Personal collection of mechanism projects.
Welcome to a small collection of various mechanisms I’ve made. Hopefully you will share the passion for kinematics with me and appreciate the beautiful geometry behind the presented mechanisms. My name is Daniel, currently a postdoc at Robotics Laboratory, Seoul National University, Korea. If you want to reach out, find my email on our lab’s website.
Visit also my GitHub · Google Scholar · Printables profiles.
Jump to a project: Fidget Bennett | Snapping four-bar | Flapping wing | Motorized six-bar | Snapping surface | Rational Linkages | Pick-and-place Bennett demo | Bi-Bennett | Shaky 3-RPR | Even shakier 3-RPR | Multimode 7R with no 7R mode | Multi-Bennett 8R mechanism | Möbius linkage | Bricard's orthogonal 6R | Bricard's line-symmetric 6R | Bricard's plane-symmetric 6R | 6-UPU platform | Custom serial 3R
My “state-of-the-art” design of the Bennett linkage toy, used for public outreach events to demonstrate the beauty of spatial mechanisms. Kids do the assembly and can take their own Bennett mechanism home. They seem to like it a lot and many fathers look jealous 😄
STL files: find on printables.com
A snapping (bi-stable) four-bar has two rigid configurations. The beautiful geometrical construction that relates to the two limit poses of Henrici’s flexible hyperboloid was done by Hellmuth Stachel, TU Wien, Austria, as part of our joint work.
Video: zenodo.org/records/14206067
Stachel, H., and Huczala, D. (2025), From Henrici's flexible hyperboloid to snapping spatial four-bars.
Paper DOI: 10.1016/j.mechmachtheory.2025.106057
Two Bennett linkages are serially coupled to form a flapping wing mechanism. Only one linkage is actuated, the second has an embodied passive folding based on the dynamics of the motion.
Video: zenodo.org/records/18765525
Huczala, D., et al. (2026), Bird-Inspired Spatial Flapping Wing Mechanism via Coupled Linkages with Single Actuator.
Paper DOI: 10.48550/arXiv.2604.07677
Rational 6R mechanism with 1 DoF, whose coupler motion is parameterized by a cubic rational function. Collision-free line model was proposed by Zijia Li from the Chinese Academy of Sciences, China. Solid curved-link model was made using Rational Linkages.
Video: https://youtu.be/SC_mPBAiBr0
Rational Linkages docs: rational-linkages.readthedocs.io
Li, Z., Nawratil, G. et al. (2020), Invertible Paradoxic Loop Structures for Transformable Design.
Paper DOI: 10.1111/cgf.13928
A surface composed of snapping four-bars. The construction is derived from quad nets on Study quadric via Whiteley’s de-averaging, and it relates to differential geometry and discrete minimal surfaces. It was a group effort at my former Unit at the University of Innsbruck, but I must especially mention Gudrun for her contribution in the construction methodology.
Video: zenodo.org/records/19216474
Szewieczek, G., Huczala, D., Pfurner, M., and Schröcker, H.-P. (2026), Bistable Quad-Nets Composed of Four-Bar Linkages.
Paper DOI: 10.48550/arXiv.2604.00527
Although it is a Python library rather than a mechanism,
I created this interactive toolbox with much help
from my colleagues during my postdoc at the University
of Innsbruck, Austria. It is open-source
(code on GitHub)
package for synthesis and rapid prototyping of rational linkages,
and you can easily get it via «pip install rational-linkages»
as it is available on PyPI.
Rational Linkages docs: rational-linkages.readthedocs.io
Huczala, D. et al. (2023), Rational Linkages: From Poses to 3D-printed Prototypes, arXiv:2403.00558.
Paper DOI: 10.1007/978-3-031-64057-5_27
This beautiful manipulation demo using the Bennett mechanism was made by Tomáš Poštulka, VSB - Technical University of Ostrava, Czechia. I helped him only a little with the very first design of the linkage. After Tomáš finished, I had to make and assemble one also for myself asap. Based on experience from public outreach events, some people come repeatedly and stare at it in amazement.
