Category Archives: Video

Catch-12

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(3 quadrocopters = 12 rotors)

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To toss the ball, the quadrocopters accelerate rapidly outward to stretch the net tight between them and launch the ball up. Notice in the video that the quadrocopters are then pulled forcefully inward by the tension in the elastic net, and must rapidly stabilize in order to avoid a collision. Once recovered, the quadrotors cooperatively position the net below the ball in order to catch it.

Because they are coupled to each other by the net, the quadrocopters experience complex forces that push the vehicles to the limits of their dynamic capabilities.

Master of My Domain

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Making magnets speak: the Barkhausen effect

There are two important aspects to this “snapping” of a domain wall past a defect. First, it explains how iron can stay magnetized after the applied field is shut off: the domain walls try and return to their original position, but they routinely get “stuck” on a defect, leaving the metal partially magnetized. Second, this “snapping” results in a tiny spike in the magnetic field produced by the metal — and these tiny sharp changes in the magnetic field are what we are hearing in the Barkhausen effect!

The March of the Metro Gnomes

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Yay for mechanical coupling, which is enough of an effect to drive these into synch as long as they are all naturally oscillating close to the same frequency. This same effect is/was used in clock shops — pendulum clocks hung on a wall would similarly synchronize, giving the illusion that they must all be wonderfully precise clocks, to all be ticking at the same rate and in phase like that.

Spoiler alert: nothing dramatic happens in the last minute of the video — they just tick away. It’s tempting to try a cadence (There she was, just a-walkin’ down the street…), but the ticks are a bit fast.