--- license: apache-2.0 task_categories: - robotics tags: - humanoid - motion-tracking - locomotion - ff-master - phc viewer: false --- # motionSample — FF Master motion references Joint-space motion references for the **FF Master** humanoid (31 DoF), stored in the **PHC-style pickle** format used by the humanoid motion-tracking codebase family (PHC / H2O / OmniH2O / ASAP / HumanoidVerse). Interactive viewer: **[Master Motion Sample Space](https://huggingface.co/spaces/faradayfuture/MotionSampleViewer)** | | | |---|---| | Clips | 2 (one file each) | | Frames | 2759 total | | FPS | 120 (inferred — see below) | | DoF | 31 | | Robot | FF Master (URDF `x2_ultra`) | **One file per clip** — they are not bundled together. `highjump` is trimmed to 5 consecutive jumps (source frames 654–1589 of a 21-jump take); `jogging` is the full take. | file | clip key | frames | duration | size | |---|---|---|---|---| | `jogging.pkl` | `jogging` | 1824 | 15.2 s | 1.3 MB | | `highjump.pkl` | `highjump` | 935 | 7.8 s | 0.7 MB | ## Loading Each file holds a `{clip_name: {...}}` dict with a single entry, so PHC-family loaders that expect a dict-of-motions read a single file without any code change. ```python import pickle d = pickle.load(open("highjump.pkl", "rb")) list(d) # ['highjump'] m = d["highjump"] m["dof"].shape # (935, 31) joint angles, rad m["root_trans_offset"].shape # (935, 3) base position, m m["root_rot"].shape # (935, 4) base orientation, xyzw m["fps"] # 120 ``` To use both at once, merge them: ```python import glob, pickle d = {} for f in sorted(glob.glob("*.pkl")): d.update(pickle.load(open(f, "rb"))) list(d) # ['highjump', 'jogging'] ``` ## Keys Key names are the **union** of what the PHC family reads. Each framework picks up the subset it knows; the extras are inert. | key | shape | read by | |---|---|---| | `root_trans_offset` | (T, 3) | all | | `root_rot` | (T, 4) **xyzw** | all | | `pose_aa` | (T, 1+31, 3) | PHC / H2O / OmniH2O | | `dof` | (T, 31) | all | | `fps` | int = 120 | all | | `dof_pos` | (T, 31), same array as `dof` | ASAP / HumanoidVerse | | `dof_vel` | (T, 31) | ASAP / HumanoidVerse | | `root_lin_vel` / `root_ang_vel` | (T, 3) | ASAP / HumanoidVerse | | `contacts` | (T, 2) left / right foot | — | | `com_pos` | (T, 3) whole-body centre of mass, world frame | — | | `total_mass` | float = 42.0 kg (from the URDF) | — | | `dof_names` / `body_names` | list | — | | `dof_axes` | (31, 3) | — | | `quat_order` | `"xyzw"` | — | ### `pose_aa` Per-body local rotation in axis-angle form, root first. For a 1-DoF revolute joint the local rotation is a turn of `q` about the URDF `axis`, so the axis-angle vector is just `axis * q`: ``` pose_aa[t, 0] = axis-angle of root_rot pose_aa[t, 1 + j] = dof_axes[j] * dof[t, j] ``` `dof_axes` ships with the file, so `pose_aa` can be rebuilt or cross-checked without the URDF. ### Conventions - **Quaternions are xyzw** (PHC / Isaac). MuJoCo and USD use wxyz — reorder when crossing over. - **z up, soles at z = 0.** Ground alignment uses the *stance-phase median* height, not a per-frame clamp (a per-frame clamp would flatten the high jump's flight phase). After alignment the stance-phase foot height IQR is within ±0.5 cm. - **Velocities are stored**, low-passed at 20 Hz zero-phase. Most loaders finite-difference them at load time instead, which yields noisier values than these — pick one and be consistent. ## Known characteristics and limits These clips are human motion capture retargeted onto the Master kinematics — no physics engine was involved in producing them. **They have been run on the real robot**: a whole-body motion-tracking controller follows them successfully on hardware. Everything below describes the **reference trajectory itself**, not what the robot can do. A tracking controller *approximates* a reference; it does not replay it frame-for-frame. So "the reference carries 0.72 g through flight" and "it runs on the real robot" are both true and not in conflict. Read this section before using a clip as a **per-frame** tracking target, or before assuming a number in it describes the machine. ### Flight-phase gravity is 0.72 g Fitting a parabola to the centre-of-mass height over the middle two thirds of each of `highjump`'s 5 flight phases gives a vertical acceleration of **−7.090 ± 0.057 m/s²**, not −9.807 — a consistent **0.723 g**. The spread across phases is 0.8 %, so this is systematic, not noise, and it is a property of the retargeted reference rather than of the robot. The likely cause is retargeting that rescaled the motion **spatially** to the robot's proportions while keeping the human's **original timing**. Froude similarity requires time to scale as √s when length scales by s; s = 0.723 implies the timeline should be compressed by √0.723, i.e. replayed at 120 × 1.176 ≈ **141 Hz**. That reading is self-consistent: s = 0.723 against the URDF's 0.602 m standing pelvis height implies a 0.833 m human pelvis, i.e. a subject about 1.57 m tall — a plausible capture subject. **This dataset ships at the source timing, un-retimed.** Retiming was tested and does fix the gravity (−9.843 ± 0.080 m/s², 0.37 % residual), but it pushes a few joints marginally past the URDF velocity limits (`jogging` 1/31 at 106 %, `highjump` 3/31 at 105 %) and raises the jogging cadence to 195 steps/min. To apply it yourself: resample the timeline by 1.176 and leave the joint angles untouched. ### `jogging`'s contact pattern is a walk, not a run Cadence is fine (166 steps/min) and swing clearance reaches 22 cm, but each foot is loaded **79 %** of the time, double support is **65.6 %**, and flight phases have a median of only **17 ms**. Real running has a duty factor below 0.5 and 100–200 ms of flight. Good enough as an AMP style prior; per-frame tracking will not teach running dynamics. `highjump`'s phase structure is sound: 73.8 % double support, 25.5 % airborne, 5 flight phases with a 400 ms median. ### Other limits - Residual ground penetration at the deepest frames: −1.9 cm (`jogging`), −3.6 cm (`highjump`). - **Base pose is not robot-measurable.** It comes from the capture system, so it is valid as an offline reference only — never as an observation the robot could produce on its own. - Joint angles are all within the URDF position limits, and joint velocities stay inside the URDF velocity limits (0/31 violations, peaking at 95 % of the limit). So the clips are **kinematically legal**; the trajectories are just not rigid-body-consistent on their own, which is normal for retargeted references and is what the tracking controller absorbs. ## Validation ```bash python3 validate.py # keys, shapes, quaternion norms, pose_aa round-trip, contact phases, # and flight-phase gravity computed from the shipped com_pos ``` ## Why 120 Hz The source files carry no sample rate. 120 Hz is inferred from `jogging`'s cadence: the knee angle's dominant period is 80–86 frames, which at 120 Hz is 166–180 steps/min — the normal jogging band. 60 Hz would give ~87 steps/min (a stroll) and 240 Hz ~340 (impossible). The gravity result above suggests the *dynamically* correct playback rate is ~141 Hz, so treat 120 Hz as the source timing rather than a physically validated one.