Proceedings - Rochester Institute of Technology



Project Number: P18482manually Powered Rock DrillJillian MamminoMechanical EngineerDavid SicilianoMechanical EngineerAnya CummingsMechanical EngineerWyatt SchieIndustrial EngineerFigure SEQ Figure \* ARABIC 2: Completed Drill64706571120385572069850Figure 1: CAD Assembly AbstractThe purpose of this project was to design and build a manually powered rock drill. The need of the drill is that it make holes 18-24" deep in bedrock for the purpose of setting rebar in the construction of anchors for the bridges. This project is for the benefit of a charitable organization called Bridging the Gap Africa. This organization assists remote African communities in the construction of footbridges that improve local access to healthcare, education, or commerce. This project is restricted to a $1,000 budget. This technical paper will detail the design objective and process with initial customer and engineering requirements and will include feasibility analysis, concept selection, theoretical analysis, construction of the prototype, recommendations for future projects, test results, and the detailed bill of materials and budget. introductionThis project is for the benefit of Bridging the Gap Africa. Bridging the Gap Africa is a charitable organization that assists remote African communities in the construction of footbridges that improve local access to healthcare, education, or commerce. Remote African communities contact Bridging the Gap Africa and the organization provides materials, tools, blueprints, and management to assist the local communities in the construction of a needed bridge. Additionally, the communities work together with Bridging the Gap Africa to provide much of the labor necessary to complete the construction. This allows a sense of ownership and participation in the building process that benefits the communities and ensures that the bridge is well received by the people using it.The drill is a necessary part of footbridge construction. Specifically, the drill is used to make 18"-24" holes in bedrock used to set rebar that assists in anchoring the bridge. Bridging the Gap Africa previously supplied an expensive electric powered hammer drill to complete this stage of the bridge building process. Due to the remote construction locations, electric power and generators are not readily available. This situation requires that Bridging the Gap Africa supply an electric generator and gasoline to support the electric drill. Unfortunately, these electric drills and generators have become targets of theft in the poverty stricken areas that the organization provides assistance to.To remedy these issues, Bridging the Gap Africa determined a manual rock drill would be necessary. However, manual rock drills of the type required by the customer are not available on the market, and the few that do exist are rare and poorly documented antiques. Bridging the Gap Africa sought the assistance of Rochester Institute of Technology, and our senior design team was tasked with the design and construction of a manual rock drill. The purpose of this rock drill is to fulfill the function of an electric powered drill, but without the need to transport expensive and cumbersome electric powered equipment, gasoline and generators. Our team used specific customer requirements and a $1000 budget to research, design, prototype, and manufacture a manually powered rock drill for use by the customer. process182943564135Customer Requirements:Figure SEQ Figure \* ARABIC 3: Customer RequirementsThe first step in the process was gathering the customer requirements. Figure 3 details each specific requirement from the customer, and the importance of each requirement was noted. The categories of “convenient” were considered qualitative, whereas the categories of “cost,” “durable,” “functional,” and “portable” were considered quantitative. A priority rating was assigned to each requirement, indicating the importance of meeting that requirement. Requirements with a priority value of 9 are high priority, and requirements with a priority of 3 were lower priority. The listed requirements below were those set initially by the customer. One requirement, that the hole be 1" in diameter, was amended at a later date to allow for holes that are only 3/4" in diameter.Engineering Requirements:The engineering requirements followed a similar process, using the same rating system. All engineering requirements were quantitative. Marginal and ideal values for specific drill details were sourced from an electric hammer drill similar to the one used by Bridging the Gap Africa. (figure 4). Other values, such as component weight, were provided to our project team by Bridging the Gap AfricaFigure 4: Engineering Requirements185356564135Functional Decomposition:A functional decomposition (figure 5) was constructed to determine which functions the drill needed to accomplish and to assist our team in the design process. The three key functions were determined to be breaking the rock up, removing the rock powder from the impact site, and ensuring the drill point remains on target and stable.Figure 5: Functional Decomposition TECHNICAL FEASIBILITYConcept Development and Concept Selection:To assist in the development of design ideas to prototype, a chart of all possible concept designs was developed (figure 