AeroAlign/hardware/schematics/cog_scale_wiring.md

SkyLogic AeroAlign - CoG Scale Wiring

Version: 0.1.0
Date: 2026-03-11
Scope: planned CoG scale node that shares the same Master and ESP-NOW fabric

Overview

The CoG extension is based on two supports:

• front support load cell
• rear support load cell

The recommended first implementation uses:

• 1x ESP32-C3 or 1x ESP32-S3
• 2x HX711
• 2x single-point load cells or your existing suitable load cells

One HX711 per support keeps calibration and diagnostics simple.

Functional Model

The CoG node reports three live values to the Master:

• front_weight_g
• rear_weight_g
• cog_position_mm

These values already fit the shared telemetry packet used by the current Master firmware.

Recommended Electronics

Part	Qty	Notes
ESP32-C3 or ESP32-S3	1	same ecosystem as AeroAlign
HX711 amplifier	2	one per support
Load cell	2	typically 3 kg to 10 kg depending on model size
LiPo or bench supply	1	portable or fixed jig
TP4056 + regulator	optional	only for portable scale

Wiring Strategy

HX711 #1: Front support

HX711 pin	Connection
VCC	3V3
GND	GND
DT	GPIO6
SCK	GPIO7

HX711 #2: Rear support

HX711 pin	Connection
VCC	3V3
GND	GND
DT	GPIO8
SCK	GPIO9

These GPIOs are recommendations for the future CoG firmware. They are not yet hard-coded in the repo.

Load Cell Wiring

Most 4-wire load cells expose:

Wire	Meaning
Red	E+
Black	E-
Green	A+
White	A-

Connect each load cell directly to one HX711.

Important

Wire colors are not universal. Validate your load cells with the supplier datasheet or a multimeter before soldering.

Mechanical Layout

aircraft
  |
  +--> front support --> load cell #1 --> HX711 #1
  |
  +--> rear support  --> load cell #2 --> HX711 #2

The support spacing L must be known and entered into the system profile.

CoG Formula

With front support at x = 0 and rear support at x = L:

x_cog_from_front_support = rear_weight / (front_weight + rear_weight) * L

If you measure relative to the wing leading edge:

x_cog_from_leading_edge = support_offset_from_leading_edge + x_cog_from_front_support

Calibration Plan

Each support needs:

1. zero / tare
2. scale factor from known weight

Recommended workflow:

1. tare both supports empty
2. place known weight on front support only
3. save front factor
4. repeat for rear support
5. validate with known total weight centered between supports

Current Repo Status

• shared protocol support exists in telemetry_protocol.h
• Master can already display CoG-style nodes in the existing UI
• dedicated HX711 firmware is not implemented yet

Next Firmware Target

Create a new node type, likely firmware/cog_slave, with:

• HX711 reading
• tare and scale calibration
• CoG computation
• ESP-NOW transmission using DEVICE_TYPE_COG_SCALE