arche/two-link-arm

Two-link arm

A two-link arm hanging from a fixed shoulder, a motor and an encoder at each joint, and a controller that cancels gravity and reaches its pose; its plant in MuJoCo (archec gen --target mujoco), its test cases run against it (archec sim --plant … --test).

plantmujocorobotarmcontrolgravity-compensation

archec add main.arche arche/two-link-arm@^0.1

Package

Kind	template
Version	0.1.0
License	Apache-2.0
Export control	none
Works with	archec `>=0.10`
Edition	0.12
Handlers	the action language (```arche), run as TypeScript from its code
Home	https://github.com/arche-lang/arche-lang

Model

Systems	`Arm`
Components	`Link` `Motor` `Encoder` `Controller`
Requirements	2
Messages	2

Code it brings

Where	Language	Lines
`main.arche · Controller.on_shoulder.body`	arche	4
`main.arche · Controller.on_elbow.body`	arche	11

Two-link arm

A two-link arm hanging from a fixed shoulder: two 0.5 m links of 1 kg, a motor (N·m) and an encoder at each joint. Its controller cancels gravity and adds a PD law on top, so it reaches its targets — a plain PD, as examples/arm has, stops short of them, held back by gravity.

| | | |---|---| | Plant | 2 hinges (y), 2 torque motors (±20 N·m), 2 encoders, 1 ms step | | Controller | τ = G(q) + KP·(target − q) − KD·q̇, 100 Hz; KP 40, KD 6 | | Requirements | REQ-ARM-REACH (within 0.02 rad in 2 s), REQ-ARM-HOLD | | Test plan | TP-ARM: reach the first pose, hold it, a second pose |

archec new my-arm --template two-link-arm     a project from it, yours to change
archec gen main.arche --target mujoco -o out
archec sim main.arche --plant out/mujoco/plant_bridge.py --test
python3 out/mujoco/plant_bridge.py --viewer

In MuJoCo (4.0), from 0, 0 to 0.6, 0.9 rad: within 0.02 rad at 0.78 s, and 2·10⁻⁶ rad off at 3 s. Change the targets (controller.target_shoulder, target_elbow) or the links' mass and length — G(q) uses LINK_MASS and LINK_LENGTH, so change them together.

Versions

Version	Published	archec	State
`0.1.0`	2026-11-12	>=0.10	public

Signature

Signed by arche with key e660d0a8851875b9. Files: 3, fingerprint sha256-4b62d917af56341075e5…. archec add checks both before it writes anything.

Discussion

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