## Re: [Gumstix-users] use of an accelerometer.

 Re: [Gumstix-users] use of an accelerometer. From: Black, Michael - 2007-07-23 21:18:30 ```All 3 axes will show 0 (or close to it) if it's in free-fall (parabolic or not -- rotating or not). Unless you have some other external force besides gravity acting on it (like wind maybe). Accelerometers do not measure absolute acceleration (though you can compute it from the data) -- it measures relative acceleration (i.e. the force being exerted against external forces). =20 ___________________ Michael D. Black -----Original Message----- From: gumstix-users-bounces@... [mailto:gumstix-users-bounces@...] On Behalf Of Julien Lebot Sent: Monday, July 23, 2007 4:06 PM To: gumstix-users@... Subject: Re: [Gumstix-users] use of an accelerometer. Quoting Craig Hughes : > This is a 3-axis accelerometer. > > You are actually accelerating during free-fall, at a constant 9.8m/ > s^2. Your velocity cannot change unless you're accelerating. The > accelerometer is not really measuring your acceleration, it's > measuring strain on a MEMS crystal; when you're at rest, the crystal > is being tugged on by gravity, but the table or whatever you're > sitting on is countering that force, and thereby creates strain in > the crystal. When you're in free-fall, you're accelerating at the > same speed as the crystal, so there's no strain in the crystal, and > so it measures 0. > > C The fact that the falling object might be in translation when falling=20 should be considered too, the case where the object simply fall along=20 an axis is a particular case. Parabolic motion is also a free fall is=20 there is only gravity affecting the object, therefore all three axis=20 are involved. I'd check all three axis for motion, the object could also have rotated=20 (and could still be rotating). Julien ------------------------------------------------------------------------ - This SF.net email is sponsored by: Splunk Inc. Still grepping through log files to find problems? Stop. Now Search log events and configuration files using AJAX and a browser. Download your FREE copy of Splunk now >> http://get.splunk.com/ _______________________________________________ gumstix-users mailing list gumstix-users@... https://lists.sourceforge.net/lists/listinfo/gumstix-users =20 =20 =20 =20 =20 =20 =20 This electronic message and any files transmitted with it contain = information which may be privileged and/or proprietary. The information = is intended for use solely by the intended recipient(s). If you are not = the intended recipient, be aware that any disclosure, copying, = distribution or use of this information is prohibited. If you have = received this electronic message in error, please advise the sender by = reply email or by telephone (301-939-7000) and delete the message. ```