I wanted to avoid the hassle of hunting down a 90-degree N20 motor from random sellers overseas, so I stuck with a standard straight-output N20, which is much easier to buy, and worked out the right-angle drive myself. That meant getting to grips with the Gears workbench in FreeCAD and designing a simple 1:1 bevel gear pair to turn the drive through 90 degrees within the tight space available. It solves the problem neatly, keeps everything based on easily sourced parts, and gives me a reusable little gear setup I can drop into future chassis designs.
Bevel Gear Specification (N20 300 rpm, 1:1 drive)
Gear type: Involute bevel gear pair
Gear ratio: 1:1 (same gear both sides)
Shaft angle: 90°
Common gear parameters (both gears):
- Module (m): 0.7
- Number of teeth: 20
- Pressure angle: 20°
- Pitch cone angle: 45° (for 1:1 bevel pair)
- Face width: 4 mm
- Backlash: 0.05 mm (for FDM clearance)
Resulting overall size:
- Outside diameter: ≈ 15.4 mm (fits within 17 mm limit)
- Axial length: 4 mm gear face (hub length is user-defined)
Bore dimensions (example values – adjust to suit shafts):
- Motor shaft (N20): 3.1–3.2 mm hole for a 3 mm shaft (push-fit / light glue)
- Driven axle: 4.1–4.2 mm hole for a 4 mm axle (push-fit / light glue)
Space constraints:
- Maximum available diameter: 17 mm
- Maximum available length (axial): 17 mm along driven axle