dwl1437/quadrotor_assets

Quadrotor Assets

This repository contains the USD/URDF assets for the five-inch quadrotor and the aerial manipulator. Large geometry and USD files are managed with Git LFS.

Layout

• aerial_manipulator/aerial_manipulator.usd: canonical aerial-manipulator asset loaded by Isaac Lab.
• aerial_manipulator/configuration/: generated base, physics, sensor, and texture layers.
• aerial_manipulator/kinematics/aerial_manipulator_urdf/: local URDF, meshes, kinematics helper, and PyBullet checks. This directory is currently ignored by the root .gitignore.
• five_inch_drone/five_inch_drone.usd: canonical five-inch quadrotor asset.

Path policy

• USD layers and material textures use paths relative to the containing asset directory.
• aerial_manipulator/config.yaml records paths relative to aerial_manipulator/; run a converter from that directory or resolve them against the config file location.
• The Python asset configs derive the USD path from __file__. The resulting runtime path is absolute, but it is portable and contains no machine-specific hard-coded prefix.
• Do not commit machine-specific absolute filesystem paths or file-URI references into asset/config files.

Aerial manipulator parameters

Mass and inertia

Item	Current value
Airframe without manipulator (base_link)	1.8 kg
Complete aerial manipulator	1.9314 kg
Base center of mass	(0, 0, 0.01) m
Base diagonal inertia	(0.01316967, 0.00984785, 0.01512289) kg m²
Upper arms	3 × 0.0163 kg
Lower arms	6 × 0.007 kg
Vertical follower placeholders	6 × 0.001 kg
End-effector prismatic placeholders	2 × 0.001 kg
End effector	0.0325 kg

The airframe mesh origin is its center of gravity. Its placement is (0.0000804517, 0.0013449539, 0.0095604723) m in base_link, which puts it 40 mm above the centroid plane of joint1, joint2, and joint3.

Kinematics and coordinates

• Commanded joints: joint1, joint2, joint3.
• Active-joint axis: local +Y; range: 0 to π/2 rad (0–90°); effort limit: 100; velocity limit: 1 rad/s.
• Each upper arm connects to its two lower arms at x = 0.1 m and y = ±0.013 m in the upper-arm frame.
• Lower-arm initial pitch compensation: 0.4277448288 rad (24.508°).
• End-effector follower ranges: X/Y ±0.15 m and Z [-0.3, 0.1] m.
• Visual geometry uses DAE; collision geometry uses OBJ. Carbon-fiber and lower-arm thread textures live beside the source meshes and are copied under configuration/materials/textures/ for USD.

USD conversion snapshot

Setting	Value
Instanceable	true
Fixed base	false
Merge fixed joints	false
Collider	convex_hull
Self collision	false
Drive type / target	force / position
Imported drive stiffness / damping	100 / 1
Articulation inventory	19 bodies, 18 DOFs

Isaac Lab runtime configuration

• Initial root position: (0, 0, 1.5) m; gravity enabled; gyroscopic forces enabled.
• Solver iterations: 16 position / 4 velocity.
• Sleep threshold: 0.005; stabilization threshold: 0.001.
• Commanded-joint implicit PD: stiffness 10000, damping 1000, effort limit 1e6.
• Follower-joint stabilization PD: stiffness 10000, damping 1000.

The follower joints are conceptually passive, but the current aerial_manipulator_cfg.py attaches a stabilization PD group to them. Removing that group changes the dynamics and should be treated as a separate controller change, not a documentation cleanup.

Validation

From aerial_manipulator/kinematics/aerial_manipulator_urdf/:

check_urdf urdf/urdf/aerial_manipulator.urdf
python test/visualize_pybullet.py --headless --cycles 1
python test/visualize_pybullet.py --animate --headless --duration 3

The canonical USD should be tested through an Isaac Sim/Isaac Lab application before changing mass, joint, collision, or material layers.

Git LFS

Initialize LFS after cloning:

git lfs install --local
git lfs pull

Without the LFS clean/smudge filter, git status can report hydrated USD/DAE/URDF files as modified even when their SHA256 is identical to the committed LFS object.