- Project Description:
Our main concern through the course of the project was to make sure our mechanism was strong. At the first design review, we noticed different parts of our base and arm bending and twisting. At this stage our servo worked and the mini-arm moved, but did not lift the weight at all. We realized that our main problems were the following:
- Our structure was not strong enough and we were losing much of the servo’s capability in the bending and twisting of our base and arm. We saw this especially with the twisting of the arm. Because we had the servo mounted to one side of the arm, the force of the weight was not being evenly distributed and the arm was wholly twisting to one side, and all of the servo’s torque was being used to twist the arm instead of lift the weight.
- The servo was not at an ideal distance from the weight. It was rather far from the weight, and this way we were not using the servo to its full potential.
Between the first and second design reviews we made many changes to our project. First and foremost, we concentrated on strengthening our structure. We added many more supports to the base and arm and added an extra boxlike structure that added height and gave support to the arm. Next, we moved the arm forward to allow the servo to be closer to the weight. Despite the extra efforts we put into supporting the arm, it was still twisting to the side of the servo (thought much less). We decided to change the orientation of the servo such that instead of being parallel to the arm and mounted to the side, it was mounted perpendicularly on the front of the arm. Though we had some success lifting the weight two inches in the nights before the review, the night of the review our project was only able to lift the weight a little over an inch. Our main problems at this stage were the following:
- Though we changed the orientation of the servo in order to distribute the force of the weight more evenly, we had miscalculated and the servo was much too close to the weight to lift it the full two inches. We could not utilize the full torque of the servo from this position.
- We were going to have to change the orientation of the servo once again and would most likely have to solve the problem of the twisting arm.
- Despite the relative strength of our structure, there were parts aside from the arm that were still bending slightly.
After discussing our options, we decided to change the position of the servo back to its original orientation, parallel to the side of the arm. However, after doing some more careful calculations, we moved the servo closer to the weight in order to utilize more of its torque. Because we were afraid that the servo would be unable to lift the weight the full two inches, we attached a counterweight to the mini-arm. We played with the design of the mini-arm and counterweight until we had it in a position that did not allow it to touch the ground when lifting (as this was against the rules) and that caused the force of the counterweight to act as far away from the servo as possible (maximizing the moment it caused). We also spent time adding a few more supports to the arm and tightening all of the screws holding our structure together. Unfortunately it was only at this point that we decided to weigh our project and see if we met the weight requirement of 20 ounces. The mini-arm and counterweight alone weighed 5.7 ounces and our entire project weighed over 27 ounces. We struggled to remove every little piece of our project that was unnecessary. However, we were afraid to remove any supports. We removed the counterweight and attempted to lift the weight without it, but the weight did not move at all. Unfortunately we could not permanently remove the counterweight and save ourselves 5 ounces or so. We reattached the counterweight and weighed the structure. The lightest we could make it without sacrificing its strength was around 26 ounces. At the final design review we lifted the weight twice in 30 seconds, as was required. Our first lift was about four inches and our second lift was about 3 inches.