Planar n-link forward kinematics

Planar n-link forward kinematics. Parameterized bounded JSON adapter; numerical operation, no hardware execution.

pythonrobotics-planar-fk | Record version: 1.0.0

Record JSON | Markdown recipe | Complete search index

Fetch and prepare

curl -fsSL https://hub.superfastrobotics.com/skills/pythonrobotics-planar-fk/skill.json
curl -fsSL https://hub.superfastrobotics.com/skills/pythonrobotics-planar-fk/README.md
python /PATH_TO_SKILL/scripts/rsh.py inspect pythonrobotics-planar-fk --json
python /PATH_TO_SKILL/scripts/rsh.py prepare pythonrobotics-planar-fk --project ./experiment --expected-source-commit cdd0cc888802b584c2d654ca85e3c5460973487d --expected-record-version 1.0.0 --plan --json

Inspect the requirements, then remove --plan to prepare a project. Preparation verifies the archive SHA256 and preserves exact source pins. --install-deps explicitly installs dependencies. Run the returned simulation command separately.

Environment

Runtime

pythonrobotics cdd0cc888802

Robot

mathematical-model

Controller

json-contract-v1

Observation

explicit-json-input

OS / architecture

windows / x86_64

Python

>=3.10,<3.11

Compatibility status: hub_verified

Runtime

pythonrobotics cdd0cc888802

Robot

mathematical-model

Controller

json-contract-v1

Observation

explicit-json-input

OS / architecture

linux / x86_64

Python

>=3.10,<3.11

Compatibility status: hub_verified

All inputs and outputs follow interface v1. Simulation adapters query exact synthetic simulator state; no perception or physical sensor compatibility.

Requirements

• x86_64 CPU; no GPU or robot required

No display. Matplotlib Agg for numerical imports; PyBullet DIRECT for simulation.

Packages: contourpy==1.3.2, cycler==0.12.1, fonttools==4.65.0, kiwisolver==1.5.1, matplotlib==3.9.4, numpy==1.26.4, packaging==26.3, pillow==12.3.0, pyparsing==3.3.3, python-dateutil==2.9.0.post0, scipy==1.13.1, six==1.17.0

Runtime dependency versions are pinned for the supported Python 3.10 x86_64 CPU environments and checked against execution receipts. Platform-specific wheel hashes are not represented as a universal artifact lock; prepare captures pip freeze.

External API keys: none.

Invocation

Executable interface

{
  "version": "1",
  "kind": "algorithm",
  "abstraction_level": 0,
  "execution_domain": "computation",
  "language": "python",
  "input_transport": "json_file_or_inline",
  "output_transport": "json_stdout",
  "conventions": {
    "linear_unit": "m",
    "angular_unit": "rad",
    "time_unit": "s",
    "coordinate_frame": "arm_base_xy; +z revolute axes; base_to_tip_array_order",
    "joint_order": "input_array_order",
    "quaternion_order": "not_used"
  },
  "input_schema": {
    "type": "object",
    "required": [
      "link_lengths",
      "joint_angles"
    ],
    "additionalProperties": false,
    "properties": {
      "link_lengths": {
        "type": "array",
        "minItems": 2,
        "maxItems": 8,
        "items": {
          "type": "number",
          "minimum": 0.1,
          "maximum": 5
        },
        "x-unit": "m",
        "x-frame": "arm_base_xy; +z revolute axes; base_to_tip_array_order",
        "description": "link_lengths; units=m; frame=arm_base_xy; +z revolute axes; base_to_tip_array_order"
      },
      "joint_angles": {
        "type": "array",
        "minItems": 2,
        "maxItems": 8,
        "items": {
          "type": "number",
          "minimum": -10,
          "maximum": 10
        },
        "x-unit": "rad",
        "x-frame": "arm_base_xy; +z revolute axes; base_to_tip_array_order",
        "description": "joint_angles; units=rad; frame=arm_base_xy; +z revolute axes; base_to_tip_array_order"
      }
    }
  },
  "output_schema": {
    "type": "object",
    "required": [
      "joint_angles_rad",
      "end_effector_xy_m"
    ],
    "additionalProperties": false,
    "properties": {
      "joint_angles_rad": {
        "type": "array",
        "minItems": 2,
        "maxItems": 8,
        "items": {
          "type": "number",
          "minimum": -100000,
          "maximum": 100000
        },
        "x-unit": "rad",
        "x-frame": "arm_base_xy; +z revolute axes; base_to_tip_array_order",
        "description": "joint_angles_rad; units=rad; frame=arm_base_xy; +z revolute axes; base_to_tip_array_order"
      },
      "end_effector_xy_m": {
        "type": "array",
        "minItems": 2,
        "maxItems": 2,
        "items": {
          "type": "number",
          "minimum": -100.0,
          "maximum": 100.0
        },
        "x-unit": "m",
        "x-frame": "arm_base_xy; +z revolute axes; base_to_tip_array_order",
        "x-order": [
          "x",
          "y"
        ],
        "description": "end_effector_xy_m; units=m; frame=arm_base_xy; +z revolute axes; base_to_tip_array_order; component order=x,y"
      }
    }
  },
  "preconditions": [
    "Ideal planar serial chain; no joint limits, collision geometry or dynamics.",
    "IK uses the upstream 0.1 m convergence tolerance and at most 1000 iterations."
  ],
  "postconditions": [
    "All declared checks must pass and all outputs must be finite.",
    "Success applies only to this operation and model, not higher-level task completion."
  ],
  "failure_codes": [
    "invalid_input_or_environment",
    "execution_failed",
    "task_failed"
  ],
  "composition": {
    "depends_on": [],
    "automatic_frame_conversion": false,
    "automatic_hardware_execution": false
  },
  "output_selector": "outputs",
  "origin_reference_ids": [],
  "origin_relationship": "adapted_from; inspect declared model and inputs, not original robot compatibility"
}

