Abstract - Mike Knoop



Development and Optimization of a Soft-Projectile Launcher Utilizing Mechanical EnergyFinal ReportDecember 05, 2011MAE 4980 Capstone Fall 2011Michael Knoopmwktgc@mail.missouri.edu314.703.3936Aaron Wagneraswwv5@mail.missouri.edu573.289.7586Table of Contents TOC \o "1-3" \h \z \u Abstract PAGEREF _Toc310506566 \h 4Introduction PAGEREF _Toc310506567 \h 5Background Information PAGEREF _Toc310506568 \h 5Motivation for project PAGEREF _Toc310506569 \h 5Current Products PAGEREF _Toc310506570 \h 6Current Product Data PAGEREF _Toc310506571 \h 6Problem Definition PAGEREF _Toc310506572 \h 7Objectives PAGEREF _Toc310506573 \h 7Design Strategy PAGEREF _Toc310506574 \h 8Designing an Initial Prototype PAGEREF _Toc310506575 \h 8Defining Effectiveness PAGEREF _Toc310506576 \h 8Concepts to Achieve Torqueing PAGEREF _Toc310506577 \h 8Quality Function Deployment PAGEREF _Toc310506578 \h 9Muzzle Velocity Analysis PAGEREF _Toc310506579 \h 10Motor Speed Analysis PAGEREF _Toc310506580 \h 10Initial Concept Model PAGEREF _Toc310506581 \h 12Construction PAGEREF _Toc310506582 \h 15Initial Prototype PAGEREF _Toc310506583 \h 15First Iteration PAGEREF _Toc310506584 \h 16Second Iteration PAGEREF _Toc310506585 \h 17Barrel Iteration PAGEREF _Toc310506586 \h 19Final Design PAGEREF _Toc310506587 \h 20Failure Mode Effects Analysis PAGEREF _Toc310506588 \h 20Analysis of Iteration PAGEREF _Toc310506589 \h 21Analysis of Final Design PAGEREF _Toc310506590 \h 24Conclusion PAGEREF _Toc310506591 \h 25Future Work PAGEREF _Toc310506592 \h 25Appendices PAGEREF _Toc310506593 \h 26Appendix A. Highspeed (2000fps) Soft Projectile Launcher Angle Test, 0 Degrees per Wheel PAGEREF _Toc310506594 \h 26Appendix B. Highspeed (2000fps) Soft Projectile Launcher Angle Test, 2 Degrees per Wheel PAGEREF _Toc310506595 \h 27Appendix C. Highspeed (2000fps) Soft Projectile Launcher Angle Test, 4 Degrees per Wheel PAGEREF _Toc310506596 \h 28Appendix D. Highspeed (2000fps) Soft Projectile Launcher Angle Test, 6 Degrees per Wheel PAGEREF _Toc310506597 \h 29Appendix E. Highspeed (2000fps) Soft Projectile Launcher Angle Test, 8 Degrees per Wheel PAGEREF _Toc310506598 \h 30Appendix F. Highspeed (2000fps) Soft Projectile Launcher Fishtailing Downrange PAGEREF _Toc310506599 \h 31Appendix G. Highspeed (2000fps) Nerf Longshot No Rotation Verification PAGEREF _Toc310506600 \h 32Appendix H. Highspeed (2000fps) Power-increased Nerf Longshot Velocity Test (29 m/s) PAGEREF _Toc310506601 \h 33Appendix I. Highspeed (2000fps) Soft Projectile Launcher, 0 Degree, Velocity Test (28 m/s) PAGEREF _Toc310506602 \h 34Appendix J. Highspeed (2000fps) Soft Projectile Launcher, 6 Degree, Velocity Test (25 m/s) PAGEREF _Toc310506603 \h 35Appendix K. Tabular Data of Meas. of Failure and Rotational Speed when Varying Wheel Angle PAGEREF _Toc310506604 \h 36Appendix L. Tabular Data of Wheel Distance vs. Dart Travelled Distance PAGEREF _Toc310506605 \h 37Appendix M. Final Design With vs. Without Dart Rotation PAGEREF _Toc310506606 \h 38Appendix N. Failure Mode Effects Analysis PAGEREF _Toc310506607 \h 39Appendix O: Longshot Test Results PAGEREF _Toc310506608 \h 40AbstractThis capstone group seeks to improve a soft projectile launcher (SPL) by adding rotation to the projectile. Traditional SPLs do not rotate the projectiles. A Nerf Longshot is used as a comparison SPL. Nerf darts are used as the projectiles. This group proposes a mechanical method to impart torque using flywheels inset into the barrel of the SPL. An iterative design approach is taken to investigate the problem domain and find an optimal design configuration. To deal when the open ended nature of the problem, several design iterations were necessary to create a working prototype. Design parameters include flywheel angle and flywheel distance apart. This group finds that flywheels set at 4 degree angles each (8 degrees total) and a wheel distance spacing of 0.35 in. is optimal. With these parameters, average shot distance is increased by 4.6 ft. (+14%) and the standard deviation is decreased by 2.3 ft. (-40%). The most surprising result is that darts with higher rotational speeds are less able to self-correct due to centerline misalignments. Thus, lower rotational speeds (less than 1500 RPM) are desired when torqueing Nerf darts.IntroductionSoft projectile launchers (SPLs, also known as foam dart launchers) are currently extremely popular with certain groups of college students. However, one serious flaw that exists for commercially available products is their lack of power. To get around this issue, many owners modify their devices at home to increase the velocity at which darts can be launched. Unfortunately, this leads to another problem. As power