6). These were compiled from similar, antique manual rock drill designs found on YouTube. Viable combinations of various features were listed in a Pugh Chart (figure 7). This Pugh Chart was used to compare combinations of various features determined by our team to be realistic. The goal of this exercise was to establish a starting design with which we could continue to build on. Factors such as cost, level of complexity, ease of use, number of parts, serviceability, system integration, ease of obtaining parts, reliability, magnitude of force delivered vs. input, and weight were generated from our customer and engineering requirements. A “datum” combination of features was used to assign a rating in each of the listed factors. An “+” was assigned when a design was theorized to perform better than the datum, a “-“ for a poorer performing design, and an “s” for a design that is likely to perform equally.The result of this exercise was a tie between the two designs using a camshaft, with one using a ratchet and pawl, and the other using a worm gear. To determine which project we should select, we contacted Rochester Institute of Technology professor William Humphrey for advice on which of the two would be preferable to index the drill bit. William Humphrey was recommended to us by our project guide due to his accomplishments and expertise in mechanical engineering. He suggested that we use a Geneva gear instead of a ratchet and pawl or a worm gear, and explained to us that it would perform substantially better than either of the two other designs on the metrics of reliability, level of complexity and system integration. It was apparent from his explanation that the Geneva gear would be the best approach to index the drill bit, and he agreed with our team’s selection of a camshaft 3081655675005and drill for the purpose of supplying vertical force to hammer the drill bit.Figure 6: Chart of Potential Design FeaturesFigure 7: Pugh Chart -57594590805Theoretical Calculations:23526750At this point, it was decided that our team needed to calculate the time to drill a hole and the impact force of the drill striking the rock. We also calculated the number of Geneva gear slots that were needed. Using equations based off RPM and BPM of the drill, as well as impact energy, it was determined the optimal design would be one which required approximately 3.43lbs of input force. It was found that the drill should drill one 18" hole every 9.8 hours. Finally, it was determined that 14 Geneva gear slots were needed to maintain an index angle of 25.7 degrees, which was acceptable based on previous research. These determinations were made with considerations into the path the pin takes when entering and exiting the slots of the Geneva gear. It was paramount that the pin would index the gear smoothly. If these calculations were incorrect, then the gear would not work.Figure 8 SEQ Figure \* ARABIC : Governing Equations for SimulationDesign Process and Technical Challenges:Due to the lack of existing devices with which to base the design of our drill, the design process required many changes and revisions along the way. Our project team used a six step problem solving process to identify the problem, analyze the problem, generate potential solutions, implement those solutions and conclude by evaluating our solution (figure 9). Problems were classified as either critical, major or ordinary in decreasing order of severity. Fortunately, our project team experienced no critical issues and only three major issues. The rest of the issues were ordinary, and resolutions to these problems were simple. One major issue was that the "water jet" cutter was non-operational and awaiting repairs. Our project team was given a vague, but substantial estimate for when it would be running again. Fortunately, the machine was fixed in only a matter of days, and our team was able to use the machine to cut our Geneva gear. A second major issue was that the bipod design was unstable. Fortunately, this was corrected by the use of a base stand constructed out of 80/20 material. The 80/20 base allows the operator to stand on the base and provide additional stability. In the evaluation of our final, implemented base it was found that a minor wobbling issue was present on the vertical pole on which the drill housing is mounted. This was quickly corrected by the addition of an extra support beam. The final major issue was that hypothesized to be caused by the cams, and then the subsequent implementation of problematic cams. The cams prevented a consistent crank, and there was too steep a buildup and drop off when the hammer dropped. This was corrected by designing a new cam with a more gradual buildup and a smaller drop off, providing for a more consistent and ergonomic crank.469901350645Other than resolving issues, much of our design process revolved around the integration of the subsystems inside the drill housing. Although the Pugh Chart assisted us heavily in determining which features to use, it was also necessary to purchase and design our drill housing to accommodate support components that facilitated the function of these features. For example, a crank shaft required handles to operate and bearings on which to rotate. This was accomplished by our team through the use of a CAD model and drawing printouts (figures 10, 11, and 12). As our team noticed