Obstacle Avoidance¶
Why Bennu Does Not Include Obstacle Avoidance¶
Bennu is a survey drone that flies pre-planned grid missions at 50--80m altitude. At survey altitude, there are no obstacles to avoid — the drone is well above trees, buildings, and towers. This matches how the entire commercial survey drone industry operates.
Safety Without Obstacle Sensors¶
Bennu relies on flight planning discipline and PX4 failsafes instead of obstacle sensors:
| Safety Feature | Mechanism |
|---|---|
| Fly above obstacles | Survey altitude (50--80m) clears all ground obstacles |
| Geofence | PX4 enforces max distance (200m) and max altitude (120m) from home |
| RTL on RC loss | Automatic return-to-launch if RC signal is lost |
| RTL on data link loss | Automatic return-to-launch if telemetry link drops |
| Battery RTL | Returns at 25% battery, lands at 10% emergency |
| RTL altitude | Returns at 30m — set above known obstacles near launch point |
| Pre-flight site survey | Pilot identifies power lines, towers, and tall trees before flight |
Power Lines
Power lines are the #1 cause of survey drone crashes. No consumer obstacle avoidance sensor can reliably detect thin wires. The only mitigation is pre-flight planning — identify and mark all power lines in the survey area.
When Obstacle Avoidance Would Be Needed¶
| Mission Type | Altitude | Obstacle Risk | Avoidance Needed? |
|---|---|---|---|
| Photogrammetry survey | 50--80m | None | No |
| Infrastructure inspection | 5--20m | High | Yes |
| Indoor/confined mapping | 1--5m | Very high | Yes |
| Urban mapping between buildings | 20--40m | Medium | Maybe |
Future: Adding Obstacle Avoidance¶
If Bennu is extended for low-altitude inspection work (Config B: RGB + thermal), obstacle avoidance sensors can be added. PX4 supports obstacle avoidance via the px4_avoidance ROS2 package, which requires a depth sensor connected to the companion computer.
| Sensor | Range | Weight | Price | Notes |
|---|---|---|---|---|
| Luxonis OAK-D Lite | 0.3--15m | 61g | ~$150 | Best value — stereo depth + onboard AI |
| Intel RealSense D435i | 0.3--10m | 72g | ~$300 | Proven, well-supported |
| Benewake TF02-Pro | 0.1--40m | 12g | ~$60 | Single-point LiDAR (altitude hold only) |
Adding a depth camera costs ~60g of weight (~2 min flight time) and requires the ROS2 companion computer (Pi 4) to run the avoidance planner. This is a future upgrade, not part of the initial build.