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Trebuchet Part 1
Next Assignment: Trebuchet Part 2
  1. Step 1: Functional Requirements. Design a trebuchet or catapult that meets the following functional requirements:
    1. Launches a rubber ball that weighs 27 g.  See the required distance in the grades section below
    2. Is made of:
      • 1/4" acrylic rod for the main am pivot point
      • rope or string of your choice - I bought some 2 mm braided nylon rope.
      • fabric of your choice - I bought some cotton canvas for you to use.  
    3. I have also provided 1/8" MDF for you to use.  You can 3D print parts if you like, or use outside parts. 
    4. Uses a servo controlled by an Arduino board to trigger to device. The trigger must be made from the same materials given above.  The servo must be able to be removed from the device after completion of the assignment.  No tape either!
    5. Uses the supplied weights.  
  2. Step 2: Generate Solutions / Analysis
    1. Modify the Matlab scripts found here to find the dimensions of your design that launch the required distance with the largest possible time window of launch.  If you need to use the Virtual Computer Lab to run Matlab, find the instructions here.   
    2. Plot the launch window in 25 iterations of two of the four parameters shown in the diagram below (L, l, n, or r).  That means you need to generate 25*25=625 data points to plot.  This would be crazy to try to do by hand, but some students have tried in the past.  You will not get any credit for doing this by hand.  Refer to your lecture notes to determine how this should be presented.  It is your choice as to which parameters you would like to change. An example of this was given in class.
    3. Plot the maximum reaction force acting on the main trebuchet pin as a function of the two parameters of your choosing in 25 intervals, same as above. 
    4. Based on the two plots, find values for all four parameter and identify the reaction force for those values. 
    5. Calculate the deflection of the "main arm pivot axle (the part made of 1/4" acrylic)" as a function of "main arm pivot axle" length and plot it.  Based on that plot, find a length for the "main arm pivot axle" that works for your design and doesn't lead to too much deflection. You must use your best judgement to decide what constitutes too much deflection.  Your grade for this part will depend as much on your judgement as your math skills. 
    6. Based on that length, calculate the stress on the "main arm pivot axle" and prove that the maximum reaction force will not break the main arm pivot axle.   
    7. Sketch your design. Be as detailed as you can.
    8. Design a trigger to release your mechanism.  Prove that your trigger will work with the 350 Nmm servos.  To prove this, you need to show that the torque acting on the servo caused by the counterweight (M) is less than the servo's static torque.  

Grading - 8 pts

  1. Matlab Code + figure plotting launch window vs the two chosen parameters + figure plotting reaction force vs two chosen parameters.  Use a log scale on the z-axis if necessary. 
  2. Sketch of design
  3. Sketch trigger plus trigger analysis
  4. Pin deflection and stress analysis

Educational Goals

  1. Apply what you learned in CS 104 to a real world problem.  
  2. Improve your hand sketching skills
  3. ​Use your analytical skills to choose the "optimum" design before prototyping.