From: Robin Hollands Subject: Re: HOME-BREW: Cheap accelerometer input devices Date: Wed, 23 Apr 1997 15:41:31 +0100 Message-ID: <335E1F9B.5AF3@shef.ac.uk> Organization: Automatic Control & Systems Engineering, University of Sheffield Michael J. Sinclair wrote: > > For you home-brewers out there, there are a number of relatively > inexpensive (and untapped) markerless tracking sensors ready to be > incorporated. We use both linear and rotational (gyro) accelerometers > for position and attitude tracking. > > Check out Crossbow's 1, 2, or 3 linear accelerometers (compliments of > the auto air-bag industry) at > > www.xbow.com Since accelerometer based devices offer the promise of truely limitless tracking, its perhaps surprising that no-one is commercially producing a tracker based on them. The truth is that although rotational gyroscopes are usuable for orientation tracking (although they still suffer from drift to varying degrees), the use of linear accelerometers is extremely difficult. I wrote an article on this for VR News last year some time, and the only company who had got close to harnessing their power was Angularis Intertial Technologies. However, even they only used the linear accelerometers for fast, extremely short-term tracking, and had to constantly recalibrate them using a slower, more reliable technlogy (e.g. ultrasound or electromagnetics). I've come across a few students and various homebrewers of have tried to use linear accelerometers in the past, but all say that air-bag accelerometers are targetted for acclerations far higher than those experienced during normal motion, and therefore the resulting errors introduced through the double differentiation process make them unusable. That said, I'd be more than pleased to hear if someone has cracked the problem at long last. Michael, what positional accuracies are you getting with your system, and do you apply any special filtering algorithsm? Cheers, Robin Email: r.hollands@sheffield.ac.uk WWW: http://www.shef.ac.uk/~vrmbg/staff/rjh/rjh.html BOOK: http://www.shef.ac.uk/~vrmbg/vrhmhb/vrhmhb.html