---
title: 'Husky Carbon: Legged-Aerial Hybrid Robot'
url: https://www.emergentmind.com/topics/husky-carbon
type: topic
---

# Husky Carbon: Legged-Aerial Hybrid Robot

Searching arXiv for Husky Carbon and closely related papers.
Husky Carbon is a lightweight quadrupedal robot under development as a **legged–aerial multi-modal platform** that combines **legs for terrestrial locomotion** with **thrusters for aerial or partially aerial mobility**. In the Husky Carbon literature, “multi-modal locomotion” denotes the integration of grounded legged locomotion, thrust-assisted locomotion, and intended legged-to-aerial and aerial-to-legged transitions within a single machine rather than the addition of propellers as a mere stabilization aid. The platform is motivated by bird locomotion, especially the coexistence of intermittent ground contact and aerial force generation, and by field-robotics use cases such as **search and rescue**, **inspection**, and **reconnaissance** in cluttered, damaged, or unstructured environments [2207.12254].

## 1. Definition, development trajectory, and problem setting

The Husky Carbon project is explicitly framed as an exploratory robotics program rather than a completed flying quadruped. The 2021 design paper presents Husky Carbon as a **morpho-functional hybrid robot** intended to combine **quadrupedal legged locomotion** and a future **aerial/rotorcraft mode** within a single platform, while the 2022 progress report emphasizes hardware integration, simulation infrastructure, and demonstrated locomotion behaviors rather than an end-state multimodal system [2104.05834] [2207.12254]. The 2023 thesis and subsequent incline-walking papers extend the program toward **trotting-hovering** and **thruster-assisted incline walking**, especially through simulation of WAIR-inspired behaviors [2306.00179] [2312.08621].

| Stage | Paper | Reported emphasis |
|---|---|---|
| 2021 | "Generative Design of NU's Husky Carbon, A Morpho-Functional, Legged Robot" [2104.05834] | MVAM, front-heavy morphology, additive manufacturing, preliminary untethered trotting, gait simulation |
| 2022 | "A Letter on Progress Made on Husky Carbon: A Legged-Aerial, Multi-modal Platform" [2207.12254] | Integrated custom hardware, sensing and control stack, multimodal planning simulation, tethered trotting |
| 2023–2024 | "LeggedWalking on Inclined Surfaces" [2306.00179], "Quadrupedal Locomotion Control On Inclined Surfaces Using Collocation Method" [2312.08621], "Thruster-Assisted Incline Walking" [2406.13118] | WAIR-inspired modeling and thrust-assisted steep-slope locomotion |

The central research problem is the coexistence of **antagonistic design constraints**. Aerial mobility favors low mass, low drag, and tight power budgets; legged mobility favors structural robustness, support-polygon margin, and actuation against ground reaction forces. The Husky Carbon papers repeatedly treat this not as a secondary implementation difficulty but as the defining systems problem of the platform. The resulting machine is therefore best understood as a testbed for morphology, actuation, control, and planning under conflicting terrestrial and aerial requirements rather than as a narrowly optimized quadruped or a conventional multirotor [2207.12254].

## 2. Morpho-functional design and the Mobility Value of Added Mass

The 2021 design study formulates Husky Carbon through the **Mobility Value of Added Mass (MVAM)** problem, a morphology-driven mass-allocation problem restricted to the relation between **morphology** and **energetic efficiency of legged mobility** [2104.05834]. MVAM asks, in effect, how mass should be distributed so that **Total Cost Of Transport (TCOT)** is minimized while preserving payload margin for future aerial hardware. The key descriptors used in the MATLAB evaluation are the fore–aft and vertical COM positions, \(C_x\) and \(C_y\), together with the sagittal-plane mass moment of inertia \(I_b\).

The generative-design workflow couples **Grasshopper** inside **Rhino 6**, **Galapagos** as the evolutionary solver, and a MATLAB dynamics evaluation. The parametric design space includes the location of **harmonic drive components**, **electronics**, housing sizes, body-frame dimensions, and connecting-rod geometry. Candidate morphologies are then evaluated under comparable predefined forward walking gaits rather than co-optimized gait–morphology pairs. The authors therefore identify morphology-to-efficiency trends, not a full-body optimal-control solution.

The main reported result is that **front-heavy morphologies outperform back-heavy ones** for the constrained forward walking task. The authors state that in forward walking “hosting larger added mass in a front heavy morphology is less costly,” that such morphologies achieve **lower TCOT**, and that they retain larger allowable margins on sagittal-plane inertia \(I_b\) [2104.05834]. In the simulation reported for the selected front-heavy morphology, the authors give a **forward walking speed** of **0.2 m/s**, **gait period** of **0.25 s**, and **TCOT** of **0.2**. They also note an important limitation: because the gait was predefined, the front-heavy conclusion is task- and gait-dependent.

A plausible implication is that Husky Carbon’s morphology was never intended to minimize mass in the abstract. Rather, the project treats morphology as a reserve-allocation problem: every gram assigned to structure, actuation, or sensing competes with future multimodal capability. That systems perspective is one of the project’s most distinctive features.

