Eliana Abbas, Alec Church & Jasmine Lim
There are several key features which helped us reliably succeed in lifting the weight.
KEY FEATURES
END LOOP (F)
In order to maximize the lifting capacity of the crane, we wanted to convert as much of the arm's movement into vertical force as we could. We achieved this by adding a movable loop at the lifting end of our crane arm.
The loop wrapped around the lift bolt on the weight. When the crane moved upward, it pulled upward and backward on the weight. The weight rotated to follow the loop, and the loop was almost always vertical, indicating that all the lifting force was in the vertical direction.
BASE (A)
TRUSS ARM (B)
The structure of the base was critical in reducing the truss arm deflection while lifting.
During tests, we noticed that the truss arm was deflecting downward excessively, preventing the lifting arm from having much effect. To solve this problem, we reinforced the base with members from corner to corner to increase its rigidity. We also added a reinforcement between the top of the base tower and the top of the truss arm.
In order to decide where to place reinforcing members, we observed the movement of the entire structure, and chose points that moved a significant distance relative to each other. We then connected these points directly with our reinforcing members. Since aluminum deflects least in axial loading, using reinforcements in tension dramatically reduced deflection in our structure.
One of the greatest challenges in this project was maintaining an extremely stable design while still remaining below the required weight limit. We achieved this through our truss design.
This truss combined knowledge from Statics with the Stress Analysis Design project. It is extremely stable thanks to its pattern of interlocking diagonals, and the thin aluminum and small cross-sectional area keeps the total weight low.
GENERAL PERFORMANCE
Our crane starts with a stable base (A) connecting to the long truss arm (B), built to support the weight without warping significantly. The mount at the end of the truss (D) serves to hold the servo (E), which in turn supports the counter weight (C) and lifting mechanism (F).
On the lifting mechanism, the hook fits around the bolt. During the lift, the servo motor spins 90 degrees, moving the counterweight down to assist with lifting the weight upwards.