the need for a support feature or a minor design change, we would mark it on a printout of the CAD model and have it updated digitally by one of our mechanical engineers. Although this approach may not work for a more complex project, each of our team members possessed the capacity and detailed knowledge of our project that this approach was very successful in allowing rapid and beneficial design modifications. Figure 9 SEQ Figure \* ARABIC : Problem Tracking and ManagementEngineering Drawings:The engineering drawings were created using Solidworks [4].3249930228609715552070 Figure 11: Final Cam DesignFigure 10: Geneva Gear3956685130175Financial Feasibility:Throughout the design process a bill of materials was constantly updated. The $1,000 budget constraint caused our team to be resourceful, sourcing much of our aluminum and steel material from scrap bins in the RIT Brinkman Lab. All of our 80/20 material used in the construction of the base was also sourced from the scrap bin of the RIT Brinkman Lab. These were important finds, and saved our team hundreds of dollars. The most expensive expenditures our team needed to make include the bevel gears (2 x $64.91) the drill chuck ($55) and the rail mount and brake for attaching the 80/20 to the drill housing ($90.52). Additionally, $75.12 was spent on twelve corner brackets needed to construct the base out of 80/20. These expensive, but necessary, expenditures are the reason our team required a $500 budget increase from the initial $500 price point. The total amount spent by our team was $1001.73, very close to the budgeted amount. However, this total would not have been met without finding substantial amounts of free scrap metal early in the project lifespan.Construction:Figure 12: Final Assembly DrawingDrill Housing:The drill was built by our team with the help of the machinists employed by the Brinkman Lab. The first step of construction was to build the drill housing. The drill housing is made out of 3/8" thick aluminum. The sides and shelves were measured and cut on a bandsaw. Holes for placement of the axles, drill bit, bearings, etc were cut using a vertical end mill. Steel bar stock was used for the cam shaft and vertical axle and was machined to a polished finish using a lathe. The aluminum parts were fit together using clamps with the cam shaft and vertical axle inserted as a means to stabilize and ensure a proper fit. The welding was performed by a Brinkman Lab employee under our team's direct supervision.Impact Force Subsystem:The cams were cut using a water jet cutter. The cams are made out of steel and are 3/8" thick. Due to the specialized nature of the water jet, and the training required to use it, CAD drawings were submitted to the Brinkman Lab and the cutting operation was performed by Brinkman Lab employees. The camshaft was cut on a lathe and key slots for attaching the cams were cut using a vertical mill. A vertical mill was also used to cut the matching key slots into the cams. The handles used to power the drill were purchased, but modified by our team to allow for the use of a quick release pin, allowing faster assembly and disassembly. The end cap for the hammering mechanism is made of hardened steel, and was manufactured using a CNC machine. It attaches via an external thread and a pin, which were also cut using a CNC machine.Indexing Subsystem:Both the driven and drive wheels of the Geneva gear were cut on a water jet cutter. The wheels are made out of steel and are 3/8" thick. CAD drawings were submitted to the Brinkman Lab and the cutting operation was performed by Brinkman Lab employees. The pin is made of copper and was cut to size with a bandsaw and sanded using a belt sander. A press was used to permanently push the pin into the driven wheel of the Geneva gear.Support Structure (base) : The base is made of 80/20 material. Parts were cut to length using a bandsaw and the base was constructed using screws and brackets made specifically for 80/20 material. The 80/20 bearing was installed onto the back of the drill housing by using a drill press to drill holes into the housing, and then using screws and nuts to ensure a secure but easy to disassemble fit.Testing:351917073025The primary test performed was accelerometer testing. We used an accelerometer attached to the impacting shaft to gather data to be used for analyzing the impact energy of the drill under the assumption that all the energy will be transferred to the drill-bit. The first data collected was the baseline of the drill without the added spring installed. The average velocity of the shaft was calculated by finding the area under the acceleration vs. time curve. This was then used to find kinetic energy of the shaft, which without a spring was calculated to 2.97J – a higher than expected value. The large peaks seen in the figures below come from the impacting of the shaft onto the 2nd shaft which is attached to the drill-bit. These peaks were determined to be the result of vibrations and impulse.3463290289560Figure 13: Spring Not InstalledThe 2nd set of accelerometer testing was performed with the spring on the shaft. Based on calculation results the total kinetic energy increased to 144.8J, with the shaft travelling at an average velocity of 12.51 m/s. These results are not the most accurate of nature, due to the large sampling rate of the