On 7/23/07, Dave Hylands <dhylands@gmail.com> wrote:

There is a nifty one produced by Analog Devices, which incorporates
and calibrates a 3-axis acclerometer and a 3-axis gyro in the same
< http://www.analog.com/en/prod/0%2C2877%2CADIS16350%2C00.html>

Assuming your device is reasonably large, you could put 3 of the significantly cheaper accelerometers at or near the corners of the device, and, with a bit of math (ok, maybe a lot of math), get the same results, unless you expect to be in freefall for long periods of time (no skydiving robots). Even 2 accelerometers should get you decent results except in the case of spinning on the axis described by the two units.

You would still need to rely on a GPS unit to give you a reference point once in a while, to compensate for drift.

If you only needed direction and orientation (and not location), one of these could work as a reference as well: http://www.electronicproducts.com/ShowPage.asp?FileName=hlcn1.jan2006.html