Disorienteering

[bnewman]

Something I read recently reminded me of this idea I once had.

Orienteering is the sport of navigating with a map and compass. I've done some orienteering activities at camps, it's fun — of course, competitive orienteering requires that you be a good navigator and a fast runner/biker/etc., and I'm only the former.

The basic idea of navigating with a map and compass is that you can use the compass to orient the map to the terrain. This works because the Earth's magnetic field is approximately uniform over a small area. However, the Earth's isn't the only magnetic field! "Disorienteering" is the (so far imaginary) sport of navigating with a map and compass through an obstacle course of strong, local magnetic anomalies. Puzzles involved in a disorienteering course might include instructions to turn electromagnets on or off to alter the course, instructions to travel in the straight line indicated by a bearing or to follow a (curved) magnetic field line, unmarked reference points located at the intersection of two path segments, etc.

One thing I'm curious about is how much hardware you'd need to set up a disorienteering course. The Earth's magnetic field isn't all that strong, but to create a magnetic obstacle course big enough for a person to get lost in (if you can't get physically lost in it, might as well just call it a board game...) might call for a lot of electromagnets...

Comments

[orawnzva.livejournal.com]

I'm not sure that would be less expensive overall than running a lot of DC current through wires strung across the arena — the Earth's magnetic field is approximately equivalent to that from a 250-amp current line at a distance of 1 meter, and (assuming you are inside the circuit, so the path of current going back the other way is not too near the first current) that falls off linearly. It also negates the neat thing of being about magnets — the insight that a compass operates by detecting some physical force which can be manipulated, rather than by orienting you absolutely in space. Come to think of it, doing it by GPS is exactly backwards!

Maybe a board game like Stratego, but where some units contain magnets (including current lines — it would be fairly simple to run a few volts between two layers of the board and have pieced bridge between them) and some units contain compasses?

[sildra.livejournal.com]

That's why you'd use solenoids rather than simple current lines. Give copper's low resistance, you would be using considerably less power. When we just have to compensate for Earth's magnetic fields at work, we're typically using well under 1 A.

[orawnzva.livejournal.com]

Right, but you're not trying to do so over whole room, are you? The field from a solenoid falls off as r^-3, while that from a current line falls off as r^-1, so, if you want to paint a whole room with magnetic field lines, you'll probably need less current with the lines — on the other hand, you're running that current through a greater length of circuit, requiring more wire and more energy. Hmmm...

As mentioned elsewhere in these comments, I think some kind of board game is much more plausible. As for field disorienteering, I can imagine that, somewhere in the world, there was a bed of magnetite which, after having crystallized in alignment with the Earth's magnetic field at the time, was broken up by glaciers and deposited in the form of randomly oriented magnetic boulders scattered across a wooded area. Or not. But that's where you'd go to practice disorienteering.

[sildra.livejournal.com]

But the field from a current line goes in a circle, while the field from a solenoid goes straight. We aren't compensating over a whole room, but we are compensating over several cm. We do it with three pairs of Helmholtz coils--one pair for each axis. You probably wouldn't care about up-down, so you'd only need two pairs of Helmholtz coils.

P=I²R, so adding more wire doesn't require as much energy as raising the current. Also, in my experience, it's harder to find high current power supplies. Doing the calculations, though... it might still be prohibitively expensive.