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  1. DennisK

    Electric and Counter Rotation

    lol, that's an interesting mental image :) The battery and ESC would have to spin along with the stator unless you can get enough power through a slip ring, or the fuel tank with an engine unless you can get fuel across the moving joint. The variable blade pitch is a good idea. Command both...
  2. DennisK

    Electric and Counter Rotation

    You just need to control the motors in torque/current mode rather than the usual velocity/voltage mode. They will each spin up to whatever RPM draws the requested amount of current, reaching the same equilibrium that they would with the differential gearbox. But most airplane/multirotor ESCs...
  3. DennisK

    Affordable Homebuilt Aircraft Kit With Homebuilt CNC

    It would be better as a community project than a business, because the main advantage of this approach is that once the g-code and instructions exist, they can be copied infinitely for free. Trying to maintain control of the data would be a losing battle and a waste of potential, but if the goal...
  4. DennisK

    Would planes be better if they were more like birds?

    Great story! That kind of thing is why I'm interested in direct joint control of robotic wings, rather than auto-flapping just for thrust. No fear of getting caught in updrafts either, since you have control over your wing area. I've seen birds fly in some crazy wind conditions. Or in the...
  5. DennisK

    Would planes be better if they were more like birds?

    Did my PM fail to go through? Sent Jan 10, titled "Control of robotic wings and tail" For those interested in following my feathered wing development work, here's a new video of it finally moving under its own power :) All the parts for the 3-axis shoulder are finished too, so it's only a...
  6. DennisK

    Would planes be better if they were more like birds?

    Always nice to hear reports of that. It will be convenient if humans can fly with wings only. I haven't come up with a good way to control a tail during takeoff and landing when your hands are busy with the wings and legs are busy running.
  7. DennisK

    ornithopter ,video

    This is the original paper A Novel Actuation Strategy for an Agile Bioinspired FWAV Performing a Morphing-Coupled Wingbeat Pattern Unfortunately behind a paywall, but it does have some viewable videos that give a good view of the internal structure. It has elbow/wrist extension motion...
  8. DennisK

    Vertical Load on pin

    If you add up all the forces outboard of the joint you get 2375lbs. Shared between the two pins, that's 1187.5lbs each, which is pretty close to his 1182lbs. That's probably what he's referring to, though I'm not sure why the small discrepancy. So the moments cause a large horizontal load on the...
  9. DennisK

    Hoverbike debuts at Detroit Auto Show. Let the Stupidity loose

    The overall layout looks good, using two large fans for lift and four small ones for control, with all the ducts and gratings providing a decent amount of protection for bystanders. I wonder if the large fans are driven directly by the engine, or indirectly by electric generator+motors. Seems...
  10. DennisK

    Another nail in the coffin...?

    80% of all US dollars ever created were in the last two years, and there's no sign of that slowing down. But 99% of the value of the US dollar had already been stolen since the creation of the Federal Reserve in 1913, so this is just the last 1% fizzling away. Best start paying attention to...
  11. DennisK

    Human Powered Flight

    What sort of fiber orientation did you use on that? Just stacked up sheets of woven fabric with various rotations? Or is there some trick to make sure all fibers in the narrowest points between the holes are oriented radially? It also looks like those skinny spots are not all the same width. Is...
  12. DennisK

    3D printed Carbon Fiber Wing Ribs???

    Dang it, the answer was right there in my own post, but it took me until now to see it! I still haven't gotten to trying the electroplated carbon myself, but I think even better than using it directly, it will make an excellent core material for traditional epoxy carbon fiber. Moldable, variable...
  13. DennisK

    3D printed Carbon Fiber Wing Ribs???

    Yeah, I've been wanting to try the foaming PLA as a core material as well. It's actually not terribly expensive when you consider the density, since it's sold by weight. Another interesting possibility is using HIPS and then dissolving it out afterward with d-limonene to leave a fully hollow...
  14. DennisK

    3D printed Carbon Fiber Wing Ribs???

    That reminds me, there's another brand of metal-filled FDM filament called Filamet if you prefer to do the sintering step yourself. Prices are around $200/kg. Another interesting approach I've seen is to have the printer use hoppers full of metal powder and sand to build up the model and mold...
  15. DennisK

    3D printed Carbon Fiber Wing Ribs???

    With room-temperature resins, amateurs can use 3D printed single-use mandrels. Good place to use foaming PLA filament for quicker printing and lighter weight. But yes, filament winding machinery does look difficult to get working well. Specifically getting the tool path just right so the fiber...
  16. DennisK

    Ion Engines

    You technically could still run on 20kV, but would need huge current. 50kV gets around 1 gram of thrust per Watt, so that would need almost 1MW to hover, or around 18A. But thrust per Watt increases with voltage to 1.9 power, so if you go up to 500kV, then thrust should be ~80g/W, or around...
  17. DennisK

    Ion Engines

    I wrote my thoughts in this thread a few months ago Ion craft
  18. DennisK

    The concept of flapping flight will eventually succeed!

    I think power to weight ratio is the main issue, though I'm not sure exactly what biological factors limit it. There are two allometric bird scaling equations derived from measurements of real birds: wingspan = mass^0.4 and power = 60*mass^0.667. The higher wing loading makes sense because speed...
  19. DennisK

    The concept of flapping flight will eventually succeed!

    During cruise it's only thrust that goes away for part of the flap cycle. Lift is produced continuously due to forward airspeed, and angle of attack can be manipulated to keep it relatively constant throughout the cycle. But yes, low speed flight is much more demanding both physically and...
  20. DennisK

    The concept of flapping flight will eventually succeed!

    It's a little more complicated than that since you also have to account for the lift from forward airspeed. Let's try some math. From this video of a macaw cruising around a park Flap rate seems to be 5Hz or a bit less. If we guess 3.4ft wingspan, then wing length is maybe 1.6ft. Guess 60...
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