Re: noob laser question

Hi Jon,

the optical sensor or the glue point and the brushes is just for the
balancing operation. I need a point on the rotor that periodically
breaks the 5 V to identify the heavy spot. The only problem to the
optical sensor is it needs to trigger the signal in a window of about
5 microsecs ( the time you need to sweep one degree at 30 krpm ).

--- In CAD_CAM_EDM_DRO@yahoogroups.com, Jon Elson <elson@...> wrote:
>
> Cristi wrote:
> > 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.
> As I said in my last post, all real stable platforms (not
> including steady-cams) use rate sensor gyros that correct the
> platform orientation through amplifiers and torque motors.
> I am quite certain that if you strap down 3 gyros to a
> gimbal-mounted platform, you will have HORRIBLE drift. After
> weeks of tweaking to balance the thing, you will maybe be able
> to get the drift down to a couple degrees a minute, even with
> really GOOD gyros. It is the amplifiers that improve the drift
> problem by many orders of magnitude, by isolating the gyros from
> the imbalances on the platform.
> > 1-2 degrees per hour is not such a big problem, although I would hope
> > for better.
> You will never get there without rate gyros and amplifiers.
> Better? Serious inertial nav systems costing several hundred
> thousand $ don't do a whole lot better than this!
> > 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?
> You are going to have a 2" disc spinning at 30000 RPM, with
> brushes riding on it? How much heat will that produce? What
> motor will be able to keep the gyro spinning with that drag?
> The glue will handle the brush going over it 1.8 million times
> (one hour at 30K RPM)?
> > The second approach will be an optical sensor - but I don't know what
> > type of optical sensor should I use.
> If you are a tinkerer, you've seen the optical slot sensors in
> old floppy drives and such, an object gets between emitter and
> detector and breaks the light beam. There are very similar
> devices that work by reflection, look in the Digi-Key catalog
> under opto-electronics. What do you need a sensor on the
> rotational position of the gyro for, anyway?
>
> Jon
>