Re: noob laser question

>
> Cristi wrote:
> > Hi,
> >
> > I basically try to create an inertial platform with 2 gyros at 90

> 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
>