Yet Another Arduino-based KAP Transmitter - with Hover Rig

edited November 2016 in Control Systems
Some of you may have noticed this album of photos on Flickr of a KAP transmitter and rig under construction. I've now added a page to my website giving (much) more details.

The TX uses an X1TX0 r/f board extracted from a Spektrum DX4e transmitter. This is a full-range board, unlike the 'park-flyer' X10EMTX board I used in my previous TX but is programmed in exactly the same way (using the serial output pin of the Arduino). The KAP controller also has a Hover switch, since my new EOS M rig has Hover capability (a first for me). It also has a 5.8GHz video downlink (another first).

The page has downloadable wmf plans for the transmitter box and rig, as well as a downloadable Arduino 'sketch'.


  • Hi Dave,

    simply GREAT and always a positive surprise,... well done

    SMAC from Italy
  • edited November 2016

    Really useful stuff, my confidence in the project is growing. Having repackaged a transmitter (at hefty expense) in an industrial enclosure

    I was gutted to find I'd killed the radio range. The enclosure forms the counterpoise to the Tx antenna and I'd ruined that.

    I wonder if you have conducted range tests with the set up you describe?

    I tend to find my rig a huge distance down wind on Bft2 days and that's when the range limit finds me out. I have improved things a bit by using a proper Spektrum Rx with carefully positioned antennae but I reverted to an unmodified DX5e which seems to work fine although it's bulky and fragile.
  • No range test yet, but I plan one soon. The DX4e range is supposed to be at least 1000' (300m).
  • Hi Dave,

    Well done on your new KAP transmitter - it looks like a labour of love, as these things are meant to be!!. Your code looks well commented and as such should provide a useful tutorial to other Arduino fans like me! The use of a serial data stream rather than PPM is also very interesting and something new to me.

    Hi Bill,

    I’ve dismantled a few 2.4 GHz antennas and found that they are generally ground independent and do not require an external counterpoise.The common antenna arrangement uses an internal coaxial counterpoise in the form of a skirt which attaches to the end of the coaxial cable’s shield, leaving a quarter wavelength of bare coaxial inner conductor to act as the radiating element.

    I wonder if you have a transmitter or coax cable problem. Do you have a way of measuring the transmitter output power at the antenna connector? I’m lucky enough to have an ancient HP power meter, but there are a few low cost items which might work available on ebay these days:

  • I've pulled apart a number of 2.4GHz rubber ducky antennas - and can confirm Al's comments.

  • For various reasons Ive not been able to do much testing of the new TX and rig. However I did manage to do some ground-based tests today. Everything seems to work fine, at least at a range of 20 feet or so! The video is very sharp and there's no interference at all between the 2.4GHz rig control and the 5.8GHz video. The little GTeng video receiver is now velcroed to the TX box (I've removed the wrist strap).

    I've added some photos (and a very short video) to the Flickr set here. Sample photo below.

  • Congratulations Dave! Very neat...looking to see it airborne!

    Intrested to see how the GTeng reciever holds up with 200m+ range. BTW which 5.8Tx are you using with it?

    Getting the oportunity to fly when we are beset by short days, high pressure, fog and lightwinds takes some patience. . but if you get the chance this is the season of low light and dramatic shadow.

    Seasons greetings from the fen.


    ps fixed my range issue with a tweaked Rx antenna.
  • edited December 2016
    Hi Bill - I'm using this video transmitter. Very small and very cheap (somewhat over-powered though). The other (minor) snag is that, like all the video TX's I've come across, it needs 12v. I'm using a little Pololu converter to turn the 5v from the 4AAA pack into the 12v the TX needs.
  • At last I managed a real-life test of the TX, rig and downlink - a brief visit to Paignton sea front about 6 miles from home. As usual the sun was directly behind the kite making life difficult, but everything worked perfectly. The rig was never much more than 150' away, but video reception was excellent and despite the small screen quite sufficient to aim at largish targets.

    You can see a few of the resulting shots here.

    PS I forgot to test the HoVer switch! Next time ....
  • Success!

    I was looking at your EXIF data and am curious as to what settings you employed. Aperture was either f/7.1 or f/8, ISO was consistent at 100, and the shutter speed was 1/200sec to 1/320sec.

  • A bit of a cock-up Kevin. Somehow the Mode Dial of my EOS M had been switched to "Scene Intelligent Auto" (A+) without me noticing. Not sure what effect that had on exposure etc. It's now back to standard Still Photo P mode.
  • Classic. I've done that dial 'trick' several times myself!
  • I've added pages describing the AutoKAP version and the continuous panning servo version of the transmitter (and updated the main page to point to both of them).
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