Variable table values

Summary¶

This article is the authoritative value reference for the libdrone V2.4.6 parametric variable table. It lists every variable across all 15 sections, with its alias name, current value, and purpose. Use it to verify a populated spreadsheet, to manually enter a missing variable, or to understand what a variable controls before changing it. For how the variable system works — alias syntax, FreeCAD Spreadsheet mechanics, and the FCMacro — see variable-table-structure.

Concept¶

Derived values and chain dependencies¶

Some variables are derived from others. FreeCAD computes them automatically when the driving variables are set. Key chains to understand:

Sandwich height chain: SandwichHeight = PETGBotLayerThick + 3 × PCCFLayerThick + PETGTopLayerThick = 3 + 9 + 4 = 16 mm ArmHeight = SandwichHeight = 16 mm (arm shaft must equal sandwich height) TabThick = SandwichHeight = 16 mm (tab fills full slot height)

Rod channel chain: RodDia = 2.0 mm (physical rod) RodDiaChannel = 2.2 mm (clearance — PCCF and PETG non-core zones) RodDiaChannelCore = 2.1 mm (interference fit — PETG bottom layer core zone only) The 0.1 mm interference (RodDiaChannel − RodDiaChannelCore) is intentional. PETG deforms elastically and grips the rod. PCCF would crack — PCCF layers always use the clearance value.

GX12 D-D bore chain: GX12BodyFlatFlat = 10.60 mm (physically measured on connector body) GX12ChimneyBoreFlatFlat = 10.80 mm (+ 0.20 mm print clearance) GX12BodyOD = 11.67 mm (physically measured) GX12ChimneyBoreOD = 11.87 mm (+ 0.20 mm print clearance) The bore is a D-D profile (two arcs + two parallel flats), not a round hole. If only a round bore is used, the connector spins when payloads are plugged in.

What changes when wheelbase changes¶

If Wheelbase is edited to adapt the frame to a different prop size, these variables need independent recalculation — they do not scale automatically from Wheelbase:

• ArmShaftLength — verify in FreeCAD Assembly (rod clearance at arm tip)
• RodLength — verify in FreeCAD Assembly (rod must not protrude past arm tip)
• PlatformLength — electronics layout is fixed; does not scale with frame
• GX12_PositionY — connector position is fixed relative to electronics
• BattZoneFront / BattZoneRear — battery dimensions are fixed

Wheelbase directly drives: arm angle geometry, prop clearance. Everything else must be re-verified independently. → See scaling-libdrone.

Reference¶

[1] Frame geometry¶

[2] Arm geometry¶

⚠ Verify ArmShaftLength in FreeCAD Assembly after any wheelbase change — CF rods must not protrude past the arm shaft outer face.

[3] Rod architecture¶

Rod Z positions by arm orientation: - FL/RL arms (normal): +5.0 mm and +2.0 mm - FR/RR arms (inverted): −5.0 mm and −2.0 mm

Rod cut length: 333.0 mm (derived from 258 mm at 255 mm wheelbase — confirm in FreeCAD Assembly at current wheelbase before cutting rods).

[4] Sandwich body geometry¶

Derived — sandwich bolt pattern: - 6 bolts total - 4 corner bolts at (±18, ±18 mm) - 1 nose bolt at (0, +22 mm) - 1 tail bolt at (0, −22 mm)

Layer stack (bottom → top): PETG 3 mm / PCCF 3 mm / PCCF 3 mm / PCCF 3 mm / PETG 4 mm

V2.4.6 note: MIPIChannelDepth and MIPIChannelWidth describe Platform geometry, not X body top layer. The X body PETG top layer is a clean structural surface.

[5] Tab geometry¶

T-slot clearance: T-slot pocket width = TabWidth + 0.2 mm per side (clearance fit). Verify against Coupon 8 print before committing to X body PCCF layers. Adjust TabClearance variable if coupon shows tight or sloppy fit.

[6] Motor mount geometry¶

Derived: ORingRimOD = ORingCBoreDia + 2 × ORingRimWall = 8.0 mm

[7] Cable management geometry¶

V2.4.6 note: All cable management features have moved from the X body PETG top layer into the Platform. These variables now describe Platform geometry.

[8] Battery spoiler — DEPRECATED (V2.4.6)¶

Section 8 is retired. All #Spoiler variables are removed. Do not reference in CAD. The always-on fan replaces spoiler function. Section retained as deprecated placeholder to preserve section numbering continuity.

[9] GX12-7 dual payload connector geometry¶

Polarity: drone side = GX12-7 male panel mount (pins face upward toward payload). Payload side = GX12-7 female cable mount.

Shared geometry (both connectors identical):

Chimney bore profile — D-D shape (critical for anti-rotation):

The bore is NOT a round hole. In FreeCAD Sketcher: 1. Draw circle diameter GX12ChimneyBoreOD (11.87 mm) 2. Add two parallel lines at ±(GX12ChimneyBoreFlatFlat / 2) = ±5.40 mm from centre 3. Trim circle arcs outside those lines

Result: D-D profile that prevents connector rotation. Print Coupon 10 and verify fit before printing the full Platform. Adjust GX12ChimneyBoreFlatFlat by ±0.1 mm if coupon is tight or sloppy.

