Cyrus Tabrizi, 12/26/12

      The rest of the body consists of an undercarriage, eight plastic bottles, two paddlewheels, a motorized lift tray, and a working winch. The undercarriage itself faces two challenges: how to brace and position the bottles in a suitable position and how to support the weight of the entire upper arm on top of the forces presented by the eight bottles.


      The bottles are of critical importance to this robot –they are its main and only means of floatation. There are three large (32 oz each) and five medium bottles (roughly 20 oz each) mounted below the robot, most of which are at near–vertical positions. Most of the robot's weight can probably (highly likely –not tested) float on the three large bottles. The reason for this is that the robot doesn't have a problem with buoyancy (three bottles or less are enough to float it), but rather the problem is the distribution of this water displacement. For the robot to float, balance, and remain stable, the water displacement must be spread in a particular manner. Not only must there be a large contact surface, but the outer edges of this surface must be far enough away from the robot to keep it from tipping over or flipping. One might decide that making a raft whose bottom is completely flat to distribute weight evenly would be the best idea, but if the center of gravity is high enough, the raft will surely flip over –this is because the entire raft becomes the floating pivot for which it will flip on itself. This robot has most of its bottles standing around the perimeter at angle that makes them lean into the robot. On the individual bottle scale, this would encourage it to tip over in the direction it was leaning and make it harder to fall over in the opposite direction. On the scale of the entire robot however, these bottles are all leaning in against each other, keeping it stable and making tipping in any particular direction much harder than it would be if the bottles were completely vertical. In fact, mounting the bottles at a near–vertical angle (not too steep though) makes it easier to brace than if they were in any other position. One bottle, however, is left mounted completely horizontal in the center simply to divert any splashing water from hitting the battery box, wires, and the motors in the front and rear.