Newsgroups: comp.robotics,sci.electronics
Path: cantaloupe.srv.cs.cmu.edu!das-news2.harvard.edu!news2.near.net!howland.reston.ans.net!ix.netcom.com!netcom.com!nagle
From: nagle@netcom.com (John Nagle)
Subject: Re: Inertial Gyro Specs <Help>
Message-ID: <nagleCznGsI.67u@netcom.com>
Keywords: Inertial gyro
Organization: NETCOM On-line Communication Services (408 261-4700 guest)
References: <calvinCzJA8w.Gqw@netcom.com>
Date: Tue, 22 Nov 1994 03:38:42 GMT
Lines: 41
Xref: glinda.oz.cs.cmu.edu comp.robotics:15546 sci.electronics:108864

calvin@netcom.com (John Calvin) writes:
>In doing my usuall rounds to Silicon Valleys best junk stores,
>I've run across some interesting Gyro modules 

>Althougth the claim they were inertial, a closer examination of
>the pods insides would indicate that its a mechanical Gyro.
>Manufacturer: Bosch
>Part Number: 8-638-710-419
>Serial Number: 800268

     Went down to Haltek in Sunnyvale to take a look.  These turn out
to be the gyro from the Etak Vehicle Navigation System, circa 1988,
as manufactured by Bosch to Etak specs.  It's a two-axis rate gyro
and a two-axis liquid inclinometer in one box.  Runs on 5V, 50ma.
You get four analog outputs, which swing from 0 to +5V.

      This is a rugged device, intended to be hard-mounted to the
frame of a car.  The rate gyro is a uniquely cheap mechanism; the motor
rotates a flexible metal plate, and the distance from the plate to a
parallel stationary circult board is measured capacitively.  You can open
up the unit by removing the four screws and take a look at how it's done.

      The inclinometer is a small cup of liquid, with an inner cup so 
there's only a thin layer of fluid between the inner and outer cups.
The viscosity of the fluid was chosen to provide some damping; remember
this thing hard-mounts to a car.  The position of the fluid is sensed
with four capacitor plates.

      The original system also contained a flux-gate compass, a
control unit with an 8088 CPU, wheel encoders for the non-driven wheels,
a casiette tape drive, and a display.  Using all this information
along with stored map data, the system could keep track of the car's location
and display it on a map display.  Who needs GPS?

      The rate gyro is really intended
only to provide some short-term correction info for the magnetic
compass; if you integrate the output of the rate gyro, drift rates
will be several degrees per minute.  This is a low-precision device.
Original price was around $120.
        
					John Nagle
