This started out as an attempt to make a Gyrocompass from 3 hard drives; and ended being a Dead Reckoning Navigation Device (keeps pointing at its initial heading).

A gyrocompass is designed to find and point to true north, however in this case I think there is too much friction, and not enough rotational inertia for it to work.

I'll run through the theory and build anyway, and maybe somebody will have a suggestion to get it working? or will be able to build one better!

What it does now, is look really cool, spin up to around 12,000 rpm, and maintain its current heading. Because it maintains its heading while the base is moved, the degree markings can be used to obtain the new heading with respect to the original. In this way it can be used as a dead reckoning navigator. It is also very educational, I already knew theoretically how a gyro worked, but this puts it into perspective a lot better.

What you need:
2 hard drives
Assorted materials to create brackets/gimbals, I used brass and aluminium
Depending on your hard drive circuitry, you may also need a BLDC motor controller.

Equipment required:
Hand tools for dissasembly/assembly (hard drive take torx head screwdriver bits)
Metal working equipment to make brackets and gimbals

Step 1: The Theory

Once you get your head around precession, a gyrocompass is really a fairly simple device.

I found an article which had a very good explanation, and the figures are taken from that.

Firstly, a gyro works by using a spinning disc of high rotational inertia, gained by having large mass towards the edge of a disc spinning at high RPM.

The first figure shows a free gyro, with three axis of freedom, two are on pivots while the third is the gyro wheel's spin axis. A free axis gyro will keep a directionally constant spin axis as there are no forces acting on it. 

Precession is how a gyro resists the change in direction. When a torque is applied to a gyro, it applies a precession torque perpendicular. One of the more practical instances of this is countersteering on a motorcycle, as the rider aggressively twists the bars (by pushing on the inside bar), the front wheel generates a torque to lean the bike into the corner, allowing the motorcyclist to change direction very quickly.

The second figure shows the type of gyro I have made; a Pendulous Gyro. This is just a free gyro, but with a weight at the bottom. This weight applies a torque to ensure the spin axis is always horizontal. Because this torque is applied to a gyro, it in turn applies a precession torque, which rotates the gyro around its vertical axis.

The third figure shows how this is used to create a gyro compass. As the earth spins, the horizontal heading changes unless the gyro is pointing along the same spin axis as earth. The gyro attempts to follow the horizontal heading due to the torque from the pendulous weight. Once the gyro spin axis is aligned with the earth's spin axis there is no applied torque to the gyro, and its heading stabilizes.
<p>to make a gyrocompass from a rotating disk, you have to make it point to earth's meridian/vertical axis... simple design is by putting ballistics on both side of the rotational plane... note that plane of rotational axis does not point in a direction on earth, it points a direction in space. it means that as earth rotates your plane of rotational axis tilts vertical and moves horizontally as well to remain pointed in that direction in space(gyroscopic inertia). so to finally make it point to earth's vertical axis... we put ballast to either side such when the rotational plane tilts due to earths rotation, a force due to gravity is applied about the vertical axis, which means it will move horizontally(precession) as the rotational plane precesses towards earths vertical axis, it will continue to precess towards the opposite side(east to west) in this manner the side now facing east (which was facing west before) now begins to tilt, as it tilt(note that in this case now the spin is opposite of the other side) it will precess but this time towards the other direction(west to east). this oscillation will continue until it settles down on the vertical axis of earth... to dampen the oscillaiton an off centered weight is added(about its horizontal axis).... i hope this helped... an important note also is that mass should be concentrated on the rim of the disk to get max effect... add me on facebook for more. i hope this helped.</p>
<p>I had always figured that a gyrocompass acted as a sensor of precession torque which was then amplified (mechanically or electrically) and used to move an indicator needle, but according to the Wikipedia article the torque effect is increased by friction with a fluid or gimbal bearings. So perhaps you need MORE friction. The fact that that your gyro can maintain a heading after four hours is impressive. The initial orientation can make a difference too. Did you try testing the drift over a period of time starting from different attitudes? I realize this is an old project, so you have probably moved on, but I'd like to hear if you made any updates or discoveries in the last two years.</p><p>What BLDC controller did you use?</p><p>Really nice work, by the way. I particularly like you reused the heads and bearings.</p><p>Minor, off topic note: a motorcyclist does not aggressively twist the bars. To lean the bike one barely nudges the bars. Even on twisty roads the motion wouldn't be called aggressive. Flat track and supermoto racers do cross up their steering, but they take corners while sliding the rear the entire time.</p>
Beautiful work! I'm sorry to hear it doesn't work quite as you wanted, but it looks totally amazing!
I have since talked to a guy who services shipboard nav gyros, he said the rotors they use on similar RPM units weigh upwards of 10kg, and are larger diameter. So my gyro is probably getting about 5% of the rotational inertia that the commercial units use.
Love this! No idea why it doesn't do what you expected, did you wait for like a day with it running? I'd assume it would need that general range of time to observe the effect, since despite how fast the earth's surface moves, the change of angle with respect to north would go pretty slowly. But I don't really know what I'm talking about, this is just a guess.
The article said about 80 minutes for a cycle. The earth rotates at 15 degrees an hour, and applying just a minuscule force (and less than one degree) to the pendulum (to change its orientation as the earths spin would) causes the heading indicator to move. So I would expect the 4 hours I left it going for should have generated some perceivable movement. <br> <br>But on the plus side, it can hold it's current heading for at least four hours! <br> <br>Thanks for your comments though.
Very neat work!
Amazing work, this is beautiful to look at.

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Bio: I work in IT, but enjoy a variety of things. I'll usually do something until I'm almost good at it and then move ... More »
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