AntAIO

Open-source antweight / beetleweight combat-robot all-in-one controller — an ExpressLRS receiver, a 6-axis IMU, and a triple brushed-DC ESC on one tiny board, in the spirit of the Malenki Nano. Built on the OpenRX-Lite ELRS core (ESP32-C3 + SX1281, 2.4 GHz) and forked from incutec-hw/OpenRX.

Warning

Prototype — not validated, not fab-ready. This board has open safety-critical issues (uncommanded drive-motor motion at power-up, and the programming interface shares pins with the motor outputs). It drives combat-robot motors including a weapon — do not build or power it without reading the review first. See hardware/REVIEW.md (full design review) and CHANGELIST.md (verified to-do list).

What it is

A single 10.00 × 21.50 mm, 6-layer board that replaces the usual RX + 2 drive ESCs + weapon ESC + gyro stack of an antweight robot with one MCU-driven combo:

• Radio link — ExpressLRS 2.4 GHz (Semtech SX1281) for RC control + telemetry, plus the ESP32-C3's own Wi-Fi for OTA config.
• Motion sensing — LSM6DS3TR-C 6-axis IMU (gyro + accel) for heading-hold / self-right / melty-style control in firmware.
• Three brushed-DC motor channels — two drive + one weapon, each a TI DRV8212 H-bridge fed directly from the battery.
• Single-cell-friendly power — buck-boost holds a 5 V rail as the pack sags under weapon load, with a linear 3.3 V logic rail and reverse-polarity protection.

Everything is controlled by the ESP32-C3: RC decode, mixing, gyro stabilization, and the three motor PWM outputs all run on-chip.

Architecture

            +BATT (1–2S LiPo)
              │
        Q2  AON7407  ── reverse-polarity P-FET
              ├─────────────► VM ─► DRV8212 ×3 ─► LEFT / RIGHT drive + WEAPON motors
              │
        U8  TPS63070 buck-boost ─► +5V ─► U4 TLV75533 LDO ─► +3V3 (logic)
                                                              │
   ┌──────────────────────────────────────────────────────────┤
   │                                                            │
 U1 ESP32-C3 ──SPI──► U3 SX1281 (2.4 GHz ELRS) ─► FL1 BPF ─► link antenna
   │            └────► U2 LSM6DS3TR-C IMU                 ESP Wi-Fi ─► AE1
   ├── 3× PWM ─► DRV8212 IN/EN  (U6 LEFT, U10 RIGHT, U11 WEAPON)
   ├── ADC ──── VSENSE (battery voltage divider)
   └── GPIO ──► WS2812B status LED (D1)

Specifications

Block	Part	Notes
MCU	Espressif ESP32-C3FH4 (U1, QFN-32)	RISC-V, 4 MB embedded flash, 2.4 GHz Wi-Fi
Link radio	Semtech SX1281 (U3)	2.4 GHz, internal DC-DC, 52 MHz TCXO (OSC1), BPF FL1 (2450FM07D0034T) → link antenna
IMU	LSM6DS3TR-C (U2)	6-axis accel+gyro, 4-wire SPI on the shared radio bus, dedicated CS
Motor drivers	3× TI DRV8212DSGR	U6 = LEFT drive, U10 = RIGHT drive, U11 = WEAPON; PH/EN mode; VM = +BATT
Buck-boost	TI TPS63070 (U8)	+BATT → 5 V; holds the rail across the 1S–2S sag range
LDO	TLV75533PDQNR (U4)	5 V → 3.3 V logic rail
Reverse protection	AON7407 P-FET (Q2)	on +BATT
Status LED	WS2812B (D1)	addressable RGB
Battery	1–2S LiPo (≤ 8.4 V)	DRV8212 VM is 12 V abs-max — 2S is the hard ceiling; 3S destroys the drivers
Board	10.00 × 21.50 mm, 6-layer	components both sides

I/O pads

Solder pads carry the external interface (silk in parentheses):

Pad	Net	Function
+ / –	+BATT / GND	Battery in (1–2S)
5U	+5V	5 V buck-boost output (servo / accessory)
GND	GND	Ground
S	GPIO	Signal / spare control pad
BOOT	GPIO 9	Hold low at power-up for UART download mode
R / T	UART0 RX / TX	Flashing & serial console (also the right-drive lines — flash with motor battery OFF)

Motor outputs (OUT1/OUT2 of each DRV8212) and the weapon channel land on the large copper pads along the board edge.

ESP32-C3 pin map (as currently drawn)

GPIO	Pin	Function	GPIO	Pin	Function
0	4	VSENSE (battery ADC)	8	14	WS2812 LED (strap)
1	5	Radio DIO1	9	15	BOOT (strap)
2	6	IMU CS (strap)	10	16	WEAPON_EN
3	8	Radio BUSY	18	25	LEFT_PH (USB D−)
4	9	SPI MOSI	19	26	LEFT_EN (USB D+)
5	10	SPI MISO	U0RXD	27	RIGHT_PH
6	12	SPI SCK	U0TXD	28	RIGHT_EN
7	13	Radio NSS	GND/EP	33	GND

Important

The drive-motor enables currently sit on the USB (GPIO18/19) and UART0 (U0RXD/U0TXD) pins, which are driven high at reset — enabling both drive motors before firmware runs. The planned fix re-maps PH↔EN onto reset-quiet pins and gates the H-bridges behind a default-off arm switch. Do not treat this pin map as final — track it in CHANGELIST.md.

Flashing

• UART: hold BOOT low, power-cycle, flash over the R/T (U0RXD/U0TXD) pads with the motor battery disconnected (these pins also drive the right motor).
• Wi-Fi OTA: ExpressLRS SoftAP, after an initial wired flash.

The ELRS link runs upstream ExpressLRS (Unified_ESP32C3_2400_RX, ≥ 3.5.0). The combat-robot mixing, IMU stabilization, and motor-PWM control are application firmware layered on top (separate; not in this hardware repo).

Repository

AntAIO began as a fork of incutec-hw/OpenRX — the OpenRX-Lite ELRS core (ESP32-C3 + SX1281) extended into a combat-robot all-in-one. The other OpenRX receiver variants are not part of this repo.

AntAIO/
├── hardware/             AntAIO board: ELRS RX + IMU + triple brushed ESC
│   ├── AntAIO.kicad_{pro,sch,pcb}
│   ├── esp32c3_sx1281_lite.kicad_sch   ELRS core sub-sheet
│   ├── REVIEW.md         full design review (pin/datasheet/electrical)
│   └── DESIGN.md
├── shared/libs/          project-local KiCad symbols / footprints / 3D models
├── shared/elrs-targets/  ExpressLRS hardware-target JSON
├── images/               board renders
└── CHANGELIST.md         verified open / done items

KiCad 9/10; project-local libraries only (no global dependencies). Board renders are produced with the shared render_board.py tool (vias + solder paste stripped, transparent square).

License

Hardware: CERN Open Hardware Licence Version 2 — Strongly Reciprocal (CERN-OHL-S-2.0). See LICENSE. Firmware: MIT.