is increased, the accuracy of the launcher suffers significantly. This report details the design process which was followed as well as the results obtained while attempting to resolve the loss of accuracy issue. Background Information Motivation for projectMotivation for the project primarily came from this group’s background experience with the group MU Humans vs. Zombies. This campus group is responsible for running a week long, 24/7 game of moderated tag commonly played on college campuses. A group of human players attempts to survive a “zombie outbreak” by outsmarting a growing group of zombie players. Human players protect themselves by shooting zombies with Nerf darts or socks. Many players modify their Nerf guns to get as much power out of them as possible. Stronger springs, removal of air restrictor systems, and reinforcement of the plastic shell with metal parts are all commonplace. The most common issue encountered when completing these types of modifications is the extreme loss in accuracy experienced as a result of the increased power that the blaster produces and applies to a lightweight foam dart. The easiest way to minimize this issue is to also modify the darts themselves, by adding fishing weights or BBs to increase the weight of the dart. While this is an effective method of stabilizing the dart and improving the accuracy of modified blasters, it also introduces an important safety issue. Heavy darts flying at high speeds can lead to painful bruises and potentially permanent damage if the dart was to make contact in a critical location (eyes, etc.). Because of this safety issue, most moderation teams choose to ban modified darts, and the penalties for ignoring such rules is severe. Based on the safety issue discussed, this group wanted to explore other potential methods of improving blaster accuracy which would not pose an increased safety risk for players.Fig. SEQ Figure \* ARABIC 1: Type of Nerf Dart (Streamline) Used in this Group's ResearchOther potential benefits of finding a way to improve accuracy while maintaining current safety standards also exist. If the current issue of loss of accuracy from increasing power can be solved, a new niche market could be opened up. The motivations for teenagers, college students, and young professionals, especially those who are involved in Humans vs. Zombies or Nerf wars, are obvious. Several risks, which are inherent with modifying a blaster at home, exist. Voidance of the product warranty, increasing chances for product failure and breakage, as well as loss of blaster function all must be accepted as possible results when modifying a blaster at home. Obviously, it would be much simpler to purchase a blaster which is already stronger and more accurate than current products without having to modify it yourself. If a solution can be created, a manufacturer could easily capitalize on this market which has not yet been opened up.Current ProductsThere are currently several different companies which manufacture and market soft projectile barrel systems. Perhaps the most well-known brand, Nerf, is owned by Hasbro. Under the Nerf brand, Hasbro sells a multitude of different foam dart launchers, ranging from small pistol like launchers to large rifle and machine gun styles. The other large producer of these types of toys is Buzz Bee Toys, Inc. While the visual styles of both companies’ products vary greatly, most of their designs use some sort of plunger system which pushes large amounts of air behind the dart, forcing it out of the barrel and downrange. Most of these launchers are designed for children and are not very powerful. One new design that Hasbro has begun to sell, the Vortex line, uses small foam discs rather than darts. While this line of products can achieve long distances because of the lift generated by the disc, the kinetic energy of the disc is extremely low. This results in a launcher that can shoot extremely far, but with little power behind the projectile. While some can find uses for this, it doesn’t achieve the requirements (power and distance) that an older user would desire. Electric powered launchers, such as the Nerf Stampede and Nerf Barricade, have also recently entered the market. These electric powered systems use small flywheels rather than plungers to propel the dart downrange. Out of the box, their performance is similar to air powered rifles. These electric Nerf launcher systems serve as some inspiration to the product team and will be further discussed in later sections. One final product currently available to consumers is homemade launcher systems. The easiest and most popular of these is simply a small PVC pipe, between 1 and 3 feet in length. The