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Conundrum

Sat Jun 29 2013, 10:22AM

Registered Member #96 Joined: Thu Feb 09 2006, 05:37PM
Location: CI, Earth
Posts: 4062

Hi all.
One of my friends has a missing R/C aircraft, lost in a fairly large area.
Does anyone have any suggestions to locate an unpowered Wifi/GPS equipped
model when it is likely to be stuck in a tree?

I thought of detecting the magnetic fields from the motors, as these NIB magnets are
quite powerful and if I was to offset the Earth's field and compensate for tilt then
there's some chance of at least a directional vector.

Have some HMC5843 sensors and am also going to attempt to build a superconducting
impedance shift quantum sensor now my graphite is here.
Even if it doesen't work at least I can compare it with the 5843 and see if there is any
improvement with a ferrite rod.

Kind regards, -A

Houdini0118

Sat Jun 29 2013, 03:25PM

Registered Member #8558 Joined: Thu Dec 06 2012, 11:38PM
Location: usa
Posts: 57

Sorry i can't add anything useful but i am curious is a superconducting
impedance shift quantum sensor a real thing? does it require liquid nitrogen? But i can add that its very unlikely that the field from the magnet will reach far enough to be of use because of the size. A compass works anywhere because the earth is so large that the field doesn't fall of as fast but small magnets its practical gone by a few feet.

Conundrum

Tue Jul 02 2013, 07:27AM

Registered Member #96 Joined: Thu Feb 09 2006, 05:37PM
Location: CI, Earth
Posts: 4062

Yes it is, I have discussed it with some physicists and my colleagues and they say if I can make the superconductor's Tc high enough ie >200K with the aid of a Peltier stack it should work.
A SQUID is basically just a pair of shaped niobium-titanium blocks on a non conducting substrate with a tiny nano-sized gap, that senses magnetic fields by measuring the change in supercurrent flowing across that gap.
So it should work at higher temperatures if the superconductor is correctly engineered.

The graphite is used as an interface, also it happens to be similar to the SC pellet in consistency so changes in temperature shouldn't affect it too much.
Also pyrolytic graphite has been known to exhibit a Tc-like effect when illuminated with laser light so it might be possible to build a better
magnetometer this way.

For more information see

The device might resemble a wafer stack, with the graphite at the top and bottom and the flat superconducting pellets in the middle
separated by a thin layer of glass (SiO2) and insulated with low temperature Epoxy to stop water getting in.

-A

johnf

Tue Jul 02 2013, 08:53AM

Registered Member #230 Joined: Tue Feb 21 2006, 08:01PM
Location: Gracefield lower Hutt
Posts: 284

Like all energy sources the inverse square law comes into effect.
Fluxgates will work down to picotesla and are easy to make on am radio ferrite rods. The detecting lockin amp not so easy but possible either in software or chips like those from AD

Uspring

Tue Jul 02 2013, 08:58AM

Registered Member #3988 Joined: Thu Jul 07 2011, 03:25PM
Location:
Posts: 711

Static dipole fields drop off fairly fast with distance, i.e. 1/r^3. You might try experimenting on how far you'll be able to detect a magnet with a simple needle (field in comparison with the earths field) and then extrapolate from that to get a large distance value. There'll also be interferences from variations in the earth field.

Sulaiman

Tue Jul 02 2013, 11:51PM

Registered Member #162 Joined: Mon Feb 13 2006, 10:25AM
Location: United Kingdom
Posts: 3140

I'd be inclined to go for a uhf transmitter with a Yagi type antenna
and receive frequency = transmit frequency x2
as the semiconductor junctions in the electronics will create harmonics.
VHF (transmit) and UHF (receive) handheld transceivers are quite cheap (on eBay) compared to other options,

I doubt that a model aircraft up a tree will give much magnetic signature compared to underground stuff etc.

Dr. Slack

Wed Jul 03 2013, 07:54AM

Registered Member #72 Joined: Thu Feb 09 2006, 08:29AM
Location: UK St. Albans
Posts: 1659

Back on the magnetometer track, it's fairly straightforward to make a very sensitive and portable proton precession magnetometer, or better still a gradiometer - that's two on a pole some suitable distance apart like 1m to 3m, especially if you use some processing smarts (raspberry PI or similar) to measure the frequencies that are generated.

HV Enthusiast

Wed Jul 03 2013, 02:18PM

Registered Member #15 Joined: Thu Feb 02 2006, 01:11PM
Location:
Posts: 3068

wrote ...

Have some HMC5843 sensors and am also going to attempt to build a superconducting
impedance shift quantum sensor now my graphite is here.
Even if it doesen't work at least I can compare it with the 5843 and see if there is any
improvement with a ferrite rod.

Is the cost / labor in trying to build something to detect and locate this RC aircraft more than what the RC aircraft costs?

Conundrum

Fri Jul 05 2013, 10:00AM

Registered Member #96 Joined: Thu Feb 09 2006, 05:37PM
Location: CI, Earth
Posts: 4062

At this point it is turning into a "neat project" but yes there are other applications for this technology.
Kind regards, -A

klugesmith

Fri Jul 05 2013, 02:30PM

Registered Member #2099 Joined: Wed Apr 29 2009, 12:22AM
Location: Los Altos, California
Posts: 1716

Uspring said it first:
the far field strength of a magnetic dipole falls off as the inverse cube of distance.
Higher order moments fall off even faster.

Also remember that external fields from motors is wasted permanent magnet energy.
Good designs will minimize that.

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