design and construction of mobile surveillance robot

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ALTERNATIVE DESIGNSSession 4CThere were three different designs considered for use: ahanging weight design [1], a “hamster ball” drivendesign[2], and a dual-tread design[3]. The capabilities andrequirements were considered along with several othercriteria when generating these design possibilities.The hanging weight design consisted of a central shaftwith a carriage hanging from the shaft as displayed in Figure2. The carriage would have the ability to rotate around theshaft which would allow for movement forward andbackwards. The carriage would also have a small weightinside which would shift side to side to allow the sphere totilt from side to side while moving forward or backward, andin so doing provide a turning capability.FIGURE 3HAMSTER BALL DRIVEN DESIGNThe dual-tread design would contain two wheels thathave the ability to turn in opposite directions to allow for azero turn radius. The design would not be perfectlyspherical, but would still retain the benefits of a sphericaldesign. A model of the dual-tread design is displayed inFigure 4.FIGURE 2HANGING WEIGHT DESIGNThe “hamster ball” design would operate similar to howa hamster is able to move around in a plastic ball. A robotwould be contained within a clear plastic sphere withcontrollable wheel(s) at the bottom that roll along the insideof the sphere. The wheel(s) would be able to rotate so thatthe sphere could travel in any direction. It would alsocontain stabilization arms that would keep the robotcentered, the wheel(s) in contact with the sphere, and wouldalso protect the components inside the robot if the spherewere to suffer a sudden impact. A sketch for the “hamsterball” design is displayed in Figure 3.FIGURE 4DUAL-TREAD DESIGNAll three of these designs were evaluated using adecision matrix that included several design criteriaimportant to the project. The results can be seen in Table 1.Pittsburgh, PA March 26 - 27, 2010ASEE North Central Sectional Conference4C-2
Session 4CTABLE 1DECISION MATRIXCriteriaWeightHanging Carriage Hamster Ball Dual-Tread SphereScore Total Score Total Score TotalStability 25 0.0 0.0 0.5 12.5 1.0 25.0Cost 10 1.0 10.0 0.3 3.3 0.0 0.0Durability 8 0.5 4.0 0.0 0.0 1.0 8.0Power Use 6 1.0 6.0 0.0 0.0 0.5 3.0Feasibility 10 1.0 10.0 0.0 0.0 1.0 10.0Mobility 15 0.0 0.0 0.8 11.3 1.0 15.0Ease of Assembly 8 1.0 8.0 0.3 2.7 0.0 0.0Size 5 0.0 0.0 0.7 3.3 1.0 5.0Complexity 5 1.0 5.0 0.0 0.0 0.3 1.7Clarity 8 0.3 2.7 1.0 8.0 0.0 0.0Total 100 45.7 41.1 67.7The design that was selected based on the specifiedcriteria was the dual-tread design. It was determined that thedual-tread model would be the most stable and the mostmobile due to its wheeled design. It should also be easier toinsert equipment inside of the dual-tread design, allowing fora smaller size which will benefit the mobility of the robotboth in-use and for transportation.PROPOSED SYSTEM DESIGNThe design chosen to fulfill the requirements is a dual-treadrobot with a capsule shape as shown in Figure 5.The middle cylindrical-section of the robot is stationarywhile the two wheels are domed on the outside and arecontrolled separately, allowing for a zero-turn radius. Themechanical, controls, data acquisition, and powersubsystems are contained within the middle section of therobot.The elements of the subsystems are mounted in such away that the center of gravity is well below the geometriccenter of the robot. The camera and transmitters are mountedcloser to the center of the section, on the shaft. This allowsfor a minimization of interference in the signals due to themotors and power systems. The power subsystem ismounted near the bottom of the containment section toprovide stability and to also prohibit interference from themechanical systems to the power performance.The different subsystems are hard-mounted to the shaftfor strength and stability. The central shaft remains relativelystationary as the wheels rotate around the shaft. The outershell of MSR is made of polycarbonate to increase strengthand durability, while also allowing for optical clarity.Polycarbonate also has a low electrical conductivity, whichis beneficial for the power system design.FIGURE 5DUAL-TREAD ROBOT DESIGNDESIGN OF MECHANICAL SUBSYSTEMThe drive train for the Mobile Surveillance Robot consists oftwo (2) electric motors, four (4) gears, a stationary shaft, andtwo (2) wheels with bearings. The motors drive the two setsof gears, which are attached to the wheels. The wheels arePittsburgh, PA March 26 - 27, 2010ASEE North Central Sectional Conference4C-3
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design and construction of mobile surveillance robot

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