Check out those flips! From Hackaday:
Straight from the Aerospace Controls Laboratory comes a variable-pitch quadrocopterdesigned 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.
Comments
@Daniel: We used the Unmanned Innovation boards during the prototyping phase. Since then we have been using the UDB4 with a 2000deg/s rate gyro (see Buddy's comment above). Good luck with the variable-pitch quad!
We haven't done that test exactly, but I'm fairly confident that the efficiency is quite lower with the variable-pitch setup, most likely due to the fact that we are using a symmetric airfoil with the variable-pitch blades instead of typical cambered, fixed-pitch blades..
Have you guys done any work to compare, all-else-being-equal, the thrust production efficiency (thrust/watt) of different propeller types? ie: typical fixed-pitch props, the props that you are using, or helicopter-style rotor blades?
I've seen a couple variable pitch quads, and they tend to use say, a 600-class helicopter tail gearbox (variable pitch, but no swashplate) with 450-size main heli blades stuff into them. I have wondered about the efficiency of heli blades compared to a more profiled blade such as a fixed-pitch.
Robert, right now I'm keeping the motor command and pitch relatively fixed. As the pitch is increased or decreased, the motor command is increased or decreased to compensate for the change in drag and keep the motor speed more or less constant. This gives the fastest thrust response by essentially eliminating the motor dynamics.
I've not considered ducted fans, but it sounds cool!
Mark, do you use motor speed control for stabilization or altitude control? Or are they relatively fixed?
Have you ever thought about using ducted fans with variable-area nozzles in a similar way?
Awesome! thanks Mark!
Sure. It is mechanically quite simple. I'm using Axi 2208/34 hollow shaft motors with MKS 480 servos. The variable-pitch actuation is accomplished using the EVPU (http://www.modelmotors.cz/index.php?page=101) from MsComposit. There are four Mikrocopter ESCs allowing us to update the motor speeds at 1kHz, while the servos accept commands at 333Hz. Everything is bolted to a sheet of carbon fiber/balsa sandwich board, with the UDB4 on top for control.
Mark
Mark do you mind sharing the hardware specs of the quad?
Hi Chris,
Thanks for linking to my work. It is an honor as you are somewhat of a UAV legend in my mind.
It's nice to see that there are people interested in variable-pitch quadrotors. I was a little worried that the response from the DIY community would not be favorable since the variable-pitch propellers are a bit redundant on a basic quadrotor.
Thanks for all the work in the DIY world. In our lab at MIT (ACL), we use your forum posts and information a lot. Also, the UDB4 is awesome!
Mark
I think it's a camera system in the room. In some of these labs, the position and much of the flight-control is done by external computers, and only trajectories are sent to the quads. In some cases, I think the external systems just crunch the data and feed a position info to the quads, similar to a private GPS system.
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