Eliana Abbas, Alec Church & Jasmine Lim
These calculations served as the foundation for our crane’s design. The first things we had to consider were the actual requirements of the project: namely lifting a one-pound weight through a height of two inches. This create some limitations on the design of our lifting arm, but also gave us a starting point from which to work. With those two variables locked, along with the known maximum torque to be provided by our motor, we set about designing a lifting arm which would meet our requirements.
Our largest concern regarding the lifting arm was the counterweight. Obviously, the more moment our counterweight could produce, the easier it would be for the motor to lift the one-pound weight. However, it couldn’t exceed the strength of the motor, since our crane would have to stand idle, and unsupported, which gave us an upper limit on our counterweight design.
However once we had come up with a design for our lifting arm, the rest of our crane’s rough design essentially fell into place. The length of the lifting arm and the position of the weight determined the placement of the motor, and the design of the rest of the crane, a fairly straightforward one, followed suit.
The final major design consideration for us was the nature of the crane’s arm. We opted for a triangular design, with diagonal struts for added rigidity, taking inspiration from cranes and other machines we had observed in the real world. What we have since learned has confirmed our instinct to be reasonable, since we concentrate all of our material to the outside of the structure to the outside of the structure, where the stresses would be at maximum. This made our structure rigid under the torsion produced by the mounting of the motor along the outside, as well as against the bending moment produced by the weight when it was lifted.