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12. Design & Build a Machine

For this group assignment, we had 2 weeks to design and build a functioning machine.
We at FabLab Kamakura decided to make an Onigiri (Japanese Rice Ball) shaping machine.

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Assignment objectives for 9th Apr - 22 Apr:
1. Mechanical Design: Design a machine that includes mechanism + actuation + automation + application. Build and assemble the mechanical parts, and operate it manually.
2. Machine Design: Actuate and automate the machine.

In this page I document my contribution, which was to design and build the Iris mechanism for shaping the onigiri from 3 sides. The overall machine building process is documented on the group documentation page.

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Halfway through, due to disagreements about realistic scope of machine and how to allocate tasks, we were asked by the node to work in separate locations. Although I was not confident to finish my assigned task on time and successfully, I did not have another choice (other than to do my groupwork individually), so this is a documentation of my best endeavor.

Although I did not manage to complete the machine in the end, this assignment gave me a taste of Designing Mechanisms, and I’m happy with the progress I made in a little over a week. I wish I could also have had a chance to explore the Machine Design aspect of the assignment, which I’m sure is a wholly different challenge!

Concept:

While we were exploring the best approach for shaping the rice ball, the Iris Mechanism was suggested to us by Nagano san and Rico. It’s a mechanism used in camera lenses and some valves, for controllling the exact amount of light/substances flowing through a hole. We thought this might potentially be a great approach for making an expandable triangle-shaped mold.
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An iris inside the camera lens & surrounding 007

The beauty of this mechanism is its ability to intricately control the size of lens aperture with just one motor. This makes it perfect for cases where precision is important, but I eventually realised that it might not be a sensible approach for shaping something more substancial like rice.

In addition, I didn’t think I could finalise the mechanism by myself in the remaining 2 days without my team member’s help, so we dropped this mechanism and settled on a much simpler “Plan B”.

Mechanism Design:

1.Cardboard Prototype

Apr 12th (Sat)
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After the instructors showed us this mechanism, I tried making a life-sized prototype for testing it on real rice. Although this mechanism is supposedly easy to make according to my instructors, trying to recreate it was not easy for me!

2. Testing the prototype

Apr 13th (Sun)
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Next morning, we tried the cardboard prototype on real-rice.
It seemed to shape the rice quite well, so we all agreed to proceed with this approach.

At the end of the day, we discussed the task allocation, and I was tasked with building the whole Iris mechanism. I tried to delegate some tasks to other members, since I was not confident to finish everything by myself, however this was dismissed as it was apparently the easiest part…
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3. CAD design

Apr 14th (Mon) - 16th (Wed):
I spent a couple of days modelling the Iris mechanism. In this step, I struggled with figuring out the correct measurements (lengths and angles) to fit the design inside our frame. In addition, halfway through, my team members found an alternative frame, and I had to redo the sizes again.

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I found this tutorial helpful in completing the CAD model.

3.1 Designing the Main Iris Part

As I had forgotten all my high school trigonometry I used this site to calculate the angles and lengths.

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I also managed to animate the Iris on Fusion360, but I didn’t manage to document that part. If you’re interested you can follow this tutorial.

3.1 Designing triangle blocks

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3.2 Designing Gears

Yamamoto san initially recommended using TinkerCAD but their feature only supported up to 200 teeth (I needed 256). Then Tsuchiya san recommended this tutorial page which helped me understand how to use Fusion360’s “Utility” tab.
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I also added gear teeth to the base edges.
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4. Test-Fabricate

Apr 17th (Thu)
I laser-cut a 1/36th scale model to test that my design works.
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Here I made a mistake of printing it too small (although it was a conscious decision in order to save materials), as the gear teeth were too small for it to be tested properly.

Based on this test model, I refined my design further, such as making the center circle more light-weight, making the slot thicker in width for smoother movement, etc.

5. Fabricate

Apr 18th (Fri)
Next day, I laser cut everything at life-size, and assembled it to test that it works ok. I also tested that the gears work well together. I found that gears work better when 3D printed than when Laser-cut, due to the resilience of material. I also completed the remaining design, such as figuring out all the layers in order to calculate the length of the 3D printed rod. alt text

6. Assemble and Test

Apr 19th (Sat)
Finally, I 3D printed the triangular molds and the rod, and assembled all the parts, including attaching tiny wheels to help with the gear movement. I had to make some extra parts to adjust the heights, but in the end, I managed to get it working quite smoothly.
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7. Actuate

Apr 20th (Sun)
Based on yesterday’s test, I added some extra parts for supporting the vertical structure and for fixing the motors in place. In the afternoon, Tsuchiya-san helped me connect the gears to the motor and we actuated the mechanism with a stepper motor. alt text

I also tried to shape real rice, first without the motor (moving the gears manually), but I found it surprisingly difficult to mold the rice (it took a lot of force to close the iris). Also, the extra parts I made in the morning seemed to have made the movement less smooth, and I couldn’t get it to work like yesterday anymore. By this time I became sceptical of the machine completing successfully on time.

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Also, I modelled and 3D printed some casing to attach the motor securely to the frame.
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Finally, we motorised the rice shaping, but as I feared, our motor was not strong enough to shape the onigiri.
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Since I only had the rest of the day to fix it, I thought it could be difficult to investigate all the errors and fix them by myself before the deadline. So we as a group decided to drop this mechanism and complete a much simpler machine.

Bill of Materials (BOM):

Files:

Please see Group Page.

Reflections:

What worked well?
Although the final result wasn’t perfect, I did manage to build a basic mechanism, and if I had 1 more week, I might have got it working moderately well.

What didn’t work?
We experienced some issues with our groupwork, mainly around agreeing on the machine’s concept and scope. Although we tried to reach a convincing agreement, ultimately we ended up with an unrealistic plan, and unfair task allocation.

In terms of my Iris Mechanism, my biggest mistake was not having a robust plan of action. Ideally, I should have started with listing up all the parts, systematically designing them step by step, so that I had clear idea up front of what needed to be made or bought, by when. But I also think the difficulty of the task and many unforeseen changes in plan midway made that difficult.

What are opportunities for improvement?
2 potential improvements to my mechanisms would be; Addition of another motor, to have it working from 3 sides, and better consideration of Joint clearance for smoother gear movement.
In terms of groupwork, I need to work on staying calm under heated situations and keeping asssertiveness to define the scope more effectively.

Assignment Checklist:

  • Documented the machine building process to the group page
  • Documented my individual contribution to this project on my own website
  • Linked to the group page from my individual page as well as from group page to my individual pages
  • Shown how my team planned, allocated tasks and executed the project (Group page)
  • Described problems and how the team solved them (Group page)
  • Listed possible improvements for this project (Group page)
  • Included my design files (Group page)
  • I need to present my machine globally and/or include a 1 min video (1920x1080 HTML5 MP4) + slide (1920x1080 PNG) (Group page)