Mounting the Phone
The Physical Link
Unlike a standard GPS module which is light and insensitive to vibration, a smartphone is a heavy, complex sensor package. How you mount it directly affects flight performance.
Hard vs. Soft Mounting
For MAVLink GPS, Hard Mounting is generally preferred.
Why Hard Mount?
- The "Zero Clamp": The app uses the phone's internal accelerometer to detect if the drone is stationary. If you mount the phone on soft foam or a swaying gimbal, the phone will "feel" motion even when the drone is loitering. This prevents the Zero-Velocity Clamp from engaging, leading to drift.
- Latency: Soft mounts introduce a mechanical phase lag. The phone moves after the drone moves. This adds to the existing USB/EKF latency, destabilizing the control loop.
Vibration Concerns
While ArduPilot's internal IMU needs vibration isolation, modern phones have aggressive internal filtering on their IMUs. They can handle the high-frequency vibe of a rigid mount better than the low-frequency sway of a soft mount.
Placement
- Center of Gravity: Mount the phone as close to the center of the drone as possible.
- Lever Arm Effect: If you mount the phone far out on an arm, a simple yaw rotation looks like a lateral translation (X/Y movement) to the GPS. The EKF can compensate (
GPS_POS_X/Y/Z), but it adds complexity.
Orientation
- Sky View: The top half of the phone (where the GPS antenna usually is) must have a clear view of the sky (or ceiling/WiFi APs).
- Camera: If using Visual Odometry features (future), the camera needs a clear view.
- Compass: Keep the phone away from high-current ESC wires to prevent magnetic interference.