Comments on: Hangtimer – Dude, How Long Was I Up There?

By: RocketScientist

RocketScientist — Fri, 09 Mar 2007 01:10:57 +0000

The HangTimer does use freefall (Zero-G) as part of it’s measurement, but it’s more complicated than Adam suggests. Exact details are confidential

In answer to your question Austin, it does measure from the moment you leave the ground till the moment you return (going up and coming down).

By: Austink

Austink — Thu, 08 Mar 2007 06:20:43 +0000

Is airtime different then hangtime? If my resoning is correct, this device only starts counting at the point you start falling?

By: Austink

Austink — Thu, 08 Mar 2007 06:01:13 +0000

Thanks Adam, that was extreamly helpful!

This thing is really cool, cant wait to get one

By: Adam

Adam — Wed, 07 Mar 2007 21:48:54 +0000

Freefall (or hang time) is the point at which a body is accelerating toward the earth at the same rate gravity is pulling them toward the earth. Since these two forces are opposite, then the individual feels absolutely no “gravity” or acceleration, even though they are accelerating toward the ground.

The accelerometer measures acceleration in three axis. If you place it on a table, it will measure 1G of acceleration just sitting there, because gravity is pulling it downward, but it can’t move due to the table, so it can sense the force.

If you drop it then it will experience no force internally until it hits the ground, at which point it will experience a force several times normal 1G, and then the normal 1G once it has stopped bouncing.

So the accelerometer in the hangtimer simply looks at all three accelerometers, adds up the total acceleration, and if it’s 0, then it starts a timer until the acceleration suddenly spikes (landing) and settles at 1G again.

I suppose I ought to put up an accelerometer tutorial on my website…

-Adam

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