This years' CO2 car projects definitely raised the bar from last years' group (http://www.thingiverse.com/thing:332868). We had cars ranging from a semi to the bat mobile and many others in between. This year I had my students incorporate more math into their projects by having them come up with an equation that would allow them to figure out the weight of their cars before they printed them. This actually was very successful and most students were with a gram or two with their estimated and actual weights. I was also able to involve two different high schools for this years' race which really raised my students' levels of interest and drive to do well. I hope to expand this race to even more schools in the future. Here is a link to my students' designs this year: http://www.thingiverse.com/corben33/collections/co2-car-projects