Large Tip Driven Copter Turns Very Slowly

Picking propeller size for any aircraft, but especially VTOLs, it’s a tradeoff between size and RPM. You can either move a large volume of air slowly or a small volume of air quickly. Small and fast tend to be the most practical for many applications, but if you’re thinking outside the box like [amazingdiyprojects], you can build a massive propeller and make it fly at just one revolution per second. (Video, embedded below the break.)

One of the challenges of large propellers is their high torque requirements. To get around this, [amazingdiyprojects] drives the 5m diameter propeller from the tips using electric motors with propellers. The blades are simple welded aluminum frames covered with heat-shrunk packing tape, braced with wires for stiffness.

The flight controller, with its own battery, is prevented from spinning with the blades by counteracting the spin of a small DC motor. Each blade is equipped with a servo-driven control surface, which can give roll and pitch control by adjusting deflection based on the blade’s radial position.

[amazingdiyprojects] control setup is very creative but somewhat imprecise. Instead of trying to write a custom control scheme, he configured the old KK2.15HC flight controller for a hexacopter. Each control servo’s PWM signal routes through a commutator disc with six sectors, one for each motor of the virtual hexacopter. This means each of the servos switches between six different PWM channels throughout its rotation. To compensate for lag when switching between channels, [amazingdiyprojects] had to tune the offset of the commutator disc otherwise it would veer off in the wrong direction. After a second test flight session to tune the flight controller settings, control authority improved, although it is still very docile in terms of response.

[amazingdiyprojects] is no stranger to giant VTOL aircraft, having built and flown in his own manned drones, powered by both internal combustion and electric motors. This latest craft is very similar to [Nicholas Rehm]’s spinning tricoper, and might be able to take advantage of the control scheme.

21 thoughts on “Large Tip Driven Copter Turns Very Slowly

  1. Do larger blades driven from the tips offer any benefit in terms of efficiency? Given the extra mass, I doubt it, although the drag might be less since drag isn’t linear with speed. Certainly the responsiveness is a lot worse.

    1. a larger dick area will always give you a more energy efficient, just like larger wings on a glider are more energy efficient then small wings. the wing tip engines aren’t working a 10th as hard to maintain that altitude as they would be by themselves.

      but you do lose trade speed for longevity

  2. Large very slow rotor is not new. The Hughes XH-17 had a tip powered two blade rotor of 130′ diameter which spun at 88 rpm. It could lift 10,000 lbs in 1955 but proved two cumbersome to be practical.

    1. My first thought was tip-jet helicopters: with that heavy tubular spar construction, the tip BLDC fans could be removed, a single larger BLDC ducked fan positioned in the centre blowing into all 3 spars, and simple ports added to the tips of the rotors spin them up. Moves mass from the tips of the rotors back to the hub reducing inertia and aiding stability.

    2. Almost forgot about that beast. Quite the hacking feat in its own right
      Front wheels from a B-25 Mitchell, rear wheels from a C-54 Skymaster, Fuel tank from B-29 Superfortress, cockpit from a Waco CG-15 military glider, and tail rotor from a Sikorsky H-19 Chickasaw

  3. I think everything is mounted on bearings, but how is that base/Stand not moving even a little bit? I would thing there would be at least a tiny bit of drag through how many bearings, at least four?

    1. There’s a gearing system shown at 1:05 which seems as though it keeps the center column stationary. Not completely sure why this is needed, except that the legs need to be stationary to land reliably… Does seem like only the minimum is kept stationary for this purpose, though definitely adds some weight.

    2. At 1:05 a gearing system is shown to counteract the rotor rotation and keep the center rod stationary. I’m guessing that’s to facilitate landing (keeping the legs still).

  4. Lol .. i was about to submit this one to you guys at hackaday …. luckily i checked if you already had it..

    I love it ….. it looks really good levitating on it’s own ……. and he made ah so cool stuff already..

    Nice to see him linked here! ;)


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