How it works
LapDog is a single-pilot lap timer for practising at home. It sits by your gate and watches your video channel. When you fly through, the signal peaks; LapDog notes when, and tells you the lap time.
The radio is the receiver
Classic lap timers (RotorHazard, Chorus, PIDFlight) use an RX5808 video receiver module to measure signal strength. LapDog doesn't need one.
The ESP32-C5 has a dual-band Wi-Fi radio that tunes from 4.8 to 6.0 GHz, which covers every 5.8 GHz FPV band, including Raceband and Lowband. ESP-SDR, from the ESPARGOS project, taps a debug I/Q path in the chip so the radio can be used as a software-defined radio. LapDog uses it to measure the power in your video channel's bandwidth hundreds of times a second, computed on the chip.
Finding the gate pass
- Smooth. Raw band power is noisy, so it's smoothed with an exponential moving average.
- Enter and exit. A pass starts when the smoothed level rises a set number of dB above the room's baseline (enter), and ends when it falls back below a lower threshold (exit). The gap between the two (hysteresis) stops a wobbly signal from counting twice.
- Peak = pass. The pass time is the moment of the highest smoothed sample between enter and exit.
- Lap = time between passes. Lap time is measured on the timer's own clock, never by when a message arrives.
The first pass after arming starts lap 1. In a race, the first pass after GO is the holeshot.
False reads
- Minimum lap time. A peak sooner than this after the last lap is a crash into the gate or a bounce back through it, so it doesn't count.
- Parked quads. A peak longer than about 1.5 s is a quad sitting at the gate, not a flyby. Without this, picking up a crashed quad would count as a lap.
Ignored passes are reported, so you can see how many were ignored and why.
Where the laps go
The C5 has a single RF chain: it can't listen and transmit at once. So LapDog listens, and right after a pass (when you've just left the gate and nothing is lost) it sends a short burst, then goes back to listening.
| Output | Reaches | Notes |
|---|---|---|
| USB | A phone or computer | Always on. Also used for settings. |
| Bluetooth | The LapDog Android app | Short advert bursts. Works with the phone unplugged. |
| ESP-NOW | HDZero goggles, RacePanel | ELRS Backpack OSD messages, the same as a club race day. |
Bluetooth and ESP-NOW are one or the other. Pick the one that suits the session in settings.
Practice and race
- Practice: arm, fly, and your first pass starts lap 1. No limit.
- Race: the goggles show ARM NOW, then GO! after a random 1–3 s hold. Race to a lap or time limit, then FINISHED!.
Heats number themselves on the timer, along with the event name. Both are broadcast with your laps, so the goggles and the app always agree.