The original tricorder.

The green line shows acceleration as the kite zoomed up and down in the wind. You can see that the highest acceleration was up. That’s in the frame of reference of the kite, though, not the Earth, so it often accelerates to my left or right while the acceleration shown here ends up being upward. Red is left or right in the kite’s orientation, which is odd. I really didn’t expect the acceleration to hit the 2Gs the iPhone can register in that direction.

The really interesting thing is acceleration in Z, shown here in blue. Notice the rapid acceleration changes around 6-7 seconds into the flight. That’s when the kite buffeted violently as I caught a strong wind. I suspect the weight of the iPhone was a bit too high or low, causing a minor instability. This isn’t something I usually see with the kite, and I only saw it with the iPhone attached whenI got a good strong wind.

Here’s the rotation. The iPhone measures rotation in radians per second. Here you see it in revolutions per second. The program shows that the conversion is pretty simple: you just divide by 2π.

The interesting thing here is the rotation about the Z axis, shown in blue, which shows the turn speed I got from the kite. You can see that this maxed out at about 1.5 turns per second. The green line shows the rotation as I tugged on the strings. This tracks pretty well with the blue line, showing this kite is really pretty responsive. The red line shows rotation from buffeting in the wind.

We had a pretty good time collecting and analyzing the data. If you’d like to try this yourself, start with the source code (below), which you can load onto your iPhone or iPad using iTunes. I actually used both--the iPhone to record the data, and the iPad, with it’s larger screen, to analyze and plot the data. Like programs, data files can be moved back and forth from one device to another with iTunes. The download also includes the data file used to create the plots from this article.

The programs should work for lots of things besides a stunt kite, too. After all, they are general programs for collecting data and plotting it--there was nothing specific about kites in the programs. The same day, we taped an Phone to the leg of a ballerina!

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