The Truss Tester is an excellent starting point for conducting a bridge building activity. Students can evaluate how trusses fail and what they can do to improve their performance. They may discover that the trusses usually fail in a particular way and that including a brace at the point of failure provides a significant improvement in its ability to sustain a load. They can also test more complex structures, such as a bridge or crane.
The truss tester was designed for use with 1/4 in. square balsa wood or 3/32 in. balsa planks up to 3/4 in. wide.
Note: Other materials may work, but these materials are readily available and are known to work with the design parameters of the Truss Tester and the VSMT.
Figure 1 Truss constructed of 1/4 in. square balsa truss with reinforced corners
Figure 2 Truss constructed of 3/32 in. balsa planks
Figure 3 Truss with supporting members
The crossbars on the VSMT were set for a 16 cm span to carry a truss width of 18–20 cm in order to provide a range of potential angles that will fit within the truss holder dimensions.
The Truss Tester Accessory comes with two corner brackets that are useful in quickly constructing triangular trusses. The brackets slide onto the bottom member and can be pinned in place with a small nail, brad, or small piece of 1/16 in. or 3/32 in. diameter piano wire. The angled members can be cut to length and allowed to push against each other with or without glue or gussets.
An alternative to using the brackets is to glue the joints together. Lap joints with lots of surface area overlap work best, especially when trying to optimize truss design. Hot gluing balsa, with a little practice, provides a quick and strong bond.
Figure 4 Note that the angled members are free to push against each other
Tips for integrating this accessory with the VSMT can be found at http://www.vernier.com/vsmt