robot_forklift_simple_3sw

robot_forklift_simple_3sw is a package that models a family of forklifts with three steerable wheels.

The description above uses the term family because the package is designed to support multiple robot variants, providing a base robot version to which extra capalities can be added to constitute new versions. The core version is the base robot with a fork and motion capabilities, and the v1 version extends the core robot with a specific sensor set. In the future, more robot versions can be added, v2, v3, etc., each with their own set of capabilities and sensors, but all sharing the same base robot description and kinematics.

The term simple refers to the fact that the fork used in this family of robots is a basic fork; simple enough to model a fork, with two tines and a core body that links the tines together, but without the extra details of a real fork, such as the hydraulic system, the lifting mechanism, or the tilting mechanism. The simple fork is sufficient for simulation and testing purposes, but it is not intended to be a detailed model of a real forklift fork. The fork model used in this packages is imported from the robotics_description package, which provides simple fork models. Specifically, the simple fork model used in this package is the fork_simple model, which is derived from a reference fork mesh and can be geometrically scaled.

Thefore, the robotics_description package is a dependency of this package, and it is provided in the file ./deps.repos

For a user of the package, the important pieces are:

• the robot launch file
• the example parameter files
• the example simulation and bridge files

Quick Start

Launch the robot without simulation:

ros2 launch robot_forklift_simple_3sw robot.launch.py robot_version:=core

Launch the v1 robot:

ros2 launch robot_forklift_simple_3sw robot.launch.py robot_version:=v1

Launch the robot in simulation mode:

ros2 launch robot_forklift_simple_3sw robot.launch.py robot_version:=v1 use_sim_time:=True

When use_sim_time:=True, the package also launches the Gazebo bridge automatically.

Main Launch File

The entry point most users want is:

• launch/robot.launch.py

Useful launch arguments:

• robot_version: robot variant to launch, for example core or v1
• use_sim_time: set to True for simulation
• robot_name: robot instance name
• namespace: namespace prefix for the robot resources
• params_file: kinematics / node parameters file
• sim_file: simulation plugin configuration file for the selected robot version
• bridge_file: Gazebo bridge channel configuration file used by robot.launch.py

To inspect all launch arguments:

ros2 launch robot_forklift_simple_3sw robot.launch.py --show-args

robot.launch.py --show-args shows the launch arguments that are declared statically in launch/robot.launch.py.

This output does not include the xargs that are declared dynamically after robot_version is read. Those xargs are created from the YAML file that corresponds to the selected robot version. For example:

• core uses robot_forklift_simple_3sw/xargs/core.yaml
• v1 uses robot_forklift_simple_3sw/xargs/core.yaml plus robot_forklift_simple_3sw/xargs/v1.yaml

This means that --show-args is useful to inspect the static launch arguments, but it is not a complete listing of the xargs that the selected robot version accepts.

Configuration Files

Example files are stored in:

• config/example_core.yaml
• config/example_v1.yaml
• config/example_core_simulation.yaml
• config/example_v1_simulation.yaml
• config/example_core_bridge.yaml
• config/example_v1_bridge.yaml

Typical use:

• use example_*.yaml for robot and kinematics parameters
• use example_*_simulation.yaml for Gazebo plugin configuration
• use example_*_bridge.yaml for ROS <-> Gazebo channel configuration

If params_file or sim_file are not provided, the package picks the matching example file for the selected robot_version. If bridge_file is not provided, robot.launch.py picks the matching example bridge file for the selected robot_version.

sim_file belongs to the xargs set of the selected robot version, so it is part of the dynamic xargs mechanism described above. That is why sim_file can be accepted by the launch file even though ros2 launch ... --show-args does not list it.

Robot Versions

Currently the package exposes at least these robot versions:

• core
• v1

core is the base robot.

v1 extends the base robot with the currently integrated sensor set.

Advanced Use

Most users should prefer launch/robot.launch.py, which now launches robot_state_publisher directly and keeps the robot description, kinematics, and bridge aligned.

robot.launch.py is now the single launch entry point for the robot, including the Gazebo bridge.