Group 20 Final Design Report

Hailey Tannenbaum, Katie Sharkey, Vicky Povolotsky

 

Mechanism:

                Our design features a simple base optimized to resist bending and torsion resulting from the long moment arm and the heavy weight relative to the size of the mechanism. The crane is angled on its base such that the loop at the end of the motor arm is perfectly aligned underneath the screw extending from the weight. The design of the loop allows for easy setup as its shape automatically cups the screw such that there is no chance of disconnect between the motor arm and the weight. The motor arm also features a counter-weight that is calibrated to combat the moment created by the force of the weight. This means that lifting the weight requires less power from the motor.  Previous design iterations featured motor supports of flat pieces susceptible to bending. The new design corrected this problem by adding stability, and as a result the whole crane experienced less effects of torsion and was able to lift the weight higher.

 

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Theoretical Predictions:

 

Sum of Moments about the center of the motor:

(10.8 in)(.28lbs)-(3.75in)(2lbs) = -4.476 lb-in

 

Maximum motor power = 72oz-in = 4.5lb-in

Lift of our mechanism theoretically requires (4.476)/4.5 = 99.5% of total motor power.

 

Maximum theoretical lift:
α= 180-60-45= 75 degrees

R=

X = sin(75)() = 6.8 inches theoretically, if the arm was free to rotate 90 degrees, which it is not because of the way it is connected to the weight.

 

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Interesting Features:

-Lift Loop: provides contact with weight,

                   provides easy setup

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-Long Lift Arm: square cross-section resists bending

 

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-Design of Support Beams: takes into account type of load

 they would encounter (tension vs. compression)

 

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-Motor Support: resists bending and stable hold on motor

 

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