Foldable Quadrotor is Origamilicious

A team at the École Polytechnique Fédéral de Lausanne has developed and built a quadcopter with arms that unfold just before takeoff. The idea is that you can fold the device back up when you’re done with it, making it possible to store a bunch more of the quads in your backpack for instance.

The unfolding mechanism relies on the torque of the rotors spinning up to swing the arms into place. Once fully extended, a spring-loaded flap folds up, catches on some magnets, and forms an L-shaped structure that won’t re-fold without human intervention.

quadcopter_animUnder normal flying conditions, quads have a two left-handed propellers and two right-handed ones and the motors spin in opposite directions. In order to do the unfolding, two of the motors need to run essentially in reverse until the frame has clicked into place. They use a sensor (Hall effect?) to detect the arm locking, and then the rotors quickly switch back to their normal rotation before the quad hits the floor. In the video, they demonstrate that they’ve got this so well tuned that they can throw it up into the air to launch. Wow.

Everything’s still in prototype phase, and one of the next goals is “strengthening the arms so they can withstand crashes”, so don’t expect to see these in your local hobby store too soon. In the mean time, you’ll be able to see them in the flesh if you head up to the IEEE International Conference on Robotics and Automation in Seattle that started today and runs through Friday. If anyone goes, take more video and post in the comments?

13 thoughts on “Foldable Quadrotor is Origamilicious

    1. Newtonian physics. The prop spinning one way causes the copter to spin in the opposite direction. Another prop spinning the other direction counterbalances this.

        1. It’s actually possible to have all rotors spinning in the same direction, angling them all to provide opposite torque while hovering, but this means that to control yaw you will then need to tilt one of the rotors, and that means one additional servo. Having the rotors torque balanced means you can control yaw by slowing down one pair while speeding up the other. That’s also why the rotors are arranged in diagonal pairs, otherwise a yaw input would also mean a tilt input, and vice-versa.

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