Michael Antoine, Jack Connolly, Andrew Evans, Khalid Jebari. Intro to Engineering Design (ENGR 1500) Section 43. Ping Pong Ball Launcher.

Transcription

1 Michael Antoine, Jack Connolly, Andrew Evans, Khalid Jebari Intro to Engineering Design (ENGR 1500) Section 43 Ping Pong Ball Launcher Group 5 22 February 2017

2 1 Table of Contents Abstract Introduction Background Methodology Alternative Design Solutions Final Design Solution Raw Materials Fabricated Components Construction Procedure Record of Testing Recommendations Conclusion Peer Evaluations Bibliography Appendix Gantt Chart Meeting Notes Communication Sample CAD Drawings Base block Bat PVC Ramp Short support post Long support post PVC mounting blocks Hardstop block

3 2 Abstract The design challenge the group was tasked with was to launch a standard ping-pong ball ball over a 2 meter distance into a bucket. Bisecting the trajectory was a 1 meter wall. The group began by understanding the problem and physics behind this project. With a launch angle of 50 and a launch velocity of 3.8 m/s in mind, the group moved towards the engineering design process. After defining the problem, the group conducted more research on previous ball launchers and began to brainstorm what solutions could solve the problem. The designs were narrowed to four designs: a cannon, a ramp, a flywheel, and a bat design. Positive aspects of these designs were combined so a single solution was developed. The design included a bat to hit the ball up a PVC ramp using elastic bands as a source of energy. This design was prototyped such that the core functionality was proved to work and meet the specifications. Once the concept was proved, the final product was fabricated using wood (2x4), PVC, elastic bands, and screws. Preliminary testing was conducted and the final product was tweaked to fix these problems. On test day, the launcher failed due to several reasons: uncalibrated rubber bands, unexpected ball size, and too much ball spin and compression. The group took a risk with a unique design. Although it didn t perform as expected, the learning experience was well worth it. Introduction The aim of this ping pong ball launcher is to launch a ping pong ball over a two meter distance and ideally land it into a bucket 0.15m high and 0.3m wide and keep the ball inside the bucket. The launcher also needs to clear a one meter high plexiglass wall placed one meter away from the ping pong ball launcher (View figure 1 below). The launcher needs to be less than a meter high, use of explosives, firearms, hair dryers and chemical mixtures is also prohibited. The launcher must also be able to launch 25 balls within five minutes. With these constraints put aside, the group began to brainstorm ideas. Figure 1

4 3 Background The ping pong ball used for this project was a regulation ping pong ball. This ball meets the specifications of Table 1. Mass ( m ) Diameter ( d ) Coefficient of Restitution 1 ( C R ) 2.7 grams 40 mm Drag Coefficient ( C D ) 0.4 Terminal Velocity ( v t ) 8.8 m/s Table 1 1 This coefficient describes how high the ball will bounce of a surface relative to its starting position (refer to equation 1). Where h f = h i C R h f = Ensuing bounce height (m) h i = Initial drop height (m) C R = Coefficient of Restitution Equation 1 The motion of a ping pong ball can be simplified to projectile motion including air resistance as shown in Figure 2. The range of a ping pong ball in such motion can be analyzed with Equation 2. Figure 2

5 4 Where R = [v o v t cos(θ)] g R = range (m) v o = initial velocity v t = terminal velocity Θ = launch angle ( ) g = acceleration due to gravity (m/s 2 ). Equation 2 The range ( R ) of the ball is expected to be 2.15 meters. The edge of the bucket is 2 meters away and has a 0.3 meter diameter, therefore the target range was set as 2.15 meters. The group decided the launch angle ( Θ ) to be 50. A launch angle closer to 0 would provide a more horizontal trajectory, increasing the likelihood that a ball would remain inside the bucket when on target. However, a launch equal to or below 45 would be physically impossible because of the geometry of the bisecting wall and launch distance (see Figure 3). In other words, the projectile wouldn t clear the top of the wall. Figure 3 A launch angle of 50 was chosen because it would likely clear the wall even with the harsh air resistance. Using these values for range (R) and launch angle ( Θ ), Equation 2 can be solved to find the required launch velocity as shown in Equation 3. [ R g ] [ cos(θ) v t ] = v o Equation 3

