Rotate Disks to Reach Farther: Design and Modeling of a Novel Reconfigurable Tendon Driven Manipulator

Sabyasachi Dash; Yangkun Liu; Will Hunter; John Golden; Girish Krishnan

cs.ROAug 16, 2026

Rotate Disks to Reach Farther: Design and Modeling of a Novel Reconfigurable Tendon Driven Manipulator

Authors: Sabyasachi Dash, Yangkun Liu, Will Hunter, John Golden, Girish Krishnan

Organizations: Department of Industrial & Enterprise Systems Engineering, University of Illinois Urbana-Champaign · Department of Mechanical Science & Engineering, University of Illinois Urbana-Champaign

Abstract

Rerouting the tendon path in tendon driven continuum manipulators (TDCMs) enables a broad range of deformation modes. This work presents a Reconfigurable TDCM design which allows independent rotation of intermediate spacer disks, thereby locally rerouting the tendon and achieving non-trivial backbone spatial deformations. Two such designs, (a) Manual Disk Locked (MDL) and (b) Continuous Disk Rotor (CDR) manipulators are presented to achieve disk rotations before and during operation, respectively. A predictive static model based on the piecewise constant strain (PCS) assumption is developed within a potential energy minimization framework, incorporating (a) disk rotations, (b) discrete tendon paths between disk segments, (c) rigid thickness of spacer disks, and (d) elasticity of the tendons. The model is validated against experimental results, demonstrating an average tip error of $1.2\%$ of the manipulator's total length for parallel tendon routing and around $3\%$ for the case when multiple disks are rotated. The computation time is an order of magnitude lower than the state of the art Cosserat rod solver.

Figures & tables

Fig. 1: Conventional TDCMs (a) rely on fixed predefined parallel tendon routing which constrains their attainable deformation modes. The proposed RTDCM design (b) leverages intermediate spacer disk rotation to locally reroute the tendon allowing more versatile backbone spatial configurations. Though the backbone deforms as a smooth continuous curve, the tendon follows a discrete linear path between the rotated disk segments (II).

Fig. 2: The spacer disk for the MDL manipulator (a) is split into two main components, with the top bushing (1) attached to the backbone using epoxy and the bottom disk (3) freely rotating on the bearing (2) to locally reroute the tendon. A desired tendon configuration is locked by inserting the cotter pin (4). The CDR manipulator (b) enables active tendon rerouting using the servo motor (1), which sits on the larger top bushing (2) attached to the backbone and is meshed with the rotating disk (5) via the spur gear (3).

Parameter	Symbol	MDL	CDR	Unit
Number of segments	$n$	10	8	–
Segment length	$L_{\mathrm{seg}}$	27	69	mm
Backbone diameter	$d_{b}$	1.0	1.5	mm
Backbone density	$\rho$	6450	6450	kg/m 3
Tendon Young’s modulus	$E_{t}$	4.5	4.5	GPa
Tendon radial offset	$R_{\mathrm{rad}}$	8	34	mm

TABLE I: Manipulator Design Parameters

Fig. 3: Representative manipulator description (left) with piecewise constant strain segment (right) illustrating the various parameters and notations used in the model. $\mathbf{p_{0}}$ and $\mathbf{R_{0}}$ correspond to the base frame pose.

Routing	Avg. RMSE (cm)	Avg. Tip Error (cm)	Avg. Time PCS (s)	Avg. Time VC (s)
Parallel	0.0144	0.0309	0.7925	7.65
D6 $90^{\circ}$ CW	0.0778	0.1476	0.7769	9.75
D6 $90^{\circ}$ CW + D9 $90^{\circ}$ CCW	0.1737	0.3022	0.7761	15.7362

TABLE II: Model Comparison

Fig. 4: The MDL manipulator (4) is suspended within an enclosure, with the tendon being actuated by the stepper motor (1). Two cameras (2,3) capture the manipulator’s deformation by reconstructing the spatial coordinates of the spacer disks.

Fig. 5: The PCS model is validated against experimental results in three different tendon routing scenarios (a)-I: parallel, (b)-I: disk 6 rotated $90^{\circ}$ CW, and (c)-I: disk 6 and 9 rotated $90^{\circ}$ in opposite directions. The second row (II) demonstrates the model deformations for different tendon actuation using smooth curves, compared with black filled circles denoting experimental data, for each of the three routing scenarios (a)-(c). The RMSE and tip errors are plotted for each routing scenario in row (III).

Fig. 6: CDR manipulator demonstrating tendon rerouting on-the-fly achieving a helical deformation profile from an initial parallel configuration

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Apr 14, 2026J/K move · Enter open · S save

Actuation space reduction to facilitate insightful shape matching in a novel reconfigurable tendon driven continuum manipulator

Sabyasachi Dash, John Golden, Girish Krishnan

Department of Industrial and Enterprise Systems Engineering, University of Illinois Urbana-Champaign · Department of Mechanical Science and Engineering, University of Illinois, Urbana-Champaign

Tendon-Driven Actuation Continuum Robot Control

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In tendon driven continuum manipulators (TDCMs), reconfiguring the tendon routing enables tailored spatial deformation of the backbone. This work presents a design in which tendons can be rerouted either prior to or after actuation by actively rotating the individual spacer disks. Each disk rotation thus adds a degree of freedom to the actuation space, complicating the mapping from a desired backbone curve to the corresponding actuator inputs. However, when the backbone shape is projected into an intermediate space defined by curvature and torsion (C-T), patterns emerge that highlight which disks are most influential in achieving a global shape. This insight enables a simplified, sequential shape-matching strategy: first, the proximal and intermediate disks are rotated to approximate the global shape; then, the distal disks are adjusted to fine-tune the end-effector position with minimal impact on the overall shape. The proposed actuation framework offers a model-free alternative to conventional control approaches, bypassing the complexities of modeling reconfigurable TDCMs.

Abstract

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