Summary: I designed and built an autonomous RC airplane from scratch, airframe, avionics, and control code, through bench/taxi tests and a few short flights, got basic stabilization working.
Goal — Build a reusable RC platform/system for autonomy.
Approach — Simple foamboard airframe with onboard control logic and SD-card logging. Signal flow: IMU + RC receiver → control laws on the microcontroller → mixer/override → servos/ESC. Tested and iterated using software-in-the-loop (SITL) and hardware-in-the-loop (HIL).
Results — Achieved liftoff and short controlled segments, validated the stabilization code, and created a platform for tuning and future iterations.
What’s next — Integrate airspeed sensing, add waypoint navigation, refine gains/control laws, and keep polishing the system.
| Area | Summary |
|---|---|
| Timeframe | May–Aug 2025 • Solo |
| Airframe | Foamboard + basswood; tricycle gear; ~30″ fuselage, ~40″ wingspan |
| Objective | Stabilized flight testbed for future autonomy |
| Control Architecture | IMU + RC receiver → control laws (PD/PID + state machine) → mixer/override → servos/ESC |
| Data | On-board logging (attitude + rates); MATLAB/Simulink SITL checks |
| Test Flow | Bench → Taxi → Flight; liftoff + short controlled segments |
| Toolchain | Excel, SolidWorks, XFLR5, MATLAB/Simulink, Arduino IDE/C++ |
Airframe: Front and top-down views showing basic sizing, control surfaces, and tricycle-gear placement near the CG.
Layout: Battery/ESC up front with a removable avionics tray mid-bay for quick iteration.
Avionics: Microcontroller + IMU wiring paths; RC override and on-board logging.
CAD: Representative model used for sizing/mounts; the final build iterated from this geometry.
flowchart LR
subgraph Onboard System
IMU["IMU<br/>(attitude & rates)"]
RC["RC Receiver<br/>(sticks, switches, knobs)"]
Control["Control Laws<br/>(PD/PID + State Machine)"]
Mixer["Command Mixer<br/>(override + trims + limits)"]
Servos["Servos<br/>(elevator / rudder / aileron)"]
ESC["ESC / Throttle"]
Logger["Logger"]
SD["SD Card"]
Health["Arming & Failsafe"]
end
IMU -->|sensor data| Control
RC -->|channels| Health
Health --> Control
Control --> Mixer
RC -->|override| Mixer
Mixer --> Servos
Mixer --> ESC
%% Logging
IMU --> Logger
Control --> Logger
Logger --> SD
%% Offboard sources (dashed)
Sim["MATLAB/Simulink & XFLR5"] -. "models/params" .-> Control
Tuning["Ground Tuning<br/>(knobs/switches)"] --> RC
Behavior notes
- Arming / Failsafe: arms only after a short delay with throttle low and a good radio link; any disarm or radio loss cuts the throttle.
- State machine: modes are switch-driven (easy to drop back to MANUAL). Typical flow: IDLE → throttle ramp → elevator ramp → climb → cruise.
- Override & Mixer: in MANUAL, RC goes straight through. In some AUTO modes I blend manual input with the autopilot command and enforce trims/limits before sending PWM to the servos/ESC.
Logging is implemented. See data/sample.csv for a short capture during THROTTLE_RAMP.
Columns: Time_ms, Phase, Pitch (deg), PitchRate (deg/s), Elevator cmd, Yaw (deg), YawRate (deg/s), Rudder cmd, Throttle (µs).
Power rails: ESC BEC provides +5V_BEC to the receiver, servos, and Teensy VIN; the IMU is powered from the Teensy 3.3 V rail. All grounds common.
Signals: PWM_EL → pin 6, PWM_AIL → 7, PWM_RUD → 8, PWM_TH → 9, SDA/SCL → 18/19, iBUS → RX1.
Safety notes: Avoid powering system from usb and battery at the same time
| Function | Teensy pin | Connector pin | Net |
|---|---|---|---|
| Elevator signal | 6 | SERVO_ELEVATOR.1 | PWM_EL |
| Aileron signal | 7 | SERVO_AILERON.1 | PWM_AIL |
| Rudder signal | 8 | SERVO_RUDDER.1 | PWM_RUD |
| ESC throttle signal | 9 | ESC_THROTTLE.1 | PWM_TH |
| Receiver iBUS → RX1 | 0 (RX1) | RECEIVER.1 | RX1 |
| I²C SDA / SCL | 18 / 19 | BNO055 SDA / SCL | SDA/SCL |
| Power rails | VIN / 3.3V | +5V_BEC / 3.3V | +5V_BEC / 3.3V |
All firmware lives in /firmware. It’s Arduino C++ for a Teensy 4.1 with a BNO055 IMU and iBus RC.
Build notes and library list are in /firmware/README.md.
- Add airspeed sensing (Pitot or inferred) and tune gains/gain scheduling.
- Logging polish (file rotation, timestamps, selected signals) and simple plotting notebook.
- Learning how to implement 3D printed components.
- Hardware: gear alignment, motor-mount reinforcement, cleaner wire routing.
- New airframe with different goal.