`description` — Robot Model Assets¶

The description package holds all ** kinematic and simulation assets** for the fishing arm: URDF/xacro, MuJoCo MJCF, and STL meshes.

Source: software/src/description/
Auto-generated tables: description

There is no runtime Python node — this package is consumed at launch time when xacro generates the URDF and when MuJoCo loads the MJCF scene.

Asset inventory¶

Asset	Path	Used by
Xacro macro	`urdf/fishing-robot.urdf.xacro`	`bringup` → `robot_state_publisher`, ros2_control
Sim URDF	`urdf/fishing-robot_sim.urdf`	Preprocessed reference
HW URDF	`urdf/fishing-robot_hw.urdf`	Preprocessed reference
MJCF scene	`urdf/fishing-robot_sim.xml`	`mujoco_ros2_control` plugin
Meshes	`meshes/*.STL`	Visual/collision geometry

Kinematic tree (both modes)¶

        flowchart TB
    BL["base_link"]
    L1["Link_1"]
    L2["Link_2"]
    RT["rod_tip_link"]
    BL -->|"Joint_1 revolute (yaw)"| L1
    L1 -->|"Joint_2 revolute (pitch)"| L2
    L2 -->|"rod_tip_joint fixed"| RT

Joint	Type	Axis	ros2_control interfaces
`Joint_1`	revolute	Z	position cmd; pos/vel/effort state
`Joint_2`	revolute	Y	position cmd; pos/vel/effort state
`rod_tip_joint`	fixed	—	Defines load cell frame

Simulation adds:

Joint	Type	Purpose
`fish_swim`	prismatic	Virtual fish slide DOF
`fish_link`	—	Fish body frame

The `use_sim` xacro switch¶

fishing-robot.urdf.xacro accepts:

Argument	Default	Effect
`use_sim`	`true`	Select hardware plugin and sim-only joints/sensors
`headless`	`false`	MuJoCo viewer visibility (sim only)

Simulation block (`use_sim:=true`)¶

<plugin>mujoco_ros2_control/MujocoSystemInterface</plugin>
<param name="mujoco_model">.../fishing-robot_sim.xml</param>
<param name="initial_keyframe">starting_pose</param>
<param name="headless">...</param>

Additional ros2_control entries:

fish_swim joint with effort command interface
tension_sensor FTS sensor mapped from MJCF tension_sensor sensor

Hardware block (`use_sim:=false`)¶

<plugin>dynamixel_hardware/DynamixelHardware</plugin>
<param name="usb_port">/dev/ttyUSB0</param>
<param name="baud_rate">57600</param>

No fish joint, no FTS sensor — only Joint_1 and Joint_2.

MJCF simulation scene¶

fishing-robot_sim.xml defines:

Arm bodies matching URDF kinematics
Line tendon between rod tip and fish (stiffness, rest length, damping — must match sensors — Line Tension Sensing sim_line_* parameters)
tension_sensor force/torque sensor at rod tip
fish_force motor on fish_swim
starting_pose keyframe applied on boot

The MuJoCo plugin reads the MJCF path from the URDF <param> tag — no separate launch argument needed.

ros2_control joint ↔ Dynamixel mapping¶

Joint	Dynamixel ID	Limits
`Joint_1`	1	±π rad
`Joint_2`	2	±π rad

Effort limit: 2.5 N·m; velocity limit: 5.76 rad/s (from URDF).

Interactions¶

Package	How it uses `description`
bringup — Launch Orchestration	Processes xacro with `use_sim`, `headless`; passes URDF to all nodes
`mujoco_ros2_control`	Loads MJCF, steps physics, exposes sim joints/sensors
`dynamixel_hardware`	Maps URDF joints to USB servos
sensors — Line Tension Sensing	TF frame names; tendon parameter consistency
planning — Virtual Fish (Simulation Only)	Fish joint exists in sim URDF/MJCF
diagnostics — Recording & Bring-Up Tests	MJCF path for animation renderer

description — Robot Model Assets¶

Asset inventory¶

Kinematic tree (both modes)¶

The use_sim xacro switch¶

Simulation block (use_sim:=true)¶

Hardware block (use_sim:=false)¶