Position variables:

Vibration retention: single nut insufficient. Use double nut + Loctite 243 blue (medium strength) on outer nut thread.

[9b] Battery rail geometry¶

Reference battery: Tattu 150C-1800mAh-6S-XT60 — 78 × 40 × 53 mm (L×W×H). Battery centred on X body core: front edge +39 mm, rear edge −39 mm. Battery exits RIGHT. Endstop wall on LEFT end.

Verify rail fit with Coupon 11 before printing full Platform. Adjust BattRailInnerWidth by +0.5 mm if coupon slides too tightly.

[10] Mast interface geometry¶

Note: with Pi bay fitted (always), effective mast mounting surface is 6 mm above Backplane surface. Mast height references are unchanged — the bay height is accounted for in the stack geometry.

[11] GPS / camera bracket geometry¶

V2.4.6: bracket carries GPS (top) + camera (middle) only. VTX has moved to the Platform electronics zone. Camera tilt is field-adjustable via two-bolt arc-slot mechanism (0°–30°).

Camera plate: 26 mm × 22 mm × 4 mm. Camera slot: 19 × 19 mm (HDZero ±0.5 mm). MIPI cable (225 mm) runs nose-to-tail through Platform MIPI channel. Camera-to-VTX distance: ~198 mm. Service loop: ~26 mm.

[12] Assembly offsets and clearances¶

[13] Platform geometry (V2.4.6)¶

Three-layer architecture: X body sandwich (structural) / Platform (electronics) / Backplane (payloads).

Platform has stepped width: 40 mm in battery and nose zone; 50 mm from Y = −44 mm (electronics zone front) to tail.

All Y positions measured from X body centre. Positive = nose. Negative = tail.

Prop clearance at tightest point (electronics zone, 50 mm width): Motor at Y = −116.7 mm → 15.7 mm clearance per side. This is above the 15 mm design minimum but has zero headroom. Verify in FreeCAD cross-section view BEFORE printing the Platform. If CAD reads < 15 mm, reduce PlatformWidthElec from 50 mm to 48 mm.

[14] Backplane geometry¶

Attachment post positions (3 pairs, integral to Platform): - Post pair A: Y = +39 mm (battery front) - Post pair B: Y = −39 mm (battery rear) - Post pair C: Y = −148 mm (fan rear / backplane tail)

Battery zone right side is fully open — no lattice beam in RIGHT edge between Y = +39 and Y = −39 mm. Battery exits RIGHT under open lattice.

Fan exhaust zone (Y = −138 to −148 mm): no lattice — fully open for exhaust.

[15] Pi bay and companion interface geometry¶

Pi bay is mandatory on every build across all platforms. Empty bay uses a printed cover plate. Pi Zero 2W installs in 15 minutes when ordered.

Pi bay raises the payload mast surface by PiBayInternalHeight (6 mm) above the Backplane surface. Mast height references account for this. Bay is fitted on all builds.

Procedure¶

Verifying the populated spreadsheet against this article¶

1. Open the FreeCAD document. Double-click Variables in the Model Tree.
2. For each section in this article, spot-check 2–3 values against the cell in column B. Click the cell — Properties panel shows the alias name.
3. Verify alias name matches exactly (case-sensitive). A mismatched alias means no sketch that references that variable name will resolve correctly.
4. Pay particular attention to: RodDiaChannelCore (2.1 mm, not 2.2 mm), GX12ChimneyBoreFlatFlat (10.80 mm, not 10.60 mm — different from BodyFlatFlat), SandwichBoltCornerOffset (18.0 mm, not 20.0 mm — older docs say 20 mm).
5. If any value is wrong: double-click the cell, edit the value, press Enter. All sketch dimensions referencing that alias update automatically.

Critical first-print adjustments (adjust these variables from coupon results before full build)¶

→ See coupon-validation for full pass/fail criteria and measurement procedure.

Rationale¶

Why SandwichBoltCornerOffset is 18 mm and not 20 mm¶

Some earlier documents (including the V2.4.5 Master Specification draft) used 20 mm as the corner bolt offset. The FreeCAD Cookbook, which is the more precise source, uses 18 mm — measured from the actual model geometry rather than the approximate stated value. 18 mm is the adopted value. All new builds and all PCCF layer prints use 18 mm. Do not use 20 mm.

Why the GX12 bore values are physically measured and not nominal¶

GX12 connectors are manufactured to a nominal 12 mm designation, but the actual body dimensions vary by supplier. The values in section [9] (10.60 mm flat-to-flat, 11.67 mm OD) were physically measured on the parts sourced for V2.4.6. A different supplier batch may require different clearance values. Always print Coupon 10 first. The 0.20 mm clearance applied to both flat-flat and OD values is a starting point, not a guarantee.

Why PiBayInternalHeight matters for payload design¶

Every payload mast height calculation must include the 6 mm Pi bay height. A mast designed to sit at 40 mm above the Backplane surface will actually sit at 46 mm above the Platform surface (40 + 6). Payload designers who omit this will produce connector geometry that is out of reach. The Pi bay is permanent; it is not removed for payload swaps.

Connections¶

requires: - variable-table-structure related: - frame-structure-overview - sandwich-structure - cf-rod-architecture - scaling-libdrone - coupon-validation leads_to: - freecad-document-setup