How to make a Tabletop trebuchet Developed by Brian Bowes Meason Kolkhorst, Carl Schwab and Randy Scrudder June 2008 Supplies You Will Need The Following: Safety Glasses Approximately 70 Craft Sticks Glue Gun (Low Melt) 2 - 3 Hot Glue Sticks Approximately 7 feet of String/Twine Approximately 4” X 6” Piece of Cloth Paperclip 1/4” Wooden Dowel (4) 1” Wooden Wheels Large Empty Medicine Bottle Plastic Golfball or other Projectile Empty Soda Cans (Castle Wall) Before You Begin Always wear safety glasses while you are working on your project. Hot glue burns! Keeps your fingers away from the melted glue and the tip of the gun. Making the Base Step 1 Begin by gluing three sticks together like this. Step 2 Now, turn it over, add another stick to the top. Step 3 Add two more sticks on top of what you did in Step 2. Your sticks should be glued together like this. The end structure will be 6 sticks glued together alternating 1 stick, 2 sticks, 1 stick, 2 sticks. Step 4 Repeat Steps 1 thru 3 and make another one so you have two of them. You have now manufactured the left and right sides of the base. Step 5 With both sides facing the same direction, glue a stick between the two as shown. Make sure that you glue the stick INBETWEEN on each side. Step 6 Turn the base around and glue another stick on the other side. Step 7 Add two more sticks to each end on the bottom of the base. It should look like this. Put this piece aside for now. You will need in later. Making the Sides Step 8 Now you are going to make the sides of the trebuchet. Using 3 sticks, stack and glue them together similar to what you did in Step 1. Make four pieces that look like this. Step 9 Using two of the pieces facing opposite of each other, criss cross two of the side pieces. Do not glue these together until Step 10. Step 10 Glue one stick to each side of the long end of the “V” that you have created. DO NOT glue the top of the “V” until you get to Step 22 Step 11 Repeat Steps 8 thru 10 so that you have made two side pieces. Put these pieces aside for now, you will need them later. Throwing Arm Step 12 It is now time to make the throwing arm. Start by gluing 5 sticks together as shown. Step 13 Repeat Step 12 so that you have two identical 5 stick long pieces. Please note that the long side has 3 sticks and the short side has 2 sticks. Step 14 Glue the two pieces from Step 13 together. Be sure that they are facing the same direction. The ends of the two pieces should be even with each other. Please note again, that the long side has 3 sticks and the short side has 2 sticks. Step 15 Glue on two more sticks on the long side of the throwing are. It should look like this. Step 16 Finish the throwing arm by adding two additional pieces to each side of the throwing arm. This will add strength to the arm. Step 17 You must now determine where the axle for the throwing arm should be attached. There is a ratio for determining where that point is. That ratio is 4:1. Where a Fraction is the proportion of a part of something compared to its whole, a Ratio is the proportion of a whole compared to its parts. They are always expressed as whole numbers, never as fractions. Non-Example: 5:1/2 Example: 10:1 A ratio of 4:1 means that you have a measurement of 4 units on one side, and 1 unit on the other side When you add this together, you will have a total of 5 units. : 1 4 5 Now you need to measure the length of your throwing arm in inches. Once you have that length, divide it by 5. This will allow you to determine the measurement for one unit. Measure that length from one end of the throwing arm, and mark it with a pencil. This is where you will attach the axle for the throwing arm. Step 18 Retrieve a dowel and measure and cut a 6 inch piece from one end. This will be the axle for your throwing arm. Step 19 Place a drop of glue on your throwing arm at the spot you measured in Step 17. Center and attach the 6 inch dowel to the throwing arm. Step 20 You now need to cut a piece of string that is approximately 3 feet or 36 inched long. Step 21 Lash the axle to the throwing arm with the 3 feet of string. Wrap the string tightly and use a little hot glue to help hold it in place. The picture below is from the Boy Scout Handbook, and it describes how to lash the two pieces together tightly. Attaching Sides Step 22 Retrieve your base and (2) sides. Center the sides inside the base and glue them in place. Be Sure You *Align * the sides so that the tops of the “V”s are parallel to each other, and so that the sides are perpendicular to the base. Glue the tops of the “V” in place so that they do not move around. Step 23 Once the sides are in place, glue on support sticks. Make sure that they are attached to the base and the sides. Step 24 Next, glue an upright support piece on both sides. The stick fits in-between the two sticks which are at the bottom of the side structures. Step 25 Now, glue a cross member support piece as shown. Do this for both sides. This cross member can also help to make the sides more perpendicular by placing the stick on the inside or the outside of the trebuchet. Step 26 Create a platform for the projectile to rest on while it is being hurled. Use 5 or 6 sticks and glue them to the support sticks you attached in Step 23. Wheels Throwing Arm Wheels help to “soak” up the energy created by the heavy counterweight. They also help the trebuchet hurl the projectile further. Step 27 Now gather your (4) wooden wheels and the drinking straws. Cut the straw