6 5 Calculations: [2.15 m 9.8 m/s 2 ] [cos(50 ) 8.8 m/s] = v o v o = 3.72 m/s This launch velocity can be used to determine the amount of energy needed to be put into the ball. Using the ball s mass and launch velocity, the energy transferred into the ball can be calculated (see Equation 4). Calculations: ½ kg (3.72 m/s) 2 = E cannon potential E cannon potential = J 2 E cannon potential = E ball kinetic = ½ m v o Equation 4 After these calculations, it was noted that the ping pong ball did not need a huge amount of energy, but more importantly that it had the required velocity as it exits the launcher. Methodology In order to better understand the problem, the group looked at the task at hand from a very broad sense. The need was defined: We need to move a ping pong ball over a 1 meter wall into a bucket 2 meters away. With this in mind, the group was able to move forward and brainstorm several solutions to the problem. In order to gain inspiration for solutions, research was conducted to investigate previously constructed ping pong ball launchers. Other types of ball launchers (like a football passer) were researched. After the brainstorming session was done, the solutions that didn t meet the specifications of this project had to be filtered out. All ideas that used any of the prohibited methods or the solutions that would be less likely to be realized before the deadline were crossed off of the list. The solutions list was narrowed to four general designs mentioned in the section Alternative Designs : cannon, ramp, flywheel, and a bat design. As a group, the final design was developed as a combination of these designs. It would (in theory) provide all of the benefits of each design.

7 6 For the first prototype the group built an unrefined version of the final project. Using duct-tape and imperfect dimensions a prototype was put together within two lab periods. The prototype proved that the launcher was capable of meeting the requirements and also following the constraints. After testing the prototype it was clear that with some tweaks and precise measurements, a second more efficient launcher could be built, which would function more reliably. Testing was done in two places, the project lab and Jack s dorm room. A two meter distance was measured and tape was placed on the ground at 0m, 1m and 2m. 0m is where the launcher was placed and 2m was where a makeshift replica of the bucket was placed. At the 1m mark a string one meter off the ground was horizontally taped to 2 surfaces, the string represents the one meter high plexiglass wall that would be used during the actual test. The goal was to get the ball over the string and into the bucket. Each group member then took turns launching 25 ping pong balls, while another group member documented how many balls went into the bucket and stayed in it, how many balls went in then bounced out and how many balls missed the bucket. A table of this data can be found in the Record of Testing section. Alternative Solutions 1. Cannon The cannon idea utilizes a PVC tube with a spring at one end of the tube. Slits would be cut into the sides of the the PVC tube and a launching piece, made of cardboard or wood would be inserted into the tube. The launching piece would have handles that protrude out of the PVC tube, these handles would be used to pull the launching piece down the tube. The ball would sit on the launching piece and the launching piece would be pulled down against the spring and released at a certain angle. The launcher height would be adjustable,somehow. View design drawings in Figure 4 below for an idea of what the launcher would look like.

8 7 Figure 4 2.Ramp The Spring loaded-ramp solution consists of using a spring at the top of a slide to launch the ball. The spring would be inserted and glued to the end of the PVC tube and to the launching platform. The ball would be pushed inside and a trigger mechanism would be used to launch it. When the trigger is pulled, the spring would expand and push the ball down the slope to clear the obstacle and land in the bucket. Below (Figure 5) is a simplified drawing of the launcher. Figure 5

9 8 3. Flywheel After researching several types of ball launchers, a common design utilized one or two flywheels. For example, a football launcher has two flywheels, one horizontal to give the ball its trajectory, and one slightly offset to give the ball its spiral. See Figure 6. Figure 6 The other design using a flywheel only used one wheel. A concentric ramp around the wheel provides a track for a ball to roll along, and the wheel propels the ball around the track. At the end of the track, the ball is released. It is drawn below in Figure 7. Figure 7 A benefit of this design is its speed; we would have no problem shooting a ball every 12 seconds. Additionally, the ball s trajectory would likely be very consistent because the flywheel would remain at a constant speed (for the most part). However, there were some critical problems with this design. A ping pong ball is somewhat rigid, so compressing the ball the correct amount would be difficult. Additionally, the complexity of such a design would difficult to construct. Electronics would very likely be involved to spin the wheel. It would likely need a high variety of materials as wheel, including a pneumatic wheel, wood, motors (electronics), and bearings. For these reasons, it was decided that the flywheel design was not appropriate for this project.

