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Communication

The serial port

The control board appears on the PC as a serial port over USB: COMx on Windows, /dev/ttyACMx on Linux and /dev/cu.usbmodem… on macOS. The commander takes COM5 or ttyACM0 in its connection field; the Python API's controller takes --serial COM5 or --serial /dev/ttyACM0, or finds the port from PAROL6_COM_PORT.

  • Windows: Device Manager, Ports, shows the number. If the board is missing, try another cable or port; the board enumerates only when it has power.
  • Linux: ls /dev/ttyACM*. Permission denied: sudo chmod 666 /dev/ttyACM0, or add yourself to the dialout group and log in again.
  • Connect fails the first time in the commander: press Connect again; two or three tries are normal.
  • The port is busy: another program has it, often a previous instance of the controller.

The test firmware answers, the main firmware does not

A board from the shop carries the test firmware, which talks in text. Upload the main firmware (Firmware).

The 100 Hz loop

The PC must send a packet every 10 ms. The commander prints Time between 2 commands in ms in its terminal output; it should sit near 0.010. The number is in seconds, despite the label: 0.010 is 10 ms. If it is often higher, the robot stutters and the position tracking suffers.

  • Close browsers and other heavy programs; disable power saving on the USB port and the CPU.
  • A faster PC: six cores from 2017 or newer (What you need).
  • The Python API's controller logs loop overbudget by +N% when its loop runs late, and shows the figures in loop_stats(); it also accepts a lower PAROL6_CONTROL_RATE_HZ, at the cost of smoothness, and runs worse with TRACE or DEBUG logging on.

The connection drops

A USB cable without ferrite near the motors, a hub, or a long cable: use a short, shielded cable straight into the PC. When packets stop, the firmware keeps executing the last one: after a move to a position the joints stop near that target and hold, but a joint that was jogging in the commander keeps turning until it reaches its blocker. Keep the mains switch of the power supply within reach (Emergency stop).

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