> ## Documentation Index
> Fetch the complete documentation index at: https://docs.almond.bot/llms.txt
> Use this file to discover all available pages before exploring further.

# tune.friction

> Identify the friction-model parameters for one joint via a velocity sweep.

Identifies the four friction-model parameters for one joint via a bidirectional velocity sweep. Gravity is computed centrally from the URDF (see [Gravity compensation](/cli/gravity-comp)), so this command only fits the friction half-difference and a constant offset.

**Friction model:** `τ = Fc·tanh(0.1·k·v) + Fv·v + Fo`

| Flag                     | Description                                                                                                                                                                                                     |
| ------------------------ | --------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- |
| `--l` / `--r`            | Arm side (required)                                                                                                                                                                                             |
| `--joint JOINT`          | `shoulder_1`, `shoulder_2`, `shoulder_3`, `elbow`, `wrist_1`, `wrist_2`, `wrist_3` (required)                                                                                                                   |
| `--kp FLOAT`             | Proportional gain (default: from `AxolConfig`)                                                                                                                                                                  |
| `--kd FLOAT`             | Derivative gain (default: from `AxolConfig`)                                                                                                                                                                    |
| `--velocities V [V ...]` | Velocity setpoints in rad/s (default: \~0.1, 0.3, 0.6, 0.9, 1.3)                                                                                                                                                |
| `--lo RAD`               | Override lower joint limit for the sweep                                                                                                                                                                        |
| `--hi RAD`               | Override upper joint limit for the sweep                                                                                                                                                                        |
| `--dump-csv [PATH]`      | Write per-bin `(v, q, tau_fwd, tau_bwd, tau_avg, tau_halfdiff)` rows to a CSV for offline plotting / arm-vs-arm comparison. Pass without a value to auto-name as `logs/friction_<side>_<joint>_<timestamp>.csv` |

```bash theme={null}
axol tune.friction --l --joint shoulder_1 --kp 30 --kd 0.8
axol tune.friction --r --joint elbow --kp 20 --kd 0.6
axol tune.friction --l --joint wrist_1 --velocities 0.2 0.6 1.0
axol tune.friction --l --joint shoulder_2 --dump-csv
```