Entrypoint: python run.py

{
  "argv": [
    "{python}",
    "{recipe_dir}/run.py",
    "--source-dir",
    "{source_dir}",
    "--example"
  ],
  "inputs": {
    "link_lengths": [
      1,
      1,
      0.5
    ],
    "joint_angles": [
      0.1,
      0.3,
      -0.2
    ]
  },
  "outputs": {
    "format": "single JSON object on stdout",
    "payload_selector": "outputs",
    "schema": {
      "type": "object",
      "required": [
        "joint_angles_rad",
        "end_effector_xy_m"
      ],
      "additionalProperties": false,
      "properties": {
        "joint_angles_rad": {
          "type": "array",
          "minItems": 2,
          "maxItems": 8,
          "items": {
            "type": "number",
            "minimum": -100000,
            "maximum": 100000
          },
          "x-unit": "rad",
          "x-frame": "arm_base_xy; +z revolute axes; base_to_tip_array_order",
          "description": "joint_angles_rad; units=rad; frame=arm_base_xy; +z revolute axes; base_to_tip_array_order"
        },
        "end_effector_xy_m": {
          "type": "array",
          "minItems": 2,
          "maxItems": 2,
          "items": {
            "type": "number",
            "minimum": -100.0,
            "maximum": 100.0
          },
          "x-unit": "m",
          "x-frame": "arm_base_xy; +z revolute axes; base_to_tip_array_order",
          "x-order": [
            "x",
            "y"
          ],
          "description": "end_effector_xy_m; units=m; frame=arm_base_xy; +z revolute axes; base_to_tip_array_order; component order=x,y"
        }
      }
    }
  }
}

Success: Exit 0, status=task_complete, success=true, finite outputs satisfying interface.output_schema and all declared numerical/model checks. This is not a physical robot or general task-success claim.

Timeout: 30 seconds. Caller must terminate the separate adapter process after 30 seconds; adapters bound iterations/scene steps and close simulation clients.

Failure modes

• Invalid or oversized JSON
• Source checksum mismatch
• Unavailable pinned dependency
• No valid path or postcondition failure
• Execution exceeding the declared bounded algorithm budget

Source and license

Repository

https://github.com/AtsushiSakai/PythonRobotics

Authors

Atsushi Sakai and PythonRobotics contributors

Commit

cdd0cc888802b584c2d654ca85e3c5460973487d

Archive SHA256

6d3ccf43be4ae770a9e8dffd463c2561665847df5b7ddf693b01130004dbcee5

License

MIT

Hub commit

39b06d7a6016edcea27e348e49ffd86f29ec1811

• ArmNavigation/n_joint_arm_to_point_control/NLinkArm.py
• ArmNavigation/n_joint_arm_to_point_control/n_joint_arm_to_point_control.py
• InvertedPendulum/inverted_pendulum_lqr_control.py
• LICENSE
• Localization/extended_kalman_filter/ekf_with_velocity_correction.py
• Localization/extended_kalman_filter/extended_kalman_filter.py
• Localization/unscented_kalman_filter/unscented_kalman_filter.py
• PathPlanning/AStar/a_star.py
• PathPlanning/BSplinePath/bspline_path.py
• PathPlanning/BezierPath/bezier_path.py
• PathPlanning/BidirectionalAStar/bidirectional_a_star.py
• PathPlanning/BidirectionalBreadthFirstSearch/bidirectional_breadth_first_search.py
• PathPlanning/BreadthFirstSearch/breadth_first_search.py
• PathPlanning/Catmull_RomSplinePath/catmull_rom_spline_path.py
• PathPlanning/CubicSpline/cubic_spline_planner.py
• PathPlanning/DepthFirstSearch/depth_first_search.py
• PathPlanning/Dijkstra/dijkstra.py
• PathPlanning/DubinsPath/dubins_path_planner.py
• PathPlanning/DynamicWindowApproach/dynamic_window_approach.py
• PathPlanning/GreedyBestFirstSearch/greedy_best_first_search.py
• PathPlanning/PotentialFieldPlanning/potential_field_planning.py
• PathPlanning/ProbabilisticRoadMap/probabilistic_road_map.py
• PathPlanning/QuinticPolynomialsPlanner/quintic_polynomials_planner.py
• PathPlanning/RRT/rrt.py
• PathPlanning/RRT/rrt_with_pathsmoothing.py
• PathPlanning/RRTStar/rrt_star.py
• PathPlanning/ReedsSheppPath/reeds_shepp_path_planning.py
• PathTracking/pure_pursuit/pure_pursuit.py
• PathTracking/stanley_control/stanley_control.py
• utils/__init__.py
• utils/angle.py
• utils/plot.py
• ArmNavigation/n_joint_arm_to_point_control/__init__.py
• ArmNavigation/__init__.py
• __init__.py
• Localization/__init__.py
• PathPlanning/__init__.py
• PathPlanning/CubicSpline/__init__.py
• PathPlanning/DubinsPath/__init__.py
• PathPlanning/RRT/__init__.py
• PathPlanning/RRTStar/__init__.py
• PathTracking/__init__.py

Evidence

Runtime: task_complete / task_complete

Three frozen positive cases passed against this exact adapter; see per-case receipts. This does not estimate general accuracy.

Reviewer: Hub maintainer runtime harness | 2026-10-19

• python tools/verify_executable_recipes.py --source-cache SOURCE_CACHE --output OUTPUT --backend pythonrobotics

Submitter reports and hub verification remain separate. Source review does not establish task success.