Zurich team develops walking, jumping, balancing, Cubli (w/ Video)

Dec 21, 2013 by Nancy Owano report
Cubli balancing on the corner.

(Phys.org) —Researchers from the ETH Zurich's Institute for Dynamic Systems and Control have developed the Cubli, a device that can walk, jump, and balance itself on a corner. The name "Cubli" is derived from the English word and the Swiss German diminutive.

The creators explain what Cubli is and what it can do: "The Cubli is a 15 × 15 × 15 cm cube that can jump up and balance on its corner. Reaction wheels mounted on three faces of the cube rotate at high angular velocities and then brake suddenly, causing the Cubli to jump up. Once the Cubli has almost reached the corner stand up position, controlled motor torques are applied to make it balance on its corner. In addition to balancing, the motor torques can also be used to achieve a controlled fall such that the Cubli can be commanded to fall in any arbitrary direction. Combining these three abilities—jumping up, balancing, and controlled falling—the Cubli is able to 'walk'."

The designers have presented a video showing the device in action, which is fun to watch, but the Cubli is also a serious exercise as the Institute continues its work in exploring various design challenges. Building on principles in mathematics and physics, their research may involve aerial vehicles, combustion engines, or robot systems, studying dynamics and control "crucial to the efficient monitoring, control and design of complex systems." Earlier this year, Mohanarajah Gajamohan, Michael Muehlebach, Tobias Widmer, and Raffaello D'Andrea presented their paper, "The Cubli: A Reaction Wheel-based 3D Inverted Pendulum," for the 2013 European Control Conference (ECC) that was held in July in Zürich. The paper tracked the development of their cube, described as a 3D inverted pendulum "with a relatively small footprint."

This video is not supported by your browser at this time.

The authors called attention to the fact that inverted pendulum systems are nothing new; they have been a part of the controls community for slightly more than a century and utilized to test, demonstrate and benchmark control concepts and theories. They also said, "Algorithms for controlling pendulum systems are an active area of research today."

What makes their cube stand out, they said, are two unique features. First, their device has a small footprint and, second, Cubli can jump up from a resting position without any external support, by suddenly braking its rotating at high speeds.

Explore further: Quantum inverted pendulum: Control scheme dynamically maintains unstable quantum system

More information: www.idsc.ethz.ch/Research_DAndrea/Cubli
www.nt.ntnu.no/users/skoge/prost/proceedings/ecc-2013/data/papers/0829.pdf

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User comments : 12

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TheGhostofOtto1923
1 / 5 (2) Dec 21, 2013
Coming soon to your Edmund scientific catalogue-
JRi
5 / 5 (1) Dec 21, 2013
I love it! Cool idea.
PhotonX
5 / 5 (1) Dec 21, 2013
This is magnificent! I have long said that what the world needs is a cube that can balance itself on one corner, and now here it is.
grondilu
not rated yet Dec 22, 2013
It seems to me that robotics does not use enough reaction wheels. These things are seriously cool.

For instance, could we attach a rotating blade to this thing and make it fly? I mean, the reaction wheels would be used both to compensate for the momentum of the blade and to steer the device. Maybe it'd be energetically competitive compared to multirotors.
antialias_physorg
3 / 5 (2) Dec 23, 2013
the reaction wheels would be used both to compensate for the momentum of the blade and to steer the device.

The trick here is that it can push against something while resting (the ground) and 'slowly' rev up its reaction wheels without moving (due to friction with the ground). Then suddenly stop them to effect motion by overcoming that friction (stop them a little to get balancing or a lot to get it to flip over).

Once you would get this airborne this wouldn't work anymore as you would have nothing to push against while re-energizing the momentum in the reaction wheels. You'd only have the momentum stored before launch to counteract the rotation of the rotor blades - and that would be spent in seconds.

After that it'd just spin and drop.
TheGhostofOtto1923
1 / 5 (1) Dec 23, 2013
The trick here is that it can push against something while resting (the ground) and 'slowly' rev up its reaction wheels without moving (due to friction with the ground)... Once you would get this airborne this wouldn't work anymore as you would have nothing to push against while re-energizing the momentum in the reaction wheels
Heres me, surprised. Remember the last time we had this discussion? These things dont need anything to 'push against'.

