This module was originally developed as an actuation module for a springtail-inspired jumping robot. Springtails employ a bi-stable jumping structure: elastic energy is stored by folding a bi-stable tail structure and then released by triggering it through body deformation. This requires two muscle actuation functions: (1) folding the tail structure to load and store energy, and (2) inducing a body-shape change to trigger release[1] (see the schematic illustration in [1]). A key is that the tail-folding actuator can resist the rapid unfolding motion during release, so it must be decoupled at the moment of triggering.

To address this, I implemented a direction-dependent transmission using a planetary gear mechanism around the motor. In one motor direction, the gear passively engages and transmits torque to the loading path; when the motor reverses, the gear disengages and the power path is cut off, allowing free release of the bi-stable structure. Using this design, I built a springtail-inspired prototype and validated the concept.

Furthermore, unlike cam-based mechanisms that store/release a predetermined amount of energy, this module allows the desired preload level to be set by motor rotation and enables on-demand rapid release via a simple reversal. Finally, we integrated the module into a height-adjustable jumping system for a “Jump-RoACH” robot.

[1] J. Brackenbury, H. Hunt, Jumping in springtails: mechanism and dynamics. Journal of Zoology. 229 (1993), pp. 217–236.