accelerometer. The sampling rate was not small enough to gather the entire downward velocity of the shaft and spring – so at best these calculations are an estimate. The peaks seen in the data from the impact force indicate that the spring causes larger than initially predicted energies. This means that the realistic time to drill is most likely shorter than our initial calculations.Figure 14: Spring InstalleddiscussionThe performance of the drill appears to meet the most important customer design requirements. Beyond the testing done by the accelerometer, practical use of the drill has indicated that the drill is fully capable of drilling holes 18"-24" deep into hard bedrock, the primary engineering goal of this project. The three customer requirements related to convenience (qualitative requirements) were met. The drill only requires one person to operate, the set up of the drill from partial breakdown to functional drill takes only a few minutes, much shorter than the 30 minute allowance, and the drill is mostly field serviceable. Parts that are difficult to replace, such as the Geneva gear and cams, are made out of steel plate, ensuring that they will not be a point of failure. The drill arguably meets the goal of being "inexpensive" when necessary material costs are considered. Thorough online research was done to find the cheapest vendors of necessary components and materials. The $1000 budget was only surpassed by slightly under $2, and only because the shipping cost is not made available to our team until after the order is placed.The durability and reliability of the drill is very good and considerations were taken into account for the potential abuse the drill may take in a remote construction environment. The welded aluminum housing provides protection against drops, as evidenced by our own experiences moving the drill. The internal components are simple, and problems that may occur should be easily visible and correctable.The functional requirements given were that the hole be at least 3/4" in diameter, that the drill must be manually powered, that the drill be capable of drilling 18"-24" holes, that the drill be capable of drilling granite, and that the drill be stable on uneven surfaces. The drill meets the requirements that the hole be 3/4" due to the selection of a 3/4" drill bit. The drill is capable of drilling holes 18"-24" in depth due to the adjustable 80/20 bearing attached to the back of the drill housing. The drill is manually powered by two crank handles. The drill is likely capable of drilling through granite, but at a slower pace than our test materials, which include rock of unknown origin and a softer soapstone. The drill base is stable on uneven surfaces, but the drill housing has a slight wobble caused by the mounting design. This wobble is not a result of instability of the drill and does not pose a hazard to any operator using the drill.The final two customer requirements were that the drill be portable, with each component weighing under 50 lbs, and that the drill be easily transportable. Related to the weight restriction, the drill housing with all components installed weighs 56lb. This is easily reduced by the removal of some internal components. For example, the 80/20 mount is easily detached through the use of an Allen key. The handles are easily removed with quick release pins. The crank shaft can be removed by loosening the screws in the bearings, the screws in the cams, and removal of the machine keys pinning the cams. The 80/20 base weighs under 50lbs and does not require disassembly. However, it can be disassembled and reassembled through only the use of Allen keys. The portability of the drill is good, but not ideal. The customer presented portability to us as the ability to transport it by motorcycle. The drill housing should be simple to attach to a motorcycle, the 80/20 base may be possible to transport by motorcycle without disassembly, but it is likely that at least the mounting rod be removed. With the mounting rod removed, it should be very easy to transport by motorcycle.ConclusionOverall, our project team considers this project to be a success and our process was without any major issues. If future work were to be performed on this project, we would highly recommend that the future team familiarize themselves with the videos we used in our initial stages of idea generation. In relation to specific features, we would recommend that the implementation of ergonomic carrying handles be performed to optimize the portability of the drill. Organization of the assembly and disassembly into equally weighted kits that could be easily transported is also likely to be beneficial to the end user. Furthermore, considerations should be taken regarding the position of the drill in the late stages of drilling an 18"-24" hole, as it is likely that an operator would be required to kneel, potentially causing discomfort.ReferencesAdd youtube video links from 3 videosAdd solidworks and creo citationAdd Patent information (maybe?)consult team if they used any other sources that need including.AcknowledgmentsChris Leibfried – GuideArthur North – GuideWilliam Humphrey – Design Feedback and AdviceBridging the Gap Africa – CustomerThe Rochester Institute of Technology Brinkman Lab – Manufacturing Support ................
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