GRAFT: Geometry-Aware Residual Adaptation for Foundation Trackers
Organizations: Xiaomi Robotics Lab. · HKUST(Guangzhou).
Abstract
Humanoid behavior foundation models (BFMs) provide reusable whole-body motion priors: given a kinematic reference, they generate coordinated joint commands for motion replay, teleoperation, and VLA control. However, trained primarily on flat-ground motion, BFMs lack an explicit mechanism to adapt foot placement, swing clearance, and contact timing to local terrain. Many terrain-aware BFM approaches address this limitation by retraining or fine-tuning the tracker together with perception, incurring substantial data and computation costs while coupling ordinary tracking to the perception pathway. To bridge this gap, we propose GRAFT, a geometry-aware residual adaptation framework for frozen behavior trackers. GRAFT preserves the BFM parameters and motion-reference interface, while a lightweight adapter adds terrain-conditioned corrections only to lower-body execution targets. The adapter is trained with task and foot-geometry rewards, regularized to suppress unnecessary corrections on flat ground, and distilled from privileged terrain observations to onboard depth. Because the frozen BFM already provides whole-body reference tracking and nominal locomotion, GRAFT reduces terrain learning to a focused execution-adaptation problem. We instantiate the framework on four frozen trackers and evaluate stairs, gaps, and platforms in simulation. We further validate it through real-world deployment on a Unitree G1, where the adapted SONIC tracker traverses terrain with onboard depth and unmodified references.
Figures & tables
| Method | Whole-body reference | Terrain sensing | Base intact | Plug-and-play | Multi-base |
|---|---|---|---|---|---|
| Behavior foundation models | |||||
| SONIC [ 1 ] | ✓ | – | – | – | |
| Humanoid-GPT [ 2 ] | ✓ | – | – | – | |
| Perceptive locomotion | |||||
| DPL [ 8 ] | ✓ | – | – | – | |
| Terrain-aware BFM | |||||
| Success | Flat resid. | ||||
|---|---|---|---|---|---|
| Adaptation | Up stairs | Down stairs | Gap | Platform | |
| Action residual (ours) | 1.00 | 1.00 | 1.00 | 0.90 | 0.0520 0.0019 |
| Depth student (ours) | 1.00 | 0.80 | 1.00 | 1.00 | 0.4491 0.3071 |
| LoRA (decoder) | 1.00 | 0.90 | 1.00 | 0.60 | 0.6929 0.7173 |
| One-stage depth | 0.40 | 0.90 | 0.70 | 0.20 | 1.5930 0.0212 |
| Motion-token residual | 0.00 | 0.00 | 0.00 | 0.00 | 4.7025 1.2187 |
| Success (base/GRAFT) | Flat resid. | ||||
|---|---|---|---|---|---|
| Base | Up stairs | Down stairs | Gap | Platform | GRAFT |
| SONIC | 0.00/ 1.00 | 0.30/ 1.00 | 0.00/ 1.00 | 0.00/ 0.90 | 0.0520 0.0019 |
| H-GPT | 0.00/ 1.00 | 0.20/ 0.90 | 0.10/ 1.00 | 0.00/0.50 | 0.0781 0.0021 |
| HoloMot. | 0.00/ 1.00 | 0.80/ 0.90 | 0.00/ 1.00 | 0.00/ 1.00 | 0.0648 0.0009 |
| ScaleBFM | 0.00/0.30 | 0.10/0.00 | 0.10/ 0.90 | 0.00/ 0.80 | 0.0928 0.0024 |
Humanoid Robot Locomotion
Humanoid robot locomotion studies how bipedal robots walk, run, recover from disturbances, and traverse varied terrain.
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