Re: [CAD_CAM_EDM_DRO] Re: noob laser question

Cristi wrote:

> Hi,
>
> I basically try to create an inertial platform with 2 gyros at 90 deg.

I think you need THREE gyros all orthogonal to each other.
If you plan to make the gyros keep the platform stable, I think
you will have even more horrible drift. As I understand it, all
stable platforms for inertial navigation use rate gyros that
sense the movement of the platform, and then use amplifiers
and torque motors to correct that movement. With this scheme,
the drift of the platform can be reduced by a factor of several
thousand.

What ARE your drift requirements? Are we talking degrees per
hour, degrees per day, ???

They have some really nice quartz spheres coated with
superconducting Niobium in the spacecraft Gravity Probe-B.
Gyro drift is supposed to be on the order of fractions of an
arc-second per year. But, we can only dream of such perfection
with a mechanical gyro. I really doubt you will be able to
build a gyro good enough for a stable platform in the "home
shop". First, achieving even a degree per minute with plain
gyros fixed to the platform will be impossible to achieve, due
to outside influences. With rate gyros, amplifiers and torque
motors, you might get down to a few degrees per hour. Have you
ever SEEN the inside of a stable platform? Do you know why they
make everything out of Invar and such? The motors to spin the
gyros produce heat, as that heat causes the whole platform to
expand, the platform is thrown out of balance. That change in
balance causes a torque on the platform, and is indistingushable
from precession of a gyro. Thus, any thermal gradient on the
platform imbalances it, and causes drift. Just exhale on one
side of the thing, and it will start drifting!

I think you need to do a LOT more research. There is a LOT of
info on the net. Here's one tidbit to tantalize you, but not
really something you want to aim for :
http://nuclearweaponarchive.org/Usa/Weapons/Airs.html

Jon