Variable Pitch Quadrocopter Flies Upside Down

Straight from the Aerospace Controls Laboratory comes a variable-pitch quadrocopter designed by [Mark Cutler] and [Jonathan P. Howe]. While real, full-sized helicopters always have variable pitch rotors, changing the pitch of the blades on remote control aircraft is a fairly uncommon modification. When it’s done right, though, being able to easily change the thrust direction of a propeller leads to very cool flights, like having an airplane hover nose down.

[Mark] and [Jonathan] identified two interesting techniques that a variable pitch quadrotor can bring to the table. The first is trajectory generation  – because of the added maneuverability, their quadrotor can perform more aggressive banking turns when following a preprogrammed path. The second benefit to their design is quick deceleration. In the first video after the break, you can compare the deceleration rates of a variable pitch and fixed pitch quadrocopter. While the fixed pitch quad continues climbing after being commanded to stop, the quadrocopter outfitted with variable pitch rotors can stop on a dime.

We’re still waiting for the equivalent of the Red Bull Air Races for quadrocopter builds, but when it comes we know what would win the slalom event.



50 thoughts on “Variable Pitch Quadrocopter Flies Upside Down

    1. Myopic people stifle creativity. Ever heard the term “shoulders of giants”? I enjoy reading/learning about other peoples experements in varied diciplines. Good Job Hackaday!!

    2. I actually like posts about quadrotors. If anything, I think Hackaday should stop posting about all these electronic hacks and arduino hacks.

      That probably sounds preposterous to you, but I just skip reading them and I’m fine with that. :)

  1. It looks like MIT was starting to get envious of the amazing work 6 hrs South at UPen and decided to up the complexity. I for one and grateful for their use of a tripod to shoot the videos; it is maddening to watch shaky handy cam footage taken in a room full of motion capture cameras.

    One thing I’d like to see is a multi-copter with a swashplate / cyclic pitch control / collective / kitchen sing for each rotor. I don’t know what it would accomplish but the control theory alone would be noteworthy.

    – Robot

    1. I don’t see how cyclic pitch controll wolud be useful. On a sigle rotor aircraft it makes sense since it lets you move the area generating the lift in respect to the center of gravity. As a result, the aircraft will lean this way or the other, somit can move sideways.

      A quad rotor already has that abillity, just by having several rotors, making cyclic pitchc controll redundant.

      (a middle ground would be dual rotor helis, that need the cyclic pitch to move sideways. )

      1. Depends on what your quad(or higher) is flying around,and how quickly. From the video it looks like it can do rapid altitude changes and stop within inches instead of a foot or so. Will make it much easier for the hunter killers to fly through urban environments and windows!

      2. What you get is faster response times. Changing the speed of the rotor disk changes the amount of lift, sure, but you have to wait for the rotor to slow down, or speed up to do so. There is noticeable lag when trying to go faster. Having the rotor spin at a constant speed, and then changing the pitch of the blades does not give you the same response lag.

    1. Yep. The quadrocopter is restrained by strings tied to two of its arms. The video describes this as an experiment where the device is constrained to a single axis to demonstrate its ability to flip, so I don’t think they were hiding anything. You’ll also notice that the tied-off motors aren’t spinning.

  2. This is pretty interesting, it brings a few new things to the table. Quads can now have a motor or maybe even two fail and still stay aloft. I’ve seen on previous threads the idea of a full-sized quad was quickly (pardon the pun)’shot-down’, but has anyone been thinking about a predator-drone sized equivalent for urban environment missions? it seems feasible now that they can take a few hits before going down, also we’ve already seen what sorts of gaps the littler ones can wiggle themselves into.

    A quad of quads attached to a + shaped frame that also doubles as a main battery-pack would be interesting to see. they could detach at will to become a swarm. maybe even have a fifth copter in the middle as an extra, but again with the variable pitch now that might not even matter.(think of an entire quad being a single rotor)

    1. One of the things that makes a drone useful is it’s capacity to loiter in the field for many hours (according to Wikipedia 40.5 hrs for the Predator.) I have a hard time imagining a quadcopter achieving that sort of endurance. Maybe a fixed wing drone could launch a swarm of little quadcopters?

      Hell, I bet there is a DARPA grant just waiting for that proposal.

      – Robot

    1. I didn’t go to MIT, I am just a fan but I was lucky enough to go to college in Boston and made a lot of MIT friends, went to crazy MIT parties got to mess around in their labs and even worked on some silly projects. There exists a culture at MIT that promotes learning, collaboration and experimentation outside of the classroom. Unlike my school the learning at MIT does not stop outside of the classroom. That made me crazy because I was studying engineering to make awesome robots; I couldn’t understand how uninterested my classmates were in applying what we were working so hard to learn. I had to make that culture for myself and Boston was a good place for it. Keep in mind that you too can have that experience without going to MIT, hacker spaces and nerdy friends can help you to do the same. But if you think you have the chops for a place like MIT go for it with all of your heart. None of my friends regret it.

      – Robot

  3. I have to wonder if they need variable pitch for that or if implementing real motor controls could take care of it for them by reversing the rotor. I know those tiny machines can take the torque to flip rotation like that but I don’t know what it would do to the control stability.

  4. Since a variable pitch quad copter doesnt rely on adjusting motor speeds for control it would be possible to use a single central nitromethane fueled rc engine with drive shafts instead of multiple electric motors.

  5. @Elias Same here, not a bit of nose down hovering in that video.

    As for why you’d want cyclic pitch control on a quadcopter is so it could move around without tilting or by drastically reducing the amount of tilt needed. By driving two rotors clockwise and two counter-clockwise, trailing blade stall can be ignored, just like with concentric mounted counter rotating rotors and Kaman style “eggbeater” intermeshing rotors.

    A central engine driving all four rotors, each with cyclic pitch control, would be the ultimate in maneuverability. Inverted flight would also be possible because it’s a feature of fixed pivot RC helicopter rotor heads.

    Full size manned helicopters have been able to do the same by scaling up the RC rotor designs, which were originally developed as a much simpler design than copying the hinged rotor system.

    Same thing happened with racing sailboats. Model boaters came up with the long, slender “dagger” keels because they were far simpler to build than accurate scale copies of traditional sloop, ketch and yawl keels. The boat racers noticed and copied the models to make their big boats lighter and faster.

    Now, when will we see some of these extreme maneuverable drones in a movie chase scene?

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