Building

After our class had made our designs on paper and computer, we decided to split into groups, one for base construction, one for the arm, another for the wheels, and a last group for the counterweight basket and axles. After rigorous concept models and a truck full of wood, we began our project.


 * The base** was built of mainly 2x6's which were laminated and screwed together. we started by building the bottom rectangular shape which is approximately 4'x8'. We built the rectangle two 2x6's thick and then added our vertical support for the "triangle" shaped uprights. The vertical support was then sandwhiched in by two more 2x6's and more than 3 extra support pieces. The vertical "triangle" shape was first built with one layer of 2x6's and more were added later. The hole for the arm, and wheel axles were then drilled and the axles and wheels put in place. The solid aluminum axle was then pounded in and the arm placed on it. The axle was then bolted down to the base and reinforced. 2x6's were placed in between the 8' sections of base perpendicular, and a piece of composite plywood was layed down as our chute.


 * The wheels** were a long process. We started off making square wheels, roughly 13 X 13. They had 2 layers, with each layer having 3 boards glued side by side. The 2 layers were then glued back to back with the wood grains opposing eachother. These little details helped create optimum strength. After the glue had dried the next step was to make them round. We made a jig that held the square wheels by a nail, then we roughed them in on the band saw by rotating the wheel on the nail. This was a tedious job, because of the blade kept bending, but afterwards the job looked nice, and was ready for the next step. I took the newly rounded wheels home, and drilled a 1 inch diameter axle hole with a drill press. They were then slid on a 1 inch axle that was placed in a horizontal lathe. The outer diameters were cut to exactly 12 inches, and then the wheels were removed. The last step was putting each wheel directly in the lathe chuck to cut the final concentric axle hole.


 * The axles** were some of the last parts to get done. We made all the axles out of 1 inch, scheduale 40, piping. The bearings were made of 1 and a 1/4 inch, scheduale 40, piping. We pressed a bearing in each one of the wheels, and a pair of bearings were welded in the uprights of the counterweight. Two 1 inch axles were placed in the base for the wheels, and the other was placed through the arm for the counterweight. The only other axle was the arm's main axle, the fulcrum of the trebuchet. The axle was made up of a solid 2 inch aluminum rod that was mounted on the A frames of the base. A 2 inch pipe was pressed through the arm, and was slid on the 2 inch rod. All the axles were heavely greased by our professional grease-man, and the end of each axle had washers on it, and kept its attachment on with snap rings.


 * The counterweight** was one of the hardest parts to build and design, being made completely out of steel. we started out by seeing how many weights and space we had to work with. The next step was to build a framework to hold these weights. The sides of the carriage were made of 4 inch channel-gauge steel, in a upside down "T" shape. Now the 2 sides were connected with 6 horizontal peices of angle iron. One more piece of channel-gauge was also run horizontally for the tractor weights to hook onto. The 1 1/4 inch piping was welded through the uprights/ sides of the carriage; this made up the counterweight axle. The whole carriage was tack-welded together at first, then was completely welded at the end. Some things we used to build the counterweight were spacers, lots of clamps, hydraulic jacks, a shop torch, and a multi-purpose circular saw. The biggest problem arose when parts were welded; the parts actually flexed, making it important to keep constant dimensions for the weights for the closest possible fit. In the end it held 12 tractor weights, weighing in at over 1000 pounds.


 * Adjustable firing finger** This is the mechanical mechanism that the sling attached to. It was completely adjustable by turning a threaded rod. the rod then changed the angle of the finger. It was made of a aluminum block, threaded rod, and 2 ajustable pipe rings.


 * Steel bands** The trebuchet project broke 2 times. The first time the arm split about one and a half feet from the finger. we glued the wood back together and rapped sheetmetal around. Our new design proved to be much stronger. The second time it broke was because of too much force from the counterweight. We had made the counterweight uprights longer to increase vertical drop. When we tested it it split the 2x6's at the base of the trebuchet. It was then that all the 2x6's were rapped with steel bands


 * Release pin** The arm in the cocked postion needed to be secured, so we came up with an elaborate design of a release pin. The release pin was made of a steel cable that wen from one A-frame to the other. One side of the cable was securley attached, and the other end had a loop. The pin was inserted in the loop and then into a shaft through the A-frame. A person or 2 would then pull a rope attached to the pin which would release the cable.


 * The winch** We used a electric winch, hooked up to a car battery, to pull the arm down. the winch cable was strung through a pulley and then attached to the arm.

Go BACK