Rate Gyroscope circuitry explained

rate-gyroscope-driver

Hackaday alum [Adam Munich] shot a tutorial video on using a rate gyroscope.

Here he’s showing off the really fancy piece of ancient (technologically speaking) hardware. It would have set you back about fifteen grand in the 1960’s (inflation adjusted) but can be had these days for around $30. What a deal! These are not small, or power efficient when compared to the components that go into smart phones or gaming controllers, but they’re a heck of a lot more accurate than the ubiquitous modern parts. That’s because a rate gyroscope — which is the gold cylinder on the left — actually incorporates a spinning motor and a way to monitor how it is affected by changes in gravity. The driver/interface circuitry for this gets hairy relatively fast, but [Adam] does a solid job of breaking down the concept into smaller parts that are easy to manage.

Wondering what is different about this compared to a MEMS accelerometer? We know they’re really not the same thing at all, but wanted a chance to mention [The Engineer Guy's] video on how those parts are made.

Comments

  1. medix says:

    C’mon guys: rate gyro != accelerometer.

    Not even close.

    • Hyratel says:

      operation may be different but it’s used for the same job a MEMS Gyro-cellerometer is used for. and THOSE are just torqual accelerometers so shush

      • medix says:

        Rate gyro gives you rate of rotation (deg/sec – not angular acceleration) which you cannot get form an accelerometer (at least, not that I know of anyway). Ideally, you need both pieces of hardware, not just one.

        • Richard Mathie says:

          you can get rotation rate by placing accelerometers a fixed distance apart. the Coriolis and centrifugal acceleration in the reference frame of rotation can be found giving angular rate.
          see

          http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3274293/

          and https://edit.ethz.ch/idsc/Research_DAndrea/Cube/paper/ICRA10_1597_web.pdf

          needless to say the accuracy is lousy and construction difficult.

          • medix says:

            I stand corrected!

            That’s really awesome. Seems like it would just be easier to use a MEMS rate gyro and be done with it. Now the question remains: why would you do it this way? Seems overly complicated (especially after having a look at the paper).

            I only commented initially because there have been other instances here where the terms ‘rate gyro’ and ‘accelerometer’ are used interchangeably. ;)

          • Blue Footed Booby says:

            @medix
            Not an engineer, but the three big reasons for the accelerometer approach that I can think of off the top of my head are when:
            -you don’t want any moving parts for some reason
            -you already need an accelerometer or two, and you’re playing games with parts count or variety to get unit cost down
            -the particular problem doesn’t require a whole lot of granularity, like distinguishing between not rotating at all and rotating a whole lot

    • anon says:

      A better comparison would me a MEMS 3-axis accelerometer, but these are actually *far* more accurate than the rate gyro in this post.

  2. Joe says:

    I know you stated more accurate than what’s found in various devices… but I can’t picture this being more accurate than the MEMs gyros found in a variety of relatively cheap head-holding r/c helicopter gyros. There’s a reason those things can head hold.

    • AKA the A says:

      Look at some of the datasheets, you will find that the cheap MEMS gyros are…well, toys…
      The really nice ones are near impossible to get by normal people, since apart the sky high pricing it’s also an ITAR restricted item…

      These old bangers could guide an ICBM literally from the other side of the planet into a spot with a diameter of less then 1km (~0.625 miles), try that with a toy quadrotor :P

    • fartface says:

      call me when your toy helicopter can fly from NYC to LA and be within 50 feet of the landing glide path. The real things can do that.

      • Queeg says:

        NYC to LA and be within 50 feet of the landing glide path. The real things can do that.

        Not without being updated by reference to an external signal such as GPS or DME/DME. Going coast to coast purely on inertial and being within 50 feet isn’t going to happen with anything you and I have a security clearance to see.

        A couple miles, yes. 50 feet, no.

  3. I disagree with his assertion that micromechanical gyros are “crap”.

  4. Brian says:

    I bet that most of the circuitry could be replaced with a microcontroller, just leaving the AB-amplifiers. But some guys is apparently desperate to make it big and complicated.

  5. RP says:

    I normally hate long videos but that was worth the watch just for the discussion of Op Amp circuit design.

  6. In the name of... says:

    That looks like a rate gyro out of a certain shoulder fired, uh, fireworks shooter… What application do you think one would use a gold cased hardware gyro for exactly? and do you honestly think a modern mems device out of a cell phone is as accurate as that and as hardened to uh, the fireworks field, as that thing is? and do you think they don’t still use those, even if you can get them as surplus? You kids need to understand not everything made was inteded to go in your pocket and send text messages….

  7. YS says:

    Sine wave amp looks very strange… Did he mixed up inverting and non-inverting inputs (’cause it looks just like inverting amplifier, but has opposite input designations)?

    • eric says:

      yes it’s wrong…the clue is that the feedback resistor should always go from the output to the ‘-‘ terminal. if you connect it the other way around you get a comparator circuit.

  8. An really interesting version is the “FOG” gyro. Used on in spacecraft IIRC.

    “A fibre optic gyroscope (FOG) senses changes in orientation, thus performing the function of a mechanical gyroscope. However its principle of operation is instead based on the interference of light which has passed through a coil of optical fibre which can be as long as 5 km”

    http://en.wikipedia.org/wiki/Fibre_optic_gyroscope

  9. mefornow says:

    OH man, I was in the mood for some semantics based hacking-penis contest. Good thing I checked the comments.

  10. ddaygold says:

    Where do you buy one of these for $30?

  11. eric says:

    i found one of these rate gyros in my junk box, so i tried out the circuit presented in the video. it worked with two modifications.

    1. the sine wave op amp required a rewire (set as a noninverting amplifier with a gain of 2).

    2. the output stages tended to go into thermal runaway because the VBE generator diodes had a slightly greater voltage drop than the two base emitter junctions, so there was shoot-through current. i found that just using 1 diode was enough, and no diodes also worked but with crossover distortion (as expected).

    instead of building that crazy frequency divider circuit i just used a function generator.

  12. Chris says:

    gyro operation has nothing to do with gravity.
    Google “Conservation of angular momentum”

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