""A control momentum gyroscope (CMG) is an attitude control device generally used in spacecraft attitude control systems. A CMG consists of a spinning rotor and one or more motorized gimbals that tilt the rotor's angular momentum. As the rotor tilts, the changing angular momentum causes a gyroscopic torque that rotates the spacecraft."
http://phys.org/n...ots.html

-Why dont you read it again and try to figure out what you missed.
antialias_physorg
4 / 5 (4) Dec 24, 2013
Heres me, surprised. Remember the last time we had this discussion?

Yep. And the last time you were wrong, too - remember?

"A control momentum gyroscope (CMG) is an attitude control device generally used in spacecraft attitude control systems.

Look up the word "attitude" (I seem to remember telloing you this the last time, too). Then go back to school.
antialias_physorg
3.7 / 5 (3) Dec 24, 2013
Look, it's very simple: A gyroscope stores ANGULAR momentum. A motion is LINEAR momentum. You cannot transform angular momentum into linear momentum (or vice versa) without something to push against - otherwise you'd be breaking conservation laws and newtons laws of motion (and would be able to create a perpetuum mobile)
TheGhostofOtto1923
1 / 5 (1) Dec 24, 2013
"Attitude:
3. The orientation of an aircraft's axes relative to a reference line or plane, such as the horizon.
4. The orientation of a spacecraft relative to its direction of motion."

-MEANING, it can change its orientation in space without having to stick its foot out and kick off something.

This is what they do. Perhaps if you want to understand specifically how this is done, you may want to do a little independent research.

I assume they play the different wheels off against each other. Ever try to rotate a gyroscope perpendicular to its axis? A single spinning wheel can be used to change orientation in 2 different directions. Three wheels would allow unlimited rotation. Each wheel could spin up by working against the force generated by the other wheels.

Perhaps you are talking about this cube traveling by rolling itself over and over? Well of course in space you need thrusters for this.
and 'slowly' rev up its reaction wheels
Nope you are talking about orientation?
antialias_physorg
5 / 5 (1) Dec 26, 2013
-MEANING, it can change its orientation in space without having to stick its foot out and kick off something.

Exactly. Notice the word 'orientation'. It doesn't move about (in x, y, z) simply using an angualr momentum store.

However this doesn't help, as the motion of a helicopter blade continually pushes against the air and imparts angualr momentum to the cube (thereby rotating one way) while at the same time the store in the cube must compemsate (by giving up some of its stored angular momentum in the other direction).

What they do here in the article is 'simply' the same thing a Segway does - only in a very controlled manner around multiple axes. Why this involves friction you can easily see if you imagine what would happen if you placed this on a zero friction ground.

The store isfinite. As soon as its used up the thing will just spin in the air like a helicopter without a stabilizer rotor (that's what the stabilizers are there for, you know?)
TheGhostofOtto1923
1 / 5 (1) Dec 26, 2013
It doesn't move about (in x, y, z) simply using an angualr momentum store
...So you were actually assuming that someone would think that a cube could move about in space or in the atmosphere just by tumbling. Is this right??
the motion of a helicopter blade continually pushes against the air and imparts angualr momentum to the cube (thereby rotating one way) while at the same time the store in the cube must compemsate (by giving up some of its stored angular momentum in the other direction)
No, because in this case the helicopter blade would be pushing at right angles to the gyro on a perpendicular axis. But who was talking about helicopters? I think youre confused.
involves friction you can easily see if you imagine what would happen if you placed this on a zero friction ground
Segways are in contact with the ground. In space this cube can reorient itself by spinning up rotors against the other right angle rotors and then applying the brakes.
TheGhostofOtto1923
1 / 5 (1) Dec 26, 2013
Heres a test of a pole-mtd control momentum gyroscope. Its reorienting itself by pushing against the other rotors.
http://www.youtub...8w33gDPs

Heres a test of an attitude control system with unlimited movement
http://www.youtub...sXojvZZM

Here are simple setups
http://www.youtub...39p8i2Aw
http://www.youtub...JsjQlFqQ

-Heres a commercial model:
"Maxon Motor U.K. and Clyde Space together have developed a full three-axis attitude control system based on a torque reaction positioning system that uses a reaction/momentum fly wheel. The reaction wheel is driven by a Maxon brushless dc motor. By changing the speed of the flywheel, a reactionary torque is applied to rotate the satellite around an axis and by maintaining the rotation the CubeSat is stabilized. Several reaction/momentum wheels are used to provide FULL 3 AXIS ATTITUDE CONTROL AND STABILITY."
http://www.design...mission/

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