The goal of this design project is to create a purely mechanical trap thrower that randomizes the trajectory of clay pigeons when launched. A wide range of horizontal angles will be utilized to simulate different flight directions; this will closely resemble the flight pattern of a bird. This randomization aspect will simulate a real life hunting experience. In addition to being a great practice aid, the trap shooter will serve as a fun component to recreational shooting. Whether users are shooting for practice or fun, this trap shooter will bring more to the table than just increased functionality. Current trap shooters on the market today are most commonly powered by a battery. By creating a purely mechanical shooter, it will eliminate the need for an electric power source. This will prove to be more simple and convenient for users of the machine. It will also allow consumers to go trap shooting in any location without the worry or hassle of a large battery.
The team’s design consists of nine main parts. These include the base, the feet, the foot pedal, the foot pedal spring, the rack and pinion, the ratchet, the bevel gears, the four-bar linkage, and the thrower. To begin, the base will house all of the components, and the feet will provide stability. The user will actuate the foot pedal. The force from the user’s foot will cause the gear rack to slide along a rod. The rod will have a square cross section to restrict rotation, and the foot pedal will be spring loaded so that it returns to the original position after being pressed. The motion carried by the rack will turn a gear mounted on a horizontal shaft. The horizontal shaft will be connected to a ratcheting system. The ratchet and pawl will prevent the input shaft from rotating in both directions; which will allow the four-bar linkage to only rotate in one direction. For the ratcheting system, we chose to use a bicycle freewheel, as shown in Fig. 1 below.
Fig. 1: A picture of the freewheel that we used for our ratcheting system.
The other end of the ratchet is connected to a meshing pair of bevel gears. The bevel gears will translate the horizontal rotation to vertical rotation. The vertical rotation will then turn the first bar in the four-bar linkage. The four-bar linkage will move the thrower back and forth through an angle of 80 degrees to produce a pseudo-random throwing direction. The thrower will be mounted on the end of the four-bar linkage and will serve the purpose of launching the clay pigeon. To ensure smooth rotation at joints, ball bearings will be placed at locations of rotation, and the majority of the base will be welded together. In Fig. 2, a picture of our SolidWorks model is shown, and Table 1 outlines the function of each component.
Fig. 2: A SolidWorks model outlining the key components of the design.
Table 1: A table of the functions for each component.
Detailed Design Overview
According the target market, a randomizing purely mechanical trap thrower is in great demand. In order to meet these consumer’s qualitative specifications, BC3D Engineering had to develop quantitative design specifications. These are including in Table 2 below.
Table 2: Engineering Design Specifications
Calculations were performed to ensure that the quantitative design specifications could be met. These calculations included a variety of techniques including optimization, kinematic analysis, and energy balance. Optimization was used to find the appropriate linkage lengths to yield a symmetrical launch angle distribution, and kinematic equations and energy balance derived the necessary spring constant. We designed for various factors including, one man operation, ease of manufacturing and easy handling.
The fabrication of the trap thrower will include the use of CNC milling machines to cut the aluminum bars, and a lathe to machine the rods. Additionally, there will be minimal welding necessary to the attached two sections of the base together, and most of the assembly will be done through the utilization of common, 1/4-20 screws. Finally, testing the trap thrower will be outlined by the engineering design specification shown in Table 2. The outlined procedures for testing, according to the specifications are shown below in Table 3.
Table 3: Testing Procedures
For the Proof of Concept, BC3D built a prototype of the trap thrower. The goal was to validate the primary function of the trap thrower: randomization. The trap thrower prototype was built using a Lego Robotics Kit rented from the DeLaMare library at UNR. Once the kit was checked out, the team began building the base of the trap thrower. The base needs to be well thought out because it would house all of the components of the design. By using large frame-like Lego pieces for the base, it allowed us to construct a versatile structure. Once the base was built the gear system and the foot pedal needed to be built simultaneously so that these two parts could come together correctly. Fitting a small gear and a rack together was the first step in building the foot pedal. Housing the rack to rigid shafts allowed for vertical motion of the rack and a simplified motion of the foot pedal. The rack meshed with the gear that was fitted to a shaft that allowed for the transmission of linear motion to rotational motion. At the other end of this shaft, there was be a bevel gear. This horizontal-axis bevel gear meshed with a vertical-axis bevel gear to transmit the motion ninety degrees. Once this was completed, the final part of the Proof of Concept was built. The piston system includes a rigid beam that translated rotation from the vertical bevel gear shaft into a back and forth motion that will randomize the direction that a clay pigeon is thrown. Figure 3 shows the actually trap thrower versus the SolidWork model.
