Minimal Admittance Controller — README

What it is

A single-file, first-order admittance controller that:

• Loads a URDF from the current folder (default: meca_robot_with_botaandshaft.urdf).
• FK via urdfpy; 6×N Jacobian via pykin (if installed) or numeric finite differences.
• Maps an EE wrench → joint velocities using damped least squares (no ROS, no optimizers).

Public API (matches original): dq = AdmittanceController(cfg)(target_poses, q, tau, ee_wrench, collision=None)

Dependencies (Python 3.10)

Core: urdfpy==0.0.22, numpy>=1.23, scipy>=1.10,<1.12, lxml>=4.6,<5, trimesh>=4.0, networkx==2.8.8
Optional (robust import / rendering): pyrender==0.1.45, PyOpenGL==3.1.0, freetype-py, pyglet<2.2, pillow
Optional (analytic Jacobian): pykin

Quick setup (recommended: clean venv)

python3 -m venv ~/venvs/urdfctrl source ~/venvs/urdfctrl/bin/activate python -m pip install --upgrade pip pip install --no-deps urdfpy==0.0.22 pip install "networkx==2.8.8" "numpy>=1.23" "scipy>=1.10,<1.12" "lxml>=4.6,<5" trimesh pip install "pyrender==0.1.45" "PyOpenGL==3.1.0" freetype-py "pyglet<2.2" pillow

optional:

pip install pykin

Run

python admittance_controller.py

Principle (first-order admittance)

1. Body-frame mapping: v_b = k_f * f_b, ω_b = k_τ * τ_b
2. World-frame conversion (R_we from FK): v_w = R_we v_b, ω_w = R_we ω_b
3. Joint velocities via damped least squares: dq = J⁺ [v_w; ω_w], J⁺ = Jᵀ (J Jᵀ + λ² I)⁻¹

Notes:

• No inertia/second-order dynamics; this is a minimal variant.
• If pykin is missing, the Jacobian falls back to central-difference FD.
• The controller outputs joint velocities; integrate externally if needed.