I decided to go with a side-by-side tandem bicycle concept for this year’s Kensington Kinetic Sculpture Derby. To start we acquired 2 gently used bicycles at exceptional discounts from the Trenton Bike Exchange and two trailer bicycles as well. To attach the bicycles together we purchased 1” square tube stock from Finkles Hardware Store in Lambertville, NJ.
The primary design constraint was to be able to fit everything in the back of my minivan for transportation so the cross members were spaced at 22” apart. This eventually turned out to be just sufficient room for my son and I to pedal shoulder to shoulder side by side. The side by side tandem bike was accomplished with two cross members welded between the bikes. The first steel member was placed directly between the fixed portion of the front steering joint and the second member was placed immediately below the seat. The rear cross member had to be carefully placed or it could potentially interfere with the pedaling motion.
For steering I welded one flange off of the front outer fork on each bike and then attached with 2 threaded Rod end joint bearings. The connecting steering member for the side by side tandem bike was fabricated from steel tube and two corresponding nuts welded onto each end. To finish off the quad bike setup we mounted the two rear trailer bikes onto the seat posts (as designed) of the two front bikes. Test drive revealed the bike was easy to steer and the whole concept worked. Success! I later experimented with a removable cross member for rear trailer bikes for better stability of the rear riders but it significantly negatively impacted the ability of the turn radius, so I scrapped that idea. The biggest lesson learned for the side by side tandem bike is you really have to get the alignment correct such that both bikes are perfect parallel to each other and perpendicular to the ground. The flex in the base can create some unnerving leaning or tilting while riding side by side and any mistake in welding up the two together will further amplify this challenge.
Kinetic Derby Theme: Queen of Hearts
We chose the theme of Queen of Hearts for our kinetic derby bike. We used the vinyl cutter to cut a massive Queen of Hearts vinyl decal and then mounted it to a thin plywood base with XL playing cards glued down around it. This piece was conveniently cantilever mounted to the front welded cross member of the side by side tandem bike. We fabricated a heart out of leftover pink insulation foam (from the old rhombus body) and spray painted it red and then cantilever mounted it to the rear cross member. The whole thing amazingly was able to be broken down and shoe-horned into the back of my mini van as intended (just barely).
Derby Day
We got soaked! It rained off and on most of the day. I was dismayed to see a few floats break down after the first corner. Thankfully our bike assembly held up except for a blown tire in my rear bike about mid-race. Somehow we were able to finish the race on one flat tire and make it to the mud pit.
At the award ceremony we won the Media Choice Award which was a thrilling end to the day. Thank you Kensington!