Fig. 3: The actual Proof of Concept activity and the SolidWorks model.
To test the Proof of Concept, the team actuated the foot pedal a random number of times and recorded the launch angle. This procedure was repeated 50 times. With this data, the frequency was plotted against the launch angles; where the launch angles were given in increments of 5 degrees. This can be seen in Fig. 4 below.
Fig. 4: The lab data from the POC testing.
From the data above in Fig. 4, it can be concluded that the launch angles were mainly distributed to the right hand sector of the throwing area. This was validated using theoretical calculations. A SolidWorks sketch was automated using a Visual Basic macro to increment the input angle and record the resulting launch angle. There were 5000 iterations performed, and the distribution data was plotted using excel. This can be seen in Fig. 5 below.
Fig. 5: The distribution of launch angles for the POC four-bar linkage lengths.
Because of the undesirable frequency of launch angles on the right half of the throwing sector, the team decided to optimize the four-bar linkage lengths in order to obtain a more symmetrical distribution. This was done using geometry. After the appropriate linkage lengths were found, 5000 random angles were selected again and plotted using excel. The new, symmetrical distribution with the new linkage lengths can be seen below in Fig. 6.
Fig. 6: The distribution of launch angles after the linkage lengths were optimized for a more symmetrical distribution.
The process of fabrication began with our raw materials. All of our parts were ordered through the vendor, McMaster-Carr. The first part of the fabrication process was machining the six foot aluminum bar stock. This would be used for the base, feet, and the four bar linkage. Each piece had to be cut to size and milled correctly to minimize the weight of the entire project. A band saw was used to cut the aluminum and a CNC mill was used to remove the excess material from the base piece. Next we drilled and counter bored the holes for the housing of the bolts. This was done by using the mill with specific bits to achieve our dimensions. The mill is shown in Fig. 7.
Fig. 7: Mill used to drill and counter bore.
Once all of the holes and counter bores were drilled, the team then had to tap the necessary holes by hand. The CNC was used again to mill out the holes for the bearings. These had to be very accurate because the bearings needed to be press fitted into the aluminum. Once all of the machining was completed on the aluminum bars, the team attached the free wheel ratcheting system, the spur gear, and a bevel gear to the rotating shaft. Attaching the ratcheting system was done by using the lathe to fit the outer diameter of the shaft to the inner diameter of the free wheel. The ratchet, the spur gear, and the bevel gear were then press fitted to the shaft accordingly. This was done through the use of a hydraulic press. The aluminum bars were then press fitted together using small rods of aluminum, the pieces were bolted together, and team BC3D Engineering recruited a third party to perform the welding. The pieces were welded in the proper configuration according to the assembly drawings. After welding, the trap thrower was attached to the base. The finished product is shown at Innovation Day in Fig. 8.
Fig. 8: Fully Mechanical Randomizing Trap Thrower shown at Innovation Day.
Finally, a light-hearted video is shown below summarizing the need for such a trap thrower.
Blake McCoy (left) – Blake is a senior mechanical engineering student from Carson City, Nevada. His passions include weightlifting and binge watching Netflix. Blake has had an internship at CGI Inc. where he created SolidWorks drawings and learned about manufacturing. Blake is the group’s analytical specialist and brings his manufacturing experience to the team.
David Bart (middle) – David is a senior mechanical engineering student from Spring Creek, Nevada. David’s hobbies include making people laugh on Sundays, hiking, sports, and music. David is the group’s safety and theory specialist.
Chris Steele (second from right) – Chris is a senior mechanical engineering student from Carson City, Nevada. Chris’s hobbies include sports and mountain biking. He has had an internship at Zodiac Inflight Innovations where he was the Flow Analysis specialist. Chris brings time management and production based skills to the team.
Chad Landman (second from left) – Chad is a senior mechanical engineering student from Henderson, Nevada. He is also pursing a MBA in Business. His hobbies include archery and running. Chad specializes in creative design and business management.
Connor VanKalmthout (right) – Connor is a senior mechanical engineering student from Folsom, California. His hobbies include hunting, trap shooting, and gun collecting. Connor is the team’s hunting expert and once killed a bear with his bare hands.