Open RSSI Antenna Tracker

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Rob Thomson
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Open RSSI Antenna Tracker

Post by Rob Thomson » Sun Oct 13, 2013 4:29 pm

Well... Title pretty much says it all.

I have been building an rssi tracker for my FPV models.

A little video of the results of my diy can be seen in this video.

https://www.youtube.com/watch?v=aa654Xc ... ata_player

I will post a build log and arduino code to this thread soon.

Rob

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Re: Open RSSI Antenna Tracker

Post by kaos » Wed Oct 16, 2013 12:30 am

that looks like child abuse to me. :P Just joking!

I see you have two helical and two circular ant on it. why not put helical for video as well?

This is interesting. Do you have a detailed plan/diagram?

How would this rssi/diversity compared to a GPS tracking system? I think Brent was talking about that a while ago. Don't know what happened to that project. He was looking for a mathematician.

Just received my 2W wifi booster today. This tracking ant thing is probably not too far from my 'working list'. ;)

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Re: Open RSSI Antenna Tracker

Post by Rob Thomson » Wed Oct 16, 2013 5:07 am

There ate actually 4 antennas.

two five coil helix on the outside.
1 three turn helix up front
1 clover on top

The system aims to keep the front antenna pointed at the model. What it also then does is to use a video switcher to auto switch feed to the stronger antenna.

So if you you fly overhead... Then clover takes over :)

It tracks very well.

I will hopefully have a build guide up today.

Rob


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Re: Open RSSI Antenna Tracker

Post by Rob Thomson » Wed Oct 16, 2013 5:56 am

Ok.

Not going to go into heave detail here.

The system is very easy to build. The base platform ideas cam from this thread.

http://www.rcgroups.com/forums/showthre ... 08&page=22

At a basic level your parts list is:

1 center antenna
2 outer antennas
3 receivers
1 360 degree servo
1 slip ring
1 arduino (almost any should work)
1 lazy susan bearing
1 fpv video switcher

The system works by measuring the RSSI values from each antenna.

Getting an RSSI value from it is easily done using PIN six on the module.

Image

You can happily leave out the buffer circuit shown. I did originally have them, but scrapped it due to heat issues melting my insulation. All that is needed for my tracker is the lead from pin 6 on the rf module - but if you want the buffer. No issue. It will still work.

Each of these values is measured, then used to drive a servo left/right depending on which one is the strongest.

Have a read of the rcgroups thread, and check these videos

Thead:
http://www.rcgroups.com/forums/showthread.php?t=1337608


Video:
http://www.youtube.com/watch?v=V2W9wiUJuf4

They will give a good idea of the construction of this sort of tracker.

What I have done is to provide a 'digital' control board to replace the analog one they use.

This is much more flexible, and general more 'stable'.

Attached is the arduino code. Very simple to follow :lol:

Shout if any questions.

Rob
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Re: Open RSSI Antenna Tracker

Post by jhsa » Wed Oct 16, 2013 6:37 am

Ha ha, that picture came from my friend Michael's website.. ;)

I saw him at the field with his equipment.. His tracker seems to be working well. He wasn't doing FPV there (because it is not allowed at the field), but just flying his twinStar LOS and we were watching the video.. the antenna tracked very well

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Re: Open RSSI Antenna Tracker

Post by Rob Thomson » Wed Oct 16, 2013 6:43 am

Cool :)

He has done similar trackers the mine.

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Re: Open RSSI Antenna Tracker

Post by kaos » Wed Oct 16, 2013 3:14 pm

OK (you said shout ;) )
the 3 helical are for radio tx and use the circuit to track? I also see 2 circular ant. Those are for video? if so why two (any diversity circuit for these two?) Why not use helical for video as well, I read with a CL on vTx and a helical on vRx will get a longer range and better result. Where did I get this thing wrong?

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Re: Open RSSI Antenna Tracker

Post by Rob Thomson » Wed Oct 16, 2013 3:34 pm

Ah...

My setup is as follows

1 x 3 turn helix on left
1 x 5 turn helix in middle
1 x 3 turn helix on right
1 x clover on top (receive)
1 x clover on back (relay to goggles)

The one on the back is not really relevant to the circuit as just a 10mw tx module wired to the AV feed from the receiver.

