An open hardware, open firmware, open data quadruped-base humanoid reference design — the third morphology in the OpenIE humanoid family alongside the bipedal Free Humanoid Platform and the wheeled Free Humanoid Wheeled. A humanoid torso on a wheel-leg-hybrid quadruped base, targeted at rough-terrain mobile manipulation: shoal dock-A wetlands deployment, post-disaster building inspection, agricultural-site monitoring, civil-infrastructure maintenance. Shielded by the Free Humanoid Corpus.
Status: scaffold (v0.1). This repository establishes the project's positioning, governance, and architectural commitments. It is not yet a buildable robot. The architectural decisions are resolved in ARCHITECTURE.md §9; each commitment is shielded by a corpus-cited prior-art chain. Detailed CAD, vendor-pinned BOM, and physical-build documentation are the next deliverables.
Free Humanoid Centaur is the third morphology in the OpenIE humanoid family. It inherits the bipedal sibling's torso, arms, hands, head, sensing, compute, and safety supervisor architecture verbatim. It replaces the bipedal legs (and the wheeled sibling's wheeled-base-with-tower-stand) with a four-leg quadrupedal locomotion base whose feet carry small powered wheels — a wheel-leg hybrid that gives the platform paved-surface speed in wheel mode and rough-terrain capability in leg mode. The design domain is intentionally narrower than the bipedal sibling and intentionally wider than the wheeled sibling: anywhere paved-environment wheeled cannot reach but a full bipedal humanoid would be overkill or operationally fragile.
The project sits at the intersection of five projects:
-
OpenLoco — the substrate. The platform compiles from a single UDD JSON file to URDF, MJCF, STL, BOM, and assembly through OpenLoco. The centaur is a
humanoid_quadrupedmorphology (orcentaur— see ARCHITECTURE §3 for the naming choice) in the same compiler. OpenLoco's existing quadruped morphologies (mit-cheetah,mini-cheetah,anymal,anymal-wl) are the substrate from which the legs are sourced. -
Free Humanoid Corpus — the prior-art commons. Every non-trivial design choice cites a specific corpus entry, the same governance posture as the bipedal and wheeled siblings.
-
Free Humanoid Platform — the bipedal sibling, the upper-body donor. The 21-DoF upper body of this morphology is the upper body of the platform; this repo cross-links rather than duplicates that work.
-
Free Humanoid Wheeled — the wheeled sibling. Centaur shares the wheeled morphology's hot-swap battery interface and shoal cartridge-swap pattern; centaur is the wetlands counterpart (dock-A) to wheeled's urban posture (dock-B).
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shoal — the deployment partner. Centaur is designed to integrate with the shoal dock-A protocol (autonomous benthic dock for remote rivers, marine, and wetlands). See shoal ARCHITECTURE §3.2 for the dock-A spec.
These are tenants of one another. The centaur morphology is the rough-terrain / off-pavement service-environment tenant of the bipedal upper body and one of three service tenants of the shoal fleet.
| Quantity | Bipedal | Wheeled | Centaur |
|---|---|---|---|
| Locomotion | 2 legs (12 DoF) | 2 drive wheels + 2 casters + tower lift | 4 legs (12 DoF) with powered wheel feet (wheel-leg hybrid) |
| Total mass | ~50 kg | ~70 kg | ~120 kg |
| Sustained payload at extended reach | 5 kg | 30 kg | 50 kg |
| Battery | 1 kWh + 0.1 kWh UPS | 2 kWh + 0.2 kWh UPS | 3 kWh + 0.3 kWh UPS |
| Peak ground speed | 1.0 m/s | 1.5 m/s | 2.0 m/s paved (wheel mode) / 1.0 m/s rough (leg mode) |
| Stair / curb capability | Yes | No (paved only) | Yes (leg mode) |
| Off-road / wetland capability | Limited | No | Yes |
| Footprint (base) | ~0.30 m × 0.40 m | 0.6 m × 0.8 m | ~1.2 m × 0.8 m |
| Height (head, standing) | ~1.70 m | ~1.40–1.70 m | ~1.50 m at shoulder, head higher |
The centaur is not the heaviest possible humanoid — it is the heaviest of the three OpenIE morphologies because legs are heavier than wheels and four legs are heavier than two, but its mass is shielded against the corpus quadruped class (anymal-d-eth-rsl-2022 ~50 kg robot dog alone, bigdog and alphadog 70–150 kg load-carrying class, ge-walking-truck 1400 kg historical bound) with the upper body adding another 60 kg.
| Deployment target | Bipedal | Wheeled | Centaur |
|---|---|---|---|
| Indoor urban service (offices, hospitals) | Best | OK | Overkill |
| Stormwater outfall / harbor dock (paved) | OK | Best | OK |
| Wetlands / remote river / marine shore (shoal dock-A) | Marginal | No | Best |
| Post-earthquake building inspection | OK (slow) | No (debris field) | Best |
| Post-flood building inspection | Marginal | No | Best |
| Agricultural-site monitoring (row crops, fencing) | Marginal | OK (paved farms only) | Best |
| Civil-infrastructure (bridge underside, levee, dam) | OK | No | Best |
| Stair-rich indoor environment | Best | No | OK |
| Long-range paved road traversal | No | OK | Best (wheel mode) |
| Forest / boulder field | No | No | Best |
The deployment line is paved + indoor → wheeled or bipedal; paved + outdoor → wheeled; rough or wet → centaur. The wheeled humanoid handles dock-B sites (urban paved infrastructure); the centaur handles dock-A sites (remote wetlands and rivers) and the broader rough-terrain mission space.
