Tilt-X: Enabling Compliant Aerial Manipulation through a Tiltable-Extensible Continuum Manipulator
Authors: Anuraj Uthayasooriyan, Krishna Manaswi Digumarti, Jack Breward, Fernando Vanegas, Julian Galvez-Serna, Felipe Gonzalez
Organizations: QUT Centre for Robotics, Queensland University of Technology, Brisbane, QLD Australia 4000 · School of Electrical Engineering and Robotics, Queensland University of Technology, Brisbane, QLD Australia 4000 · REF,Queensland University of Technology, Brisbane, QLD Australia 4000
Aerial manipulators extend the reach and manipulation capabilities of uncrewed multirotor aerial vehicles for inspection, agriculture, sampling, and delivery. Continuum arm aerial manipulation systems offer lightweight, dexterous, and compliant interaction opportunities. Existing designs allow manipulation only below the UAV which restricts their deployability in multiple directions and through clutter. They are also sensitive to propeller downwash. Addressing these limitations, we present Tilt-X, a continuum arm aerial manipulator that integrates a tilting mechanism, a telescopic stage, and a cable-driven continuum section. We present its design and kinematic model and validate it through flight demonstrations. Tilt-X enables a volumetric workspace with up to 75 mm extension and planar orientations between 0∘ to 90∘. Experiments comparing end effector pose with and without downwash quantitatively measure its accuracy, providing critical evidence to guide the design and control of reliable aerial manipulators. Results show stabilisation of end effector pose as the manipulator extends out of the propeller influence zone.
Figures & tables
Fig. 2 : The electrical (a) and mechanical (b) architecture of the Tilt-X system showing the various components. (c) an illustration of the tilt and telescoping mechanism that forms the basis of our design.
Fig. 3 : Forward kinematics map from the actuator-space ( q1 - q5 : motor angles) to configuration-space (curvature κ , bending plane angle ϕ , arc length ℓ , tilt angle α , linear extension β ) to task-space pose of the end effector THE .
Fig. 4 : (a) A schematic of the system showing the key coordinate frames - {W} : world, {U} : UAV, {H} : hinge on the UAV, {B} : base of the Tilt-X, {T} : tip of the telescopic mechanism, and {E} : tip of the continuum section. (b) The position of the cables 1-3 relative to the bending plane on the triangular base. (c) The routing of the cables through a pulley system at the hinge is on the bottom right.
Fig. 5 : Workspace of the Tilt-X system. (a) Isometric view colored by radial distance. (b) Front view (X–Z). (c) Top view (X–Y). (d) Side view (Y–Z).
Fig. 6 : (a) Bench-top experimental setup, (b) setup to evaluate wall effect in which a board is placed next to the UAV, (c) setup to evaluate ground effect in which the UAV approaces close to a board and (d) the location of test points around the UAV used for comparing model with experiments.
Exp.
Propeller
Influence
Tilt α
Tilt α
ON/OFF
(wall/ ground)
β = 0 mm
β = 75 mm
1
OFF
N/A
0∘ , 30∘ , 90∘
0∘ , 30∘ , 90∘
2
ON
Free
0∘ , 30∘ , 90∘
0∘ , 30∘ , 90∘
3
ON
Wall
-
90∘
4
ON
Ground
-
0∘ , 30∘
TABLE I : Conditions in the Bench-top Experiments
Fig. 7 : The x,y,z positions of the end effector when only the continuum section is actuated with no tilt present, at an extension of 75 mm.
Fig. 8 : Variation of Euclidean error of positions of the end effector compared to the model when only the continuum section is actuated while no tilt present.
Fig. 9 : Position error under 100% throttle level with reference to the mean position at no throttle. The lines represent the mean and the shading shows the standard deviation.
Fig. 10 : Orientation error under 100% throttle level with reference to the mean orientation at no throttle. The lines represent the mean and the shading shows the standard deviation.
Continuum manipulators mounted on multi-rotor UAVs enable compliant aerial manipulation, but payloads and propeller downwash amplify out-of-plane bending and twisting that degrade end-effector pose accuracy. To address this problem, we present a universal-joint-based continuum manipulator designed to improve resistance to out-of-plane deformation during aerial manipulation. The proposed design uses a tubular backbone with spring-reinforced universal joints and an integrated conduit for internal routing and fluid delivery. We evaluate the design in still air and under peak propeller downwash across varying payloads, and benchmark it against a prior Nitinol-backbone CM. Bench tests show improved resistance to out-of-plane deformation across all conditions. Under peak downwash, the proposed design reduces mean error by 2.5-4x in yaw, 2-45x in y-axis, and up to 5x in roll compared to the NiTi-backbone design. We further analyze hover stability through in-flight coupled-disturbance tests over varying payloads and actuation speeds, and demonstrate the system in water sampling, spot spraying, and object transport.
Continuum arm aerial manipulation systems leverage soft-manipulator compliance and dexterity for tasks in confined or hazardous environments, but propeller downwash can degrade performance, particularly near walls and the ground. This effect remains uncharacterized for continuum manipulators. This letter experimentally studies downwash-induced kinematic deviations of a tendon-driven continuum manipulator integrated with a multirotor platform. Under still-air conditions, the CM is compared with a constant-curvature (CC) model. Downwash- induced end-effector pose deviations are then quantified relative to the mean still-air experimental baseline at four propeller throttle levels in free space, and at maximum throttle near a wall, and near the ground. Vertical position and yaw show the largest deviations and are amplified by ground effect. A CC-guided Gaussian process regression (GPR) residual model is learned from experimental data that improves forward pose prediction RMSE (position by 89-95%, orientation by 47-79%), and support compensation-oriented, downwash-aware modeling of continuum arm aerial manipulation systems.
Aerial manipulation extends robotic operations to previously inaccessible aerial environments. Unlike arm-equipped aerial systems, tiltable-multirotors can directly generate six-degree-of-freedom wrenches through their flight bases, enabling both efficient movement and omnidirectional operation by tilting the thrust direction. This work presents a design analysis and a wrench-based control framework for tiltable-multirotors in aerial manipulation. We show that a four-rotor tiltable configuration provides a balance between interference-free propeller sizing and hovering efficiency across different attitudes, and its null-space redundancy is crucial for traversing singular configurations under physical constraints. We further show that an upward end-effector placement yields a favorable trade-off between geometric clearance and available wrench. To address disturbances, we propose a dual strategy consisting of a modified integral term for model error and an acceleration-based estimator for external wrenches. Building on these insights, we develop an effector-centric nonlinear model predictive control (NMPC) framework that integrates design choices, singularity handling, and disturbance compensation into a unified formulation. The proposed framework runs fully onboard at 100 Hz on a custom-built tiltable-quadrotor. Real-world experiments, including a 90-deg step cartwheel rotation, whiteboard pushing, and continuous 360-deg valve turning, demonstrate the feasibility of wrench-based omnidirectional manipulation with singularity traversal on a one-DoF-per-arm tiltable-quadrotor.
Jinjie Li, Yicheng Chen, Johannes Kübel +3
All authors are with the DRAGON Lab, Department of Mechanical Engineering, The University of Tokyo, Tokyo 113-8656, Japan