The diversity circuit for the outer two is not strictly necessary. I simply added this because it gives me an extra degree of redundancy. What really matters for your actual feed is the center helix, and the clover.

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Re: Open RSSI Antenna Tracker

Post by kaos » Thu Oct 17, 2013 1:27 am

so this is only for video signal tracking? why not add the helical ant for radio as well?

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Re: Open RSSI Antenna Tracker

Post by Rob Thomson » Thu Oct 17, 2013 5:44 am

I do.

I take the best signal from all the antenna, and use that one.

But it is not 100% necessary if just building a simple unit.

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Re: Open RSSI Antenna Tracker

Post by Kilrah » Thu Oct 17, 2013 6:05 pm

I think he means adding a directional antenna for RC.

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Re: Open RSSI Antenna Tracker

Post by kaos » Thu Oct 17, 2013 6:09 pm

yep. ;)

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Re: Open RSSI Antenna Tracker

Post by Rob Thomson » Thu Oct 17, 2013 6:32 pm

I see.

You could do that.

Actually something I have considered - hence my threads a week or so back regarding repeating an frsky signal :)

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Re: Open RSSI Antenna Tracker

Post by kaos » Thu Oct 17, 2013 9:53 pm

Cool. That is what I am thinking when building a tracker system. let us know your result. :)
I read only one time someone put a wireless relay station for RC, wonder what kind of 'lag' that would add to the control.

so in theory, you only need to add a helical for RC parallel with the center video helical, right?

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Re: Open RSSI Antenna Tracker

Post by Rob Thomson » Fri Oct 18, 2013 4:28 am

I would personally use a patch. But no real difference.


I would also consider placing it on an arm - maybe half a meter away from the other antennas.


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Re: Open RSSI Antenna Tracker

Post by kaos » Fri Oct 18, 2013 5:29 am

I would like to see how you aim these two ant exactly parallel. ;) Isn't the patch ant only covers ~7 degree at distance?
wait, don't you need a 'tilt' tracking for RC? In the video, looks like you only have 'pan' tracking?

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Re: Open RSSI Antenna Tracker

Post by Rob Thomson » Fri Oct 18, 2013 5:38 am

Tilt is useful.. But really no major issue for my needs.

The 4 turn helix has a 60 degree beam. That gives you quite allot of altitude. (And my antennas are pointed upward to prevent wastage of signal in the ground.

If the model flies overhead, out of the beam, the clover would automatically take over.

For the of, I would use this.

https://www.hobbyking.com/hobbyking/sto ... ules_.html

It is pretty much a wide beam, out the front of the antenna.

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Re: Open RSSI Antenna Tracker

Post by kaos » Fri Oct 18, 2013 6:23 am

hmm, forgot about that patch antenna, I have one too. with my 2W wifi booster and this tracking, that may get me to 15Km range. :mrgreen:

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Re: Open RSSI Antenna Tracker

Post by Rob Thomson » Fri Oct 18, 2013 6:31 am

Correct. It will also avoid issues with polarisation - hence my reason for thinking a patch :)

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Re: Open RSSI Antenna Tracker

Post by Rob Thomson » Sun Oct 20, 2013 6:07 pm

My tracker has been through a few 'upheavals'.

Testing of the system found that whenever the servo triggered, I would get interference on my video.

By the look of it, it is power/ground loop related - but I need to test more to find the source.

In the mean time, I have stripped out the video switcher code, and the switching device.
- in this case I found that the power/ground issue was feeding through via this unit. I will need to investigate more to find a cure.

Additionally I have bypassed the video to goggle relay.
- My intention is to move this off the unit onto a separate small tripod. I found that the signal broadcasting so close to the receivers was just not working so well.

Overall, the code is lighter, and the changes to the wiring have mean less impact on the video signal. To that point - it is actually working perfectly!!

I went out today for a test flight, and successfully tracked the model to 600 meters. (further than I have ever flown). At that point, I decided that as I did not have a RTH system - it would be better to not risk it by flying too far away!

