Development and Optimization of a Soft-Projectile Launcher Utilizing Mechanical Energy
Final Report
December 05, 2011
MAE 4980 Capstone Fall 2011
Michael Knoop / / 314.703.3936Aaron Wagner / / 573.289.7586
Table of Contents
Abstract
Introduction
Background Information
Motivation for project
Current Products
Current Product Data
Problem Definition
Objectives
Design Strategy
Designing an Initial Prototype
Defining Effectiveness
Concepts to Achieve Torqueing
Quality Function Deployment
Muzzle Velocity Analysis
Motor Speed Analysis
Initial Concept Model
Construction
Initial Prototype
First Iteration
Second Iteration
Barrel Iteration
Final Design
Failure Mode Effects Analysis
Analysis of Iteration
Analysis of Final Design
Conclusion
Future Work
Appendices
Appendix A. Highspeed (2000fps) Soft Projectile Launcher Angle Test, 0 Degrees per Wheel
Appendix B. Highspeed (2000fps) Soft Projectile Launcher Angle Test, 2 Degrees per Wheel
Appendix C. Highspeed (2000fps) Soft Projectile Launcher Angle Test, 4 Degrees per Wheel
Appendix D. Highspeed (2000fps) Soft Projectile Launcher Angle Test, 6 Degrees per Wheel
Appendix E. Highspeed (2000fps) Soft Projectile Launcher Angle Test, 8 Degrees per Wheel
Appendix F. Highspeed (2000fps) Soft Projectile Launcher Fishtailing Downrange
Appendix G. Highspeed (2000fps) Nerf Longshot No Rotation Verification
Appendix H. Highspeed (2000fps) Power-increased Nerf Longshot Velocity Test (29 m/s)
Appendix I. Highspeed (2000fps) Soft Projectile Launcher, 0 Degree, Velocity Test (28 m/s)
Appendix J. Highspeed (2000fps) Soft Projectile Launcher, 6 Degree, Velocity Test (25 m/s)
Appendix K. Tabular Data of Meas. of Failure and Rotational Speed when Varying Wheel Angle
Appendix L. Tabular Data of Wheel Distance vs. Dart Travelled Distance
Appendix M. Final Design With vs. Without Dart Rotation
Appendix N. Failure Mode Effects Analysis
Appendix O: Longshot Test Results
Abstract
This 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.
Introduction
Soft 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 project
Motivation 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.1: Type of Nerf Dart (Streamline) Used in this Group's Research
Other 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 Products
There 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 Data
To 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 Table3 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 Table4 of appendix O.
Problem Definition
Traditional 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.
Objectives
The 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 Strategy
This 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 Prototype
Defining Effectiveness
A clear definition of effectiveness is required so that prototypes can be compared with actual SPLs. Three concepts combined define effectiveness:
- Distance
- Shot Grouping
- Consistency 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 Torqueing
This 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 Deployment
Cost of Manufacture / RPM of Soft Projectile / Distance Traveled / Shot Grouping / Weight of soft projectile / Non Custom Parts / Mass of System / Muzzle Velocity / Current Competitors / Customer Importance / Improvement RatioIncreased Effective Range / 9 / 9 / 9 / 9 / 3 / 5 / 1.7
Safety / 9 / 6 / 4 / 4 / 1
Cost / 9 / 9 / 4 / 4 / 1
Weight / 1 / 9 / 3 / 3 / 1
Durability of System / 1 / 3 / 3 / 3 / 1
Absolute Importance / 39 / 45 / 45 / 45 / 39 / 45 / 27 / 69 / 354
Relative Importance / 11 / 13 / 13 / 13 / 11 / 13 / 8 / 19
Current Competitors / 5 / 1 / 2 / 2 / 5 / 5 / 4 / 2
Technical Difficulty / 5 / 3 / 3 / 4 / 5 / 5 / 5 / 4
Target Value / a / 7.7* / b / 40
Units / $ / RPM / m / cm / m/s
Notes
a / Less than $200
b / 22.6±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 Deployment
Based 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 Analysis
Muzzle 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 Audacity
A power-increased Nerf Longshot is measured and found to have a muzzle velocity of approximately 30 m/s.
Motor Speed Analysis
Recall 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 Flywheel
Velocity can be determined from angular velocity and radius .