Laser Cut Bridge STEM Challenge!!!

This is a STEM challenge I set have set my engineering students this year. I have found this challenge a brilliant tool for teaching students how structures work and how they can be used in real life as it makes learning fun and intuitive. Unlike the my Popsicle stick challenge this challenge is good for developing cad skills. This is great because cad is such a useful skill to learn especially in a stem environment.

• laser cutter
• access to adobe illustrator, coral draw or similar
• a sheet of 3mm MDF
• weights for testing

To avoid complete anarchy, before allowing them to start I usually spend one lesson where I teach them them the basics of trusses.

I show them 6 famous examples of truss structures:

• The Howe truss
• The Pratt truss
• The Warren truss
• The Quadrangular Warren truss
• The Baltimore truss
• The camel back truss

For each truss design I explain the function of each bar and explain to them how bars are either under tension or compression by highlighting the components under tension/compression in different colours.

Once I feel that the students have grasped the concept of a basic truss and they have seen existing designs the next step is sketching truss designs. Once the team have decided on a design they should all help design the truss on their chosen cad software. It is important that they leave holes in the sides to insert crossbeams. Once done they should laser cut the pieces and start assembly.

1. Take one side of the bridge and preheat a glue gun.
2. Apply a little glue to the holes and insert the crossbeams
3. Trim away any excess glue with a knife
4. Add the second side like a sandwich

Once all the groups have completed their designs they should be weighed to test how much material was used. Next they should be placed across two tables 30 cm apart and carefully loaded with weights from the load bearing bar until they reach breaking point. Finally the strength to weight ratio should be found using the equation:

SWR=weight lifted / weight of structure

The team with the best strength to weight ratio are the winners. In the event of a draw the judge (you) must decide which team has the best:

• aesthetics
• use of structures
• use of material

I hope you and your STEM group find this fun (and educational) :) if so please consider voting for me in the STEM competition.