Building Progress 5

      After the experiment in the bathtub, we found a problem that the back side of the seaperch is too heavy that the back side is always going to sink. It will cause a big problem for us to keep the seaperch stable enough to get the water sample at different level.The reason why the back side is so heavy is that there are two motors which are located at the back giving the driving force. At first, we designed to bind a balloon at the back side of the seaperch to give an enough floating force. However, we thought the environment under the water could be very complicated. The balloon is so breakable that when it meets something sharp, the balloon will break. The seaperch will sink. In that way, we changed our idea. We sealed the two ends of the pipe located in the back side of the seaperch. We used the same theory like the balloon. If we sealed the two ends of the pipe, when the seaperch is under the water, the tube will be full of air instead of water. It can provide enough floating force. Figure 1 below is the pipe, the both ends of which are sealed.

Figure 1: The pipe with both end sealed.

     After the experiment, the method worked. With the extra help of the two pieces of round blue sponge, the seaperch can float in the water steadily. Figure 2 below shows the steady floating of the seaperch in the bath tub.

The position of the two pieces of the sponge can be adjusted to keep the level balance of the seaperch. Because of the weight of two motors, the sponge is more at the back side of the seaperch which is obvious.

More Challenge

     Because we want to make our seaperch to stay at any depth of the water, if the floating force is bigger than the weight of the seaperch, the downward movement of the seaperch can only be accomplished by the driving force from the third motor which is located in the middle of the seaperch. Whenever the motor stops, the seaperch will go up automatically. As we all know, the floating force equals to the volume of the part under the water times the density of the water and the gravity constant. After the whole seaperch is under the water, in theory, the floating force won't change anymore. Under this circumstance, we want to add some weight to the seaperch to balance the weight and the floating force when the whole seaperch is under the water. If these two forces are equal, it means the seaperch can stay at any depth of the water. We are going to get some sands and some stones into a bottle. And we will bind the bottle to the middle of the seaperch. It can both add weight and keep the balance of the seaperch. In this week, we will emphasis on this challenge by doing more experiments. It is a key step that make our seaperch to be like a depth sensor.