Could the gyroscopic influence of the pulleys pitch the nose down as well?
That's my exact set!!!!
My cat's going bonkers over this video.
Great start
If you and girl with the dogs had a conversation it would sound like aliens having a duet.
Listen how funny he sounds when he says "bearing".
you dont want to balance it to center of volume. you want it to balance at the center of lift which is way farther forward (roughly center of the wings). you can see in the test flights its still back heavy and pitching up.
I've the impression this has to have fly for longer than a quadcopter with the same battery. If you get it to fly you could do a Quadcopter vs. Ornithopter. Maybe setup a racing "track" and see which one performs better. If the ornithopter flies for longer maybe it will fail more often in taking the close curves and it'll crash more. Good Luck!
Good luck James!
your bird creates forward thrust, so you should try to make it fly like an airplane. also dihedral would help with roll stability
looking good so far adjust center of mass and add pitch and yaw angles of flow adjustment to get the motion right will be the main thing. I say about 1/2 way to a production model even with a keep it simple but working approach.
Awesome project. Tanks for sharing
surely you need the extra bend mid wing, like a bird, to reduce drag on the up-stroke? otherwise your flapping counters itself out with equal force on the up and down strokes
using some kind of hinge that only bends one way would work; this was it would naturally fold on the up-stroke and lock the wing flat on the down?
Awesome video james! It looks like you need to build a robot lawn mower ;)
I built a ornithopter out of dowels and cellophane as a kit it was a kit from hobby lobby and was a blast. Hope this works so I can 3d print one.
It looks like it would benefit from some kind of dynamic balancing.
Again a beautiful project and i am very curious how that's gonna work I am confident that you make it work beautifully and then I hopefully copy your idea to get it up and running for my children. Until the next episode.
Greeting from the Netherlands
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