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Thread: Making a mechanical gyro?

  1. #1

    Making a mechanical gyro?

    I understand I could get a laser ring gyro for around $2000, but back in the 1970's
    I worked on a missile system in the army that used a analog mechanical gyro that
    was caged at a fixed angle when started and the un-caged when in use. way I remember
    it, they spun a flywheel suspended in mercury at 8000rpm.

    is something like that still made?

  2. #2

    Re: Making a mechanical gyro?

    with only two weeks until the start of the winter season project (ABS angle senor)
    I'm still conflicted on the best technology to use. seen some good results posted on-line
    with using optical flow sensors. it seems to me if your going to test optical flow sensors
    for outdoor rover use, winter would be the time.

  3. #3

    Re: Making a mechanical gyro?

    Optical flow from a camera to detect movement and orientation isn't half bad!
    You could get a NVIDIA Jetson something-or-other and a camera for it; they already have some software demos to show how it works.
    There's also some research out of somehwere in Europe that gets excellent results for vehicle odometry.

    If you just want angle sensor, then a IMU like an MPU9050 would probably be much better. You get spin change from the 3DOF gyro part, and you get long-term attitude change from the 3DOF accelerometer part. Some of them also come with compass (magnetometer) but those are much less accurate in the short term (and may need physical hard/soft iron compensation!)

  4. #4

    Re: Making a mechanical gyro?

    jwatte, I had good results on the bench with mems based IMUs (like an MPU9050) ,the best
    bench results came from the phidgets spatial 3/3/3 (1044_1), but each failed in real world
    applications, the MPU9050 could hold an angle less then 30sec. with the 14hp gas engine running.

    the digital compass of the phidget 3/3/3 was a very sweet sensor, until you operate closes to cars,
    storage sheds , power transformers or underground power lines, the gas engine also caused distortions
    in the local magnetic fields.

    I cant'n see in my head how local things like power lines or cars or even
    the 14hp gas engine could impact
    the performance of a device like Px4flow optical flow sensor.

  5. #5

    Re: Making a mechanical gyro?

    the MPU9050 could hold an angle less then 30sec. with the 14hp gas engine running
    That's what the magnetometer (and ideally also a GPS input) is supposed to help you solve, using some kind of Kalman conditioning.
    Another option is to mount the IMU on a thick sorbothane substrate.

    The optical flow sensors are sensitive to high frequency vibration, because the optics may smudge. There's a distance/precision/sensitivity trade-off triangle in there somewhere -- optical mice work great, but only at very short distances. The Px4Flow is a camera-based sensor, so it is more sensitive to high-frequency vibration (anything higher than its frame rate.)
    Sorbothane may work there, too :-) It's a fairly expensive material, but you only need a little.

  6. #6

    Re: Making a mechanical gyro?

    plan A is to build an old school range limited gyro compass.

    pitch limit +/- 90deg.
    roll limit +/- 90deg.
    yaw limit +/- 400deg.

    with a 60mm brass flywheel spinning at 3000rpm.

    they now make a 60000cpr encoder at us digital, that would give me .001deg. resolution of the yaw axis.

    Click image for larger version. 

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    I want to build something that can give me +/- .002deg./5 minutes bias stability in real world operations.

    Last edited by Tommy_T; 11-28-2019 at 10:18 AM.

  7. #7

    Re: Making a mechanical gyro?

    Oooh, that'd be awesome!

  8. #8

    Re: Making a mechanical gyro?

    brass stock for flywheel
    Click image for larger version. 

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    plan A for powering the flywheel

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    Click image for larger version. 

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    I'v never played with these type of RC motors so I'm already working on plan B
    Last edited by Tommy_T; 12-02-2019 at 05:56 PM.

  9. #9

    Re: Making a mechanical gyro?

    Plan A

    looks like a us digital encoder that can give me 240000 counts costs $200.00(doable)

    the top shaft is longer for mounting the encoder.

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    Click image for larger version. 

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    found some .250" ceramic bearings on amazon

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    Last edited by Tommy_T; 12-03-2019 at 10:44 AM.

  10. #10

    Re: Making a mechanical gyro?

    How fast can you spin that encoder before it starts losing steps?

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