| Quantity | Target | Notes |
|---|---|---|
| Total system mass | ~120 kg | 60 kg quadruped base (4 legs × ~12 kg per leg + chassis + battery) + 60 kg upper body |
| Battery capacity | 3 kWh primary + 0.3 kWh UPS | Sized for 4–6 hours of mixed-mode field work |
| Sustained payload at extended reach | 50 kg | Statically stable on a 1.2 m × 0.8 m support polygon with the legs in stance |
| Peak ground speed (wheel mode) | 2.0 m/s | Paved-surface travel with all four wheel-feet driving |
| Peak ground speed (leg mode) | 1.0 m/s | Walking/trotting gait, terrain-dependent |
| Maximum slope (leg mode) | 30° | Hard supervisor invariant; below bigdog's reported 35° rough-terrain limit |
| Stair height (leg mode) | 220 mm | Standard residential stair tread |
These numbers are scaffold targets, not validated specifications. Iterating them against physical CAD, the wheel-leg-hybrid foot architectural call, and the shoal dock-A protocol is the Phase 1 deliverable.
The platform exists to handle service tasks where a wheeled humanoid cannot reach but a bipedal humanoid is operationally fragile:
- shoal dock-A wetlands deployment. Cartridge rotation, waste-hopper retrieval, and biology-reservoir status handshake at autonomous benthic docks deployed in remote rivers, marine, and wetlands sites. See shoal ARCHITECTURE §3.2.
- Disaster response. Post-earthquake or post-flood building inspection in environments where the floor plate may be tilted, debris-strewn, or unstable. Leg-mode locomotion with foot-fall validation handles ground that defeats wheeled platforms.
- Agricultural inspection. Row crops, fencelines, dispersed irrigation infrastructure on uneven ground. Wheel mode for transit between fields, leg mode within them.
- Civil-infrastructure maintenance. Bridge-underside inspection, levee walkthrough, dam-spillway examination. Settings where the access surface is irregular (riprap, gravel, mud) and a wheeled platform cannot operate.
The deployment unit is the platform plus a transport vehicle that moves it between sites; the platform itself is not road-going at scale (though wheel mode permits short-distance road traversal).
Same as the bipedal and wheeled siblings, with the same release-blocker note on canonical license-text inlining:
| Artifact class | License | Files |
|---|---|---|
| Hardware (CAD, schematics, PCB layouts, mechanical designs) | CERN-OHL-S 2.0 | LICENSE-HARDWARE |
| Firmware, control software, simulation, tools | Apache 2.0 | LICENSE-SOFTWARE |
| Documentation | CC-BY-SA 4.0 | LICENSE-DOCS |
| Descriptors (UDD JSON), datasets, BOM data | CC0 1.0 | LICENSE-DATA |
CC0 on the descriptor is the load-bearing license choice. The license files in this repo currently contain SPDX-tagged headers; inlining the canonical text is a release-blocker before any public push.
Inherits verbatim from Free Humanoid Platform: defensive-publication norms, examiner-citeable design rationale, no-patent-aggression contributor norm, reference-design-not-product, fail-safe-to-inert. See CONTRIBUTING.md for the full text of the contributor contract.
Per the OpenIE hosting split, OSS projects live at openie-dev.github.io/<project>/. The centaur morphology's eventual home:
- Repository:
github.com/openIE-dev/free-humanoid-centaur - Site:
openie-dev.github.io/free-humanoid-centaur/
Local-only at v0.1; no public push until the canonical license text inlining and the architectural-call resolution gates pass.
free-humanoid-centaur/
README.md this file
ARCHITECTURE.md canonical full-system spec, prior-art-cited
CONTRIBUTING.md quality bar, defensive-publication norms
LICENSE-HARDWARE CERN-OHL-S 2.0 (canonical text inlining is a release blocker)
LICENSE-SOFTWARE Apache-2.0
LICENSE-DOCS CC-BY-SA-4.0
LICENSE-DATA CC0-1.0
descriptor/ UDD descriptor — source of truth
free-humanoid-centaur.udd.json
README.md
base/ quadruped-base subsystem (the morphology-distinguishing work)
README.md
upper-body/ inherited from free-humanoid-platform
README.md
electronics/ PCB pointers, power tree, Joule SOM integration
firmware/ HAL, behaviors, MathGround safety supervisor, comms
control/ dual-mode locomotion (wheel + leg), manipulation policy
sim/ MuJoCo / Gazebo / Drake model pointers
docs/ design notes beyond root README/ARCHITECTURE
prior-art/
INDEX.md corpus entries this morphology depends on, by subsystem
Each subdirectory has its own README.md scoped to its concern.
- ARCHITECTURE.md — canonical full-system spec.
- descriptor/free-humanoid-centaur.udd.json — UDD source of truth.
- prior-art/INDEX.md — corpus citation map.
- Free Humanoid Platform ARCHITECTURE.md — for everything inherited (upper body, sensing, compute, safety, manipulation, learning policy).
- Free Humanoid Wheeled ARCHITECTURE.md — for the hot-swap battery interface and shoal-cartridge-swap protocol pattern.
- shoal ARCHITECTURE.md — for the dock-A mission integration target.
Current state is scaffold (v0.1). The morphology's shape, governance, architectural commitments, and prior-art chain are in place. Phase 1 is OpenLoco-compiler-buildable simulation (descriptor → MuJoCo → wheel-mode and leg-mode controllers → dock approach in both modes). Phase 2 is a single-leg subassembly with the wheel-foot prototype. Phase 3 is the full quadruped-base prototype with the bipedal upper body integrated. Phase 4 is the first wetland pilot integrated with shoal dock-A. See ARCHITECTURE.md §6 for the full roadmap.