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Adding parts to the CAD

Contributor workflow for new printable geometry in 3d_models/cad/TinyEngineer.f3d. For servo presets and add-in install, see parametric design. For builders printing existing parts, see 3d_models/README.md.

flowchart TD
  design["Design parametric part"]
  test["Servo Configurator: all presets"]
  layout["Copy into PRINT_LAYOUT"]
  set["Add to PartsSet"]
  export["Parts Exporter: all servos"]
  design --> test --> layout --> set --> export
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Design rules

Source of truth

Edit cad/TinyEngineer.f3d only. Never hand-edit .3mf, .stl, or .step exports — those are the release binaries. Change the Fusion source, then re-export.

Parametric, multi-servo

Drive dimensions from Fusion user parameters (servo presets in servos.json, or other shared params). Prefer referencing existing geometry (edges, faces, projected sketches) over hard-coded lengths that only fit one servo.

The design must rebuild cleanly for every predefined servo. Do not ship a part that only works for SG90.

Do not invent new keys in servos.json. Parameter names must already exist as Fusion user parameters in the .f3d. Details: Add a new servo.

Naming

Keep one name end to end:

  • Fusion component name
  • Direct child under PRINT_LAYOUT (what the exporter lists)
  • Export basename (Head.3mf, …)
  • Row in the 3d_models/README.md parts table

Print without supports

Orient and feature the part so FDM can print it without supports (no large overhangs past what your bridging/chamfers already handle). The print-ready copy under PRINT_LAYOUT must sit on a flat face on the horizontal origin.

min_wall_thickness

Use the Fusion user parameter min_wall_thickness as the floor for:

  • Walls
  • Thin horizontal layers / floors

That keeps parts printable at third-party services and on typical 0.4 mm-nozzle FDM setups. Do not go thinner than this parameter.

M2 / fasteners

Assembly uses M2 screws that thread directly into printed PLA/PETG. New screw pilots use screw_thread_diameter (related: screw_head_diameter, screw_head_height). Details: M2 screw holes.

  • No heat-set inserts unless an intentional, documented exception.
  • Prefer existing lengths M2×4 / M2×8 / M2×16.
  • If a new length is required, update the screw BOM in 3d_models/README.md and the cart in docs/shopping.md.

Clearance / fit

Design so parts and hardware fit without sanding as the happy path. Leave real clearance for servo bodies, horns, and moving links so joints do not bind.

Timeline discipline

Keep the Fusion timeline readable for other contributors.

  1. One component, one block — Create the part as a separate component. Keep all features that belong to that component (sketches, extrudes, fillets, holes, …) next to its creation on the timeline. Do not scatter edits to the same component across distant timeline positions.
  2. Components first, joints later — Create (or finish) components first. Add joints that lock assembly positions in a later timeline section, after component creation.
  3. Same rule under PRINT_LAYOUT — Inside PRINT_LAYOUT, define/copy components first; add assembly joints afterward.

Assembly vs print layout

Functional assembly

Joint the new component into the main robot assembly so it sits correctly relative to neighbors for all servo presets.

Print-ready copy (PRINT_LAYOUT)

  1. Copy & paste (not Paste New) a ready-to-print instance under the PRINT_LAYOUT component. Paste keeps the link to the source component so parametric updates stay in sync.
  2. Orient it so it lies on the horizontal origin, print face down, no supports.
  3. Lock it to the origin with a joint so the export pose stays fixed.
  4. Add it to the correct PRINT_LAYOUT / PartsSet* aggregate for its intended print color only — do not mix colors in one set. Nest/place it to keep the print bed footprint realistically compact. Lock that placement with a joint as well.

PartsSetA / PartsSetB (and similar) are aggregates of same-color parts for service orders. Home printers usually print individual .3mf files instead — see 3d_models/README.md.

Validate every servo preset

Before you call the part done:

  1. Open Utilities → Add-Ins → TinyEngineer Servo Configurator.
  2. Switch through all predefined servos.
  3. Confirm the new part and the whole design update without compute errors or warnings for any preset.

Fix failures for every preset, not only the one you design against.

Export

Use Utilities → Add-Ins → Tiny Engineer Parts Exporter to export the new part(s) from PRINT_LAYOUT into the supported formats for all supported servos. Output lands under 3d_models/parts/{servo_id}/ (3mf/, stl/, step/). Details: parametric design — Parts Exporter.

Commit both the updated .f3d and the exported meshes/STEP for the affected servos.

Docs, trademark, and license

After the CAD and exports land:

  • Docs sync — new stock part → parts table in 3d_models/README.md; color-group / aggregate change → order-parts.md; join-order change → assembly.md.
  • Trademark — do not replace or repurpose AiEmblem as branding. See TRADEMARK.md.
  • License — stock cad/ and parts/, and mod geometry under mods/<mod_name>/3d_models/{cad,parts}/, are CERN-OHL-S-2.0. When distributing Products based on these designs, keep Source Location accurate per 3d_models/NOTICE. For a mod, the Source Location is that mod’s 3d_models tree.

Optional mods

Optional elements and community mods live under mods/. Promote one into stock cad/ and parts/ only when it becomes core.

Place them under:

mods/<mod_name>/
  README.md     # optional: what it is, non-model notes
  3d_models/
    cad/        # Fusion source for the mod
    parts/      # Exported meshes, same layout idea as 3d_models/parts/
  ...           # anything that is not a model

Mirror stock 3d_models inside the mod (cad + parts). Keep CERN-OHL-S licensing consistent with 3d_models/LICENSE when you distribute Products based on these designs. Each mod may include a short README.md describing what it fits and which parts/{servo_id}/ folders were exported.

Commit and PR title: type(mods): summary — name the mod in the summary. feat(mods) / fix(mods) do not version the stock CAD revision. Promoting a mod into stock cad/ and parts/ is feat(cad). See CONTRIBUTING.md.

Checklist

  • Source of truth: .f3d edited; exports re-generated (no hand-edited meshes)
  • Naming: component = PRINT_LAYOUT child = export basename = README parts table
  • Parametric (user params / referenced geometry); works for all presets
  • No invented servos.json keys (Fusion user params first)
  • Printable without supports; walls/floors ≥ min_wall_thickness
  • M2 pilots use screw_thread_diameter; BOM/shopping updated if a new length is needed
  • Clearance for servos, horns, and moving links (fit without sanding)
  • Separate component; features grouped on the timeline
  • Timeline: components → joints (including under PRINT_LAYOUT)
  • Servo Configurator: no errors/warnings for any predefined servo
  • Copy (not Paste New) under PRINT_LAYOUT, origin joint, print orientation
  • Placed in the correct same-color PartsSet* with a joint; bed footprint kept reasonable
  • Parts Exporter export for all servos; .f3d + exports committed
  • Docs synced (README parts table / order-parts / assembly as needed)
  • AiEmblem not repurposed as branding
  • CERN-OHL-S respected; NOTICE Source Location accurate if distributing Products
  • Optional/mod work under mods/<mod_name>/3d_models/{cad,parts}/ (+ mod README)

Related

Topic Doc
Servo params, add-in install, new servo preset parametric-design.md
Print / part inventory 3d_models/README.md
Optional mods folder mods/README.md
Order aggregated sets order-parts.md
Mechanical assembly assembly.md
Trademark TRADEMARK.md
Contribute / licenses CONTRIBUTING.md