Extrinsic Motivation: Smart Antenna Tracker for R/C Aircraft

dishes

Long distance FPV (First Person View) flying can be a handful. Keeping a video feed alive generally requires a high gain directional antenna. Going directional creates the chore of keeping the antenna pointed at the aircraft. [Brandon's] smart antenna tracker is designed to do all that automatically. What witchcraft is this, you ask? The answer is actually quite simple: Telemetry! Many flight control systems have an optional telemetry transmitter. [Brandon] is using the 3DRobotics APM or PixHawk systems, which use 3DR’s 915 MHz radios.

The airborne radio sends telemetry data, including aircraft latitude and longitude down to a ground station. Equipped with a receiver for this data and a GPS of its own, the smart antenna tracker knows the exact position, heading and velocity of the aircraft. Using a pan and tilt mount, the smart antenna tracker can then point the antenna directly at the airborne system. Since the FPV antenna is co-located on the pan tilt mount, it will also point at the aircraft and maintain a good video link.

One of the gotchas with a system like this is dealing with an aircraft that is flying directly overhead. The plane or rotorcraft can fly by faster than the antenna system can move. There are a few commercial systems out there that handle this by switching to a lower gain omnidirectional whip antenna when the aircraft is close in. This would be a great addition to [Brandon's] design.

Comments

  1. strider_mt2k says:

    Super awesome.
    Older systems that tracked people in stadiums wearing wireless mics were simply pan/tilt camera systems with a directional antennas attached to them. -Keep the subject in frame and you know you have signal.
    This stuff is simply incredible.

  2. Geebles says:

    An improvement on the design would be to encode the GPS data from the aircraft in the audio stream (I think there is a commercial system that already does this), this would mean you would not need the 433/915MHz transmitter at both ends. Downside is if you completely lose signal you won’t have an alternative channel for data (maybe a backup GSM modem to send GPS as SMS message to the ground station incase video/audio signal is lost, and also if the craft is lost because you will always have GPS position where there is GSM (lets face it that is everywhere))

    • Geebles says:

      I meant to sat that if the craft was lost you could easily find it because you would get a regular text message with the location data (maybe have it two way, send a text and response is GPS)

    • yetihehe says:

      GPS by SMS is good for stationary objects, not real time tracking. By the time you get sms (several seconds later), model airplane will be in a very different place.

      • geebles says:

        Yes but as a backup, as i said in the message to use the audio channel to send GPS data, but if that was lost then you have BACKUP data via a very very long range communication method (you could be in another country and it will still get back to you).. i think it would be more useful if you lost the plane, because 433MHz/915MHz/2.4GHz/5.8GHz don’t do very well when the TX is actually on the ground (my 433MHz from 200m range at a ground height of ~1m gives little to no signal). With the SIMCOM modules you can set up GPRS which would give a lot quicker data back and cheaper too

  3. bthy says:

    OR .. you could just get a diversity controller that auto. switches between antennas to get the best signal. combined with a few directional antennas this is MUCH cheaper and MUCH more reliable !

    • Chris C. says:

      I don’t recall seeing a DIY diversity controller featured here yet. In fact I didn’t know they existed until I tried Googling them a minute ago. Might make for a good follow-up feature, HAD staff? Anyone have one they’d like to recommend?

    • Adam Fabio says:

      Will a diversity setup work with high gain/narrow beam antennas? I’d think you’d need more than just two (Unless you stayed in one quadrant of the sky)

      • pelrun says:

        As long as one antenna in your diversity setup can see the signal at any point in time then it’ll work – it doesn’t combine the signals, it just selects the antenna with the best signal. If you set your antennas poorly and have a hole in your coverage, diversity won’t save you if you fly into it.

  4. Johnny says:

    Why not just run a skype call on a smartphone over a wireless telecom link… (3G,4G) duh?

  5. static says:

    Antenna tracker is a bit of a misnomer. Basically functions like a satellite tracker. Rather than software predicting where the vehicle will be, this uses coordinates and altitude information in a data stream to determine the vehicle location. The video said that the azimuth control circuitry is removed from the final version. I would have thought azimuth much more important than the elevation control.

  6. bobfeg says:

    You make a small quad copter that is powered through a wired tether to your control point on the ground. This copter contains the radio gear to communicate with the vehicle you are flying at a remote location. Placing the quad copter at high altitude will pretty much guarantee a VERY long range of communication to the remote vehicle.

    Line-of-sight is your friend….

  7. Andrew Tridgell says:

    You might like to also have a look at the ardupilot antenna tracker (see https://github.com/diydrones/ardupilot/tree/master/AntennaTracker). It can use any autopilot board that ardupilot supports and does active tracking. It can be configured for different servo types and comms layouts. This is the one we’ve built for OBC 2014: https://www.flickr.com/photos/dburkey/14454291247/in/set-72157645517023164

  8. laazarus says:

    Its obvious a lot of work has gone into this so i don’t want it to sound like I’m putting the project down. I also fly FPV using similar flight control hardware. A solution for this already exists. this is a commercial version https://store.3drobotics.com/products/ardustation
    It’s open source to i recreated it on an arduino uno. A kit even exists for the pan / tilt mount http://www.readymaderc.com/store/index.php?main_page=product_info&cPath=11_27&products_id=96

    will definitely be interesting to see how this solution compares to the existing, the auto orientation is interesting but really only eliminates spinning the tracker round on its tripod before launch.

    Bobfeg, we have a simple solution for that as well…. a really big stick, well more commonly an extendable carp pole.

    • bobfeg says:

      Yes, any method to get an antenna up high is good.
      But imagine an antenna at even 200ft above average terrain.
      That’s no big deal for a quadrotor but it’s a mighty tall carp pole :-)

      Military drones use this system. It’s been around a few years. Pioneered in Israel.

  9. Rhino says:

    If you limit aircraft altitude while overhead and also limit the pitch range of the tracking antenna then you can capitalise on the inherent side lobes of the directional antenna.

  10. “One of the gotchas with a system like this is dealing with an aircraft that is flying directly overhead.” This, in radar engineering, is known as “the pass-course problem.” It causes angular rates to skyrocket. There are some solutions, but most involve re-acquiring the object being tracked.

    Also, I thought this article was going to be about a real, no-kidding antenna tracker, using a monopulse or conical differential signal strength measurement and a control system to match.

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