Subject:
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RE: Detecting tilt with an Accelerometer.
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Newsgroups:
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lugnet.robotics
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Date:
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Mon, 21 Oct 2002 19:40:30 GMT
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Reply-To:
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<rhempel@bmts.!StopSpam!com>
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Viewed:
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802 times
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> Stop eating for just a sec, and help me understand this.
>
> If a sensor (accelerometer) is parallel to the earth's surface, the reading
> should be zero, right? (no acceleration due to gravity)
Steve,
The accelerometer is actually a micromachined beam. Think of a miniature
version of your arm holding a 5 lb brick. Your measurement axis is
rotation about the shoulder joint.
Whether or not you or the brick are moving, the brick is under the influence
of gravity and you measure the strainn in your shoulder.
If you are in free fall (0 G), the brick feels like it has no weight, and your
is under less strain.
If you tilt back on your heels, the downward rotational strain on your
shoulder changes to a push. When you end up on your back, the weigh of the brick
pushes your shoulder to the ground, but you're not measuring in that axis.
Ever notice how hard it is to hold a brick in your
hand when bouncing on a trampoline?
Ever notice how much pain a loose brick can inflict on
you when bouncing on a trampoline?
> But, if the object holding the sensor begins to fall (ignoring the push to
> start the fall), then an accelerometer placed at the center of the object's
> mass will begin to rotate, and accelerate until the rotation is 90 degrees,
> and the acceleration = 1g. At this point the sensor is in free fall, and
> the reading would (still/again?) be zero.
The key thing to remember is that at rest, the sensor is experiencing 1G!!!
Cheers, Ralph
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Message is in Reply To:
 | | Re: Detecting tilt with an Accelerometer.
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| (...) Stop eating for just a sec, and help me understand this. If a sensor (accelerometer) is parallel to the earth's surface, the reading should be zero, right? (no acceleration due to gravity) But, if the object holding the sensor begins to fall (...) (22 years ago, 21-Oct-02, to lugnet.robotics)
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