Reading a gyroscope's orientation in a coil?

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.

  1. 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!

Dave

Reply to
dave.harper
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Yes
Reply to
John Fields

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! Rich

Reply to
Rich Grise

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.

Examples...

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

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

Reply to
CWatters

It'll work -- but metal in the region can cause eddy-current drag on the rotor.

Reply to
Don Foreman

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 seconds.

Am I correct in this statement?

Dave

Reply to
dave.harper

I believe you are correct yes.

Reply to
CWatters

There's a hobby/prototype-oriented website that sells IC gyroscopes and accelerometers. I haven't used those chips, but I did have a small PC board fabricated through their service. Otherwise, no connection.

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dhm

Reply to
dave madden

On 2 Feb 2006 10:48:49 -0800 in sci.electronics.basics, "dave.harper" wrote,

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.
Reply to
David Harmon

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 period.

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, Dave

Reply to
dave.harper

Yep!

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.

Reply to
Sjouke Burry

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

GOOD LUCK!

Jimbo

dave.harper wrote:

Reply to
Jimbo

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