Why the Neo is going to have 2 tri-axis accelerometers is beyond me. The only reason you would want to use 2 3d accelerometers is if you want higher accuracy in rotation measurements, but for the type of application I see little gain in the extra accuracy. The Nintendo Wiimote only uses 1 3d accelerometer and the sensitivity is good enough.
Here is a pdf that shows you what I'm talking about: http://kionix.com/App-Notes/AN005%20Tilt.pdf Notice how in figure 6 the angle of the different axis effect the tilt sensitivity. - David Mauro Iazzi wrote: > On 05/06/07, Tim Newsom <[EMAIL PROTECTED]> wrote: >> If your tracking movement with 2 3D accelerometers... What would another >> one provide. >> As far as I can tell (I am not an expert...) >> Tracking all 6 vectors will tell you absolute movement in space. I.e, >> when 2 vectors point in the same direction with the same magnitude at >> approximately the same acceleration as gravity.. Its probably laying or >> positioned flat on that side. > > "Probably" is the key here. with two 3d (linear) accelerometers you > cannot sense rotation around the axis between the two in an inertial > frame of reference. > Moreover you cannot distinguish if the Neo is laying face down or > pushed downwards with 2mg force. This example is somewhat artificial, > but means that you can probably find more realistic (though > complicated) movements that are not distinguishable with only two > accelerometers. > > You must then consider the errors which sum up, if you try to track. A > rough mental estimate gives that you can sum up as much as 1 meter of > error in ten seconds if you have a precision of 10^-3g over > acceleration measure. (it does not mean that you are 1 meter away from > the real position, it means that you can only be sure that you are at > most 1 meter away from that). > > Most of the time you will need good assumptions to get any information > from raw data: > > http://www.wiili.org/index.php/Motion_analysis > > can be of some help. No linear accel, no rotation, no tilt, are > assumptions which can give some meaning to the data and can be done > for single application, where you can assume the user will have some > particular behaviour (or you require it). > > Still absolute tracking won't probably be anyhow realizable. > > --mauro > > _______________________________________________ > OpenMoko community mailing list > community@lists.openmoko.org > http://lists.openmoko.org/mailman/listinfo/community > _______________________________________________ OpenMoko community mailing list community@lists.openmoko.org http://lists.openmoko.org/mailman/listinfo/community