user puts the dart into the pipe, and then blows behind it, launching it out of the tube and down range. This device can be extremely accurate because of the long, tight barrel. They can also be very powerful, although the power of the launch is entirely dependent on the user. While this homemade Nerf launcher is cheap and simple to make, the rate of fire is slow and the actual performance will vary by user.While there are many products available on the market, no commercially available option currently exists for those looking for something that can shoot a foam dart a significant distance while maintaining power on impact. At the same time, although homemade blow guns can achieve significant distances with a high degree of accuracy, the rate of fire is slow, user experience can vary significantly, and they lack the excitement factor of using something that looks similar to a real gun. Current Product DataTo aid in comparison purposes between prototype designs and current products on the market, a modified Nerf “Longshot” was test fired numerous times to quantify the actual flight characteristics of current products. The Longshot is easily one of the most popular ever rifles created by Nerf because of the large power increases which could be attained through home modification. The project team chose to use a modified projectile launcher instead of a stock device because the power output to the dart more closely matched what the project team hoped to imitate with their design. Several tests were performed to quantify the performance of the Longshot. First, an effective range test was performed. The effective range of the launcher was defined to be a range at which the device could successfully land 5 out of 6 darts on target. While this definition may seem arbitrary, it is actually based on the standard clip size of 6 darts for the Nerf Longshot. To complete this test, the launcher fired darts at varying ranges at a 0.5 m wide by 0.8 m tall target (the size was designed to be a rough approximation for a chest-sized target) and the number of shots on target was recorded. The results of this test appear in Table 3 of appendix O. Based on the results of this test, the effective range of the Longshot is 4.5 m. A second test was then used to further quantify the performance of the launcher. The Longshot was held at the previously defined effective range (4.5 m), and more darts were fired at the target. Using chalk on the tip of each dart, the location of contact on target was marked, and the distance from center was recorded. These measurements were used to examine the accuracy of the launcher. Based on this test, the Longshot had a mean distance from center of 22.6 cm ± 12.3 cm. The actual data, as well as the trial means and standard deviations can be found in Table 4 of appendix O.Problem DefinitionTraditional hard-projectile barrels utilize rifling to impart torque; however, this is not practical for soft-projectiles because rifling slows the round too greatly due to friction. Several companies manufacture soft-projectile launchers including Hasbro and Buzz Bee. Soft-projectile launchers are often powered by air or mechanical springs. Additionally, advanced users often modify these launchers to increase their power (effective range) by upgrading the air capacity or springs. Unfortunately, over-powered launchers suffer a severe accuracy decrease past a certain power increase. The goal of this research was to identify and implement a possible method to maintain accuracy as power was increased. More specifically, the project team explored the possibility of adding torque to a dart and examined if that addition would improve the launchers accuracy.ObjectivesThe project team hoped to create a solution which would allow soft projectiles to be launched at higher velocities while maintaining or improving the accuracy of the launcher as power was increased.Design StrategyThis group takes an iterative design approach to eventually arrive at an optimal design. Many of the design iterations are investigative in nature. Every iteration (including the initial prototype) is conceptualized based on hypotheses. At a high level, the goal is to generically improve an existing SPL. This group’s primary hypothesis is that rotation of the soft projectile will improve aerodynamic flight properties. To repeat, it is not known currently whether rotation significantly improves soft profile effectiveness. Additionally, this hypothesis makes the assumption that existing SPLs do not impart torque. To verify this hypothesis, a mock SPL will be developed to simplify analysis and ensure outside influencing factors of existing SPLs are reduced. If soft projectile rotation