Armour triangles would be for those right-angled parts on your prototype - the spaces between the front/back wedges and the side skirts. If a horizontal spinner came along it could catch on to the side parts of the wedge/skirts and bash the robot. Putting armour triangles across those spaces means that the spinners teeth would be more likely to glance off the armour than bite into your robot.

Hope that helps - the prototypes looking good

Lenny