DOI: 10.5061/dryad.fttdz08pb
title: Latch-based control of energy output in spring actuated systems

description: The inherent force-velocity trade-off of muscles and motors can be
 overcome by instead loading and releasing energy in springs to power
 extreme movements. A key component of this paradigm is the latch that
 mediates the release of spring energy to power the motion. Latches have
 traditionally been considered as switches; they maintain spring
 compression in one state and allow the spring to release energy without
 constraint in the other. Using a mathematical model, we demonstrate that
 changing the parameters of a simplified contact latch (latch radius and
 release velocity) can enable both this instantaneous energy release
 behavior as well as a regime that reduces and delays the energy released
 by the spring. This is true even for latches found in biology that have
 rounded edges and do not geometrically disappear instantaneously. We also
 identify a critical threshold between these instantaneous and delayed
 regimes. We validate this model in both a physical experiment as well as
 with data from the Dracula ant, Mystrium camillae, and propose that latch
 release velocity can be used in both engineering and biological systems to
 control energy output.
description: <strong>Data from Latch Physical
 Model:</strong> Experiments with the latch
 physical model described in the associated paper were recorded with a
 Photron AX-200 high-speed camera (pixel resolution: 896 x 768, calibrated
 ruler) at 10000 fps (shutter duration: 1/60000 second) and both latch
 motion and projectile motion were analyzed using tracking software (Image
 Systems, TEMA). Take-off velocity was calculated from these images at the
 point when the spring and mass separated from the substrate.
 Measuring latch delay was more challenging. In theory, the point
 of maximum projectile acceleration should equate to the instant at which
 latch force goes to zero, but this was not the case in the physical
 system. Instead, latch delay was measured when physical separation was
 visually observed between the projectile and the latch. While this method
 is expected to slightly overpredict delay, it provided consistent
 results.  Data was processed in Matlab using the
 scripts provided. <strong>Dracula ant data
 processing:</strong> Mandible tip position data
 captured on high speed video from two types of Dracula ants (larger major
 and smaller minor workers) was made available in [Larabee 2018, doi:
 10.5061/dryad.4863215]. This dataset provides x-y coordinates of the
 mandible tips for each frame along with the camera frame rate. Four ants
 of each type were analyzed over 4-5 strikes per ant as available in the
 dataset. The first mandible to move during each strike was designated as
 the latch mandible, and unlatching time was defined as the time difference
 between the start of latch mandible and strike mandible motion. Average
 latch mandible velocity was calculated as the angle over which the latch
 mandible displaced before the strike mandible began to move, divided by
 the unlatching time. The maximum strike velocity was calculated using the
 maximum angular motion of the strike mandible between two frames and
 dividing by the time interval between frames. The Matlab script used to
 process this data is included in the dataset, but the dataset itself is
 available from Larabee (doi: 10.5061/dryad.4863215). 
 <br>  
description: Readme file is included for data and code from the physical model
 of the contact latch system. Comments are included in
 the code for the ant data.