Introduction
To address these challenges, we develop Capability-Tradeoff Contact Selection (CTCS). The key idea is to separate exact verification of constraint satisfaction from the more expensive evaluation of candidate capabilities. Task and contact feasibility, which are less computationally expensive, are checked exactly, while the remaining capability evaluations, which are computationally expensive, are accelerated by grouping locally similar candidates and predicting their capabilities from exact anchor evaluations through local sensitivity analysis. The predictions are checked using selective exact evaluations, and the most promising candidates are evaluated exactly before the final contact realization is selected.
The contributions are threefold:
- A formulation of environmental support as a joint surface-and-configuration selection problem. Candidate supports must satisfy the task load and motion requirements and are further optimized using capability measures concerning residual wrench, end-effector reach, and base mobility.
- A capability-tradeoff contact-selection method. CTCS combines exact task-feasibility screening with local sensitivity-based capability prediction. Candidates are grouped within individual contact surfaces to enable reliable anchor-based prediction among locally similar realizations.
- Validation through simulation and hardware experiments. The selected environmental contacts satisfy the prescribed task requirements while providing favorable capability trade-offs.
Contact Selection
In contrast, we consider a given loco-manipulation task and jointly select a sustained auxiliary support surface and the whole-body configuration that realizes the contact.
This differs from works that assume a preselected support surface or support type and optimize how the robot uses that contact. It also differs from contact planning methods that optimize sequential footholds or environmental contacts as part of locomotion or trajectory planning.
Methodology
Evaluating the capability vector a collection of capability measures exactly for every candidate requires solving many whole-body optimization problems across the task-applicable capabilities and stance phases.
To address this, we propose Capability-Tradeoff Contact Selection (CTCS), which combines exact feasibility screening, local sensitivity-based capability prediction, and selective exact evaluation.
Selection Quality and Computational Cost
Ablations
Removing prediction validation (CTCS-NV) or replacing the local groups with a single anchor per surface (CTCS-SA) further reduces runtime but also lowers the mean objective.
The former indicates that the probe and cross-anchor checks help detect inaccurate predictions before the final selection. The latter supports the effectiveness of grouping candidates within each surface and using multiple local anchors, since candidates on the same surface can have different whole-body configurations and limiting constraints.
Finally, evaluating walking candidates using a four-foot stance (CTCS-FFS) reduces the mean objective to 3.0387 despite using the same task-feasible candidate set. This shows that selection should account for the residual capabilities under the actual trot support phases.
Conclusion
We presented CTCS to jointly select environmental support contacts and whole-body configurations for prescribed loco-manipulation tasks. Our results showed that the benefit of environmental contact depends on both the selected surface and configuration, with task-dependent selection outperforming the tested fixed-contact baseline.
CTCS closely matched the mean objective of exhaustive evaluation with less computation, while the ablations showed that local grouping and prediction checks improved selection quality. These results support treating environmental contact as a task-dependent decision.
One limitation of our approach is that it selects from sampled candidates, so global optimality over the continuous space of contact locations and configurations is not guaranteed. Future work will include candidate refinement, contact transitions between surfaces, and online reselection as task requirements change.
Frequently Asked Questions
What is Capability-Tradeoff Contact Selection? CTCS is a method for jointly selecting environmental support contacts and whole-body configurations for prescribed loco-manipulation tasks.
How does CTCS reduce computational cost? It screens task and contact feasibility exactly, predicts capabilities for locally similar candidates, and selectively evaluates predictions and promising candidates exactly.
What capabilities are considered when selecting contacts? The selection considers residual wrench, end-effector reach, and base mobility.
What is a limitation of the proposed approach? Because CTCS selects from sampled candidates, global optimality over the continuous space of contact locations and configurations is not guaranteed.