2017 STRESS ANALYSIS CRANE PROJECT(GROUP 32)
THEORETICAL ANALYSIS
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Supporting Claims
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HOW OURÂ MECHANISM WORKS
Our crane consists of a 6*6” base, a triangular truss arm, an HS-425 motor servo, and a U-shaped aluminum lever arm with counterweight plates attached at one end. We bent aluminums strips to 90 degrees to enhance the structure’s ability to withstand bending. The truss arm is comprised of truss links of 7 inches and three bent bridge arms of 28 inches. The base is consisted of four vertical bent beams, two bent base arms of 13.5 inches, two bridge supports of 11.2 inches, two unbent 4 inch base horizontal arms, two unbent 9.5 inches support stabilizers, four cross truss of 7.5 inches, three 8.4 inch trusses. The servo is bolted to a triangular shaped connection piece with two strips bent into right angles, bolted as well as tight-fitted to the triangular truss arm. The lever arm with length 12 inches is bent into three folds to ensure the screw attached to the weight doesn’t fall out of the slot. The counterweight is cut into six separate pieces to minimize the torsion in the lever arm.
TEAM MEMBERS
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From left to right
Zichen Wang
Zheyao Zhu
Fabian Aristizabal
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GROUP 32 CRANE PROJECT
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Interesting and original features
1.Flat-plated counterweight.
2.U-shape design of lever arm.
3.Tower-reinforcing cross links.
4.Motor mounting and support structure.
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How our design takes advantage of structural principles learned in the class
a. By cutting the counterweight into plates and evenly attaching them on either side of the lever arm, we have ensured that any net torque that may be produced by asymmetries in the positioning and weight distribution of the counterweight are minimized.
b. By utilizing a U-shape design for our lever arm, we were able to transform aluminum strip which is easily deformable via torsional stress, into a more rigid structure both in bending and torsion. This allowed us to use aluminum rather than delrin, thus minimizing the overall weight of the lever arm. The U-shape design also gave the bolt connected to the weight a limited, but crucial degree of freedom along the length of the arm that maximized the lift height capability of our structure.
c.Deformations in our structure’s tower and base inspired us to utilize cross links in key areas of our structure where square geometries tended to deform into rhombic lattices. By placing cross links diagonally across these square geometries we increased the rigidity of our structure two-fold. This greatly increased our maximum lift height since deformations occurred principally in our tower. Previously, these small deformations caused slight angling of our support arm which, by the product of the deformation angle and length of the support arm, significantly reduced our maximum lifting distance.
d.Our motor mount is both simple and light. By wrapping around our triangular support arm and, thus, taking advantage of its rigidity against torsional deformation, two small aluminum strips became more than sufficient for our motor mount.