Installing Fusion 360 (Free Personal Licence)

Fusion 360 is free for personal, non-commercial hobbyist use. Navigate to autodesk.com/fusion-360, create a free Autodesk account, and download the installer. The personal licence includes all core CAD features needed for drone part design — parametric modelling, assembly, rendering, and STL export. The only excluded features are advanced simulation (covered by SimScale's free tier) and multi-axis CAM.

On first launch, create a new project called "Drone Parts" and a component called "Frame Arm". This organisational structure will pay dividends when you have dozens of version-controlled parts.

Step 1: Sketching the Arm Profile

Click Create Sketch and select the XY plane. You are looking at the top-down profile of your arm. Start with the motor mount circle: create a circle of 16mm diameter (the standard motor base diameter for 2306–2407 motors). Constrain it to the origin. This is your anchor point — all other geometry derives from here.

From the motor mount centre, draw a line 95mm along the X axis (arm length for a 5-inch 225mm wheelbase build). At the end of this line, create the arm body rectangle: 14mm wide (arm width), centred on the line. Add 4mm fillets to all sharp corners — sharp corners are stress concentrators and will cause crack initiation on impact.

Constrain everything. Every line, circle, and arc should be fully defined (blue in Fusion, black when constrained). An underconstrained sketch is a sketch that will drift when you change dimensions later.

Step 2: Extrusion and Features

Extrude your arm profile to 5mm height (minimum for structural 5-inch arms — go to 6mm for CF composite printing). Add a motor mount screw pattern: M3 holes at 16mm bolt circle diameter, 4-hole pattern. Set M3 hole diameter to 3.2mm for a slip fit (hardware threading), or 2.5mm for a self-tapping fit in PETG or ASA.

Add your frame attachment points at the root end: M3 mounting holes at the exact bolt pattern of your specific frame. Measure your frame with calipers — do not trust published dimensions, they vary between production batches. A direct measurement is always more accurate than a spec sheet.

Step 3: Tolerances for 3D Printing

This is the step most tutorials skip — and why most hobbyist-designed parts do not fit on the first print. 3D printers are not dimensionally accurate by default. FDM printing typically produces holes 0.2–0.4mm smaller than nominal diameter, and external dimensions 0.1–0.2mm larger.

Apply these compensation rules to your Fusion model: M3 slip-fit holes at 3.3mm (not 3.0mm). M3 thread holes for self-tapping at 2.7mm. Motor mount base seating surfaces: add 0.15mm clearance to the nominal motor base diameter. Print a calibration gauge first — a simple ring with three nested slot sizes — before committing to a full arm print.

Step 4: Exporting to STL

Right-click your body in the browser tree, select Save as Mesh, choose STL format, refinement set to High. Verify the file in your slicer before printing — look for non-manifold edges (red highlighting in PrusaSlicer or Bambu Studio) and repair if needed using Microsoft 3D Builder's one-click auto-repair function.