The two Bennett linkages are coupled with spherical joints to form a flexible bi-pyramid with 1 DoF. It is similar to the Bricard’s flexible octahedron. The design was proposed by Georg Nawratil from TU Wien, Austria.
Georg's website: geometrie.tuwien.ac.at/nawratil
Video: zenodo.org/records/18299299
Nawratil, G. (2025), Bi-Bennetts - Flexible arrangement of two Bennett tubes.
Paper DOI: 10.1016/j.cagd.2026.102535
The structure should be rigid (imagine pneumatic actuators in the legs that maintain length in this configuration), however it is shaky (infinitesimally moveable) because the direct kinematics solutions coincide. It was proposed by Manfred Husty, University of Innsbruck, Austria.
Husty, M. (2023), Multiple Solutions of Direct Kinematics of 3-RPR Parallel Manipulators.
Paper DOI: 10.1007/978-3-031-45705-0_58
The flexibility of this 3-RPR was “enhanced” by replacing rigid bodies (base and coupler triangular platforms) and assembling them using bars in the mechanism’s co-linear configuration. The moveability is limited by self-collisions, so in reality it would be even higher portion of infinitesimal motion. It was proposed by Georg Nawratil from TU Wien, Austria.
Georg's website: geometrie.tuwien.ac.at/nawratil
Nawratil, G. (2025), A global approach for the redefinition of higher-order flexibility and rigidity.
Paper DOI: 10.1016/j.mechmachtheory.2024.105853
This multimode 7R never reaches its expected motion mode with 1 DoF and 7 revolute joints. Instead, it switches between multiple different motion modes with various degrees of freedom. It was proposed by Xianwen Kong from Heriot-Watt University, UK.
Kong, X. (2024), A Variable-DOF Single-Loop 7R Spatial Mechanism That Has No 1-DOF 7R Motion Mode.
Paper DOI: 10.1007/978-3-031-64057-5_42
Every second joint of this mechanism is part of a Bennett mechanism. It has two degrees of freedom, and when holding one joint still, every second one gets blocked. The motion is a rational surface, obtained by factorization of bivariate motion polynomials.
Frischauf, J., et al. (2023), A multi-Bennett 8R mechanism obtained from factorization of bivariate motion polynomials.
Paper DOI: 10.1016/j.mechmachtheory.2022.105143
This 9R is supposed to have 3 DoFs, but has only 1 as the axes form a discrete Möbius strip. It was proposed by Manfred Husty, University of Innsbruck, Austria.
Husty, M. (2022), Möbius Linkages.
Paper DOI: 10.1007/978-3-031-08140-8_1
Bricard’s orthogonal linkage has consecutive joint axes perpendicular to each other. The perpendicularity is the key for mobility of that mechanism.
In this Bricard’s line-symmetric linkage you can find an axis of symmetry, the configuration on one side of the line mirrors the other under a 180° rotation, enabling continuous mobility through this constraint.
Similarly, this plane-symmetric Bricard’s linkage has a symetrical plane that joint axes from one side to the other.
There is nothing special about this classic 6-UPU platform, just that the self-made U-joints move very smoothly and are easy to assemble, so it can serve for some inspiration.
This demo was created as part of my PhD, to show the capabilies of the developed methodology. The topic was focused on synthesis of serial manipulators in a collision environment. The presented 3R manipulator can reach 3 prescribed poses while avoiding the obstacles.
Video: youtu.be/KPRaVsSBQ40
Huczala, D. et al. (2022), Multirepresentations and Multiconstraints Approach to the Numerical Synthesis of Serial Kinematic Structures of Manipulators.
Paper DOI: 10.1109/access.2022.3186098
Rational Linkages · Python package that I developed for CAD synthesis and prototyping of single-loop rational linkages.
PyRigi · Python package for the rigidity and flexibility of bar-and-joint framework; I did minor contributions (#124, #156) there for generation of STL models of the framework bars.
DOI to Bibtex Apple Shortcut · Fast bibtex generation on macOS.
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