GX12 connector standard
Summary¶
The libdrone payload interface uses two GX12-7 aviation connectors as a standardised, weatherproof, modular interface between the drone and any interchangeable payload. Connector A (left, X = −25 mm) carries power and primary communications. Connector B (right, X = +25 mm) carries data and auxiliary control. Both are IP65-rated when mated and locked, rated for more than 500 mating cycles, and use a D-D bore profile in the printed chimney to prevent rotation under repeated payload swaps. A payload built to this interface standard works on any compliant libdrone platform regardless of version or manufacturer.
Concept¶
Why a connector standard exists¶
A drone platform without a defined payload interface requires custom electrical integration for every new sensor or camera. Each payload is a one-off. When the platform changes, the payloads must be reworked. This is the primary reason scientific drone payloads are expensive and slow to develop.
A connector standard inverts this. One airframe, many payloads. Any payload built to the standard works immediately on any compliant platform. An institution that invests in developing an air quality payload can also use it on a radiation survey drone, a mapping drone, or a future platform — without electrical rework. The standard creates an ecosystem where each new payload adds value to every existing platform and every existing platform adds value to every new payload.
The GX12-7 standard was chosen over custom connectors because GX12 aviation connectors are: globally available from multiple suppliers, rated IP65 when locked, rated >500 mating cycles, field-serviceable (pins are replaceable), and mechanically robust enough for outdoor and crash-incident use.
The D-D bore and anti-rotation¶
The GX12-7 male body has two parallel flats machined into its cylindrical body — a "D-D" cross-section. The printed chimney bore must match this profile exactly. A round bore would allow the connector body to rotate when a payload is screwed on or off — backing off the retention nut and eventually ejecting the connector mid-flight.
The D-D bore is not optional. It is the mechanical feature that makes repeated payload swaps possible. → See variable-table-values for the exact bore dimensions (GX12ChimneyBoreFlatFlat = 10.80 mm, GX12ChimneyBoreOD = 11.87 mm).
Post-print support removal: clear the chimney bore with a pick or wire. Never use a round drill bit — a 12 mm drill cannot enter an 11.87 mm bore cleanly and will destroy the anti-rotation flats.
Vibration retention¶
Drone vibration backs off threaded fasteners in service. A single nut on the GX12 panel mount is insufficient — it will loosen within tens of flights. Required retention: double nut (inner against Platform underside, outer locking against inner) plus Loctite 243 blue on the outer nut thread only. The D-D bore prevents rotation; the double nut prevents axial loosening.
Open standard, closed payloads¶
The CERN OHL-S v2 copyleft applies to modifications of the libdrone platform hardware. It does not apply to payload designs that implement this connector interface. A company building a proprietary sensor payload to this standard retains full ownership of that payload design. The interface is open; the payloads are yours.
Reference¶
Connector positions¶
All positions from X body centre. Y+ = nose. X+ = right.
| Connector | X | Y | Role |
|---|---|---|---|
| Connector A | −25.0 mm | −66.0 mm | Signal + power (LEFT) |
| Connector B | +25.0 mm | −66.0 mm | Data + aux (RIGHT) |
| Centre-to-centre | 50.0 mm | — | — |
Connector mechanical specification¶
| Parameter | Value |
|---|---|
| Type | GX12-7 (7-pin, 12 mm body designation) |
| IP rating | IP65 when mated and locked |
| Retention | Screw-lock ring, finger-tight |
| Mating cycles | >500 rated |
| Drone-side gender | Male panel mount — pins face upward |
| Payload-side gender | Female cable mount |
| Chimney bore | D-D profile, 10.80 mm flat-to-flat, 11.87 mm OD |
| Chimney depth | 25.0 mm below Platform surface |
| Retention | Double nut + Loctite 243 blue |
Procedure¶
Verifying D-D bore after printing¶
- Print Coupon 10 (GX12 chimney bore test — see coupon-validation).
- Insert a GX12-7 male body dry with flats aligned to the bore flats. Must seat flush with no binding and no rocking.
- Panel nut must thread onto the chimney without cross-threading.
- Body must not rotate when the panel nut is turned — the D-D flats prevent it.
- If the body is tight: increase
GX12ChimneyBoreFlatFlatby 0.1 mm and reprint. - If the body rotates: the bore is too round — check the FreeCAD sketch trim step was applied correctly.
Installing connectors in the Platform¶
- Remove all chimney support material with a pick (not a drill).
- Insert GX12-7 male connector from above, aligning D-D flats.
- Thread inner panel nut from below. Tighten until connector is flush with Platform surface.
- Thread outer nut. Tighten against inner nut.
- Apply a small drop of Loctite 243 to the outer nut thread.
- Allow 24 hours cure before first payload mating.
- Fit dust caps on both connectors. Caps are mandatory when no payload fitted.
Rationale¶
Why GX12-7 and not a single GX12-12¶
The GX12 connector series has a maximum of 7 pins — there is no GX12-12. libdrone's 12-signal interface is split across two GX12-7 connectors with one spare pin each. This split also serves an EMC purpose: signal-sensitive wires (I2C, UART4) are on Connector A, routed into the signal channel. Power and GPIO-tolerant signals are on Connector B, routed into the power channel. A single 12-pin connector could not implement this routing separation.
Connections¶
requires: - variable-table-values related: - payload-electrical-interface - payload-software-protocol - coupon-validation - power-signal-separation - pro-variant leads_to: - payload-electrical-interface - payload-software-protocol