Introducing the pirouette FPV frame for GFPV
Signed-off-by: Arnaud Morin <arnaud.gfpv@mailops.fr>
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Arnaud Morin
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README.md
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# pirouette
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Parametric [CadQuery](https://cadquery.readthedocs.io) model of a 3" FPV race
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quad frame. It is an **interlocking space frame**: the parts key into each
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other with tenons and mortises, so the joints hold it square and there is no
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jig to build and no bolted-together stack of spacers.
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Everything is generated from source — change a number, rerun, get new cut
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files. Nothing is drawn by hand in a GUI.
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```
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./build.sh
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```
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That is the whole workflow. It writes `build/`.
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---
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## Requirements
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- **[uv](https://docs.astral.sh/uv/)** — that's it. `build.sh` creates the
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virtualenv from `pyproject.toml` on the first run and reuses it afterwards.
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```
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curl -LsSf https://astral.sh/uv/install.sh | sh
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```
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- Python 3.11 or newer, which uv will fetch for you if the system one is older.
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The first run downloads about 1.7 GB. That is not a mistake: CadQuery depends
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on OpenCascade and pulls VTK and trame in with it, whether or not you ever open
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a viewer. After that a full build takes roughly 50 seconds, most of it the
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PNG renders — `./build.sh --no-png` cuts it to under 30.
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`uv.lock` pins every version, so a build here is the build you get.
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---
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## What you get
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| Directory | Files | What it's for |
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|---|---|---|
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| `build/dxf/` | 4 | flat patterns, one per carbon part — feed these to the router |
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| `build/stl/` | 7 | meshes for the slicer (the printed parts) or for a quick look |
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| `build/step/` | 7 | solid models, if you want to take a part into other CAD |
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| `build/png/` | 4 | assembly renders: iso, top, front, and a grid of all three |
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`build/` is generated and gitignored. Delete it freely.
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Only four parts get a DXF. The other three are printed, so a flat pattern
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would mean nothing for them.
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**The DXF is the exact part outline, with no kerf compensation.** Offset it by
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half your tool diameter in CAM, or every part comes out undersize by a whole
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cutter width.
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---
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## Bill of materials
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Straight from the last build — `build.sh` prints this table every time, so
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trust the run over this copy of it.
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| Part | Qty | Stock | Material | g each | g total |
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|---|---|---|---|---|---|
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| plate | 2 | 2 mm | carbon fibre | 3.86 | 7.72 |
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| arm | 4 | 2 mm | carbon fibre | 0.75 | 3.02 |
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| motor_base | 8 | 2 mm | carbon fibre | 0.87 | 6.97 |
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| spar | 4 | 2 mm | carbon fibre | 1.19 | 4.76 |
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| camera_mount | 1 | printed | TPU | 7.87 | 7.87 |
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| standoff | 4 | Ø3.5 mm | aluminium | 0.39 | 1.56 |
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| lollipop | 1 | printed | TPU | 1.15 | 1.15 |
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| **frame** | **24** | | | | **33.05** |
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Carbon at 1.55 g/cm³, TPU at 1.21, aluminium at 2.70.
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**Not counted, and not modelled:** screws, motors, props, camera, VTX,
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receiver, flight controller. The standoffs are the only hardware in the model.
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### Hardware you supply
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- 4 × M2 aluminium standoff, 3.5 mm across, **15 mm long** — that length is the
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plate gap, so the standoffs are what sets it. Different standoffs mean a
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different frame; see the levers below.
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- M2 screws for those standoffs, and for the flight controller.
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- The plates carry both a 20×20 and a 25.5×25.5 mounting pattern, drilled 2.2 mm
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for M2.
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### It is built around
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- 3" props — **78 mm**, and neighbouring discs just touch on this true-X layout.
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The renders draw them as rings so you can see that.
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- A **Foxeer Predator 5 Nano** camera, which the camera mount is cut for.
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- A **micro lollipop** antenna, held at 45° by `lollipop.py`, which clips over
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the rear standoff pair.
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---
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## Making the parts
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**Carbon** — the four DXFs cut from 2 mm plate. Every internal corner at a
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joint already carries a T-bone relief, so a round cutter can actually make the
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corner; don't "clean up" those little circles, the mating part needs that room.
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**TPU** — `camera_mount.stl` and `lollipop.stl`. The STLs are exported at 0.01 mm
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chordal deviation, far finer than an FDM printer resolves. Rerun the export at a
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tighter tolerance if you are going to resin.
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**Assembly** — dry fit before anything else. Horizontal parts (plates, motor
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bases) carry the mortises, vertical parts (arms, spars) carry the tenons, and
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every tenon should land *flush* with the far face it passes through. Proud jams
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the joint; short leaves it unseated. The four spars half-lap their neighbours at
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each corner and are handed — two notches up, two down, alternating round the
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ring — so check the renders before you glue.
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---
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## Changing it
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Shared dimensions live in `frame_params.py`, and every part imports them. The
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usual things to reach for:
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| You want | Change |
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|---|---|
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| a different prop size | the motor-to-motor gap |
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| different carbon stock | the shared thickness |
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| a shallower arm | the plate gap — costs stack room |
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| looser or tighter joints | the shared fit allowance |
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| a taller stack | the plate gap, and buy standoffs to match |
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Rerun `./build.sh` and the cut files follow. Read `AGENT.md` first if you are
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changing geometry rather than numbers — it records the invariants and the
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CadQuery traps that have already cost time here.
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---
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## Working on a single part
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Each part module builds and checks itself, so you can run one on its own
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without the assembly:
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```
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uv run python arm.py # asserts it is one solid, then reports mass
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uv run python frame.py # assembly, BOM, exports, renders
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```
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They are also CQ-editor scripts: open any of them and it shows the part.
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`frame.py` shows the whole assembly.
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---
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## Licence
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[Apache License 2.0](LICENSE). Use it, change it, build frames from it, sell
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those frames. The conditions are light: keep the copyright notice, note in any
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file you modify that you changed it, and pass on a copy of the licence.
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Two things worth knowing about the fit between this licence and a physical part:
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- **It covers the files, not the shape.** The Python, the comments and the
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exported drawings are copyrighted work and the licence governs them.
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The outline of a cut piece of carbon generally is not — functional shapes
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aren't protected by copyright. Someone who buys a frame, measures it and
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redraws it in their own CAD is outside this licence entirely. That is normal
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for open hardware, and not something a different licence would fix.
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- **It includes a patent grant.** Apache-2.0 §3 gives every user a patent
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licence covering the contributions in here, and revokes it from anyone who
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sues over the design. This is the main thing it adds over MIT.
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No warranty of any kind — see §7. Worth taking literally on a frame: nothing
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here has been flown, and the design is deliberately built close to its material
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limits. Check the parts before you trust them at 100 km/h.
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