Team members: Isaac, Christine, Lindsay
Team Fα's initial design involved several triangular extruded cuts across the robot arm template to minimize loss of the arm's structural support while removing much of the extraneous mass. The results of this design were as follows:
- Volume: 0.88 in^3;
- Displacement: 0.35 mm;
- Score: 0.308 mm*in^3.
Team members: Greg, Andrew
The premise of Team FΩ's design was to do away with extraneous portions of the given design. The result was a curved, s-shape piece that cut off the portions past the pre-cut notches under the hypothesis that these areas did not help the piece resist deformation. The curved structure was intended to eliminate the corners created by the notches so that stress could not focus on any particular spot. The results for this initial design are as follows:
- Volume: 0.90 in^3
- Displacement: 0.35 mm
- Score: 0.315 mm*in^3
Synthesis of Designs
The team decided to base the final design primarily on Team Fα's preliminary design because it performed better. The main element that we tried to maintain into our new design was the use of triangles in the central region of the arm, between each of the notches. We also cut away the portions past the notches, like in Team FΩ's design, because they did not add much structurally due to the position of the notches. The next task, which was not as directly informed by the earlier designs, was to determine how to remove mass from what remained.
Step 1 was to find the ideal arrangement and orientation of the two triangular cuts in the center of the arm, since they had been arbitrary in earlier stages. In particular, we had to determine the ideal direction of the "strut" that the two triangles created and whether the triangles performed better if they were asymmetrically sized. The purpose here was to remove as much material as possible while retaining a triangular support structure.
Middle Bar Test 1: Displacement: 0.30 mm; Volume: 0.95 in^3; Score: 0.280 mm*in^3.
Middle Bar Test 2: Displacement: 0.29 mm; Volume: 0.95 in^3; Score: 0.277 mm*in^3.
Middle Bar Test 3: Displacement: 0.27 mm; Volume: 0.95 in^3; Score: 0.255 mm*in^3.
Middle Bar Test 4: Displacement: 0.28 mm; Volume: 0.95 in^3; Score: 0.268 mm*in^3.
Middle Bar Test 2 (above) provided the lowest score and became the base model for step 2, which was to cut out a substantial, trapezoidal section near the applied force. An additional trapezoidal section was added towards the top of the arm as well. Each of the Cut Tests we performed involved different arrangements and sizes of the trapezoidal cuts. The goal here was to remove material from the end that had very little stress on it. Most of the stress was near the base of the arm, so the extra material at the end was unneeded.
Cut Test 1: Displacement: 0.36 mm; Volume: 0.70 in^3; Score: 0.250 mm*in^3.
Cut Test 2: Displacement: 0.29 mm; Volume: 0.72 in^3; Score: 0.209 mm*in^3.
Cut Test 3: Displacement: 0.28 mm; Volume: 0.72 in^3; Score: 0.199 mm*in^3.
Cut Test 3 (above) provided the lowest score and was used as the base model for the step 3, where we tested different depths of shelling. Here, the goal was simply to reduce as much weight as possible without compromising too much stability.
Shelling Test 1: Displacement: 0.42 mm; Volume: 0.50 in^3; Score: 0.210 mm*in^3.
Shelling Test 2: Displacement: 0.323 mm; Volume: 0.61 in^3; Score: 0.197 mm*in^3.
Shelling Test 2 (above) provided the best score despite being only marginally better than the score without any shelling at all. The small difference was still desirable, so Shelling Test 2 provided the base for the fourth and final step: lightening holes and filleting. Here, the goal was to round edges to decease stress build up on corners as well as to decrease volume with holes.
Lightening Holes and Filleting Test 1: Displacement: 0.33 mm; Volume: 0.59 in^3; Score: 0.196 mm*in^3.
The final design (shown below) had almost every corner rounded. This reduced the stress substantially. No holes were used in the end because they seemed to decease weight insignificantly at the expense of much higher displacements. We are happy with the final design that has measurements as follows:
Displacement: 0.29 mm; Volume: 0.61 in^3; Score: 0.17 mm*in^3.