Leader arms and USB

The app says no leader arm is found

Rule these out in order — they're listed by how often they're the answer.

1. The cable is charge-only. A charge-only USB cable is physically identical to a data cable and carries no data lines. This is the single most common cause. Swap it for a cable you know carries data.

2. A hub is swallowing it. Unpowered hubs, and hubs daisy-chained off other hubs, drop devices intermittently. Plug the arm directly into the laptop while debugging — add the hub back only once it works.

3. It's genuinely unplugged. Worth actually checking.

🚧 To write

• What a healthy detection looks like in the app.
• How to list serial ports by hand per OS (ls /dev/tty.* on macOS, Device Manager on Windows), and what the arms show up as.
• Driver requirements, if any, per OS.

If the wizard still can't see it, the CLI takes the same steps and is more verbose:

python -m lelab.nori_leader_setup ports --save

Only one of the two arms is found

Both arms share a serial bus. If two motors have the same ID, they collide and the bus misbehaves — which frequently looks like "one arm is missing" rather than a clean error.

Re-run the ID assignment:

python -m lelab.nori_leader_setup set-id --wizard

🚧 To write

Explain the ID scheme and why a motor fresh out of the box always needs an ID assigned before anything works.

The wrong joint moves, or a joint moves backwards

Two candidates:

Motor IDs are wrong. If a motor has the ID that belongs to a different joint, commands land on the wrong joint. Re-run set-id --wizard.

Calibration is stale. Calibration files persist on disk and are reused across sessions. An arm calibrated for a different arm — or before a mechanical change — will behave consistently wrongly.

Calibration lives here:

~/.cache/huggingface/lerobot/calibration/teleoperators/nori_l2_dual_leader/

Re-run calibration:

python -m lelab.nori_leader_setup calibrate

Suspect the cache before the hardware

A stale calibration file produces symptoms that look exactly like a broken arm. If an arm started misbehaving without anything physically changing, check the cache first.

The arms disconnect randomly during a session

Usually power or the hub, not the arms. See Power and brownouts.

Setup guide: Leader arms (Nori L2).