Frisbee Throwing Device by fjzhxb


									Frisbee Throwing Device
Final Report Submitted to The Faculty of Catapult LXIII Rose-Hulman Institute of Technology Terre Haute, Indiana

Group 6 Deanna Miller Andy Welsh Courtney Thomerson Isaac Wafzig University High School Heyworth, Illinois Oldenburg Academy Batesville, Indiana Lexington Catholic High School Versailles, Kentucky Terre Haute South Vigo High School Terre Haute, Indiana July 3, 2008


Introduction Frisbee throwing started in Connecticut with Yale students and a baker. William Frisbie’s pie pan proved easy to throw and light weight, the perfect combination for a Frisbee. After World War II plastic advancements made it possible to make the Frisbee what it is today (Lorenz, Ralph D. 2006). In order for a Frisbee to fly it must spin as it is propelled forward. This spinning motion is what allows the Frisbee to glide through the air and go great distances with relatively little force. The spin is the characteristic that sets the Frisbee apart from a sphere shaped ball. The historical problem with a Frisbee, however, is a person cannot play Frisbee with themselves as they can with a ball. The purpose of this project was to construct a device that would allow a person to play catch with themself. The goal of this device was to mimic the distance and speed that an average human throws a Frisbee. This distance was tested by all members of the group throwing four Frisbees each, and an average distance of 15 meters was found from this data. This distance became the goal distance for the device. In building the device it was also a goal to have it work on its own and have no need for human contact between throws. Method In the process of constructing a Frisbee throwing device many prototypes were designed. The designs were originally complex but became more simplistic as the design process continued. It was found that more complex and intricate designs proved impractical and unstable. The number of moving parts required to make the device had to be kept at a minimum to have a greater chance of success. The transition from complex to simple mainly focused on reducing the number of moving parts. Three main designs were debated before the final design was approved. The first design resembled a human arm and was very similar to clay pidgin thrower. It consisted of an PVC pipe, “arm” with a curved piece of metal “hand” at one end. This assembly was to be attached to a stationary point at the end opposite the hand. It was then to be spun around at a high speed and the Frisbee would be thrown from the arm. (Fig-1) The curved hand would give the Frisbee the desired spin to make it fly. This design was rejected because of the complexity of the reload system that would be needed in order to have the device reload a new Frisbee into the hand without human contact. Side View Arm Rotation Plan View

Figure 1-First design of Frisbee throwing device

6-2 The next design was very similar. In addition to a motor, a spring was used to propel the arm. (Fig.-2) The motor wound a string around the main shaft the arm was attached to. On the end of the string was a spring with one stationary end. As the string wound the spring was stretched. When the motor released the string the spring would recoil and cause the arm to swing and throw the Frisbee. However, the same problem of an overly complex reload system was found, and this design was also eliminated.

Figure 2-Side of second design The final design was much like a pitching machine (Fig.-3). It had two wheels spinning in opposite directions that were spaced the distance of a Frisbee apart. The Frisbee would be fed between the wheels and be propelled forward. If the speeds of the individual wheels were different then the Frisbee could spin as well as go forward. A Frisbee holder would be erected behind the device with a chain and hook to pull one Frisbee down to the machine at a time. This design became the final design because it had far fewer moving parts and was not very complex. Top View Wheel ↓ Front View


Figure 3- Final design of Frisbee throwing device A Frisbee catching device was also considered to remove any physical contact. This never got past the planning stages due to time constraints and unforeseen problems. The Frisbee catcher would have been a simple design involving a net or sheet that was set at a slight angle to catch the Frisbee and allow it to slide into the Frisbee container. Construction Construction began by building a basic model and then making small modifications as problems were found. The first problem encountered was that the Frisbees were twisting upon making contact with the wheels. The first attempt to solve this was to install a single rail made from

6-3 Plexiglas. However, this proved to be inconsistent. The rail was widened to a platform (Fig.-4) to improve stability and an additional platform was installed on top to further control the disk. A slot was cut in the middle for later installation of a guide system and cuts had to be made to accommodate the wheels and PVC supports.

