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Board to Board Connector Pin Assignment

By gugan73715 · Last updated: September 22, 2026 · Created: September 15, 2026

List of Interfaces / PWR needed between boards: (Pin Budget)

# Signal Group Count Total Pins
1 +3V3 2× 2
2 +5V 2× 2
3 +12V (Note below) 6× 6
4 GND - +12V Return Path 6× 6
5 PWM 2× 2
6 Gate Driver SPI 2× 8
7 ESC MCU UART 2× 4
8 Gate Driver EN 2× 2
9 Gate Driver nFault INT 2× 2
10 ESC Temp Sensor I2C 2× 4
11 Cell Voltages 6x 6
12 Fuel Gauge I2C 1× 2
13 Cell Monitoring I2C 1× 2
14 Camera UART 1× 2
15 Dynamixel TTL 1× 1
15 Alternating GND ~15x 15
TOTAL 66

Important Note: For +12V, Total Max Dynamixels Current at stall torque is 4.6A. Each pin in B to B connector can do 1A Max, so using 6 pins in parallel. Importantly, +12V needs to have GND very close to it for return path (Current takes the path of least resistance) or else the return current will flow through all the other GND Pins which will result in overlap of return paths of Digital / Analog signals and Noisy PWR leading to noise coupling. (Very bad from SI/PI prespective)

Choosen Connector:

Plug:

STWXE BB51-84AT-1-3HB 84 Pin Mezzanine Connector Plug

Plug Datsheet

Socket:

STWXE BB52-84AT-1-3HB 84 Pin Mezzanine Connector Socket

Socket Datsheet

Specifications:

  • 84 Pins
  • 1mm Pitch
  • 1A Max per Pin
  • Keyed
  • Mating Height: 6.35mm
  • Contact Material: Copper Alloy
  • Durability: 50 Cycles (Note Below)

Note on durabilty: 50 Cycles is very low so we need to prevent pluging and unplugging as much as possible. Keep it mated and assembled as much as possible.

Pin Assignment:

Net Pin Pin Net
V_CELL6 1        2 +3V3
V_CELL5 3        4 GND
GND 5        6 +5V
V_CELL4 7        8 GND
V_CELL3 9        10 ESC Temp Sensor I2C_SDA
GND 11        12 ESC Temp Sensor I2C_SCL
V_CELL2 13        14 GND
V_CELL1 15        16 Cell Monitoring I2C_SDA
GND 17        18 Cell Monitoring I2C_SCL
PWM1 19        20 GND
GND 21        22 Gate Driver_1 EN
PWM2 23        24 Gate Driver_2 EN
GND 25        26 +3V3
Fuel Gauge I2C_SDA 27        28 GND
Fuel Gauge I2C_SCL 29        30 +5v
GND 31        32 GND
Gate Driver_1 SPI_CS 33        34 Gate Driver_1 nFault INT
Gate Driver_1 SPI_SCLK 35        36 Gate Driver_2 nFault INT
GND 37        38 GND
Gate Driver_1 SPI_MISO 39        40 Camera TX (Camera_TX to FC_RX)
Gate Driver_1 SPI_MOSI 41        42 Camera RX (Camera_RX to FC_TX)
GND 43        44 GND
Gate Driver_2 SPI_CS 45        46 FDCAN_H
Gate Driver_2 SPI_SCLK 47        48 FDCAN_L
GND 49        50 GND
Gate Driver_2 SPI_MISO 51        52 Unassigned
Gate Driver_2 SPI_MOSI 53        54 +3V3
GND 55        56 GND
TTL 57        58 +5V
GND 59        60 GND
ESC MCU1 UART_TX (ESC_TX to FC_RX) 61        62 +12V
ESC MCU1 UART_RX (ESC_RX to FC_TX) 63        64 GND
GND 65        66 +12V
ESC MCU2 UART_TX (ESC_TX to FC_RX) 67        68 GND
ESC MCU2 UART_RX (ESC_RX to FC_TX) 69        70 +12V
GND 71        72 GND
VBAT 73        74 +12V
GND 75        76 GND
VBAT 77        78 +12V
GND 79        80 GND
Unassigned 81        82 +12V
Unassigned 83        84 GND