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DESIGN & FEATURES

1) base
2) vertical supports
3) angled supports
4) static arm
5) anti-torsion devices
6) servo
7) rotating arm
8) hooks
9) counterweight
10) strut
11) base stiffeners

We went for a lighter, more minimalistic design. We used two angled supports to connect perpendicularly to the static arm. The angled supports were supported with vertical beams placed as close as possible to the static arm to reduce the distance over which the angled supports could bend. Simple anti-torsion devices had to be attached at the junction between the static arm and the angled supports because the thin aluminum could not resist bending on its own. A strut was added, with a similar design to the supports, to restrict the length over which the static arm could bend and twist, thereby increasing the maximum height lifted. We also added some simple base stiffeners to prevent the base plate from bending upwards due to opposing vertical forces.

 

Originally, our static arm was a sideways T shape that was much easier to build and attach. Unfortunately, the T shape did not have a high enough moment of inertia to 

resist the torsion coming from the weight. To address this, we rebuilt the static arm to have a square C shape with braces all along its length to connect the two bent aluminum strips. By doing so, we greatly reduced the torsion in the arm, demonstrating the importance of geometric properties of structural shapes that we learned in class this year.

 

We attached the servo to allow the rotating arm to be as close as possible to the static arm with a custom fitted L bracket. This was done to reduce the amount of torsion on the static arm without having to add more material. The rotating arm was made of delrin and a bent aluminum piece to prevent bending along both axes. We drilled a large hole into the center of the rotating arm to allow for easy attachment to the servo. The arm had two hooks to prevent the bolt on the weight from sliding in either direction during lifting. Finally, a counterweight was attached as far as possible from the center of the servo to maximize the torque it provided.

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We were most proud of the general simplicity of our design. Certain special features, such as the anti-torsion devices and the base stiffeners, allowed our crane to maintain its minimalist design as well as execute the lift.

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