How about putting three or so of the sensors on board and having them each check the other?


"Bill Daniels" bildan@comcast-dot-net wrote in message . ..

"jmk" wrote in message oups.com...

Morgans wrote:
"jmk" wrote

Worst case for most of those RC gyros (designed for RC helicopters,
etc.) is about 3 degrees per second.

Wow, I didn't know that they sucked THAT bad! g

Remember... that's *worst case* according to their spec.

They are based on the cheap MEMS solid state chips that are so
incredibly cheap because most modern cars have a anywhere from 4 to 20
of them. Usually a couple on each wheel, and another on each wheel
that steers. They compensate for the GPS shadowing that is otherwise
unacceptable on a moving map when driving in the city or under trees
(especially if it's been raining). They are only expected (in this
application) to show the basic turn direction for a couple of seconds
until the GPS can "catch up."

There more critical function is anti-skid, ride quality, and braking
functions - again, while the application may be critical, the exact
numbers aren't.

In a reasonably constant temperature environment, with some minimal
compensation from a processor, they should do MUCH better.

However, for something like replacing the AH, they are a LONG way from
being ready for prime time - at least without major enhancement. [We
did some rather fascinating experiments with "shake and bake" when the
first uncertified units came onto the homebuilt market. Including
putting one on a battery operated record player platter and setting the
whole thing (instrumented) in a refrigerator! After a few minutes it
showed the plane flying straight and level (DG function) as it went
round and round and round... G]

Interestingly enough, they are being used as part of the replacement
gyro for the King and Sandel HSI. The catch - like the automotive
moving map in cars, they are being updated every few seconds by the
flux gate.


I've been carefully watching the MEMS AHRS and IMU units for a while. The makers claim good performance but charge
high prices.

There is another way to achieve attitude sensing and that is multi-head GPS receivers that measure carrier phase
difference between the antennas. If you combine MEMS AHRS with GPS attitude the two independent systems complement
each other such that the AHRS provides "coast-through" attitude during GPS dropouts. It's not cheap but 0.1 degree
resolution is possible.

Google "CSI Wireless". No connection.

bildan