The attached code is my latest working version. It has a new calc in it that uses some maths and a constant to improve resolution, taking distance into account.

It works well!

Rob
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Re: Open RSSI Antenna Tracker

Post by kaos » Sun Oct 20, 2013 10:44 pm

glad to see you are progressing. This radio frequency/signal interference is really 'voodoo'. I am following this carefully.;)

when you look at my other thread for video Tx/rx, I had a heck of time to get a clear image. ;)

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Re: Open RSSI Antenna Tracker

Post by kaos » Mon Oct 21, 2013 2:26 am

I was looking at this stepper motor. http://www.ebay.com/itm/221268196761?ss ... 1438.l2649
Why I never see people use this for tracking? any advantage /disadvantage of using a 360 servo and this. It is congtrolled idrectly by arduno. It seems to me this stepping motor has more resolution than a servo.

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Re: Open RSSI Antenna Tracker

Post by Rob Thomson » Mon Oct 21, 2013 3:55 am

Steppers are great.

I actually have a plan to d a version with a stepper - just not gotten round to it yet.

Guess servos are just 'easy'.


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Re: Open RSSI Antenna Tracker

Post by kaos » Mon Oct 21, 2013 4:20 am

servo are a lot more expensive when large enough to drive the turn table (and need mod) than that 2pc stepper for 5.48 with free shipping. waiting for you to come out with the Arduino control code so I can save at least 15.00 ~ 20.00 (one for pan , one for tilt). :mrgreen:

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Re: Open RSSI Antenna Tracker

Post by Rob Thomson » Mon Oct 21, 2013 4:58 am

I use a std servo. A whole $10.

If you forget about using the servo as a direct drive - it becomes easy.

The turn table sits on a lazy Susan bearing, with a slip ring in the middle to stop the wires twisting.

On the upper platter, a std servo is mounts, with a rubber wheel attached to it. The wheel is connected to the lower platter.

The result.. Turn the wheel, and the platters rotate.

Check the link to the rcgroups posts I made at the beginning of the thread. It becomes clearer :)

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Re: Open RSSI Antenna Tracker

Post by Flaps 30 » Mon Oct 21, 2013 12:30 pm

I'm trying to visualise what you are on about Rob. Do I take it that the servo feedback pot is on the turntable, instead of being in the normal place in the servo case?

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Re: Open RSSI Antenna Tracker

Post by Rob Thomson » Mon Oct 21, 2013 12:56 pm

Does this help?

https://www.youtube.com/watch?v=1QK7FZ7 ... ata_player

In then video, you can see then wheel attached to then servo on the front.

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Re: Open RSSI Antenna Tracker

Post by Bill » Mon Oct 21, 2013 1:35 pm

The 360 servo has no feedback pot and is capable of continuous rotation, it stops when the servo drive signal reverts to 1.5 ms so the feedback effectively comes from the tracker deciding its pointing at the signal and the software outputting the neutral pulse.
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Re: Open RSSI Antenna Tracker

Post by Rob Thomson » Mon Oct 21, 2013 1:41 pm

Exactly that.

The tracker simple moves the servo left or right depending on which rssi signal is the strongest.

When the difference in rssi is less than a set value, it stops the servo.

So essentially, no need to actually know the position of the servo, or the platter.


Rob

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Re: Open RSSI Antenna Tracker

Post by Rob Thomson » Wed Oct 23, 2013 4:17 pm

Current code has been moved to here:

https://code.google.com/p/open-rssi-tracker/

I am pretty happy with where the code currently is for the simple left right panning system with one servo.

I am now moving my focus to development of a two axis pan/title version of the tracker. This system will be somewhat more complex.

Planned features are:

- stepper motor control
- lcd based monitoring and configuration
- auto calibration - 1 click and will auto find / set offsets
- manual calibration via lcd & buttons
- low rssi alarm
- battery monitoring & alarm
- etc

I have already started work in this direction, even finding a perfect pan tilt mechanism.

http://www.ebay.co.uk/itm/Pan-Tilt-asse ... 51b0613f72

that includes steppers and slip rings.

Busy busy busy....

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