Circuit Design and PCB Production

Circuit Design

The previous section summarized the electrical design requirements. Our circuit requirements can be represented by the following block diagram:

flowchart LR
    A[Battery 48V] --> B[Motor switch]
    B --> B1[Motors]

    A --> C[Converter 48V->19V]
    A --> D[Digital voltage display]

    C --> C1[Mainboard switch]
    C1 --> C2[Orin AGX]
    C2 --> D1[IMU]
    C2 --> D2[Camera]
    C2 --> D3[Motor CAN bus]

    D3 <-.-> B1

In the first version of the design, we directly used NMOS transistors as switches, and an off-the-shelf voltage converter module for power conversion. The module supports 30-60 V input and provides 19 V, 5 A output. This circuit could perform its function stably when the current was relatively small, but because the peak current of 20 motors is quite high and there can also be surge current, the MOS switch was repeatedly burned out.

Circuit schematic V1

PCB layout V1

PCB hardware V1

In the second version, we added a relay and the circuit became somewhat more stable, but the relay could still break down when the battery was connected. We will need to think of a better solution in the next version.

Circuit schematic V2

PCB layout V2

PCB hardware V2

Because the motors require four CAN buses, we purchased a CAN breakout board. It takes XT60 current input, and its other four CAN plus power interfaces connect to the four motor branches. The CAN signal wires on this board happen to be reversed relative to the motor signal wires, so on the first motor connection the signal wires need to be swapped. The four CAN signals are then converted to USB and connected to the mainboard.

The converter, relay, battery, and CAN breakout board are shown below.

Converter

Relay

Battery

CAN breakout board