The idea
Reproduce a known open-source micro-quadcopter as an educational flight-control build. The valuable outcome is a repeatable assembly and test record, including faults and tuning changes. V1 follows one pinned upstream Flix revision. Autonomous positioning, a new PCB and substantial frame redesign wait until the reference build works.
The connection
A reference open-source design becomes a learning platform through careful reproduction, measurement and documented changes. The contribution is in understanding and extending it, with upstream credit intact.
How it could work
The upstream Flix design uses an ESP32, an IMU, four brushed motors and transistor motor drivers. Preserve its motor ordering, IMU orientation and electrical design when first reproducing it. Pin the firmware revision and obtain the matching assembly files; mixing a newer wiring diagram with older firmware is an avoidable source of failures. Current upstream position-control work does not establish a working APX positioning capability.
The critical trade-off is mass versus thrust. Record frame, battery, board and harness mass separately. A more substantial print can be easier to assemble but harder to fly. Use the reference print first, then compare variants using measured mass and vibration rather than appearance.
What would prove it
Stage A is a propeller-free electronics test: verify supply rails, stationary IMU readings, orientation signs, motor mapping and response to disarm or lost commands. Stage B uses the upstream simulation to investigate the same control modes. Only after those pass should a competent operator perform short low-height trials in an appropriate clear test space, with suitable protection and permission.
Proposed gates: all four motor channels respond in the correct order; motors remain off at boot and disarm; link-loss behaviour is repeatable in 10 deliberate bench interruptions; three short controlled flight trials complete without unexplained resets or sustained oscillation. A successful flight is an observed result to record, not a claim already made here.
The path to a complete build
- Archive the upstream revision, licence, parts list and frame files.
- Assemble power and sensing first; log 60 seconds of stationary IMU data and verify axis orientation.
- Add motor stages and run the propeller-free fault tests.
- Establish reference flight performance before changing frame mass or tuning.
- Store firmware settings, all-up mass, video and a flight log containing battery condition, faults and changed parameters.
Open the engineering notebook
Components, interfaces and calculations
Prepare a revision-matched bill of materials covering controller, supported IMU, four matched brushed motors, correctly fitting propellers, specified transistor stages, battery, connector, charger, frame and fasteners. Verify electrical polarity and connector ratings against the selected parts. Confirm that the intended control link works on the chosen board before soldering the whole aircraft.
Keep a wiring table with pin, signal name, voltage and corresponding firmware definition. Include the battery measurement calibration and motor-to-frame mapping. Do not assume a nominally similar transistor or IMU module is interchangeable.
Scope and development questions
Allow 4–8 sessions for a first reproduction, with extra time for soldering rework. Price the exact upstream BOM and replacement motors/propellers; include charger and control equipment if not already owned. Stop procurement if the IMU or motor substitutions cannot be verified. The first decision is whether this is an educational reproduction or a platform to develop a new APX product—those have different completion criteria.