Steven Oetjen Joshua Eickmeier Edward Burns
The truss structure, held down at four points by the clamps, goes through the larger hole in the obstacle and supports the servo within range of the weight. The arm, supported by the servo, has a counterweight on one end to increase the effective lifting torque, and a hook on the other end to catch the weight. The aluminum strips that were to undergo compression, or significant torsion and bending were bent along their length to resist these loads. The counterweight was made of a cut aluminum U-channel and delrin strips, bolted together. The total weight of the structure, servo, arm, and counterweight is 18.5 oz.
We tested our servomotor using a bottle of water which we filled to different amounts of weight. After lifting a maximum of 9.3 ounces at a distance of 4.75 inches, we determined that our motor’s practical maximum torque was 44.2 oz-inches. As a rough estimate, we figured that our motor needed to lift 16 ounces at a distance of 5 inches, meaning it roughly needed to have a total torque of 80 oz-inches. To meet this goal and have a reasonable factor of safety, we added a counterweight of 4.2 ounces at a distance of ten inches back from the servomotor. This additional torque gave us a total theoretical torque of roughly 86 oz-inches.