Re: noob laser question

Hi Jon,

thanks for the fast answer. The problem with angular sensors "piezo"
or smth like this is they are not gyroscopes ( gyroscope = keep your
spin direction in the old greek lang ) but they are angular rate
sensors. That is, they have drift in such a way that in 15 min let say
you will get report that you're spinning with 2 deg / minute. You
start to compute and after 10 min. you think you've spin 20 deg but
you haven't at all. That's why mechanical gyros have been used for
navigation while angular MEMS or piezo sensors haven't and will never
be. Today they have laser and optical gyros, as angular sensors but
with much much less drift.
1-2 degrees per hour is not such a big problem, although I would hope
for better.
As for the platform, it won't work for more than an hour. You have
spherical platforms suspended in fluid bearings to avoid gimbals lock
and increase precision.
So, going back to balancing. I will put the disc on a fixed small
table via ball bearings, and put an accelerometer on that table. My
disc is from steel and conduct electricity. I think I will connect it
to 5V via 2 small brushes. In a certain point, where one of the
brushes touches the disc, I will put a small spot of glue ( CyanoA or
smth ) so it will cut the 5V anytime the brush passes through there (
while the rotor will spin ). What do you think?
The second approach will be an optical sensor - but I don't know what
type of optical sensor should I use.

--- In CAD_CAM_EDM_DRO@yahoogroups.com, Jon Elson <elson@...> wrote:
>
> 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
>