can be shown to significantly improve effectiveness, it is a simple design effort to port the soft projectile torqueing system to an existing (or new) SPL.Designing an Initial PrototypeDefining EffectivenessA clear definition of effectiveness is required so that prototypes can be compared with actual SPLs. Three concepts combined define effectiveness:DistanceShot GroupingConsistency of (a) and (b)Increasing consistency is the primary goal of this group. Existing power-increased SPLs are extremely inconsistent leading to shots not hitting on target.Concepts to Achieve TorqueingThis group has two concepts to impart torque on a soft projectile round in barrel. The first concept consists of a set of flywheels offset at an angle will mechanically torque the rounds as they pass by. An alternative second design uses an air vortex in barrel. Since many existing SPLs use forced air, it makes sense to continue to use the same energy source.This group chooses to use mechanical flywheels for simplicity in design, construction, analysis, and because this group is primarily concerned with measuring the effectiveness of rotating soft projectiles (not which torqueing method imparts the most rotation).Quality Function DeploymentCost of ManufactureRPM of Soft ProjectileDistance TraveledShot GroupingWeight of soft projectileNon Custom PartsMass of SystemMuzzle VelocityCurrent CompetitorsCustomer ImportanceImprovement RatioIncreased Effective Range?999???9351.7Safety????9??6441Cost9????9??441Weight????1?9?331Durability of System1????3??331Absolute Importance3945454539452769354Relative Importance111313131113819Current Competitors51225542Technical Difficulty53345554Target Valuea?7.7*b???40Units$RPMmcm???m/sNotesaLess than $200b22.6±12.3*This value is expected to change once adjustments are made to account for improvements resulting from the copper breach.Fig. 2. Quality Function DeploymentBased on the QFD analysis performed in Fig. 2, the most important customer requirement is a significant increase in effective range. Current competitors, such as Hasbro and Buzz Bee, rank highly in safety and low cost, but are lacking in a large effective range. It is also important to the customer that total expenditures into this project remain within the initial budget. RPM of the projectile, shot grouping, weight of the soft projectile and muzzle velocity all have strong correlations to the effective range. However, increasing muzzle velocity or weight of the projectile decrease the safety of the system when in use. Muzzle velocity ranked highest in relative importance, with the other factors involved in effective range followed closely behind. Because the team does not plan on modifying the soft projectile itself, the weight of the projectile is not currently significant. The total mass of the system ranked lowest because the team hopes to have a prototype system completed which demonstrates the validity of adding torque to the projectile, rather than a system that can be used in production.Muzzle Velocity AnalysisMuzzle velocity is the biggest factor in soft-projectile inaccuracy. At low velocities (less than 5 m/s) projectiles do not have enough kinetic energy to travel a significant distance. Thus, accuracy is unimportant at low velocities. Mocking a real SPL is a design philosophy so a designed launcher muzzle velocity should closely approximate its real life counterpart. To do this, muzzle velocity of a real SPL must be determined. A clever strategy was developed to measure muzzle velocity because this group did not have immediate access to a high speed camera.The strategy entails firing at a hard target at a known distance. The entire shot is recorded and then analyzed in a sound editor (such as Audacity). The exact time between shot fired and shot hitting target can be seen as two separate peaks in the waveform. See Fig. 3 for an example of this analysis. Velocity can be determined by dividing known distance of target with measured time. Note this is technically an average velocity, not muzzle velocity. Reduce the target distance to approximate true muzzle velocity closer. However, the shot fired and shot hitting target waveforms become indistinguishable at a certain minimum range.Fig. 3: Sample Recorded Soundtrack in AudacityA power-increased Nerf Longshot is measured and found to have a muzzle velocity of approximately 30 m/s.Motor Speed AnalysisRecall this group intends to use flywheels to accelerate the projectile. Once muzzle velocity is determined, one can perform a simple analysis to determine the rotational speed of various sized wheels which match the measured muzzle velocity. Consider the force diagram in Fig. 3 of a simple flywheel.Fig. 4: Simple Force Diagram of FlywheelVelocity Vt can be determined from angular velocity ω and radius r.Vt= ω?r(1)Of course, solving for angular velocity is more relevant.