## 3. Embodied architecture: structure, actuation, sensing, and power

At the platform level, Husky Carbon is a **quadruped** with **four legs**, each having **3 degrees of freedom**, for a total of **12 actuated joints**. The legs are described as two pairs of identical **parallelogram mechanisms**. The body is fabricated primarily from **reinforced thermoplastic materials** using **additive manufacturing**, with a major design theme being the embedding of transmissions and actuator components directly into printed structural elements to reduce separate metal housings and fasteners [2207.12254].

Across the reports, the platform dimensions reflect different embodiments or reporting conventions. The 2021 design paper describes the implemented robot as **0.8 m** tall, **0.3 m** wide, and **4.3 kg** in mass; the 2022 progress report describes the prototype as about **0.4 m tall** in quadrupedal posture, about **0.3 m wide**, and **4.3 kg**; and the incline-locomotion work later reports a **4.3 kg** legged platform plus a **3.3 kg** propulsion unit for a total mass of **7.6 kg** in the thruster-equipped configuration [2104.05834] [2207.12254] [2312.08621].

Each of the 12 joint actuators is built around a **T-Motor** brushless winding with **400 KV**, with transmissions based on **harmonic drive component sets**. The explicitly reported gear ratios are **30:1 for the knee**, **50:1 for the hip sagittal joint**, and **100:1 for the hip frontal joint**. The progress report’s system figure names the motors as **T-Motor MN4004 400KV** and the servo drives as **Elmo Gold Solo Twitter**, while the thesis later describes **T-motor Antigravity 4006 brushless motors**, **Harmonic Drive CSF-11-30-2A-R**, **ELMO Gold Twitter servo drives**, and **RLS RMB20 encoders**. The aerial subsystem is described in multiple iterations: a conceptual 2021 design in which the legs move sideways and the knee actuator, through a **clutch mechanism**, would drive a propeller; a 2022 **top-mounted four-thruster arrangement**; and later thruster-equipped configurations using **four ducted fans** and, in the thesis, **DS-30-AXI HDS electric ducted fans (69 mm)** with **YGE 95A LV** ESCs [2207.12254] [2306.00179].

The sensing and compute stack also evolves over time. The early design paper states that the prototype **lacks exteroceptive sensors** and relies on **off-board body orientation sensing**. The progress report later specifies a **VectorNav VN-100 IMU**, an **Intel RealSense T265 tracking camera**, hall-effect encoder sensing at the joints, and a **Speedgoat IO581 Real-Time Target Machine** running **Simulink Real-Time** and communicating with servo drives over **EtherCAT**. The thesis then adds a higher-level architecture with a **ROS** controller on an **NVIDIA Jetson Nano** and a **Pixhawk 2.4.8** flight controller linked via **MAVLink** [2104.05834] [2207.12254] [2306.00179].

A persistent practical constraint is power. Both the 2021 and 2022 papers state that the prototype **currently operates using an external power supply**, and the 2022 test arena includes a **large fan** for actuator cooling. Untethered onboard power is therefore not established in the core progress report [2104.05834] [2207.12254].

## 4. Reduced-order modeling, multimodal planning, and legged control abstractions

The 2022 progress report formalizes Husky Carbon’s reduced-order kinematics by assigning each leg \(i \in \{1,2,3,4\}\) the coordinates **hip frontal angle** \((\phi_i)\), **hip sagittal angle** \((\psi_i)\), and **leg length** \((l_i)\). The resulting reduced-order model comprises **12 kinematic DOFs** and **6 dynamical DOFs**, with the robot reduced to a **single rigid body with 6-DOF dynamics** and **massless leg linkages**; the authors state that the dynamics can be derived using the **Euler–Lagrangian formulation** [2207.12254].

This reduced-order model underpins path planning and trajectory tracking. The reported planning environment is discretized in two ways for comparison: **uniform discretization** into points and a **3D MM-PRM**, i.e. a multimodal probabilistic roadmap adapted to mode switching. The reported simulation shows successful navigation together with explicit **legged-to-aerial** and **aerial-to-legged transformation sequences**. The same section notes that, in that simulation, **propellers were attached near the leg end**, which indicates that propulsion placement remained an active design variable rather than a fixed architectural decision.

On the control side, the progress report gives a partial but informative view. For legged locomotion it mentions an **RG-based framework** that manipulates kinematic references to satisfy the **friction pyramid constraint**, thereby avoiding heavier optimization-based constraint handling at the high level. The paper also reports effective tracking of predefined joint trajectories and body-pose stabilization using camera and inertial feedback during trotting-in-place experiments, but it omits the detailed reference-governor equations, objective functions, and low-level torque or position laws. A conventional flight-control design is said to be assumed but omitted. The result is a literature record that clearly specifies the modeling abstractions and infrastructure, while leaving the complete closed-form controller undocumented.

