On Fri, 9 Jul 2004 14:35:17 +0000 (UTC), Martin wrote in message 

> Arnt Karlsen wrote:
> > ..2 factors:  how does these handle planet rotation, and, how
> > accurate are these IMU's.
> Typical IMU's don't handle planet rotation at all because they never
> know _where_ on the planet they are located (you need to handle it
> different depending on which half of out earth you are sitting).

..makes sense, math 'n software job.

> Solid-state IMU's are not very accurate. As long as you have external
> references, like a camera picture, you are able to keep bank and
> attitude and navigate over short distances with a cheap solid-state
> IMU. For a flight over a long distance you have to readjust them like
> you do with the old, well known gyroscopes because the signal noise is
> too much to be used for accurate differentiation,

..true, and IMU's makes up only part of the navigation input. 

..Mat's mouse drilled-ball-stick makes sense here, it needs a 
wee springloaded weight sliding on the stick, and say a sliding 
potmeter to report the weight's position along the stick.

..the parked plane sees 1 G, dropping vertical.  Good calibration 
may even help it tell the latitude, by comparing it with known mass
forces and the observed planet spin force offsets.  ;-)

..an hacked up rodent also provides AOA, yaw etc vane circuitry, 
simply stick the mouse roller spoke wheel onto the vane axle and 
put the diodes around the wheel, and plug 'n play.

..med vennlig hilsen = with Kind Regards from Arnt... ;-)
...with a number of polar bear hunters in his ancestry...
  Scenarios always come in sets of three: 
  best case, worst case, and just in case.

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