Chapter 08 · Components
Your eyes in the air
The image takes a short, fast path: camera, transmitter, antenna, air, goggles antenna and screen. Everything in this chain must be the same system.
Analogue or digital
| System | Image | Latency | Price | Notes |
|---|---|---|---|---|
| Analogue | Low resolution, noisy | Very low | The cheapest | Compatible across brands. When the signal gets worse, the image degrades gradually and warns you. |
| DJI | The best quality | Low | The most expensive | Good range and HD recording in the goggles. |
| Walksnail | HD | Low | Mid-range | A digital alternative to DJI. |
| HDZero | HD | Low and constant | Mid-range | The favourite for digital racing. |
With digital, when the signal fails the image can freeze all of a sudden. Keep that in mind when you fly near the edge of your range.
Camera
- Size: micro (19 mm) or nano (14 mm) for analogue. It has to fit the frame.
- Light: what matters is how it copes when you go from sun to shade. An image that gets too dark under the trees will make you crash.
- Lens: wider lenses give a bigger field of view but distort the image. A field of view of around 120–150° is typical.
- Aspect ratio: 4:3 or 16:9, matching your goggles.
Video transmitter (VTX)
- Typical analogue power: 25 to 1000 mW. More power isn’t always better: it runs hotter and interferes with other pilots.
- Control from the flight controller via SmartAudio or Tramp: you change channel and power from the OSD using the sticks.
- Pit mode: transmits at minimum power while you set up, so you don’t cut out anyone else’s video.
- It needs airflow to cool down: don’t leave it powered on the ground for long.
Never power up a VTX without an antenna: it can burn out in a few seconds.
Antennas
Polarisation
Right-hand circular (RHCP) or left-hand circular (LHCP). The drone’s and the goggles’ must match; if not, you lose a lot of signal.
Omni or directional
On the drone, omnidirectional. On the goggles, ideally one omni and one directional (patch) pointing where you fly.
Connectors
SMA, RP-SMA, u.FL or MMCX. Check them before you buy: they’re easy to mix up.
Goggles
- Box goggles (one big screen, cheap) or compact ones (two screens, sharper).
- Look at the field of view, the resolution and whether you can adjust the distance between the eyes (IPD) and the dioptres.
- With recording (DVR): very useful for finding the drone after a crash. To edit the footage, see Video post-production.
- Digital goggles must be the same system as the drone’s VTX.
Latency: the delay you don’t see
Latency is the time between moving the stick and seeing the result in your goggles. It adds up from several parts, and at 160 km/h the drone travels almost half a metre every 10 ms.
| Part | Rough latency | How to reduce it |
|---|---|---|
| Analogue or HDZero video | 10–20 ms | Low-latency camera and goggles |
| DJI or Walksnail video | 30–50 ms | Higher frame rate and good signal |
| Radio link | 5–25 ms | ExpressLRS; 250 Hz is a good balance |
| Flight controller (PID and filters) | 1–5 ms | Don’t filter more than necessary |
| Motor acceleration | Up to 50 ms or more | Motors with enough torque and light props |
Rough values: every combination of parts is different and manufacturers don’t publish figures.
5.8 GHz channels
In analogue there are several bands (A, B, E, F and R, the Raceband) of 8 channels each. Raceband has the most widely spaced channels (37 MHz), but in the EU only channels between 5725 and 5875 MHz are licence-free: R1, R2 and R8 fall outside, and only a few pilots fit in this 150 MHz slice at once.
| Pilots | Within the EU licence-free band | With a licence (whole band) |
|---|---|---|
| 2 | F1 and F7 | R1 and R8 |
| 3 | F1, B6 and A1 | R1, R4 and R8 |
| 4 or more | Too tight: fly in heats | R1, R2, R7 and R8 |
Plan your session: the channel planner picks channels for each pilot taking intermodulation into account, mixes analogue and digital and flags the ones outside the licence-free band.
- Intermodulation: two signals together can generate a third one that steps on another. That’s why it’s better to pick channels from different bands.
- In a group, low power: 200 mW or less outdoors and 25 mW indoors.
- Keep analogue and digital pilots about 3–5 metres apart.
- Legal frequencies and power levels depend on the country. In the EU, the licence-free limit at 5.8 GHz is very low; higher power may require an amateur radio licence.