ω= Vtr(2)Finally, revolutions per minute, RPM, can be calculated from dimensional analysis.RPM= revmin= 1 min60 sec= 2π rad1 rev (3)From Equations (1-3) this group finds that a motor speed of 7500 RPM is required with a wheel radius of 1.5 inches. The largest available wheel has a diameter of 3 inches with a loaded RPM of 7500 RPM so it is chosen for the design. With these parameters in hand, an initial prototype concept can be modeled.Initial Concept ModelThis group looked to existing solutions for mechanically adding torque using flywheels. A football launcher, shown in Fig. 5, is a common system which imparts torque using large motorized flywheels. This group uses the design of a football launcher for the initial concept model.Fig. 5: Football LauncherTwo flywheels (properties calculated in the motor speed analysis) inset into a copper pipe serve to accelerate the projectile down the barrel. Recall this set of flywheels only serves to mock an existing SPL. Another forward set of flywheels serve to mechanically impart torque. The torqueing apparatus is the system of interest to this group. The initial prototype model is shown in Fig. 6 and a close-up of the torqueing system is shown in Fig. 7.Fig. 6: Initial Prototype Design ModelFig. 7: Close-Up of Torqueing SystemThere are four major components of the initial design shown in Fig. 6, base, bore, propulsion, and torqueing.BASEThe base is a simple wooden board to which all other parts are affixed. The base is the largest component which would not exist in an actual soft-projectile launcher. The base is for assembly convenience and allows for different bore and flywheel configurations to be tested. Each flywheel-motor-system is not rigidly fixed to the base. They are given 1 degree of freedom normal barrel to the distance between the wheels inside the bore can be adjusted.BOREThe bore is a ?” copper barrel which mocks the bore found in a traditional soft-projectile launcher.PROPULSIONTraditionally, soft-projectile launchers use air-pressure to accelerate the projectile. Some other models use mechanical flywheels to do the same. The mocked propulsion system will use a set of two flywheels driven by electric motors to accelerate the projectile to the same velocity found in the air-powered soft-projectile launchers. It is important to note the mocked propulsion system is not the system which imparts torque. The propulsion system only imparts forward velocity.TORQUINGThe torqueing system is not a mock system, that is, it does not replicate a feature found in traditional soft-projectile launchers. The torqueing system is this group’s novel method to improving the effective range of the mock SPL (and by induction, the actual SPL). It is a set of two flywheels driven by electric motors set orthogonally (or at an angle) to the bore to impart torque on the projectile as it travels down the bore.Recall this is only the initial prototype. It is designed with the intention to assemble and then iterate the design to investigate the result of rotation on a soft projectile and determine the ease at which it could be integrated into an existing SPL.ConstructionInitial PrototypeConstruction of the first prototype began by creating the rear half of the barrel system. The two rear wheels were installed horizontally and aligned with the barrel. One challenging aspect of building the initial prototype was the difficulty in aligning the center of each wheel with the center of the barrel. This was primarily a result of the inaccuracies involved with constructing the prototype from hand cut wood parts. Figure 8 shows this group’s initial prototype build.Fig. 8. Initial Prototype BuildBefore attempting to cut the forward penetrations for the angled wheels, this group fired several test shots with poor results. The results of this test were disappointing. Almost all of the test shots failed to exit the barrel and in fact only traveled several inches past the flywheels. It was theorized that the flywheels positioned to either side of the breach allowed the dart to be pulled down by gravity, which caused the rubber tip of each dart to drag along the bottom surface of the barrel and negated the forward thrust imparted by the flywheels. The inaccuracies in wheel alignment only added to this problem. With one flywheel mounted slightly higher than the other, the wheels themselves were adding a downward force to the dart. In an attempt to discover how current flywheel systems avoid the friction problem, the team examined the Nerf Stampede, which uses flywheels to launch darts