TALE-teller: Tendon-Actuated Linked Element Robotic Testbed for Investigating Tail Functions

TL;DR

Tendon-Actuated Linked-Element (TALE), a modular robotic test bed to explore how tail morphology influences function, can match the morphology of extant, extinct, and even theoretical tails by varying 3D printed bones, silicone joints, and tendon configurations.

Abstract

Tails serve various functions in both robotics and biology, including expression, grasping, and defense. The vertebrate tails associated with these functions exhibit diverse patterns of vertebral lengths, but the precise mechanisms linking form to function have not yet been established. Vertebrate tails are complex musculoskeletal structures, making both direct experimentation and computational modeling challenging. This paper presents Tendon-Actuated Linked-Element (TALE), a modular robotic test bed to explore how tail morphology influences function. By varying 3D printed bones, silicone joints, and tendon configurations, TALE can match the morphology of extant, extinct, and even theoretical tails. We first characterized the stiffness of our joint design empirically and in simulation before testing the hypothesis that tails with different vertebral proportions curve differently. We then compared the maximum bending state of two common vertebrate proportions and one theoretical morphology. Uniform bending of joints with different vertebral proportions led to substantial differences in the location of the tail tip, suggesting a significant influence on overall tail function. Future studies can introduce more complex morphologies to establish the mechanisms of diverse tail functions. With this foundational knowledge, we will isolate the key features underlying tail function to inform the design for robotic tails. Images and videos can be found on TALE's project page: https://www.embirlab.com/tale.

Figures (5)

• Figure 1: Tails with the same overall length but variable link lengths experience different bending behavior under the same displacement input. A, B, and C show three distinct tails, each pulled to 12 mm and 21 mm of tendon displacement. D shows an overlay of both displacement inputs for all three tails. Note that direction of gravity is horizontal to the right.
• Figure 2: Our robotic platform can recreate diverse biological tail morphologies and explore the performance of theoretical morphologies. A) The crescendo-decrescendo robot tail is similar to the vertebral proportions of animals that use their tails as inertial appendages Fu. B) The decrescendo only robot tail is similar to the tails of lizards nunez2018mesosaurus, which are frequently used in defense for swatting carpenter1961patterns. C) All three robot tails have the same total length but differ in proportion. The crescendo only tail (red) explores the function of a theoretical morphology not found in vertebrate tails.
• Figure 3: A) Component order of bones and joints for TALE. B) Completed TALE robot without actuation system. C) Examples of compatible actuators.
• Figure 4: A) Illustration of Instron testing setup. B) Schematic of one joint. Note that $l$ is the moment arm and $\gamma$ is the angle of the joint with respect to horizontal. Both values change as the joint deforms. $h=12$ mm, $r_1=10.2$ mm, $r_2=4.615$ mm, $l=r_2+\sqrt{\left( r_1-r_2 \right)^2+\left( h/2 \right)^2}\cos\gamma$. C) A combined plot showing the bending behavior and force-displacement curves of the joint during Instron testing (cyan), FEA simulation (red), and computational model deformation (green).
• Figure 5: Empirical and computational model results of tail bending for three distinct tails. Solid lines indicate data from empirical tests and dashed lines indicate simulated orientations from the computational model. Darker lines indicate one motor actuations and lighter lines indicate two motor actuations. Measurements were taken in 3D using motion capture and then collapsed into a single plane defined by the central axis of the tail and a radial axis originating from the center of the tail, parallel to the base. A) Tendons displaced 12 mm in testing and in simulation. B) Tendons displaced 21 mm in testing and in simulation.