## 5. WAIR-inspired incline locomotion and coordinated thrust–contact control

The most technically developed extension of Husky Carbon is **thruster-assisted incline walking**, explicitly inspired by **wing-assisted incline running (WAIR)** in chukar birds. The relevant papers treat the key problem as one of maintaining feasible **ground reaction forces** on steep slopes while respecting friction limits; the distinctive Husky capability is that the robot can add body forces through **four ducted fans** rather than relying only on posture and leg placement [2312.08621] [2406.13118].

The 2023 collocation paper introduces a high-fidelity **MATLAB SimScape** model with **18 degrees of freedom** and **13 distributed mass elements**, together with a reduced-order model, **HROM**, in which the legs are massless and the torso is a **6-DOF** rigid body. The full thruster-equipped system is reported as **7.6 kg**, with the propulsion unit contributing **3.3 kg**, and the four fans are described as each generating about **2 kg of thrust**, for a total of roughly **8 kg** [2312.08621]. The associated thesis states the friction-feasibility condition in the standard form
\[
\frac{F_h}{F_z} < \mu, \qquad F_z > 0, \qquad F_h = \sqrt{F_x^2 + F_y^2},
\]
which captures the requirement that tangential force remain below frictional support while contact remains compressive [2306.00179].

Control synthesis is posed as a finite-horizon optimization in which **joint accelerations**, **ground reaction forces**, and **thruster forces** are stacked into a single control vector and optimized by a **cubic Lobatto collocation method** solved with **MATLAB `fmincon`** [2312.08621]. The 2024 paper uses a closely related collocation formulation and reports a **30-degree slope** result with **\(\mu = 0.35\)**, emphasizing that without thrust the normal reaction can become close to zero or even negative, whereas optimized thrust keeps the active stance contact friction-admissible [2406.13118].

The broader WAIR program, however, is reported more aggressively in the 2023 thesis and the 2023 collocation paper, which simulate inclinations of **0°**, **10°**, **20°**, **30°**, and **45°**, with the headline result that Husky can walk up a **45-degree incline** in simulation [2306.00179] [2312.08621]. These papers also report an instructive force-sharing trend: **torque peaks are higher at lower inclinations**, because the legs carry more of the body weight there, whereas at **higher inclinations** the **thruster contribution becomes larger**, alleviating leg loading and keeping contact forces within friction-feasible regions.

## 6. Experimental status, limitations, and place within legged–aerial robotics

Experimentally, the most solidly documented Husky Carbon results remain terrestrial and partially assisted rather than fully multimodal. The 2022 progress report describes a **test arena** with multiple cameras, a textured padded surface, a Speedgoat target computer, an external power supply, and a large fan for cooling. The robot is tested in a **tethered** configuration with support ropes and a **pulley mechanism** that can alter effective leg loading. Within that setup, the team reports **three-contact** and **two-contact trotting in place** at different gait speeds, with phase portraits interpreted as convergence to a **stable limit cycle** [2207.12254]. The thesis later reports **Propulsion Unit tests** and **thruster-assisted trotting in place**, but not a completed hardware demonstration of sustained WAIR on physical inclines [2306.00179].

A major bottleneck across the Husky Carbon literature is **compliance**. The lightweight body and compliant legs induce body sagging at touchdown, reduce mechanical bandwidth, complicate impedance control and torque projection, and can generate large-amplitude oscillations. The narrow torso also reduces the support polygon. The progress report gives a particularly concrete consequence: when the **gait cycle time exceeds approximately one third of a second**, i.e. around a **3 Hz gait cycle**, the projected COM can approach the support-polygon boundary even with three contacts, and stability degrades further without rapid corrective action. The authors explicitly state that they intend to address this by **predicting the compliance and body center of mass using a model-based approach** for more accurate kinematic and dynamic stability [2207.12254].

Within the broader literature, Husky Carbon is positioned against **LEONARDO**, **BALLU**, and **DUCK**, which are bipedal thruster-assisted robots, and against wheeled or driving-flying hybrids such as **DrivoCopter** and **FCSTAR**. It is also contrasted with quadrupeds such as **MIT Cheetah** and **ANYmal**. The stated novelty is therefore not propeller augmentation per se, but a **quadrupedal legged–aerial morphology** that prioritizes **low mass and aerial compatibility** while accepting severe penalties in stiffness, support-polygon size, and terrestrial robustness [2207.12254].

Two disambiguations are useful. First, Husky Carbon is unrelated to the **Clearpath Husky A200** mobile base discussed in a separate configuration paper [2410.17453]. Second, it is unrelated to the theoretical carbon allotrope **H-carbon** from condensed-matter physics [1203.5509]. In the robotics literature, “Husky Carbon” refers specifically to Northeastern University’s custom legged–aerial platform.

Taken together, the published record supports a precise characterization: Husky Carbon is a serious but unfinished hybrid robotics platform that has progressed from morphology-centered co-design, to integrated custom hardware and tethered trotting, to WAIR-inspired reduced-order control and steep-slope simulation. It has not yet been experimentally demonstrated as a fully autonomous flying quadruped with reliable mode transitions and onboard untethered operation.

Source: https://www.emergentmind.com/topics/husky-carbon