downrange. The Stampede relies on two small flywheels mounted above and below the barrel to fire each dart down a wide bore. In Fig. 9, the two flywheels can be seen to the left and right sides of the picture. The left side of the view corresponds to the top of the barrel.Fig. 9. Nerf Stampede Barrel View The large barrel diameter immediately after the flywheels minimizes the possibility of the rubber tip making contact with the barrel and getting jammed. To further test this hypothesis, the polarity of the motors installed on the prototype were reversed so that the dart could be launched out of the shorter end of the breach. This test resulted in most shots successfully exiting the barrel and traveling downrange. Based on these observations, the team slightly altered the first design. First Iteration The new design repositioned the rear flywheels directly above and below the barrel, mimicking the Nerf Stampede. It was expected that the vertical mounting would make it easier to align each wheel with the center of the barrel and if any misalignment did exist, the wheels would not force the dart down into the barrel.Fig. 10. Second PrototypeThe results of test firing with the 2nd design did show an improvement over the original. However, they were still not consistent enough to be able to add another set of wheels in the front. Using high speed camera footage, the same issue of the dart tip making contact with the barrel was evident. Second IterationSince the vertical mounting system did not result in a consistent shot, this group re-examined the football launching system and chose a simpler design. The teams’ next design used a short barrel which guided the dart into 2 angled flywheels. The 2 wheel system simultaneously launched the dart forward and imparted torque.Fig. 11. Third PrototypeThis design had several advantages over the previous two. First of all was the simplicity of it. Using a two-wheel system minimized the number of possible parts that could cause any kind of failure. Secondly, the short barrel, which only guided the dart into the fly wheels, made it impossible for the dart tip to make contact with anything after being grabbed by the wheels. This system also minimized the total size and weight of the design, which would be advantageous if it was used to design a new commercial blaster or added to an existing one.The test results were significantly improved for this prototype. Every dart successfully traveled downrange. However, some inconsistencies in flight still existed. By examining high-speed footage as the dart exited the flywheels, the project team was able to see that as the dart was ejected, the rotation applied by the wheels caused the tip of the dart to dip down while the tail end came up. To resolve this issue a new barrel design was created.Barrel IterationThe new barrel used thin top and bottom guides to keep the dart on track. Although this improved the consistency of the darts flight path, vibrations in the barrel still caused some darts to experience the upward tail movement at the exit point. Another barrel prototype with a thin band around the exit point was cut and tested. However, this barrel design resulted in some darts being sliced open by the sharp edges of the stabilizing ring. Finally, the second barrel design was modified by leaving more material on the top and bottom guides. The additional material stabilized the guides, eliminating the tail end up issue. Additionally, it didn’t destroy the darts because no sharp edges existed. This barrel design was chosen as the final prototype for the launcher. Fig. SEQ Figure \* ARABIC 12. Barrel IterationFinal DesignThe final design for the soft projectile launcher used a two flywheel system combined with a half inch copper tube which acted as a guide. The tube was cut open on either side to allow the flywheels access to the dart. Several views of the final design are in Fig. 13. Each flywheel could be rotated up to 10° from the neutral (horizontal) position, which allowed a maximum angle of 20° with the two wheels combined. Several tests were performed on the completed prototype: a distance test, a test examining the effect of spacing between the flywheels, and a test examining the effects of different configurations of angled position. The results and analysis of these experiments can be found in the analysis section.Fig. SEQ Figure \* ARABIC 13. Final DesignFailure Mode Effects Analysis Several possible failure modes were identified in this analysis. The three items analyzed were the motors, the battery packs, and the darts. The possible failure modes identified were a failure of a motor to start, the battery pack wiring to become disconnected, and for