Figure 4- Platform (2 ft x 1ft 2 in) Once these adjustments were made trials became more consistent and reliable. Another problem encountered that was unintentionally solved by the platforms was getting the Frisbees to make contact with both wheels at the same time. A third problem that presented itself was propelling the Frisbee the desired distance. This was solved by the addition of two bungee cords at the rear of the device to sling shoot the disk with the desired force. Additionally, one fan motor was upgraded to a weed whacker motor to help with both propulsion and spinning. The next step in construction was to find motors to spin the wheels. Two simple fan motors were chosen to power the device. Both motors were 120 volt motors that had three speed settings. Two 5.5 inch diameter lawn mower wheels were found, each weighing 370.8 grams. The frame from a box fan was used as the base for the device. A 1’x 3’ piece of plywood was cut and used as the base for the motors and wheels. Generic 10 inch diameter Frisbees were used to ensure consistency of the launch. Custom made axle extensions were fabricated to fit the wide diameter of the wheel axle holes to the narrow fan axles. The extensions were fixed on the motors with simple set screws. In order for the Frisbee to be propelled forward the wheels had to spin in opposite directions. This was achieved by simply turning one of the motors upside-down. The rig holding the upside-down motor was originally a piece of plastic from the original fan that supported the motor while pieces of plywood elevated the motor. For purposes of stability the rig was redone with a custom fit piece of wood supporting the motor and PVC piping to provide elevation. The new rig reduced the vibration of the motor. The newly designed rig was later changed with the arrival of the new electric line trimmer motor that was obtained and installed on the opposite side. The change to the rig was to return the upside down motor to right side up. This was necessary because the new weed whacker motor spun in a different direction than the fan motor. The new motor also was shaped differently than the previous one and required modification to the design to accommodate it. These modifications included drilling a hole in the board that the original motor was attached to. This was necessary because the new motor was slightly taller than the old motor and had to sit lower in order to be level with the second motor. The weed whacker motor was also lacking the screw holes that were conveniently located on the fan motor. This problem was solved by creating a vice like grip out of two pieces of plywood. Two holes were drilled in both pieces and bolts were driven through each with the fan motor in between this secured the motor and prevented it from spinning out of place. The pieces of plywood were then attached to the board with two angles mounted on one side to allow ease of adjustment of the vice that held the motor.

6-4 With the new position of the motor the device had to be turned around for the Frisbee to be thrown in the correct direction. This rendered the previously installed hinges useless. The angle of launch was still adjustable however by wedging scrap wood underneath the front end of the device. The new motor was also much more powerful. This caused the lawn mower wheel to spin much too fast, almost to the point where it would spin the tread off the axel. This was corrected by securing the rubber to the plastic inner part of the tire with duct tape. The torque produced by the weed whacker motor also presented a problem. The force of the motor caused the entire device to shake violently. This shaking was so dramatic that it caused the fan motor to stop running. The problem was partially resolved by creating a new axle to attach the wheel to the motor. The wheel was also grinded down to balance the spin. The weed whacker motor had benefits as well. It produced much more spin on the Frisbee due to the increased power. This is crucial to prolonged flight and the stability of the disk. The amount of spin the new motor produced was much greater than the fan motor and increased the potential output of the device. (See figure 5)

Figure 5 – Final Design Results Once the device was completed, testing began. The first test involved keeping the voltage on the trimmer motor constant while varying the voltage for the fan motor. The graph below shows the result of this test. The best result, 13.9 ft, was achieved when the motor was at 0 volts. The test at this voltage was the only one to generate spin on the Frisbee. This spin caused the Frisbee to be much more stable in flight, thus allowing it to fly further.


Figure 6- Fan motor voltage vs. distance The second test involved keeping the wheel attached to the fan motor in a fixed position while varying the trimmer motor voltage. The graph below shows the results of this test. The best result, 13.8 ft, was achieved when the motor was at 50 volts.


Figure 7-Trimmer motor voltage vs. Distance Through additional tests, the furthest distance thrown was approximately 23.5 feet. Given more time and more powerful motors a further distance would be well within reach. Overall, the concept was proven. The only problem was limited resources and time.

Analyses The results were obtained depended on four main factors, power of motors, difference in voltage, force propelling the Frisbee forward, and elimination of human error. The more powerful trimmer motor gave the Frisbee ideal spin to keep it in flight. A large difference between speeds of the motors also gave the Frisbee ideal spin. This spin caused the test to be more consistent and reliable. The bungee cord attachments gave substantial amounts of force that propelled the Frisbee forward. However, the bungee cords also created inconsistency in testing due to the human error in pulling them back and releasing them to launch. Over all the results obtained are in direct relation to the force propelling the Frisbee forward and the spin of the Frisbee once released.

Conclusion Throughout the course of the project several challenges were encountered that had to be overcome. The first was coming up with a practical design. In the beginning the design was much too complex for the experience level present in the group. After much debate a relatively

6-7 simple design was decided upon. Another problem that presented itself was getting enough power out of the motors to throw the Frisbee to the desired distance. This challenge was met first with installing bungee cords to the rear of the device to get the Frisbee moving faster. A larger motor was later installed to increase speed. Also the wheels were trimmed and unnecessary parts of the inner part of the wheel were removed to lighten it. Another idea that was considered was increasing the size of the wheels to get a greater speed. However larger wheels would weigh more and therefore require more power to move possibly reducing the revolutions per minute (rpms). A third major problem was unfortunately time. The original design involved building the device such that it would be able to throw multiple Frisbees without human interference. This was to be achieved through a Frisbee container being mounted on the rear of the device. The Frisbees were to be stacked on top of on another and be pulled into the wheels with a bike chain that would have a hook like device attached to it that would snag the lip on the underside of each disk. The chain was to be powered with the same motor powering one of the wheels, which was to have a gear system also attached to it. The limited budget was not a problem however. In order to make the device more efficient, more stable materials could be used to prevent the motors from wasting energy by vibrating back and forth. Also more powerful motors could have been used. In the end the goal was not met. Bibliography Ralph D. Lorenz (2006). Spinning Flight Dynamics of Frisbees, Boomerangs, Samaras, and Skipping Stones New York, New York: Springer

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