• Status: Draft for schematic implementation
• Integrated carrier motherboard for a 4-wheel mecanum autonomous inspection robot.
• Replaces loose wiring and L298N modules with onboard power conversion, four protected H-bridges, compute-module sockets, and keyed peripheral connectors.

• Distribute protected battery power to motors and two regulated high-current rails.
• Power and interconnect the Raspberry Pi 5 and ESP32 without loose Dupont wiring.
• Independently control four mecanum motors and read their quadrature encoders.
• Provide a half-duplex serial interface and 7.4 V supply for six bus servos.
• Connect LiDAR, two ultrasonic sensors, I2C sensors, and a switched status beacon.
• Provide diagnostic LEDs and driver current/fault feedback.

• 3S LiPo input, reverse-polarity protection, main and branch fusing.
• 5.1 V / 6 A synchronous buck for Pi 5, Hailo, ESP32, LiDAR, and logic.
• 7.4 V / 8 A continuous synchronous buck with 10–12 A transient target for servos.
• Four DRV8874-class single-channel motor drivers, each supporting at least 18 V and 3.5 A peak.
• Raspberry Pi 40-pin socket and narrow 30-pin ESP32 DevKit socket.
• Four combined motor/encoder connectors.
• Two parallel STS3215 bus connectors.

Diagram

• Use a high-current battery connector appropriate for at least 30 A peak; an XT60-class connector is preferred over a 10–15 A screw terminal.
• Main fuse target approximately 30 A, with separately fused motor, servo, and logic branches.
• Reverse-polarity protection must have low loss; use a suitably rated P-channel MOSFET or ideal-diode controller rather than a series Schottky for the full system current.

• Synchronous buck, 9–12.6 V input, 5.1 V nominal output, at least 6 A continuous.
• Supplies both Pi 5V header pins, ESP32 VIN, LD19, ultrasonic modules, and logic loads.
• Include input/output bulk capacitance, local decoupling, enable configuration, feedback network, compensation if required, and power-good/test access.

• Synchronous buck, 9–12.6 V input, 7.4 V nominal output, at least 8 A continuous and 10–12 A transient design target.
• Supplies two parallel 3-pin servo bus connectors.
• Include substantial low-ESR polymer and ceramic output capacitance for torque transients.
• Six servos have a theoretical simultaneous stall demand of 18 A; firmware must limit simultaneous high-torque events because the requested regulator is not sized for six-way stall.

• Four independent DRV8874-class H-bridges on the fused battery rail.
• Each motor: 0.8–1.2 A continuous, 2.5–3.0 A stall.
• Route IN/PH/EN control, current-sense analog output, and fault output to ESP32 pins.
• Include local bulk and ceramic VM decoupling and datasheet-selected current-limit components.

• Raspberry Pi 5: 2x20 socket; pins 2 and 4 to 5V1 and all standard ground pins to GND.
• ESP32: two 1x15 sockets for a narrow 30-pin DevKit; VIN to 5V1 and all GND pins to GND.
• Pi UART and ESP32 UART use crossed TX/RX at 3.3 V logic; no level shifter is required when both sides are 3.3 V.

• Half-duplex single-wire UART transceiver using a 74LVC2G241/74HC126-class tri-state buffer arrangement.
• Provide direction control and selectable Pi or ESP32 UART ownership without directly tying two push-pull transmitters together.

• Four 6-pin JST-XH motor/encoder connectors: motor outputs, 5V1, GND, encoder A, encoder B.
• Two 4-pin ultrasonic headers with 1 kΩ / 2 kΩ echo dividers.
• One 4-pin 3.3 V I2C/Qwiic-compatible header.
• One 4-pin LD19 connector: 5V1, GND, Pi UART TX, Pi UART RX.
• One status-beacon connector with power, ground, and two low-side MOSFET control channels.

• Main power: protected VBAT_FUSED.
• Regulated rails: 5V1_SYS, 7V4_SERVO, 3V3_LOGIC, and GND.
• UART nets must be named by source and destination to make TX/RX crossing explicit.
• Encoder and motor-control signals receive unique wheel-position suffixes: FL, FR, RL, RR.

• Battery: 3S LiPo, 9.0–12.6 V, 5200 mAh, high-discharge capable.
• Runtime is strongly load-dependent; motor and servo mechanical duty cycle dominates.
• The PCB cannot support simultaneous six-servo stall plus four-motor stall indefinitely. Protection and firmware current limiting are required.

• Production-intent prototype assembled by a PCB assembly service.
• Prefer a 4-layer PCB with dedicated ground and power distribution layers due to high current and mixed compute/motor loads.
• High-current converters and motor drivers require large copper areas, thermal vias, and datasheet land patterns.
• Use real manufacturer parts and verified footprints; no placeholder power ICs.

• ESP32 PWM/direction control for four motors.
• Eight encoder inputs, four motor current-sense ADC inputs, and four fault inputs.
• UART links for Pi-to-ESP32, LD19, and half-duplex servo bus.
• Direction/ownership controls for the servo transceiver.
• Two ultrasonic trigger and echo pairs, I2C SDA/SCL, heartbeat LED, and two beacon controls.
• Boot/reset/programming access for the ESP32 must remain usable.

• Pi and ESP32 sockets accessible from the top side.
• Power and motor connectors grouped along board edges.
• Keep switching-regulator hot loops compact and separated from encoder/I2C/UART signals.
• Preserve Pi active-cooler and Hailo HAT mechanical clearance.
• Final board dimensions require placement review before routing.

• Four DRV8874-class channels replace two L298N modules.
• Separate 5.1 V compute and 7.4 V servo regulators isolate dynamic servo loading from the Pi supply.
• A 30 A-class input path and branch fusing replace the earlier inadequate 5–10 A single fuse concept.
• Use one common ground plane; manage noise by placement and current-return routing rather than splitting ground.

• The exact ESP32 30-pin DevKit pin order must be confirmed against the physical module before fabrication.
• The status beacon is compatible with low-side switching; its exact voltage/current will determine MOSFET and connector ratings.
• USB cameras and Wi-Fi adapter plug into the Pi and are not directly wired to the carrier PCB.
• Motor encoder outputs are 3.3 V compatible or open-collector; otherwise level shifting is required.

• Upgraded motor drivers for 3 A stall current.
• Added the full peripheral suite, half-duplex servo bus, and onboard 7.4 V regulator.
• Increased system power-path sizing to reflect realistic combined loads.