Quick start

Important

Changing the code for your robot might be the most important feature of the motion stack, do not underestimate the power of yourself doing a better job than me who never saw your robot. The API section explains how to make your own package, launcher and node using the motion stack API.

What’s this? A package? A workspace?

This repo is a whole workspace, this is not a package. You can easily take out and use the package src/motion_stack and src/motion_stack_msg for your own workspace. I think providing a fully working workspace instead of a lonely package is easier to understand.

Executing

.bash files are provided to build, source and launch the moonbot_zero example. You can open the files and see what commands are running. Nothing complicated, it is the standrad ROS2 launch system.

launch_stack.bash will build everything then execute the launcher for moonbot_zero.

bash launch_stack.bash

You will notice that nothing is running, warning you about missing data. This is because the Motion-Stack uses a data first approach, if data is missing it will warn you. This method avoids relying on the concept of nodes or participants that can be brittle.

Missing lvl0 data: Terminal output

[lvl2-14] [IK2] Forward Kinematics: MISSING ALL :( ['joint2_3', 'joint2_1', 'joint2_2']
[lvl1-3] [J3] Joint data: Missing for ['joint3_3', 'joint3_1', 'joint3_2'].
[lvl1-3] [J3] Joint data: MISSING ALL :(
[lvl1-1] [J1] Joint data: Missing for ['joint1_1', 'joint1_3', 'joint1_2'].
[lvl1-1] [J1] Joint data: MISSING ALL :(
[lvl2-15] [IK3] Forward Kinematics: MISSING ALL :( ['joint3_2', 'joint3_3', 'joint3_1']
[lvl2-16] [IK4] Forward Kinematics: MISSING ALL :( ['joint4_3', 'joint4_2', 'joint4_1']
[lvl2-13] [IK1] Forward Kinematics: MISSING ALL :( ['joint1_1', 'joint1_3', 'joint1_2']
[lvl1-2] [J2] Joint data: Missing for ['joint2_2', 'joint2_3', 'joint2_1'].
[lvl1-2] [J2] Joint data: MISSING ALL :(
[lvl1-4] [J4] Joint data: Missing for ['joint4_1', 'joint4_3', 'joint4_2'].
[lvl1-4] [J4] Joint data: MISSING ALL :(

Available lvl0 data: Terminal output

[lvl2-15] [IK3] Forward Kinematics: FULLY Ready :):
[lvl2-15] Pose(time=1_757_306_662_886_225_483, xyz=[-528.58 -0.00 0.00], quat=[0.71 -0.71 0.00 -0.00])
[lvl1-3] [J3] Joint data: Ready for ['joint3_2', 'joint3_1', 'joint3_3']
[lvl1-3] [J3] Joint Data: FULLY READY :)
[lvl2-16] [IK4] Forward Kinematics: FULLY Ready :):
[lvl2-16] Pose(time=1_757_306_663_315_940_102, xyz=[0.38 -528.58 0.00], quat=[-0.50 0.50 0.50 -0.50])
[lvl1-4] [J4] Joint data: Ready for ['joint4_1', 'joint4_3', 'joint4_2']
[lvl1-4] [J4] Joint Data: FULLY READY :)
[lvl2-13] [IK1] Forward Kinematics: FULLY Ready :):
[lvl2-13] Pose(time=1_757_306_664_669_044_457, xyz=[528.58 -0.00 0.00], quat=[0.00 0.00 0.71 -0.71])
[lvl2-14] [IK2] Forward Kinematics: FULLY Ready :):
[lvl2-14] Pose(time=1_757_306_664_669_067_266, xyz=[-0.38 528.58 0.00], quat=[0.50 -0.50 0.50 -0.50])
[lvl1-2] [J2] Joint data: Ready for ['joint2_3', 'joint2_2', 'joint2_1']
[lvl1-2] [J2] Joint Data: FULLY READY :)
[lvl1-1] [J1] Joint data: Ready for ['joint1_1', 'joint1_2', 'joint1_3']
[lvl1-1] [J1] Joint Data: FULLY READY :)

If it’s your first time launching, lvl1 is waiting for lvl0’s data, which comes from the rviz simulation node (or you future robot). Once simu_rviz launched the Motion-Stack will receive data, start working and output what parts of it are ready.

bash launch_simu_rviz.bash  # (separate terminal)

You should see a robot!

Note

launch_simu_rviz.bash launches rviz and a simulation node that imitates a motor’s response. When using the real robot, you must not use this additional node (it will interfere with messages from the motors). You should launch rviz without simulation using launch_only_rviz.bash

Parameters and Launchers

A customizable launching system is provided. It can be used (and modified) by your own packages.

Important

Tutorial explaining the launch API is provided in API.

• motion_stack.core.utils.static_executor.default_param defines the default parameters. - Parameter documentation is in this file. - Those can be ROS2 parameters if you are using ROS2. However, those are part of th “core”, hence defined in pure python.

• Launch APIs and tools are in motion_stack.api.launch. Those are exposed to packages outside the motion stack.

  • motion_stack.api.launch.builder.LevelBuilder will generate your nodes (and launch description) depending on:

    • Your URDF.

    • The multiple end effectors.

    • Parameters to overwrite.

  • You can import these in your own package and launcher: from motion_stack.api.launch.builder import LevelBuilder

• Sample launchers for specific robots and configurations are in src/motion_stack/launch. These Python scripts are not exposed to other packages.

  • src/motion_stack/launch/moonbot_zero.launch.py is the launcher for moonbot_zero.

Note

You do not need to use the launch API, it is just a wrapper around the standard ROS2 launch system.