Sunday, January 12, 2014

Ground Control Station

With the model aircraft hobby scaling beyond line of sight, control equipment also grows more complex and sophisticated these days. To the point where we no longer designate it of transmitter, but refer to it as "Ground Control Station".

While I am still at the visual contact level of flying, the Ground Control Station is being improved to one day getting to do some FPV type of flying.

The basic gear to allow FPV to be possible consists of:

  • A model aircraft;
  • A flight control system with features (that while optional are highly recommended) such as:
    • Flight stabilization;
    • Return to Home;
    • Loiter and/or Position Hold.
  • A flight control camera with wide viewing angle (120º or better);
  • A video transmitter rated for at least 2x the target distance;
  • A cloverleaf antenna for the transmitter (and/or for the receiver as a backup antenna);
  • A good antenna for the receiver, in the following order of preference:
    • Yagi direccional (very high gain, narrow radiation pattern);
    • Patch antenna (good gain, wide, yet directional radiation pattern);
    • Cloverleaf antenna (reasonable gain, omnidirectional circular polarization radiation pattern);
    • Omnidirectional beam - bad choice for its linear polarization and donut shaped radiation pattern, causing the antenna to be practically deaf in the top;
  • A tracking system for the antenna, in case of selecting a directional antenna;
  • A good control receiver in the model aircraft with failsafe. Some high end systems such as EzUHF enable several tens of Kms of control range;
  • A good RC transmitter with 8 or more channels, computerized setup, and all sorts features. A Turnigy 9x is a good example of a cheap yet very flexible radio:
  • OSD with some parameters such as attitude, heading, bearing (of targets such as home and/or other waypoints), altitude, ground speed, air speed, world coordinates, battery voltage, capacity, current, etc;
  • A video screen or goggles to see from inside the model in real time;
  • Long range telemetry such as 3DR Radio (optional);
  • A recording system for later visualization of the analog video transmission (optional);
  • A fixed or gimbal stabilized HD video camera onboard the aircraft (optional).
We quickly realize that the overall money expenditure is quite significant, which means that losing a model is a lot of money flying away from our hands without return. This means that it is very important be methodical with this hobby in several aspects including:
  • double check each action taken;
  • understand well the gear and its quirks;
  • validate the robustness of the setup;
  • acquire good visual control experience;
  • perform pre and post-flight checks;
  • record unexpected behaviour even if it is transient. Check the concerned component(s) after flight;
  • replace parts that have experienced abnormal stress (e.g. overtemperature, mechanical strain, collision, etc), even if are still in working order;
  • respect a conservatively defined envelope, consisting of aspects such as:
    • battery capacity;
    • radio range;
    • maximum throttle capability;
    • maximum accepted wind speed;
    • attitude angles;
    • aircraft maximum air speed;
    • maximum propeller RPM;
  • underestimate the maximum radio range when close to radio transmission towers and other high RF interference sources.
In my Ground Control Station the latest progress is the addition of a small video recording module. It consists of a match box sized extruded aluminium enclosure, featuring Audio and Video I/Os and an SD card slot. It encodes the analog video to MPEG4 files which are stored on the fly into standard SDHC cards which can reach up to 32 GB in capacity.

This little device is very useful for later evaluation of the flight, and sharing in places such as this blog.
In case of crash, having a record of the last GPS coordinate is useful for later recovery of the model.

I have added it to the stack of electronic equipment featuring my hand held ground control station:

A switch at the left side allows me to select the source to the monitor as either the video receiver directly or the video output of the recorder. Normally the video output of the recorder is better as the delay is not noticeable and it does not blank the screen on absence of signal (we always have a picture even when it is just static):

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