Electromagnetic Distance measurements

[atbaum]

I am currently designing an electromagnetic tether robot. The robot needs to stay a constant distance from an electromagnetic beacon. I am having difficulty coming up with a way to determine distance using magnetic field. I assume you run an alternating current through a solenoid to generate an elecromagnetic wave but I cant figure out how to determine the distance on the recieving end. I considered using a hall effect sensor and just producing a magnetic field but I dont think this will work for the range I need.

Any suggestions on how to approach this problem would be awesome thanks!

 

[Skogsgurra]

The distance has a lot to say. Up to around 10 mm, eddy current sensing or plain inductance measurement works. If you need more, it will be very difficult to use magnetic techniques. One way out would be to use several coils and code them using different frequencies and then use ratiometric techniques to determine distance and direction. Complicated, non-linear, not very good. But could work if you just want to keep a certain direction and distance.
Why magnetic? Is that the new trend?

Gunnar Englund

http://www.gke.org

--------------------------------------
Half full - Half empty? I don't mind. It's what in it that counts.

 

[itsmoked]

You might be able to use a "dip meter" method out farther than Skogs 10mm.

You could use "time of flight" light.

Keith Cress
kcress -

http://www.flaminsystems.com

 

[IRstuff]

You need to specify the range and the accuracy required. There are lots of ways of doing it, depending on the range. Assuming a typically plausible scenario, you could use ultrasonic, laser rangefinder, optical triangulation, GPS RTK, optical tape on the ground, EM coil on the ground, etc.

TTFN
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[electricpete]

Also, you might clarify if you also need to know the direction.


=====================================
(2B)+(2B)' ?

 

[VEBill]

We've had many threads where the OP was looking for a short range, indoor (not D-GPS), navigation solution. This one is more or less the same, except the OP has specified an "electromagnetic beacon", and hinted that it's a solenoid - this implying VLF in the kHz spectrum.

None of these threads has led to any breakthroughs in the subject of short range indoor (not D-GPS) navigation.

Because the solenoid will not be an isotopic radiator, any field strength measurement technique would require restrictions on relative orientation.

Time of flight techniques (time domain) are difficult over short distances. And would need ultra short pulse, not kHz.

I've sometimes wondered if a conceptual two-part oscillator (with the range gap in middle of the oscillator) might lead to a very sensitive ranging solution (since frequency is so trivial to measure almost anywhere in the spectrum).

Ultrasonics of course. There are Arduino modules and sample code.

The modern solution is to simply use a vision system; these days that's an MS Xbox Kinect ($100) and some reference software from the net. The EM beacon could have a blinking LED - emitting "EM" waves in the visible spectrum.

 

[atbaum]

Thanks for the tips yes this is for indoor use so a range of about 10m is sufficient I and as VE1BLL stated I am trying to use a low frequency in the kHz range. I think I have the basics of the transmitter where I can use On-Off keying to transmit data but I am unsure of how to implement the receiver to determine the distance and readjust the robot.

 

[IRstuff]

You still have not stated what accuracy you are trying to achieve.

TTFN
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[atbaum]

Sorry forgot to mention the accuracy. A 20cm accuracy will be sufficient

 

[MikeHalloran]

He's trying to come up with a robot that will, e.g. follow you around the house, or around the golf course (been done, but not cheap).

It's a serious challenge. If someone solves it inexpensively, several derivative products become possible, and profitable.



Mike Halloran
Pembroke Pines, FL, USA

 

[VEBill]

"... I am unsure of how to implement the [VLF] receiver to determine the distance... [to 20 cm resolution]"

I don't think anyone knows how to do that.

Keep in mind that a 10kHz signal (for example) has a wavelength of 30 km. And no, you can't on-off key a kHz carrier at nanosecond rates.

 

[IRstuff]

20cm resolution over a 20m distance is only 100 pixels, so even the typical cellphone camera could easily provide adequate resolution. A ceiling-mounted HD-webcam with an IR beacon on the top of the robot would seem to be the easiest thing to do. Put the robot on the same WiFi and close the loop over the WAN.

TTFN
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[mikekilroy]

would using the coil inductance change scheme of a cheap metal detector (coin hunting) provide what you need? Many offer distance to object upto 10" or so.