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TIRAS Transactions on Intelligent Robotics and Autonomous Systems An open access journal of Kaggleyes Academy
TIRAS > Vol. 1, No. 2 (August 2026) > KAGG:2608.00010
Vol. 1, No. 2 (August 2026) — Article KAGG:2608.00010

Velocity Interface Contracts: Specifications and Verification for Legged Robot Middleware

Authors: Clara Fischer, Diego Navarro, Amelie Laurent

Robot Dynamics Group, ETH Zurich, Zurich, Switzerland

[Received 2026-08-12; accepted 2026-08-23; published online 2026-08-26]

Abstract:

Navigation stacks for legged robots rely on implicit assumptions about the velocity interface exposed by locomotion middleware: how quickly a command takes effect, where it saturates, and whether the response depends on gait mode or command history. These properties are rarely documented, and their violation surfaces as degraded tracking rather than as an explicit fault. This paper introduces velocity interface contracts, a typed declarative specification of command fidelity bounds, latency envelopes, saturation regions, and mode semantics, together with a verification tool that operates in two stages. Offline, the tool checks a calibrated interface model, obtained by planner-conditioned active calibration, against the contract and returns witness commands for each violated clause. Online, it monitors the command and odometry streams with lightweight sequential statistical tests and separates transient violation events from standing violations. The tool was evaluated on a Unitree B2 and an 8-DoF research quadruped over 10 days and 214 h of logged operation, with three known but undocumented B2 firmware behaviors seeded as detection targets. The model-based monitor recorded 11 true-positive detections, against 10 for fixed-threshold monitoring and for a monitor encoding the stack's implicit assumptions, at a false positive rate of 2.8 percent, a 95th-percentile runtime of 1.9 ms at 50 Hz, and a median time to detection of 3.4 s. It flagged the B2 speed limiter 3.4 s into its first engagement, whereas the fixed-threshold monitor required 41 s. The paper also specifies the contract format and proposes an adoption path for legged robot middleware.

Journal: Transactions on Intelligent Robotics and Autonomous Systems (TIRAS)
Volume / Issue: Vol. 1, No. 2 (August 2026)
Article ID: KAGG:2608.00010
DOI: 10.5803/kagg.2608.00010
Received: 2026-08-12
Accepted: 2026-08-23
Published online: 2026-08-26
License: CC BY 4.0

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Cite this article Clara Fischer, Diego Navarro, Amelie Laurent, "Velocity Interface Contracts: Specifications and Verification for Legged Robot Middleware," Transactions on Intelligent Robotics and Autonomous Systems, 2026, vol. 1, no. 2, KAGG:2608.00010. DOI: 10.5803/kagg.2608.00010.