For the Bajaj Challenge, we essentially had to make a carriage to transport 2 ping pong balls down a zip line as quickly as possible, while ensuring that the ping pong balls did not fall out unless the Bajaj was turned upside-down.

My team focused on two main variables: weight and friction. We needed to increase the weight and reduce the friction of the cart on the string zip line.

In our first iteration, we used the heaviest and most convenient object available to us: a roll of duct tape.

We then surrounded it with thin foam sheets to ensure that the ping pong balls would not fall out at the end of the zip line. This worked perfectly, and was clearly a fantastic idea, as evidenced by the look of profound approval on Dr. Wettergreen’s face

We also came up with the idea to use a binder clip instead of a paper clip to attach our Bajaj to the string. This gave us a huge advantage in the races.

For out next iteration, we again focused on adding weight and reducing friction. To achieve the first goal, we rummaged through the metal scraps in the machine shop and found a heavy metal cylinder. We fit this inside a PVC T-connection that served as the body of our new Bajaj.

To help mitigate the force of the flying battering ram we had created, we were lucky enough to find a long compression spring that fit through a hole in the metal cylinder and went from the back of the Bajaj all the way out the front. We added a PVC end cap on the front for aesthetics and so that the metal spring would not scratch up whatever it ran into.

We also decided that it would be a good idea to further reduce the amount of possible damage by adding a rolled up sheet of foam to the front. We secured it using rubber bands and hot glue.

To keep the ping pong balls from falling out we taped a tapered piece of PVC onto the top. This funneled the balls down and out when the Bajaj was turned over, but kept them in place during normal use.

Next we focused on reducing the friction on the string. We set up a practice zip line in the OEDK to test different methods, and ended up using a pulley we found. This again gave us an advantage in the races. To use it, we slipped the body of the pulley over the string, then held the bearing in place and secured it with a nut and bolt. This process was significantly easier and faster with two people. Then we just hooked the wire on our Bajaj onto the hook.

My main concern was that the string would slip off the pulley and get caught between the body and the bearing, but fortunately this did not happen. My other main concern was that we were going to break something with our battering ram AKA Bajaj. Unfortunately, this kind of did happen. Our Bajaj impacted the column at the end of the string so hard that it left a mark on the white paint, and it also broke some of our rubber bands, and even put a dent in the metal cylinder we used (which had a spring and padding in front of it!).

Despite this, and the fact that one of the ping pong balls fell out during our victory lap, I still think this project went quite well. We managed to win the race, and we used a simple design to do it.