[Mark McLeod]

Here's Frank's description (http://www.firstinspires.org/robotics/frc/blog/week-0.5)

Cheval de Frise

The Cheval de Frise defenses didn’t hold up well during the event, often breaking when hit by robots. This breakage was not revealed during our testing here at FIRST HQ or during the Week Zero scrimmage, and we know why. Turns out, we assembled the defenses we tested using hand tools, but when we got into production mode, we started using power drills to secure the bolts. These drills put more torque on the bolts, stressing on the planks in the defense, make them susceptible to breakage. We’ve redesigned the planks to use a counterbore, rather than a countersink, in the bolt areas. This greatly reduces the stress on the polycarbonate when tightening the bolts, and our new testing here has shown this fix works well. All events will be getting the newly designed Cheval de Frise planks, starting with this week’s events.