10 9 4.Bat The final possible solution to come out of initial brainstorming sessions was a hammer or bat that strikes the ball while it sits at the end of a ramp or other aiming device. The shape of such a launcher is included in the whiteboard drawing below (see Figure 8). Energy is supplied to the hammer in any number of ways, including springs or rubber bands. Since this is rather simple mechanism, there is a great deal of freedom in how the rest of the launcher could be designed around this action. Some merits of this design are its simplicity and adjustable power. Drawbacks include lack of free aim and the difficulty of achieving the correct amount of energy to be transferred to the ball. Figure 8

11 10 Final Design Solution The final design is based off of features from a couple of the brainstormed ideas. The design s main source of putting the ball in motion is the bat style. Once the ball is contacted by the bat, it rides up a semi-cylindrical PVC ramp inspired by the cannon design. This overall mechanism can be seen in Figure 9. Figure 9 The bat has a complex shape (see CAD Drawing 2, Appendix pg 21). Its semicircular bottom and hole allows the bolt to slide through. This bolt provides the pivot point for the bat. The notch in the back provides a consistent place for the rubber bands. The slanted top and perpendicular bolt is perpendicular to the PVC track. In this way, the PVC bolt will hit the ball so it will be hit up the track at the correct angle. Because the bolt comes down and in on the ball, it gives the ball backspin. Backspin keeps the ball in the air longer which increases the range. The posts (see CAD Drawing 4 and 5, Appendix pgs 22-23) support the PVC rail (see CAD Drawing 3, Appendix pg 21). They are cut at a certain angle and length such that the PVC will lie at an angle that is 50 in reference to the ground. The PVC rail s diameter supported the balls used for testing. They slid inside the PVC when launched without much friction and the polyvinyl surface was fairly frictionless. The idea was to use to use rubber bands to convert Elastic Potential Energy to Kinetic Energy. By pulling the wooden block, the rubber bands stretch and Elastic Potential Energy is stored in them. Once released the energy stored transforms into kinetic energy and makes the block swing and hit the Ping-Pong ball making it travel through the PVC tube. The more rubber bands the farther the ball would travel.

12 11 Raw Materials Wood (2x4, 8 feet) PVC (1.5 in inner diameter, 1.9 outer diameter) Screws, bolts, nails 1/4-20 hex head bolt (4 in length) 1/4-20 nut 5/16-18 bolt (1in length) #7-16 round head wood screws (2.5 in length) (4x) #7-16 oval head wood screws (1 in length) (2x) 8d nails (1 in length) (2x) Masking tape Rubber bands Fabricated Components This list includes all of the fabricated components of the final design. Their CAD drawings are included in the appendix. 1. Base block (appendix pg. 19) 2. Bat (appendix pg. 20) 3. PVC Ramp (appendix pg. 21) 4. Short support post (appendix pg. 22) 5. Long support post (appendix pg. 23) 6. PVC mounting blocks (appendix pg. 24) 7. Hardstop block (appendix pg. 25) Construction Procedure 1) Cut the base to length directly off the raw 2x4 using a circular saw. Pre-drill holes to later mount the supports, drill the axle hole, and cut the notch for the hammer. 2) With a band saw, cut PVC pipe to length, then in half. Drill countersinks for mounting. Deburr edges to finish the ramp. 3) Cut supports to length from the 2x4 using a circular saw. Cut the tops to the correct angle using a bandsaw. Pre-drill holes for mounting the supports to the base. The finished supports can now be mounted to the base using 2.5 screws. 4) Drive one nail halfway into each side of the short support, centered and about 1 up from the bottom. 5) Cut PVC support blocks to length from 2x4 using a circular saw. Mark and cut the arc with a band saw. Sand curve to better fit PVC piece. Drill holes for mounting to the ramp and supports. 6) Cut the hammer blank to length from 2x4 using a circular saw, then to width and angle using a bandsaw. Drill the holes for the axle and bolt. Screw the 1 bolt into

13 12 the top so that the bolt head contacts the resting ball. Install hammer by lining up the holes drilled in the hammer and the base, putting the axle through the holes, and screwing the nut onto the bolt. 7) Clamp in place the support blocks and the ramp, then screw this assembly together using the pre-drilled holes. Make sure the screws in the bottom of the ramp are sunk sufficiently below the bottom of the ramp. 8) Create a ball stop by covering the bottom face of the ramp with masking tape, then covering any space the ball could come into contact with with masking tape stuck the other direction, to create a nonstick surface. 9) Screw stop block to front support. 10) Stretch rubber bands over both nails and around the hammer to supply tension. Record of Testing Preliminary Testing: To ensure the launcher was in working order and perform to an acceptable level, preliminary testing was recorded in a mock testing site. This also inadvertently gave insight into who would operate the launcher (Andrew). This tests are recorded below in Table 2. Group Member Scoring Types Jack Andrew Khalid Mike Trial 1 Trial 2 Trial 3 Trial 4 Out Bounce Out In Total Points Table 2

