cs.ROJul 28, 2026

When Does Legacy Data Start to Help? Emergent Transfer in Cross-Configuration Robot Learning

Authors: Tao WangHudson HouYingdong HuYufeng LiuQinghai LiYingjie JiangYingzhi WangCheng Ma+2 more

Abstract

Robotic hardware evolves over time, but demonstration data is often tied to a specific sensor and actuator configuration. This raises a practical and underexplored question: when does legacy data begin to benefit an upgraded robot? We study this question on a wheeled humanoid platform across two hardware generations, where both the camera and gripper are changed while the overall morphology remains fixed. Contrary to the common assumption that more cross-configuration data is always helpful, we observe a grokking-like transition: legacy data remains ineffective until the upgraded configuration acquires a minimum level of task competence, after which co-training gains rise sharply before diminishing near saturation. We hypothesize that this task-dependent transition is governed by a transfer threshold and characterize the resulting three-phase pattern. Across real-robot manipulation tasks, we observe all three phases: no measurable benefit at low competence (10.0%10.0%10.0\% \rightarrow 10.0\%), a sharp gain after crossing the threshold (23.3%86.7%23.3\% \rightarrow 86.7\% on flower insertion), and diminishing returns at high competence (85.0%93.3%85.0\% \rightarrow 93.3\% on pen insertion). We provide a theoretical account based on gradient alignment and residual policy uncertainty, and derive a phase-aware rule for deciding when to collect more new-hardware data and when to reuse legacy demonstrations. We further validate this three-phase pattern on a mobile dual-arm watering task, with results consistent with our predictions.

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