Quadrotor With Tilting Propellers Can Twist in Midair

Some extra degrees of freedom give this quadrotor the ability to pitch and roll while hovering

2 min read
Quadrotor With Tilting Propellers Can Twist in Midair

Conventional quadrotors are what’s called underactuated robots, which means that they can move in more ways than they have independent control over. For example, they can happily yaw around to any angle you want while otherwise stationary, but if you ask them to pitch or roll, they can’t do it without also changing their position: if you try to roll a quadrotor left, the whole robot is going to fly left, and if you try to fly a quadrotor left, the whole robot is going to roll left.

Having controls coupled together like this places some restrictions on what you can do with quadrotors, but a new design presented yesterday at the 2013 IEEE International Conference on Robotics and Automation (ICRA) gets around all of that with propellers that tilt.

This level of control turns the quadrotor into a fully-actuated robot: you have complete control over its position and orientation, and as the video shows, this lets the quadrotor do things that would otherwise be impossible for a conventional quadrotor without those tilting propellers.

There are tons of ways in which this new capability can be useful, but I’d say the most obvious one is for any quadrotor that carries a camera (which is pretty much all of them nowadays): instead of having to either rely on a static camera or invest in a complicated, heavy, and expensive gimbaled mount, you can now use the entire quadrotor as a pan and tilt camera platform.

Future work will improve the capabilities of this prototype (it’s called the “omnicopter”), and the researchers also plan to start experimenting with environmental interaction tasks that require orientation control, like using tools.

"First Flight Tests for a Quadrotor UAV with Tilting Propellers," by Markus Ryll, Heinrich H. Bulthoff, and Paolo Robuffo Giordano from the Max Planck Institute for Biological Cybernetics, was presented this week at ICRA 2013 in Germany.

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Robot with threads near a fallen branch

RoMan, the Army Research Laboratory's robotic manipulator, considers the best way to grasp and move a tree branch at the Adelphi Laboratory Center, in Maryland.

Evan Ackerman

“I should probably not be standing this close," I think to myself, as the robot slowly approaches a large tree branch on the floor in front of me. It's not the size of the branch that makes me nervous—it's that the robot is operating autonomously, and that while I know what it's supposed to do, I'm not entirely sure what it will do. If everything works the way the roboticists at the U.S. Army Research Laboratory (ARL) in Adelphi, Md., expect, the robot will identify the branch, grasp it, and drag it out of the way. These folks know what they're doing, but I've spent enough time around robots that I take a small step backwards anyway.

This article is part of our special report on AI, “The Great AI Reckoning.”

The robot, named RoMan, for Robotic Manipulator, is about the size of a large lawn mower, with a tracked base that helps it handle most kinds of terrain. At the front, it has a squat torso equipped with cameras and depth sensors, as well as a pair of arms that were harvested from a prototype disaster-response robot originally developed at NASA's Jet Propulsion Laboratory for a DARPA robotics competition. RoMan's job today is roadway clearing, a multistep task that ARL wants the robot to complete as autonomously as possible. Instead of instructing the robot to grasp specific objects in specific ways and move them to specific places, the operators tell RoMan to "go clear a path." It's then up to the robot to make all the decisions necessary to achieve that objective.

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