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The robot system

A working PAROL6 is three things: the arm, the control board inside its base, and a PC running the high-level software. Each does a part of the job.

PAROL6 with the connections on its base
Figure 1.1: PAROL6 with the connections on its base.

The arm

Six revolute joints, driven by NEMA 17 stepper motors through planetary gearboxes and belts, in PETG printed links. Joints 1, 2 and 3 position the wrist; joints 4, 5 and 6 form a spherical wrist that orients the tool. Joint 6 ends in the flange the tool mounts on. The tool connections are on the forearm: an M8 connector for an electric gripper and two push-in fittings for pneumatic lines. Each joint has a limit switch or an inductive sensor that gives it a reference when the robot homes.

PAROL6 with the pneumatic gripper, its parts numbered PAROL6 with the pneumatic gripper, its parts numbered
Figure 1.2: PAROL6 with the pneumatic gripper, its parts numbered.
  1. Base, with the control board inside
  2. Joint 1 motor
  3. Shoulder, turned by joint 1
  4. Joint 2 motor
  5. Upper arm
  6. Joint 3 motor
  7. Elbow
  8. Forearm, also called the lower arm, turned by joint 4
  9. Wrist, turned by joint 5
  10. Flange, turned by joint 6
  11. Air fittings for a pneumatic tool
  12. Gripper, here the standard pneumatic gripper

The arm has no brakes and no joint encoders. The motors hold the arm while they are powered; the position is counted in steps from the homing reference. Both facts shape how the robot is used, and the Safety chapter returns to them.

The control board

The PAROL6 control board sits in the base: an STM32F446 microcontroller, six TMC5160 stepper drivers, two isolated inputs and two isolated outputs, the E-stop input, a CAN bus for electric grippers, and USB to the PC. Its firmware generates the step pulses, runs the homing sequence, reads the switches and the inputs, drives the outputs and the gripper, and exchanges a packet with the PC at 100 Hz. It does not plan motion: it executes the joint speeds and positions the PC sends it, 100 times a second.

The PC software

The PC does the thinking: kinematics, trajectory planning, the simulator, the program interpreter, the interface. There are two first-party programs, and others:

What it is For
Commander software A desktop GUI with jogging, a 3D simulator, a program editor for RBTscript, I/O and gripper tabs Using the robot by hand, teaching points, simple programs
Python API A controller process that talks to the board, and a Python client library with blocking and asynchronous calls, planned and streamed motion, tools, collision checking Programs, integrations, research, teleoperation, AI agents
ROS 2 and MoveIt A MoveIt configuration and a ros2_control hardware interface that drive the Python API's controller ROS users
Community interfaces Web GUIs, alternative firmware, vision demos

All of them speak the same serial protocol to the control board, so a board with the main firmware works with any of them.

How a move happens

  1. You press a jog button, run a program line or call move_j.
  2. The PC software computes the trajectory: the joint angles over time, with the speed profile you chose, within the joint limits.
  3. One hundred times a second it sends the control board a packet with the target position and speed of each joint, the output states and the gripper command.
  4. The board sets the stepper speeds and runs the steps; the drivers turn the motors.
  5. The board answers with the actual position and speed of each joint, the switch and input states, the errors and the gripper's status, which the PC software shows and uses for the next cycle.
sequenceDiagram
    participant PC as PC software
    participant B as Control board
    participant M as Motors
    Note over PC: a jog button, a program line, move_j: the trajectory is planned
    loop every 10 ms
        PC->>B: targets: joint positions and speeds, outputs, gripper
        B->>M: step pulses at the commanded speeds
        B-->>PC: actual positions and speeds, switches, inputs, errors
    end

Where everything is published
Mechanical files, BOM, building instructions, control board firmware, URDF PAROL6-Desktop-robot-arm
Commander software PAROL-commander-software
Python API PAROL6-python-API
ROS 2 MoveIt configuration PAROL6-ROS2-MOVEIT
This documentation PAROL-docs
Shop, videos, community source-robotics.com, YouTube, Discord

The full list is on Downloads and files.

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