the darts to become worn. None of these possible occurrences received a high risk priority number (RPN). This was a result of the small severity of any failure mode occurring. If the device were to fail, there is no significant threat to human life or property. Damaged foam darts received a slightly higher rating because of the high likelihood of it eventually occurring. Although the severity rating for this occurrence was extremely low, the prototype would show a drop in performance levels. However, this is easily fixed by changing to new darts frequently. For the full FMEA table see Appendix N.Analysis of IterationThe largest surprise during the construction iteration phase was observed fishtailing (seen in Appendix F). This group concludes that fishtailing is a combination of two factors. First, imprecision in construction causes the centerline of rotation to skew the dart off center. The centerline of rotation is shown in Fig. 14. Fig. 14. Centerline of RotationThis centerline importance is backed up by use of the highspeed camera. Imprecision in wheel placement (caused by inexact measurements, drilling, and assembly) could be reconciled by using better machining processes and parts. The second, and more surprising result, is that significant dart rotation seems to cause instabilities resulting in fishtailing. Darts with higher rotational speeds are less able to self-correct due to centerline misalignments. The highspeed footage led us to suspect this and is confirmed by measurement. Appendices A-E show darts leaving the barrel at different wheel angles. The shots in Appendices A-C appear to be much less centered than those in Appendices D-E. However, the shots in Appendices A-C did not fishtail while those in Appendices D-E did fishtail. This is contrary to what one might guess based strictly on the highspeed footage. Appendix K shows a tabular summary of measurements taken from varying wheel angle.Passing (success) is defined as “no observed fishtailing” while failure is defined as “observed fishtailing”. Fig. 15 and Fig. 16 demonstrate the fishtailing versus rotation trend.Fig. SEQ Figure \* ARABIC 15. Success Rate vs. Total Wheel Angle (summation of both wheels)Fig. 16. Success Rate vs. Measured Dart Rotation SpeedThese results suggest that a smaller wheel angle is more desirable especially when using imprecise construction and assembly techniques (which is relevant because many SPL modifications are homemade). This group recommends a 4 degree angle per wheel resulting in 8 total degrees of angle. Darts will have a rotational speed of around 1900 RPM at barrel exit.Dart rotation is always measured at barrel exit. A highspeed shot downrange is used to verify that darts maintain their rotational speed in flight. Appendix F (which also demonstrated fishtailing) shows that darts do keep their rotational speed downrange.Recall that the final design allows for easy variation of the distance between each wheel, seen in Fig. 17. For this test, the wheels are set a zero degree angle. Tabular results can be found in Appendix L.Fig. SEQ Figure \* ARABIC 17. Definition of Wheel DistanceAgain, the results are plotted in Fig. 18. Based on the wheel distance test results, this group recommends a distance of 0.35 in. between the wheels.Fig. 18. Effect of Wheel Distance d on Dart Travelled DistanceAnalysis of Final DesignBased on the “Analysis of Iteration”, a final design is proposed with wheels set at 4 degree angles each (8 degrees total) and a wheel distance spacing of 0.35 in. This final design still needs to be compared to the original design with no rotation to identify the effect of dart rotation. Twenty shots are fired on each configuration (no rotation and with rotation) and the results are shown in Fig. 19. The raw tabular data is shown in Appendix M. Fig. 19 SEQ Figure \* ARABIC : Histogram of Final DesignThe angled configuration increased the average distance by 4.6 ft. (+14%) and decreased the standard 2.3 ft. (-40%). This indicates that on average, darts with 1900 RPM travel roughly 15% farther but more importantly, nearly double distance consistency. Darts with rotation take an expected ballistic trajectory to the ground while darts without rotation sometimes take a greater-than-ballistic trajectory or travel much farther but veer drastically off target.ConclusionThis group set out to improve a soft projectile launcher by mechanically imparting torque on the rounds. This goal is accomplished. This group recommends wheels set at 4 degree angles each (8 degrees total) and a wheel distance spacing of 0.35 in. The angled configuration increased the average shot distance by 4.6 ft. (+14%) and decreased the standard deviation 2.3 ft. (-40%). The