so that you have several 1 inch pieces. Step 28 Again, retrieve a dowel and measure and cut two (2) 6 inch pieces from one end. These will be the axles for your wheels on the base. Step 29 Attach one wheel to one end of the 6 inch dowel. Secure it in place with a drop of glue. Slide two of the 1 inch drinking straw pieces onto the wooden dowel. These will be the bearings for the wheel and axle assembly which will allow your trebuchet to roll smoothly when it is firing. DO NOT glue the straws to the dowel!!! Attach the other wheel to the other end of the dowel. Secure it in place with a drop of glue. Step 30 Attach the wheels to the bottom of your trebuchet. Use hot glue to secure the straws to the bottom of the base Be sure to use enough glue to completely encircle the straw. This will prevent the wheels from falling off because the glue did not hold. Step 31 Repeat Steps 29 and 30 for the other set of wheels and axle, and again attach them to the bottom of your trebuchet. Counterweight Step 32 It is now time to Secure your counterweight (CW). If you have your medicine bottle filled with 150 pennies, you will need to have your teacher drill two holes into the lid. This will facilitate attaching it to your throwing arm. *NOTE* If you can not acquire a medicine bottle, you will have to fabricate your own CW. It is up to you to equip your trebuchet with a CW. What it looks like and how it is made is completely up to you. Remember that it must fit within the two sides of the trebuchet, and the total height must allow it to swing freely without touching the platform of the trebuchet. Determining Weight Step 33 It is now time to start determining the weight of the pieces of your trebuchet. Gather your throwing arm, counterweight, and the projectile that you will throw (see your teacher for the projectile). You will also need access to a Triple Beam Balance. Step 33 Weigh each of the pieces you have gathered. (Throwing Arm, Counterweight, and Projectile) You will need to know these weights later on in the project, but if you do not gather them now, it will be much more difficult after the trebuchet id constructed. Record the weight of each in our Student Journal. Sling Step 34 Cut a piece of cloth that is 6 inches long and 4 inches wide. The neater you cut this piece, the better your sling will work. Note: Thin cloth works much better than thick cloth. Step 35 Cut two pieces of string that are each 2 feet long. (24 inches) Step 36 Tie the end of one piece of the string around one end of the cloth. (Do not cut the extra off yet.) Wind the string around the knot about 3 times, and then tie it off again. use a little hot glue to make sure that the knot does not come undone. Step 37 With your second 2 foot piece of string, repeat Step 36 on the other end of the piece of cloth. Step 38 Locate a plastic golf ball (projectile) and place it in the sling. It should fit loosely. Step 39 Tie one end of the sling to the throwing arm. Wind the string around the knot about 3 times, until about nine inches of string is between the sling and the throwing arm. Again, use a little hot glue where necessary to make sure that the knot does not come undone. Step 40 Tie a slip knot ar loop at opposite end of the other piece of string. Again, leave approximately nine inches of string in between the cloth and the slip knot. Step 41 Retrieve a paper clip and bend one end of it straight, as show in the top picture. Then Bend half of the curved portion of the paper clip up, as shown in the bottom picture. This paper clip is going to be the prong at the end of the throwing arm. Step 42 Use hot glue to attach the paper clip to the end of the throwing arm (round end out). Be sure that you attach it to the opposite side of the arm as the axle. Your sling in now complete and attached to your throwing arm assembly. it should look similar to the one in the picture. Counterweight Attachment Step 43 Attach the CW to the short end of the throwing arm. Secure it so that it does not come loose, and does not hit the sides of the platform of the trebuchet. This may take some adjustment to be sure that it moves freely. Attachment may be easier if the throwing arm is not attached to the trebuchet while working on it. Throwing Arm Attachment Step 44 Once you have the CW attached to the throwing arm, and the frame of the trebuchet completed, you are ready to put it all together. Place the axle of the throwing arm into the top “V” on each side of the Trebuchet frame. The throwing arm should rest ON the axle when you place it in the “V”. You may secure this in place with a couple pieces of drinking straw, or leave it as is, if it seems secure enough. DO NOT glue the Throwing arm axle to the “V”s. It must move freely. Trigger Mechanism Step 45 It is your responsibility to create a firing pin or trigger mechanism for your trebuchet. You may not participate in destroying the castle if your trebuchet does not have a firing pin. The purpose of the firing pin is to allow the operator to activate the trebuchet from a safe distance. Your trebuchet must have the same consideration. Below are a few examples of trigger mechanisms. Study them and come up with a solution that will work on your trebuchet. Finished Step 46 Your Trebuchet is Finished! You will now test fire your trebuchet and begin adjusting the components of your trebuchet to optimize the trajectory of the projectile. Go Forth and Hurl Young Warrior!
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