14 13 Final Data: The following table (Table 3) shows the data from the final data recording in class. Team # In (4 pts) Bounce Out (2 pts) Out (0 pts) Points Grade % [Pts High Score] 20 = Grade % [64 64] 20 = 20% [16 64] 20 = 5% [10 64] 20 = 3.1% [44 64] 20 = 13.8% [0 64] 20 = 0% [10 64] 20 = 3.1% Table 3 Recommendations Problem: Too much Backspin - What could have been done to fix this is to have the surface of contact between the Ping-Pong ball and bolt larger so that the ball is hit from the center. Hitting the ball slightly off its center is what gives it that spin motion and makes it fly off the desired trajectory. - Too much backspin also caused the ball to fly off the track (as opposed to sliding up it. A linear bat (instead of a rotating bat) could be a solution to this. Bands wearing out - Having rubber bands going from nails on the side of the block to the nails on the base instead of them going from one side to the other around the wooden block, would have helped make the rubber bands last more. Because the longer they stretch the faster they will wear out. -Removing the rubber bands while not in use would also suffice but if the system has to launch a significant amount of balls it s better to opt for bands of a material that has better elastic characteristics or even use a spring instead of elastic bands. Ball going out of track -Using a full PVC tube of the right size would also help guide the ping-pong ball so that it keeps a straight trajectory and doesn t fly sideways.

15 14 Conclusion The goal for this project was to design a device to repeatedly move a ping pong ball a distance of two meters and over a one meter wall. Although the goal was not met well on test-day, the group succeeded in practice and fully benefitted from the process of getting to this point. Most of all, the group learned how different small design flaws affected the final product in a negative way, and how prototyping and testing can help fix these shortcomings before they impact the final product. The group decided to take a risk on this project by trying a design that was not prevalent in research; it was a unique design. The group was able to learn a lot about organization and communication as well as the engineering design process. This project was a tremendous learning experience despite the seemingly unsatisfactory outcome. Peer Evaluations Team Member Contribution (%) Comments Signature Mike Antoine 25 Responsible and willing to help fabricate parts. Large part of brainstorming process. Jack Connolly 25 Great leader. Kept the group focused and on track. Andrew Evans 25 Skilled woodworker. Brought design ideas and fabrication methods to the team. Bought materials. Khalid Jebari 25 Sometimes quiet, however Khalid brought many good design ideas and solutions to the team. Hardworking and responsible. Bibliography Fitzpatrick, R. (2011, March 31). Projectile Motion with Air Resistance. Retrieved January 26, 2017, from

16 15 Football Passing Machine. (2017). Retrieved January 24, 2017, from Kuneth, T., Dr. (2014, July). The new plastic balls. Retrieved January 19, 2017, from Nagurka, M. (2003). Aerodynamics Effects in a Dropped Ping-Pong Ball Experiment. Retrieved January 24, 2017, from APPENDIX Gantt Chart (pg 16) This chart allowed us to plan our schedule to create the launcher and the report. It was followed well and almost every date was met perfectly (with exception of the final dates due to inclement weather. Meeting Notes (pg 17) This example shows what the group discussed in a meeting on January 26. In this meeting, the brainstormed ideas were narrowed and specifics were discussed in order to develop a better understanding of each design. Sample Communications (pg 18) The group decided that text messages were the most convenient option to communicate. In this group message, team members discussed where and when meetings would take place, and what would be discussed. On page 16, an example of such communication is included (as a screenshot from Jack s phone). The group met every Tuesday and Thursday at 5:00 PM. Meetings took place in the library or in a team member s dorm room. They lasted between 30 minutes and an hour. CAD Drawings (pg 19-25) These drawings include the dimensions required to recreate the launcher that was designed. 1. Base block (19) 2. Bat (20) 3. PVC Ramp (21) 4. Short support post (22) 5. Long support post (23) 6. PVC mounting blocks (24) 7. Hardstop block (25)

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