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Unread 05-21-2010, 07:52 AM
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Jared Russell Jared Russell is offline
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FRC #0254 (The Cheesy Poofs), FRC #0341 (Miss Daisy)
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Re: New Programming Manual

Quote:
Originally Posted by rhoads2234 View Post
I've just begun adding section on how to read a sensor to control a motor (analog or digital and on the driverstation or off of it)
Sensors included are limit switches, potentiometers, general analog, analog sensor on DS, and buttons on the DS. Is there anything else I should include?

It includes code. I haven't worked with an accelerometer myself, so I don't know when or how you would use it. How it is normally used?
There are three "common" uses for accelerometers that I know of:

1. Setting an "acceleration threshold" and getting alerted when the vehicle experiences a sudden acceleration greater than this. This is how they are used for deploying airbags, for example.

2. With a 3-axis accelerometer that is stationary, you can determine the direction of gravity. Accelerometers measure acceleration relative to a free fall, so on a stationary platform, you will always read a total acceleration of +1G upwards (the normal force of the ground pushing back on you). If the Z axis is the up-down axis, then when your accelerometer is flat on the ground you expect to read +1G on the Z accelerometer, and 0G on the X and Y accelerometers. But if you are pitched 45 degrees into the X axis, you would instead expect to read +sqrt(2) G in both the X and Z axes, and 0G in Y.

3. By integrating the output of an accelerometer, you obtain a speed estimate (since acceleration is the time derivative of velocity). If you integrate it again, you obtain position (since velocity is the time derivative of position). So accelerometers can be used (typically along with gyros, magnetometers, and/or compasses for angular measurements) as part of an IMU, or inertial measurement unit. However, these systems tend to drift over time - if your acceleration measurement is noisy at all, the noise will be compounded over time by your (double) integration.
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