An Experimental Study of Downwash Effects on a Continuum Manipulator Integrated with a Multirotor UAV

Anuraj Uthayasooriyan; Krishna Manaswi Digumarti; ernando Vanegas; Felipe Gonzalez

cs.ROAug 19, 2026

An Experimental Study of Downwash Effects on a Continuum Manipulator Integrated with a Multirotor UAV

Authors: Anuraj Uthayasooriyan, Krishna Manaswi Digumarti, ernando Vanegas, Felipe Gonzalez

Organizations: QUT Centre for Robotics, School of Electrical Engineering and Robotics, QUT, Brisbane, QLD 4000, Australia

Abstract

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.

Figures & tables

Fig. 1 : (a) The mechanical and (b) electrical system architectures of the CAAMS used for the experimental study.

Fig. 2 : (a) CAAMS with the CC workspace and frames: world $\{W\}$ , UAV $\{U\}$ , CM base $\{B\}$ , and CM tip $\{E\}$ . The inset triangle marks cables C1–C3. (b) Workspace sampling: the 3D workspace is divided into four horizontal slices (HS1–HS4) and 12 vertical slices (V1–V12) about $Z_{B}$ , whose intersections define points $P1$ – $P48$ . The circular panel shows HS1 in top view with dashed vertical slices, propellers and Dashed-yellow shaded boxes: Airframe attachments causing flow disturbance. (c) Definition of position and orientation error between the expected $\{ref\}$ and measured $\{exp\}$ pose in $\{B\}$ .

Fig. 3 : Bench-top experiment setups for (a)free-space (b) wall effect where a board is placed next to the CAAMS, and (c) ground effect where the UAV is close to a horizontal board.

Experiment	Physical interpretation	Throttle levels T%
Case(i)	No DW	0
Case(ii)	DW; No influence of wall/ground	25, 50, 75, 100
Case(iii)	DW under the influence of wall	100
Case(iv)	DW under the influence of ground	100

TABLE I : Bench-top experiments under different cases

Fig. 4 : Case (i) – Euclidean (

e_{pos}

) and Cartesian EE position error components across slices with propellers off (

T=0\%

)

Fig. 5 : Case (i) – scalar quaternion errors (

{e_{ori}}

) and the extrinsic Euler components of EE orientation with (

T=0\%

)

Panel of Figure 7 — Fig. 6 : EE errors of Euclidean position $e^{\mathrm{pos}}$ and scalar quaternion orientation $e^{\circ}$ relative to mean at $T=0\%$ in Cases (ii)–(iv).

Fig. 7 : Driving motors’ (M1,M2

\&

M3) torques when operating in V1, V5 and V9 planes at

T=0\%

and

T=100\%

Case	Position RMSE (mm)	Orientation RMSE ( ∘ )	Pos. imp. (%)	Ori. imp. (%)
T0	124.56 $\rightarrow$ 8.63	28.40 $\rightarrow$ 10.86	93.00	62.42
T25	131.52 $\rightarrow$ 14.51	24.69 $\rightarrow$ 5.80	90.28	79.72
T50	130.81 $\rightarrow$ 11.94	35.20 $\rightarrow$ 18.92	91.15	47.56
T75	132.11 $\rightarrow$ 10.36	26.66 $\rightarrow$ 11.29	92.17	58.64
T100	130.90 $\rightarrow$ 14.68	24.15 $\rightarrow$ 6.72	89.86	76.77

TABLE II : Held-out RMSE of the raw CC prior and the GP-corrected predictor across still-air and DW cases.

Fig. 8 : Test points’ position errors (mean

\pm

SD) of the raw CC prior and the GP-corrected predictor for

T0

–

T100

Fig. 9 : Test points’ orientation errors (mean

\pm

SD) of the raw CC prior and the GP-corrected predictor for

T0

–

T100

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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.

Abstract

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