Assigned 11/7/97 ----- Due 11/21/97 (14 days!)

    The Save the Skeets Foundation has long railed against the inhumane treatment by trap shooters of these poor little clay pigeons, also known as skeets. Present skeet flinger mechanisms, they claim, treat the clay pigeon too roughly and also exert significant shaking forces on the trap house from which they are launched.

    A mechanism is needed that will more efficiently launch the skeet on its final trajectory without causing excessive forces on its surroundings. WPI’s R&D group has determined that a fourbar linkage arrangement might be a superior approach to those now used for this purpose. Some preliminary research reveals that the skeet, or clay pigeon, must be launched on a trajectory that will attain a peak speed of about 55 to 57 mph at apogee and reach about 60 yards down-range from the trap house. To confuse the noble skeet hunter and give the poor clay pigeon a sporting chance, each skeet is launched in a different, randomly chosen, horizontal direction within an arc of 72 degrees.

    Your assignment is to design a skeet throwing mechanism based on one or more fourbar linkages which will pick up a skeet from a magazine at zero velocity and provide suitable motions, accelerations and velocities for effective launching, and also to design the shapes, sizes and materials of the moving parts such that the reaction forces applied to the machine frame or floor are as small as possible.

    The driving-torque requirements are also of concern as they will require power from the drive motor and thus should be minimized. The pivot pins must be sized against failure, and the dimensions and materials of the links and pins specified. A multi-view, overall assembly drawing must be supplied which shows how the mechanism is assembled and how the skeet mounts to the machine.

    Luckily for you, WPI has provided a computer program called FOURBAR available on the Novell network. This program will calculate all the forces and torques on a fourbar linkage over multiple positions. You must supply to it the link dimensions, masses, and moments of inertia for your design's elements, and also supply the crank input angular velocity, and any external forces or torques. Note that FOURBAR imposes a constant angular velocity on that driving crank, which assumes that the device used has sufficient torque available at all speeds. You also have to specify what power will be required of this device. TKSolver will be an invaluable aid for calculating masses and moments of inertia of your links.

    As with any design problem, there is an infinity of solutions possible. You are expected to come up with one solution which will work and, most importantly, to understand how it works. If it doesn’t work, you should at least be able to explain in good engineering detail why it doesn’t! To do this you will have to try out many alternate designs and iterate to your 'best' solution. You should expect to go through at least ten iterations before arriving at any acceptable solution. You will need to do some TKSolver calculations for masses and moments of inertia of your proposed links before going to the computer to use FOURBAR.

    You are also required to document your solution in a professional engineering report which adheres to the Project Report Specifications document which will be distributed. This report will document the process by which you iterated to your final design as well as the design itself. Do not just describe the final result. Rather show me how you arrived at it, including the failures encountered along the way. This will demonstrate to me that you understand the engineering concepts and the relevant course material. A working cardboard model of at least one plane (one side) of your design is required. Your report should include titled (labeled) plots and tables from program FOURBAR. These graphics should preferably be imported to your word processor file using the clipboard. Remember, one purpose of the project report is to convince me that you understand your solution well enough to have been the real designer thereof!

Some suggestions to get you started:

1. Do research before trying to solve the problem! Don't 'shoot from the hip'. Avoid BFI (Brute Force and Ignorance). Engineer it.

2. Investigate the dynamic factors involved.

3. Mr. Hrones and Mr. Nelson can help.

4. Reading the textbook might even help.

5. Cardboard models make designing much easier.

6. THINK about the theory discussed in class and in your text. It IS applicable to this problem!

IMPORTANT! IMPORTANT!