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What was the process of building boat #2?

What Actually Happened:

            Because two of the members on the Blue Crew are actually on the Wellesley Crew Team, the central idea behind Boat 2 was to create a vessel that simulated a realistic rowing movement of a crew boat.  Using rotating oars and a single motor, they wanted to construct a four-man boat that was able to push through the water and transport itself to the finish line.  Although this idea was seemingly difficult, they were up for the challenge, as the Blue Crew discussed some of the ideas that could make this idea into a concrete project.


            The first model that was created included a single oar with a rotating cardboard gear.  One end of the long oar (in the picture, the oar is replaced by a long, black axel) was attached to the edge of the gear by puncturing a hole and placing a piece of clay on the end to secure the oar into place.  The middle of the oar was loosely secured to an axel that was perpendicular to the direction of the oar.  This intersection became the fulcrum.  By creating a fulcrum, the circular movement of the gear allowed the other end of the oar to follow an inverse circular path; if the end of the oar was on the top part of the gear, the oar itself would dip into the water, and if the end of the oar was on the bottom of the gear, the oar would be above the water.  Additionally, this design was capable of making the path of the oar bigger, since the closer the fulcrum was to the gear, the larger it made the circular path of the oar.  However, the Blue Crew decided to create a new model that more closely followed the oar movement of a crew boat.

            The second design of Boat 2 was centered on the idea of simulating the oar following a square path, rather than a circular path.  This was accomplished by chaining two large gears together, and attaching one end of the oar onto one of the links on the chain. By doing so, the oar followed an oval path, which captured the essence of a square path.  This second design of Boat 2 also consisted of an array of complex gear trains.  Using LEGOÒ gears and pieces, the Blue Crew created an oar model formed by a total of four gear trains branching out from a single motor.  The construction of this design raised many difficulties.  First, the team had to construct the gear train that had a perfect balance between the ratio of the gears and the amount of torque that it was able to generate.  This was an essential idea, for they wanted to make a fast boat, but at the same time, they needed to design the gears so that it gave enough power to the oars to push the water back.  Another difficulty rose in the materials they used.  The Lego pieces had fixed amount of holes in each piece, thus limiting the distance between each gears.  In order for the gear train to work, the gears could not be too close or too far away; if the gears were too close, the friction between the gears would make the gears slower, and if the gears were too far away, the gears would not consistently move in the same rate.  Through numerous trials and errors they finally constructed a final product.

            However, a problem arose when the gear train was put into the Styrofoam carving; the chained gears that were suppose to be sunk half way into the water were fitted inside the body of the boat.  To solve this problem the Crew made eight extending arms to transfer the gear movement to the side of the boat where the gears were able to go into the water.  This required using crown gears to change the direction of the circular movement, thus making the arms extend over the edge of the boat and into the water. 

           After this task was accomplished, another problem was discovered; the extended gear arms gave the boat too much weight and the complexity of the gears and arms resulted in the friction overpowering the amount of torque generated by the gear.  Essentially, Blue Crew was in a tight situation.  With only twenty-four hours left until the Robot Expo, they were faced with a pile of Legos that neither moved nor nudged.

            The final decision was made the following hour; Blue Crew decided to reconstruct the whole boat.  After discussing numerous new ideas, they made the decision to construct Boat 2 following the very first model they had constructed: the rotating oar with the fulcrum. 

            The new and improved Boat 2 was the final product presented at the Robot Expo.  I was a much simpler design, only consisting of four large gears moved by a single motor.  All four oars moved in sync, thus imitating the movement of an actual crew boat.  Although the oars had difficulty staying perpendicular to the surface of the water, Blue Crew resolved this problem by attaching a long Lego to the oar and putting two pillars on each side of it.  This design prevented the oar from rolling over, thus controlling the movement so that it remained perpendicular to the water’s surface.

- As adapted from notes written by N. Iwata '10

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