PART I: Introduction
In the midterm project, Joe and I decided to build a set of planetary gear according to the Mechanical Movement 412. As we know, the planetary gear system plays an important role in the automobile transmission system. This system is able to transfer high torques in a compact space with high performing.
I have been fascinated by this structure. Especially, during the build-up process, I realized how dedicated the great set design was. Once the gear set had a tiny angle and did not perfectly align the ring gears, it caused huge friction and could not rotate smoothly.
PART II: Workflow
This project was divided into four parts: Gate 1, Gate 2, Gate 3, and Gate 4. Joe and I attempted to complete this project step by step.
- Gate 1: Mechanical Movement and draft
In gate 1, Joe and I reviewed 507 mechanical movements and decided to make a planetary gear model. After that, we reviewed the previous class works on the blog and searched the related sources on the website. Based on the information we collected, we had a first draft with the details, such as laser cut parts, vinyl cut parts, and metal pieces, to fit the requirements.
. - Gate 2: Prototype made of cardboard
Before we started to use wood to make the movement model, we used cardboard to build a prototype. There are six parts in the model: station, stand, handle, ring gears, planetary gears and a tiny fan blade, as the pictures show below. During this process, we met some issues.
↑↑↑ Figures above demonstrate the different parts of the model made of cardboard. Figure A shows the station joints with ring gears. Figure B shows the stand connecting with two planetary gears, a handle, and a flan blade. In Figure C, you can see the whole structure of the mechanical model.
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[Issue 1]
First of all, when we printed the components, we found that the size was different than what we expected. After we went back to check the original draft, I learned that I had made a mistake that I did not check the “keep original size” box when importing files.
The oversize pieces
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[Issue 2]
When we assembled the prototype, we found that we had to consider the kerf carefully in the joint areas. Since the prototype is made of cardboard, the fault tolerance is higher. So, we created our kerf boxes based on the material we used in the model to make sure all the components could join perfectly.
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[Issue 3]
Since the planetary gear is really sophisticated, the fault tolerance of a wood-made system is quite low. In order to fix this potential issue, we decided to enlarge the size of the model when we used wood after discussing it with the TA. (increase 1.3x)
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[Issue 4]
There were different tiny pieces in each part, and some components were really similar. However, we did not store them in order. So, when we built the prototype, we took further time to arrange them. In order to fix this issue, we use the zipper bags to store them accordingly when we cut the wood pieces.
. - Gate 3: Enlarge the model size and make by wood
In this stage, we attempted to enlarge the size of the model. Also, we thought about including bearing in the model, making it decrease the friction and be able to rotate more smoothly. So, according to the size of the bearing and roads for gear transmission, we tried and error several times. In addition, we also finish the metal component cutting by using plasma cut.
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[Issue 1]
We found that the thickness of each wood we used was not quite even. Also, the texture of some areas on the same pieces of wood is different either. Thus, we have to adjust the laser cut’s parameters accordingly. Besides, we have to make sure that the joint components are cut in the close area of the wood pieces.
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[Issue 2]
Originally, aiming to reduce the friction, we added bearings into gears. However, the sites we added were wrong. The bearings reduced the friction, but it terminated the transmission. Eventually, to minimize the modification of the whole structure, Joe and I decided to remove the bearings and recut the part of the components to fix this issue.
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. - Gate 4: Complete the wood-made model and post-processing
Finally, we collected all the components for our model and assembled them. After that, we sent the surface of our model and coated a layer of wax. Besides, for the metal pieces, after the plasma cut, we remove the residues and do the sandblasting. Later, we used glue to solidify the connection between the stands and the station. On the final model, we used the vinyl cut to make a Rice logo, “R,” for the decoration.
↑↑↑ The over view of the whole model.
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↑↑↑ The metal pieces.
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↑↑↑ The metal pieces.
.↑↑↑ The mechanical model works.
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[ISSUE 1]
When we stuck the wood pieces and metal pieces, Joe and I were not clear about which was the appropriate glue. After discussing with TAs, we found that there is a useful table in OEDK. Based on the information on that table, we chose the super glue.
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[ISSUE 2]
The fan blade site had a gap between the ring gear and the stand in the prototype as picture A shown below. However, when we assembled the model, we could not be able to make the planetary gear align with the ring gear vertically. In order to fix the planetary gear in the ring gear stably, we added more spacers to hold the planetary gear in the right direction, as shown in Figure B.
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[ISSUE 3]
Since we built a multilayer structure, aligning each piece together was really important. During this process, we missed matching the spacers and the planetary gear. Thus, when we installed a rod on it, as the picture shows below, you could see the rod did not insert vertically. So, we detached the pieces and re-stuck them again.
PART III: The Work Space
The space was cleaned after used.
PART IV: Cost Estimation
| Cost Type |
Cost | Price | Source | Quantity | Total |
| Materials
|
1/4″ Baltic Birch Plywood 12″x20″ | $5.99 | woodworkerssource.com | 2 pieces | $11.98 |
| 1/4″ Steel Sheet 4″x12″ (Hot Rolled) |
$11.47 | menards.com | 3″x3″ | $2.15 | |
| 1/4″ Cardboard Sheet 12″x12″ (30 pcs) |
$25.49 | amazon.com | 3 pieces | $2.55 | |
| 1/4″ Wood Dowel 12″ (25 pcs) |
$4.99 | amazon.com | 0.5 piece | $0.10 | |
| 1/5″ Wood Dowel 6″ (200 pcs) |
$6.99 | amazon.com | 1 piece | $0.03 | |
| 1/8″ Wood Dowel 12″ (200 pcs) |
$9.99 | amazon.com | 0.5 piece | $0.02 | |
| Wood Glue (237 ml) |
$3.68 | amazon.com | 20% bottle | $0.74 | |
| Super Glue (4 g x 8 tubes) |
$8.99 | amazon.com | 1 tube | $1.12 | |
| Howard Butcher Block Conditioner (355 ml) |
$9.98 | amazon.com | 10% bottle | $0.99 | |
| Labor | Laser Cutting Operator | $20/hr | ZipRecruiter.com | 3 hr | $60.0 |
| Machine Shop Plasma Cutter Operator | $20/hr | ZipRecruiter.com | 0.5 hr | $10.0 | |
| Prototyping Engineer (You!) |
$25/hr | Indeed.com (Engineering Intern) |
7*2 (members) hr | $350 | |
| Overhead | Machine Time (Laser Cutter) |
$120/hr | lasercuttingshapes.com (Laser Cutting Cost) |
3 hr | $360 |
| Machine Time (Plasma Cutter) |
$260/hr | cnczone.com | 0.5 hr | $130 | |
| Quality Control | $22.5/hr | Glassdoor.com (Quality Assurance Inspector) |
0.5 hr | $11.25 | |
| Design | Engineering and Development | $25/hr | Indeed.com (Engineering Intern) |
3 hr | $75 |
Total: 1015.937
The total for completing the planetary gear set is $ 1015.937. Most of the manufacturing cost of our mechanical movement device comes from labor and overhand, including facility uses and quality control, with a total of $ 921.25. In the future, to scale up the device’s manufacturing, we can achieve more efficient manufacturing by implementing a lean process to take advantage of the already invested overhead cost and prototyping. With more experience manufacturing our device, we can further reduce the material cost by saving space on the laser cutting wood sheet to achieve more output from the same wood sheet. Furthermore, the manufacturing cost can be diluted with the increase in the scale that all prototyping labor and material costs will be evenly distributed with the number of devices manufactured.
