Project Description

            Our team has decided to go through the bigger hole because we think it will be easier to build our mechanism in such ways that the parts are connect together in ninety degrees. We built our part so that its height is approximately at half of the bigger hole to make sure that our mechanism will avoid from touching the wall.
            For the following analysis, we will assume that the maximum torque of the servo is 42 oz-in, which is about 2.625 lb-in and the angle of rotation is 100 degrees.
            In our lifting mechanism, we have the servo 4 inches from the weight, and a counterweight 7.5 inches from the servo. In our calculation:

            (1 lb)(4 in) = 2.625 lb-in + Wc(7.5)   *Wc = counterweight

            Thus, the minimum Wc we must have in order to lift 1 lb of weight has to be 0.183 lb (2.2928 ounces). In theory, with our configurations, our mechanism should be able to lift a one pound weight if we have enough counterweight.
            Considering the angle of rotation, to lift the weight 2 inches high with a lifting arm 4 inches long, we only need about 30 degrees of rotation. Therefore, if the angle of rotation can be as high as 100 degrees, we should have no problem lifting the weight 2 inches.
            Originally, our first prototype did not come up to be as functional as we would like it to be. One of the problems is that when we did the calculations, we always assume the lifting arm to be perpendicular to the weight. But we actually have the arm being slanted down with some angles when constructing. Another problem we have encountered is that when the arm rotates, the part with the counterweight happened to touch the platform (floor) before we could lift the weight up 2 inches. We also did not consider other factors such as friction forces and we did not have accurate measurement tools for the lengths and weights. Thus, there is much to be improved on when constructing our second prototype.
            After some discussions and having multiple prototype ideas, we eventually relocated our lifting arm further away from the weight we are lifting (from 4 inches to 4.5) to ensure that we will lift the weight by at least 2 inches before the other end of the lifting arm touches the table. We also added more counterweight as a result of a prior change, to roughly 0.28125 lb (4.5 ounces). One important improvement we found was to strengthen our structure by adding more supporting beams throughout to reduce the downward structural movement during the lifting motion. Our new calculation of the lifting mechanism becomes:

            (1 lb)(4.5 in) = 2.625 lb-in + Wc(7.5)    *Wc = counterweight
            Wc = 0.25 lb < 0.28125 lb that we used

            With the improved lifting mechanism and strengthened structural design, we were successfully in lifting the inches by more than 2 inches. Our structure measured in at 19.95 ounces, just below the requirement of 20 ounces.