Our Crane: Team 16

(Left to right): Erin Wong (erinwong), Richard Tang (ryt), Rohan Zeng (rzeng)

We were able to reduce a lot of weight by hollowing out the base of our crane, keeping just enough material to clamp on to the playing field while also retaining stability.

The Final Crane

Our final crane for Design Review 2 consisted of the original square base, a square truss system going into the hole, and just a single bent piece going towards the weight. It weighed 218 grams and deflected less than 7/8 in.

The Original Crane

Our original crane for Design Review 1 had a servo to lift the weight. We decided to remove the servo because its weight contributed a lot to the deflection of the arm, and it caused our crane to not fit within our box. Not much else was changed for the second design review because the truss functioned well in providing a stable base for our crane.

By using the full 180° range of motion of the servo motor, our crane was able to lift the weight consistently over two inches.

Interesting Features

This diagonal piece was one of the main members that allowed our crane to resist torsion so effectively.

The feature we are most proud of are the diagonal supports to resist torsion. When the truss was twisted, we realized that the top of the truss deflected more than the bottom, so we added a bent diagonal piece attached from the top of the truss to the base to add support and reduce the effect of torsion on the system.

A lot of diagonal members were used to support and stabilize different subsystems in the crane together.

We also applied this principle to the truss going through the hole as well. While our base truss was quite stable, the arm twisted and deflected a lot on its own due to the moment and force from the weight. Here, by using a diagonal piece to connect the extended arm to the base, we created an overall more stable structure that greatly reduced the deflection of the end of our crane.

Structural Principles

L-beams

We learned in class that the best shape for a beam to resist bending is an I-beam. However, as they are difficult to make, we decided to bend our pieces into L-shapes instead. This way, the beams would deflect less due to bending while also being less likely to buckle than if we had used the unbent pieces.

Here, the weight rests onto a piece bent into an L-beam, of which many were used all throughout our crane.

Pretensioning

For members in compression that were not bent into L-beams, we put them in tension when attaching them to the crane. This was to prevent buckling due to compression because it generally takes more force to pass yield strength in tension than it takes to reach the critical force for buckling.

In the above image, the diagonal member on the bottom connecting the base of the square truss to the arm was pretensioned.

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