After the almost complete failure of the original trigger mechanism, some revisions were in order (see Video shoot #1 for the issues).
As mentioned in Revised trigger mechanism design and scorpion habitat, the scorpions responded violently to being brushed or poked with a paintbrush (I assume because of the large number of contact points from the bristles). Therefore I decided to scratch the foam and pushrod design and switch to a paintbrush on the end of a swingarm. Here are the designs and pictures:
Version 1.8 (click to view, right click and “Save Link As..” to download) of my Arduino software takes commands via serial as usual, but instead of only being able to write the received angle to the servo, it can now receive “activate” and “retract”, which cause the servo to vibrate and stop respectively.
Version 1.8 (click to view, right click and “Save Link As..” to download) of my Processing code still allows for angles to be assigned to various buttons, but now also has two new buttons: Activate and Retract. Here’s a screenshot of the GUI (some buttons are currently unused):