fastgripper-openarm — DM-J4310 Worm-Gear Gripper Toolkit

Standalone control for the worm-gear gripper: calibrate, home, and drive it over CAN. No ROS required; plain Python ≥ 3.10 over SocketCAN (Linux) or gs_usb/slcan USB adapters (macOS bench use).

New here? Start with docs/QUICKSTART.md — parts to working gripper in ~30 minutes (the gripper ships without an actuator; you supply a Damiao DM-J4310).

Install

pip install fastgripper-openarm            # core
pip install "fastgripper-openarm[pad]"     # + gamepad support

(Bleeding edge, with repo access: pip install "git+ssh://git@github.com/Transcend-Mechanics/fastgripper-openarm.git".)

Python must be ≥ 3.10 (python3 --version; stock JetPack ships 3.8 — the scripts fail on it at import with TypeError: unsupported operand type(s) for |). fastgripper-gui additionally needs the system package python3-tk.

Calibration data

Tools look for gripper_cal.json in the current directory first, then ~/.config/fastgripper/gripper_cal.json. Generate it once per assembly by probing the hardstops (jaws empty!):

fastgripper-autocal full --expected_span <rad, from your gripper's label / product page> \
    --interface socketcan --channel canX

Motor IDs live in the cal file — no ID flags needed after this.

Bus setup (Linux)

The gripper speaks classic CAN 2.0 at 1 Mbit/s. Find the interface the USB-CAN adapter created (do NOT assume can1 — plug/unplug and watch ip -br link | grep can), then:

sudo ip link set canX up type can bitrate 1000000   # rerun after every reboot

Sharing an existing classic-CAN bus instead: the motor must be re-ID'd off-bus first — a factory DM-J4310 (ID 0x01) collides with OpenArm's joint 1 (their map is 0x01–0x08/0x11–0x18). Wiring: stub < 30 cm, no extra terminator mid-bus. Never share a CAN FD bus — a classic device errors on every FD frame and can disrupt the other nodes. Always pass --interface socketcan --channel canX explicitly. On a dedicated channel a factory motor needs no configuration at all.

Use

fastgripper-autocal home --interface socketcan --channel canX
    # ~20 s re-anchor against the closed stop. JAWS EMPTY. Run once after
    # unboxing, and any time behavior looks off.
fastgripper-pad --keyboard --interface socketcan --channel canX
    # hold a = open, d = close, space = stop, Ctrl-C = quit
fastgripper-pad --interface socketcan --channel canX
    # gamepad: LT = open, RT = close, pressure = speed  (needs [pad] extra)
fastgripper-drive 40 --interface socketcan --channel canX
    # scriptable: go to 40% closed and exit — read fastgripper/drive.py
    # to embed the gripper in your own Python
fastgripper-gui --interface socketcan --channel canX
    # Tk GUI (desktop session required)
fastgripper-doctor --interface socketcan --channel canX
    # no-motion diagnosis when position/state look wrong

Safety

• Jaws empty for any fastgripper-autocal run — an object in the jaws gets squeezed or fakes a stall.
• The worm gear holds position with the motor off: grip survives power cuts (feature) and will NOT release on power cut (hazard — run a tool to open).
• All tools are dead-man by construction, position-bounded to the calibration, and torque-capped. The worm multiplies motor torque into large jaw force — don't raise --tmax/--probe_tmax casually.
• Keep hands out of jaw and linkage travel while any tool is running.

Troubleshooting

fastgripper-calibrate (keyboard jog, mark endpoints by eye, real TTY required) is the manual fallback if autocal can't be tuned for your unit.