Design Review #2 - Columbia University

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Shadow IncorporatedDesign Review #2c. In a marketable design it may be important to include a safety feature which turns offthe boat automatically when an object is within a certain range.2. What if a swimmer is in distress, and wishes to use the boat for flotation?a. The prototype will most likely not be able to support a swimmer in distress, but afinal product may have space for an inflatable tube, or other form of life savingdevice.b. For the prototype a label that reads “Is not a lifesaving device” will be included inorder to cover liability.Functionality Problems:1. Will the boat be able to turn quickly enough to demonstrate in a pool?a. The longer the boat, the harder it will be to turn.b. Since two propellers angled at 90° will be used together, the boat will go straight, butby varying the speed of one from another the boat will be able to turn.c. For demonstration purposes, pools other than the Columbia University pool, whichwill restrict the distance the boat will be able to follow the swimmer, will beconsidered. Lehman College has a pool which is over 2 meters deep and 25 metersby 50 meters. This facility will make the final demonstration & test more accurate.2. How can disturbance be reduced for the sensors?a. Surface disturbance, as well as the pool walls and bottom will create noise that willmake it hard to follow the signal on the swimmer.b. The prototype model will have a ping from the swimmer using a chip from NationalSemiconductor that is designed to create a pulse at an accurate time delay. Pingingfrom the swimmer will take out the need for reading reflections, and increase thechance of the boat “hearing” the correct signal.3. How will the distance to the swimmer be controlled?a. If the boat is turning with one motor on and the other off, it may slow down too muchto keep up with the swimmer.b. There will be three sensors on the boat. Two will be attached to a processor whichwill increase or decrease voltage to just one motor depending on the direction of theboat (steering). The third sensor will be attached to a second circuit which will judgeonly the distance to the swimmer and add a voltage to both engines equally in order toincrease or decrease the overall speed of the boat.
4. What if there are multiple swimmers using a Shadow Boat?Shadow IncorporatedDesign Review #2a. The expected range of the sensors is 10 meters or less. Swimmers will have to beaware of others using the same system.Since initial tests began, several problems have been encountered with the sensors. Sonar ismuch harder to operate than expected, and there do not seem to be any standards for how to operate it.The control system for the crystals has a large influence on how the sensors work, but since each sensoris slightly different, it is necessary to try several different circuits. As of now, a sensor has yet to workeffectively in air, and has not been tested in water, so alternatives are being considered. There is achance that an IR emitter or an audible ping will be used to steer the boat using triangulation. Either oneof these options is much simpler than sonar, but has drawbacks in performance. Determining distancewill be much more difficult with other methods of sensing.Parameter AnalysisThe basic catamaran design came about through analysis of various boat types and their stabilityin the water. The biggest consideration for this project was stability and not speed since the boat will becarrying electronics, and the maximum speed only needs to be around three miles per hour. A multi –hull design naturally provides greater stability than a mono-hull design. The hull shape was chosenbased on analysis of heel angle and stability in steady water across different cross sections. Though asemi-circle provides more flexibility with the heel angle, the decrease in the water line decreases theoverall stability. Thus, as a compromise, a pentagonal shape was chosen. Though the heel angle ismoderate, only 15 – 20 degrees, general stability increases because of a larger waterline.The length of the catamaran was chosen based on the common model boat length of 29 inches.This number is also agreeable since the ratio between the height of the flagpole and the length of the hullis less than the maximum ratio of 1.6. The overall width was chosen to be 18 inches to allow for thecatamaran to maintain a square-like shape. The hull widths were chosen to be 4 inches in order to housethe motors and electronics.Calculations done for a sailboat with a 29 inch hull showed that a maximum speed of 2.1 knotscould be obtained with a waterline length of at least 25 inches. Considering sea currents are typically 2knots, this calculation shows that, even as a sailboat, the catamaran would be capable of travelingagainst the current. With propellers, the maximum speed is likely to be more than sufficient.Based on very basic geometry, calculations were performed to determine the maximum weightcapacity of the catamaran. Based on the buoyant force using the density of water and the volume being
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Design Review #2 - Columbia University

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