Hi everyone
I’m working on tuning a small quadcopter and encountered serious stability issues.
Here’s a quick summary of my setup and what I observed:
Flight Controller**: Pixhawk 2.4.8 (running the latest PX4 stable firmware)
Frame**: Small custom frame (~300 mm motor-to-motor distance)
7.5-inch FPC tripblates and 1500 KV FPV Motors
Powered by 4 XRotor-Pro-50A ESC’s and a 6s LIPO
Setup
The Quad is mounted on a test rig, free to pitch forward and backward with a bit of play left and right.
Configuration No external GPS or Magnetometer attached, only telemetry and RC receiver
Initially, after resetting the PX4 parameters to default, I noticed the drone was oscillating heavily in pitch. During test runs (with the drone fixed in the test rig for safety), the motors became so hot, one of them melted the Arm it was attached to (3D printed from PLA) and eventually burned out.
Flight Review logs show
Extreme oscillations in pitch rate (~600 deg/s)
Actuator controls (pitch) saturating rapidly
Acceleration noise is very high, especially on the Z-axis.
Motor outputs pushed to max constantly, leading to thermal overload
After investigating, I found that PX4 default PID gains are tuned for medium-sized drones (~450–550 mm frame size), according to the PX4 Control Tuning Guide.
Given that my frame is much smaller and lighter, I believe the defaults are far too aggressive for my airframe, which may be the cause of my troubles.
Also, this is the first time I am using PX4.
My questions to the community
- Has anyone else experienced similar issues when tuning small/light frames?
- What would you recommend as a safe starting point for initial PID gains for a small (~300 mm) quad?
- Any advice for safe tuning strategies after a hard reset, especially to avoid burning down more motors?
Any help would be greatly appreciated.
I’ll also share some logs if needed.