most surprising result is that darts with higher rotational speeds are less able to self-correct due to centerline misalignments. Thus, lower rotational speeds (less than 1500 RPM) are desired when torqueing Nerf darts.Future WorkThis group has several recommendations for future work. This group used imprecise machining tools and assembly because of the rapid iteration required. However, with the above recommendations, a precise design could be machined and built. This should alleviate centerline issues. Nerf darts tend to wear quickly. They lose their rigidity quickly because they are made out of foam. The less rigid darts always performed worse (fishtailed more often) than their rigid counterparts. Further study is needed to identify a way to compensate for dart imperfections. The final design this group built is still a prototype and could not be easily integrated into an existing SPL. Future groups could look into minimizing the design and integrating it into the front of an existing SPL.AppendicesAppendix A. Highspeed (2000fps) Soft Projectile Launcher Angle Test, 0 Degrees per WheelFull video: /0deg.avi or . 20. Frame 599Fig. 21. Frame 600Fig. SEQ Figure \* ARABIC 22. Frame 601Fig. SEQ Figure \* ARABIC 23. Frame 602Appendix B. Highspeed (2000fps) Soft Projectile Launcher Angle Test, 2 Degrees per WheelFull video: /2deg.avi or . SEQ Figure \* ARABIC 24. Frame 164Fig. 25. Frame 166Fig. SEQ Figure \* ARABIC 26. Frame 168Fig. 27. Frame 170Appendix C. Highspeed (2000fps) Soft Projectile Launcher Angle Test, 4 Degrees per WheelFull video: /4deg.avi or . 28. Frame 302Fig. 29. Frame 304Fig. 30. Frame 306Fig. 31. Frame 308Appendix D. Highspeed (2000fps) Soft Projectile Launcher Angle Test, 6 Degrees per WheelFull video: /6deg.avi or . 32. Frame 489Fig. 33. Frame 490Fig. 34. Frame 491Fig. 35. Frame 492Appendix E. Highspeed (2000fps) Soft Projectile Launcher Angle Test, 8 Degrees per WheelFull video: /8deg.avi or . 36. Frame 209Fig. 37. Frame 210Fig. 38. Frame 211Fig. 39. Frame 212Appendix F. Highspeed (2000fps) Soft Projectile Launcher Fishtailing DownrangeFull video: /9.avi or . 40. Frame 1770Fig. 41. Frame 1783Fig. 42. Frame 1802Fig. 43. Frame 1872Appendix G. Highspeed (2000fps) Nerf Longshot No Rotation VerificationFull video: /6.avi or . 44. Frame 1096Fig. 45. Frame 1098Fig. 46. Frame 1100Fig. 47. Frame 1102Appendix H. Highspeed (2000fps) Power-increased Nerf Longshot Velocity Test (29 m/s)Full video: /7.avi or . 48. Frame 738Fig. 49. Frame 739Fig. 50. Frame 740Fig. 51. Frame 741Appendix I. Highspeed (2000fps) Soft Projectile Launcher, 0 Degree, Velocity Test (28 m/s)Full video: /11.avi or . 52. Frame 1811Fig. 53. Frame 1813Fig. 54. Frame 1815Fig. 55. Frame 1817Appendix J. Highspeed (2000fps) Soft Projectile Launcher, 6 Degree, Velocity Test (25 m/s)Full video: /8.avi or . 56. Frame 1150Fig. 57. Frame 1152Fig. 58. Frame 1154Fig. 59. Frame 1156Appendix K. Tabular Data of Meas. of Failure and Rotational Speed when Varying Wheel AngleTable K.1. Measurement of Failure and Rotational Speed when Varying Wheel AngleTrialPosition (Degrees)Total AngleDegrees)PassFailRPMPass RatePositionFail Rate?1 (Left)2 (Right)(Degrees)1000600100%00%2000603000601224601250100%40%222460322460144860187589%811%2448513448511661260375072%1228%266123336612421881633500039%1661%28816153881633Appendix L. Tabular Data of Wheel Distance vs. Dart Travelled DistanceTable L.1. Wheel Distance vs. Dart Travelled DistanceTrialDistance BetweenWheels, d (in)123Distance Travelled (ft)MeanStd. Dev.0.509968.01.70.46252425.524.80.80.423733.53635.51.80.38363636.536.20.30.3353374645.38.00.2939493842.06.1Appendix M. Final Design With vs. Without Dart RotationTable M. SEQ Table \* ARABIC 1Distance TestDataAdjusted (+25ft)0° Position8° Position0° Position8° Position4.331529.340.0121137.036.0514.530.039.541329.038.0314.528.039.5181243.037.013.51038.535.071432.039.07.5832.533.041029.035.081133.036.017.51042.535.059.530.034.587.533.032.57.511.532.536.51410.539.035.5610.531.035.5241824.043.0251425.039.0617.531.042.5Mean (ft)32.537.1Std. Dev. (ft)5.22.9Note: Barrel Height: 39 in. off ground, levelAppendix N. Failure Mode Effects AnalysisTable N. SEQ Table \* ARABIC 2Appendix O: Longshot Test ResultsTable O.1: Effective Range TestDistance from Target (m)7654.51 = hit10110 = miss11110111011100010001ResultFailFailFailPassTable O.2: Accuracy of LongshotTrialRange: 4.5m123456ShotDistance from Center (cm)136.519.0miss26.531.028.0220.040.06.514.57.538.0335.028.04.023.08.024.5414.522.07.541.538.532.5510.510.040.014.538.514.5611.56.529.525.5miss24.0Trial Mean21.320.917.524.324.726.9Trial Dev11.712.216.210.015.88.0Mean22.6Dev12.3 ................
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