132 lines
3.0 KiB
Markdown
132 lines
3.0 KiB
Markdown
# SkyLogic AeroAlign - CoG Scale Wiring
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**Version**: 0.1.0
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**Date**: 2026-03-11
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**Scope**: planned CoG scale node that shares the same Master and ESP-NOW fabric
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## Overview
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The CoG extension is based on two supports:
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- front support load cell
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- rear support load cell
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The recommended first implementation uses:
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- `1x ESP32-C3` or `1x ESP32-S3`
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- `2x HX711`
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- `2x single-point load cells` or your existing suitable load cells
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One HX711 per support keeps calibration and diagnostics simple.
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## Functional Model
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The CoG node reports three live values to the Master:
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- `front_weight_g`
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- `rear_weight_g`
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- `cog_position_mm`
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These values already fit the shared telemetry packet used by the current Master firmware.
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## Recommended Electronics
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| Part | Qty | Notes |
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|------|-----|-------|
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| ESP32-C3 or ESP32-S3 | 1 | same ecosystem as AeroAlign |
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| HX711 amplifier | 2 | one per support |
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| Load cell | 2 | typically 3 kg to 10 kg depending on model size |
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| LiPo or bench supply | 1 | portable or fixed jig |
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| TP4056 + regulator | optional | only for portable scale |
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## Wiring Strategy
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### HX711 #1: Front support
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| HX711 pin | Connection |
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|-----------|------------|
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| `VCC` | `3V3` |
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| `GND` | `GND` |
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| `DT` | `GPIO6` |
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| `SCK` | `GPIO7` |
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### HX711 #2: Rear support
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| HX711 pin | Connection |
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|-----------|------------|
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| `VCC` | `3V3` |
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| `GND` | `GND` |
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| `DT` | `GPIO8` |
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| `SCK` | `GPIO9` |
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These GPIOs are recommendations for the future CoG firmware. They are not yet hard-coded in the repo.
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## Load Cell Wiring
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Most 4-wire load cells expose:
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| Wire | Meaning |
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|------|---------|
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| Red | `E+` |
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| Black | `E-` |
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| Green | `A+` |
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| White | `A-` |
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Connect each load cell directly to one HX711.
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### Important
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Wire colors are not universal. Validate your load cells with the supplier datasheet or a multimeter before soldering.
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## Mechanical Layout
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```
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aircraft
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+--> front support --> load cell #1 --> HX711 #1
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+--> rear support --> load cell #2 --> HX711 #2
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```
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The support spacing `L` must be known and entered into the system profile.
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## CoG Formula
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With front support at `x = 0` and rear support at `x = L`:
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`x_cog_from_front_support = rear_weight / (front_weight + rear_weight) * L`
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If you measure relative to the wing leading edge:
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`x_cog_from_leading_edge = support_offset_from_leading_edge + x_cog_from_front_support`
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## Calibration Plan
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Each support needs:
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1. zero / tare
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2. scale factor from known weight
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Recommended workflow:
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1. tare both supports empty
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2. place known weight on front support only
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3. save front factor
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4. repeat for rear support
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5. validate with known total weight centered between supports
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## Current Repo Status
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- shared protocol support exists in [telemetry_protocol.h](../../firmware/common/telemetry_protocol.h)
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- Master can already display CoG-style nodes in the existing UI
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- dedicated HX711 firmware is not implemented yet
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## Next Firmware Target
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Create a new node type, likely `firmware/cog_slave`, with:
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- HX711 reading
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- tare and scale calibration
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- CoG computation
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- ESP-NOW transmission using `DEVICE_TYPE_COG_SCALE`
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