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Comment by redthrowaway | Hacker News Reader

I wonder how smart "throw" detection is. Could I strap it to a two-stage model rocket with a couple of D class motors? Or are you limited to a single impulse event, in which case I've got a couple unfired air bags kicking around.

There's a phone recycling bin here at school; I'm tempted to grab a few old android phones and see if I can get one working well enough to try it out.

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Nope, because phones don't have altitude detection. The only thing it can go by is accelerometer data, and you can infer what that data should look like using high school physics. They probably measure the duration of "weightlessness" (freefall), and maybe also check that there are large enough spikes of acceleration at beginning and end, although those will be mostly outside the range of the accelerometer. You can probably fool it by throwing it from some high point (bridge, building) and have someone catch it at the bottom.

Presumably you could use the GPS for altitude detection?

Or the barometer.

My take on this, not:

- on GPS, as mattbessey suggested. (precision: 2m max)

- integrating accelerometer data : Very difficult, as the telephone would spin. Also: measurement errors are integrated too, so not too precise.

Best option is time based:

1) Detect launch/landing time by looking at accelerometer spikes (easy, good time precision)

2) Altitude = 1/2 * g * ((timeLanding - timeLaunch) / 2) ^ 2. Air resistance negligible. g = 9.81 m/s^2.

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