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Reading a gyroscope's orientation in a coil?

Discussion in 'Electronic Basics' started by dave.harper, Feb 2, 2006.

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  1. dave.harper

    dave.harper Guest

    I've been evaluating different methods to sense a gyroscope's
    orientation, and needed some advice in determining if one method in
    particular is sound. (It has been years since I had a class in
    mechatronics and/or generators)

    Assume a freely rotating gyroscope given an initial rotational velocity
    and then allowed to coast (unpowered):

    1. If I were to place a permanent magnet on the rotating component
    (aka the rotor) so that it's North-South orientation is perpendicular
    to the axis of rotation, wouldn't the magnitude of the voltage induced
    in the coil depend on the rotor's tilt within the coil? That is,
    wouldn't the coil AC voltage be at a maximum when the magnet was
    rotating perpendicular to the coil's axis and a minimum when the axis
    are aligned? Assume I can account for the effect the slowing speed of
    the rotor has on coil voltage.

    2. If this theory is sound, what would be the best way to digitally
    quantify the magnitude of the AC voltage? The simplest way I can think
    of is to rectify it, use smoothing cap, and read it via an ADC. I'm
    open to other, more sensitive (and easily accomplished) methods.

    If I actually play around with this idea, it will be done on a personal
    budget and on my spare time, so please keep that in mind before
    recommending extremely expensive or complex ideas.

    Thanks in advance for any help!

  2. John Fields

    John Fields Guest

  3. Rich Grise

    Rich Grise Guest

    Well, it has to have an axis of some kind, that means some kind of axle,
    with bearings at the end, and since you say "freely rotating", that
    means it's on a gimbal of some kind. Just put positional sensors at the
    gimbal's bearings, and maybe slip rings if it has to go >= 360°.

    I think sensing a PM by one coil would be more of a hassle than it's
    worth, but the obvious answer is, do it and see what happens! :)

    Have Fun!
  4. CWatters

    CWatters Guest

    Not sure if this is of interest but...

    It's possible to buy very very small Piezoelectric vibrating Gyroscopes for
    use in model helicopters and the like. I have one installed in a 1/5th scale
    Nieuport 11 to counter a the yaw motion when the tail comes up on take off.
    Some are about the size of a large sugar lump and only weigh a few grams.
    It's should be possible to obtain the sensors on their own.


    Comparison...of different technology.. (bit basic)..

    In general the larger and more expensive units have less drift and noise.
  5. dave.harper

    dave.harper Guest

    These are rate sensors, correct? If I wanted an accurate orientation
    reading, rate sensors would work so long as I gave it an initial
    orientation and integrated them (along with some tensor math) in order
    to determine my position. However, aren't these sensors somewhat
    noisy? I believe the estimated and actual orientation would diverge
    (drift) due to noise integration if I used them for more than a couple

    Am I correct in this statement?

  6. CWatters

    CWatters Guest

    I believe you are correct yes.
  7. dave madden

    dave madden Guest

  8. David Harmon

    David Harmon Guest

    On 2 Feb 2006 10:48:49 -0800 in sci.electronics.basics,
    Yes. But gyroscopes usually go to great lengths to eliminate
    friction and other effects on the rotor, and if you put such a
    magnet on the rotor the induced current in every nearby conductive
    part will
    1. suck rotational energy out that would have to be replaced at a
    much greater rate than otherwise and
    2. affect the alignment of the gyro and reduce accuracy.
  9. dave.harper

    dave.harper Guest

    I'm really only looking to have it measure orientation for, say, a
    minute (not long term). And I'd like to have it drift less than, say,
    5 deg/min. I'm making the assumption that eddies and other EM
    interactions shouldn't affect it significantly during that short time

    However, since you've brought it up and if you don't mind me asking,
    how significant do you think the eddies would be? I'm looking at using
    aluminum rings (or possibly polycarbonate if aluminum is a problem).

    Secondly, how much "drag" would be induced on the rotor by the current
    induced in the coil? Ideally, the current in the coil would be near
    zero (just enough to read via an ADC). Shouldn't that minimize the
    "drag" on the rotor from the coil?

    Thanks in advance for any extra help,
  10. Sjouke Burry

    Sjouke Burry Guest


    Seconds for the cheap ones, 10's of minutes for
    the very expensive ones.
    Also at very high rate of turn some of them
    start skipping.
    We used a 3 axis magnetic compass together with
    GPS to make a guidence system for blind people.
    (Sory ,just experimental,not on the market).
    That way, you have a consistent(but inaccurate)
    knowledge about current orientation.
  11. Jimbo

    Jimbo Guest

    Hello Dave,

    It doesn't sound like you have the option of changning the gyroscope
    itself, but If you do I suggest looking into fiber optics based
    gyroscope. There are NO MOVING PARTS and are highly accurate. Of
    course just like any technology there are pros and cons so do your
    homework. Here are some companies to get you started:

    Photonic Systems, Inc. in Billercia, MA
    Corrsys-Datron Sensorsystems, Inc. Southfield, MI
    Elektron Systems, Inc. St. Petersburg, FL
    Phasebridge, Inc. Pasadena, CA


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