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I'm currently involved in a project that involved measuring acceleration from a 3 axis accelerometer using a PIC microcontroller. And I only have high school physics.

I have 2 problems I need help with...

I want to measure foward acceleration and decceleration (it's going to be mounted on a vehicle). If the sensor was mounted level, I could just read the value of the coressponding axis and be done, but the sensor will never be mounted that way. It will most likely be mounted tilted either forward or back a bit, possibly somewhat side to side, etc...

My sensors read -1.5 G's to +1.5G's, Z should always be positive as the sensor will always be mounted upright, X is positive when accelerating, and Y is side to side (though I'm not really interested in it, but I'm guessing it's needed to find the devices "tilt" or something)

So, from what little I understand, I need to find out the tilt of the sensor, by reading how strong gravity is on the Z-axis (less measured gravity = more degrees off axis) Then somehow use that and the information from the other 2 axis's (X and Y) to find out the total speed of accelration. I also need to know if it's acceleration or decceleration, IE I know decceleration is just acceleration in the opposite direction, but I need some value to "test" to to see which of the two it is... I mean if I just plug the X,Y, and Z values into an equation and get a value with no sense of direction, I don't know if it's acceleration or decceleration (If THAT makes sense :P )

Now, as to the actual equations to do any of this, I'm totaly lost after 5 hours of google

Second problem is this, once I have the "corrected" acceleration value, it's only for that one "point" in time... I'll be taking a reading about 100 times a second, and need some help trying to figure out how much distance is traveled. I found the equation

s = ut+1/2at^2

where

s = distance

u = initial velocity

a = acceleration

t = time

however, I'm not seeing how to use this (I guess you could say "repeatedly") because after the first one, the initial velocity would be other then 0, and I don't know how to get the "new" initial velocity

Basically, I need to measure the time it takes to travel 50 feet (or like 15m) with a highly variable acceleration rate (which will sometimes be deceleration as far as the sensor is conserned, because of bumps etc,)

Any help will be most appreciated :) even a link to a page with some relevent math :D

Thanks, Thomas

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# 3 axis Acceleration

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