The exhaust flame effect on an RC car is perhaps the detail that has the most impact during demos. This blue flash followed by an orange flash, bursting on stick release or full throttle — with optional crackle, double backfire and afterburn — spectators love it. And technically, it's one of the simplest features to implement.

The physical principle

In a real combustion engine, backfire occurs when unburned fuel ignites in the exhaust manifold. The combustion first produces a blue flame (high temperature, complete combustion) then an orange flame (incomplete combustion, carbon particles). This is exactly what we reproduce with our two LEDs.

The hardware

• 1 LED bleue branchée sur le pin G2 de l'Arduino Nano ESP32 avec une résistance de 220 Ω
• 1 LED orange ou rouge branchée sur le pin G32 avec une résistance de 300 Ω

The effect sequence

The effect runs in several steps:

1. Blue LED turns on for 50ms
2. Short 40ms pause
3. Orange LED turns on for 200ms
4. Both LEDs turn off — 300ms cooldown

These durations are fully adjustable from the Flare RC app via Bluetooth, without recompiling anything.

When is the effect triggered?

Two situations trigger flames:

• Au plein gaz : de manière aléatoire (1 chance sur 8 par défaut) — ça évite que l'effet devienne prévisible
• Au relâché du stick : si vous étiez au-dessus du seuil configuré avant de relâcher. Par exemple seuil à 60% — un relâché depuis 30% ne déclenche rien, un relâché depuis 80% déclenche la flamme. L'intensité reflète le niveau de gaz juste avant le relâché.

LED positioning

For a realistic effect, place both LEDs inside your exhaust pipes, oriented toward the outlet. If your body has plastic fake exhausts, drill them carefully with a 5mm bit to slide the LEDs in. A bit of hot glue to hold them in place, and the result is perfect.