DOI: 10.4121/21666116.v2
title: 3Flex - 3D Printable Parametric Tendon-driven Manipulator

description: What is it?The 3Flex (Fused Filament Fabrication Flexible Instrument) is a parametric, 2DOF, tendon-driven manipulator design, that is 3D printable on most<sup>1</sup> home FFF printers.The idea was born as an idea for a steerable catheter design during Fabian Trauzettel's PhD project in the BITE group at TU Delft.This work was supported by the ATLAS project. This project has received funding from the European Union’s Horizon 2020 research and innovation program under the Marie Skłodowska-Curie grant agreement No 813782.The project website can be found here.<sup>1</sup>A 0.25mm Nozzle is recommended. Printing with a 0.4mm nozzle is possible, but requires some modification of the CAD model. What does it do?3Flex provides an easy to manufacture, affordable platform to build and test small-scale tendon-driven manipulators. Multiple 3Flex segments, each capable of bending in 2DOF, can be arrayed serially to create highly dextrous effectors. The design can be easily tailored to the requirements of the specific application by changing the parameters of the OpenSCAD file. This lets you modify not only broad dimensions like diameter, lumen sizes, length or maximum bending angle of each segment, but also vary more subtle parameters like the thickness of the segment helix or spine, thereby changing the stiffness of the segment. All of this is implemented taking into account the math used by Slic3r and its derivatives to make sure that the thin sections are not too thin to print, and thicker areas are composed of nice, parallel extrusion lines with no infill or gaps. Instructions for use:Download 3Flex.scad and PrusaSlicerConfig.ini.Download and install OpenSCAD and PrusaSlicerOpen 3Flex.scad in OpenSCAD and use the customizer on the right side of the screen to select your preferred segment configuration and printer settingsRender the final design (this may take some time) by pressing F6 or pressing the render icon on the editor ribbon.Export the resulting .stl file to a convenient locationOpen PrusaSlicer and go through the setup wizard for your specific 3D printer. Manual configuration for unsupported machines is also possible. Go to File&gt;Import&gt;Import Config (or press Ctrl+L) and import PrusaSlicerConfig.iniImport the .stl File from step 5 into PrusaSlicerOrient the part to lie on its flat side by clicking it in the plater window and using the "place on face tool" (or press F) and selecting the now-highlighted flat side of the shaft.Under print settings, select "new_FDMflex_0.15mm QUALITY @0.25 nozzle MK3", as well as your filament and printer settings.Click "Slice now" to generate the G-code for your printerHappy printing!Some tips:Use a craft knife or box cutter to gently separate the raft from the part, and then run the blade through the helix to remove any stringing or blobs. If you are assembling multiple segments, it is wise to alternate right and left hand helices (set "Helix handedness" to 1 or -1 in the OpenSCAD customizer) to prevent twisting of the resulting shaftTendons can be any material that is readily available, but the material should be flexible and not elongate too much under load to keep the manipulator's behaviour predictable; Spectra and Dyneema are good options and are available in a range of diameters and breaking strengths as fishing line.Tendons are threaded into the shaft from base to tip, knotted around the shaft groove at the tip, and then threaded back down the shaft on the opposite side of the shaft. This way, one piece of thread makes two steering tendons. An example image is located here.