What types to use for Accelerometer
Wed, 06/13/2012 - 18:20
I was just playing around with the CBC's built-in accelerometer. I know I need to access the values with accel_x(), accel_y(), accel_z(). I assumed that the values returned are floats, but then
printf("%f, %f", accel_x(),accel_y());
prints out something like:
-3.000000-2.000000, -4.000000-2.000000
These numbers don't look like normal floats... also, this is when the CBC is not moving, so it should be 0,0. I tried using different CBC's and tried with int's, the values still aren't 0, which seems strange to me.
Any ideas?
Hi Flacon, welcome to the Botball Community!
According to https://github.com/kipr/cbc/blob/master/userlib/libcbc/src/cbc.h the accelerometer functions return an int. Also, when the CBC is stationary, it would be expected for the magnitude of the measured acceleration to be 9.8 meters per second per second, not 0, because gravity is measured by the accelerometers. You'll notice that when you rotate the CBC in place, you can change the direction of that measured acceleration (it will always be facing the ground). This is useful because you can use the accelerometers as a tilt sensor (several teams did this to orient themselves when the Botball game board contained hills).
Hope this helps; let us know if you have any more questions. :-)
-Jeremy Rand
Senior Programmer, Team SNARC (2012-2013), Norman Advanced (2010-2011), Norman HS (2008-2009), Norman North (2005-2007), Whittier MS (2003-2004)
2012-2013 VP of Tech, 2011 President, Botball YAC (2009-2013)
Mentor, Alcott and Whittier MS
Alright I'm using an int now, but when I shake the cbc the values for each axis max out at -128,127 (8 bits) vs the 12 bit accuracy the header file you linked claims.
SO: does the -128 still = -1.5 g and 127 = 1.5 g?
Thanks for the previous reply
EDIT: I just realized the vertical nonmoving acceleration is around 64 = 1G, so it can measure +-2 G at maximum values? Also is the measured value in linear correspondance to actual G's? So if 64 = 1G then does 32 = 0.5G and 127 = 2G?
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