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.

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Comment by John Bond on February 24, 2012 at 3:34pm

"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."

That's funny.  Almost all outdoor rc helis are fixed pitch...   Right...

You can't beat a variable pitch rotor for precise movement.  If you are like the author and don't know anything about rc helis just search for some 3D aerobatic rc heli videos.  You'll see the same kind of precise control.

Comment by William Premerlani on February 24, 2012 at 3:34pm

Hi Chris,

Very impressive performance, I would like to get my hands on some variable pitch quad frames.

If you look carefully at the first picture in the project description, you will see that Mark is using a UAVDevBoard, version 4.

Best regards,


Comment by Rob_Lefebvre on February 24, 2012 at 3:53pm

Interesting.  I'd like to see some comparisons of thrust generation efficiency of the variable pitch system vs. the fixed pitch.  And I like how they did the pitch control mechanism.

I also quirked an eyebrow at the idea that variable pitch is "uncommon".  

Comment by Daniel Hibben on February 24, 2012 at 5:26pm

i am wondering about the code needed to keep this thing in the air?

it would be far more complex then anything we now run.

Comment by John Bond on February 24, 2012 at 6:59pm

The code doesn't have to be that much more complex.  For attitude change, instead of telling a motor to speed up or slow down you just tell the prop to change pitch.  Computationally that's the same thing.

Comment by OlivierD. on February 24, 2012 at 8:54pm

Way to go Bill! MIT is playing with quads using a UDB4 UAV DevBoard! How cool is that! 

A regular quad frame with 4 of these:

or these:

and a good ol UDB4 and you are off to the races!




Comment by Todd Hill on February 25, 2012 at 1:22am
I am willing to wager that this can be accomplished with the existing board and software with minimal tweeks. I purchased the gear to build a setup like this last year. it is not hard to mate the tail rotor assembly of an rc heli to an outrunner with the same shaft diameter, props are not even difficult to find. The real issue with this setup is run time and weight. This kind of system is a current hog. Single motor power source is the way ahead with this, or low current high torque motors.
Comment by John Bond on February 25, 2012 at 12:38pm

A variable pitch rotor isn't just good for aerobatics.  It can make for much smoother flight in windy - especially gusty - conditions.

A paper in the Related Publications section on the MIT website has some good data on thrust efficiency for the fixed and variable pitch methods specific to their test quad.  As expected, variable pitch is generally better, but sometimes a fixed pitch (motor speed change) wins out.  This is primarily because their quad is fairly small.  The bigger you get the more you really need variable pitch.  Of course, it always depends on exactly what you are trying to accomplish.

Comment by Rob_Lefebvre on February 25, 2012 at 1:54pm

My impression, not sure if it's true, is that variable pitch is great for being able to make really sharp thrust changes.  But I suspect that it's not as good as fixed pitch at making really small thrust changes.  The servos and linkage don't have enough resolution?

3D Robotics
Comment by Chris Anderson on February 25, 2012 at 2:05pm

My impression is that quad is flown normally, with motor RPM doing the small thrust changes. The variable pitch is just used to switch modes (upside down or right side up)


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