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Design Sprint Goals
This design sprint is intended to be a good starting point for new team members to learn about engineering concepts and how to develop a design from (nearly) the ground up. Other goals include:
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And the potentially more nuanced goal of this sprint is to design a functional trailing arm! Note that we’re going to be designing a trailing arm that will go on THE LEFT SIDE of the car. It isn’t important in the actual design, but makes the loading conditions easier to describe later on.
Topics Covered
Design Concepting
Computer-Aided Design
Design for Manufacturing (DFM)
*Design for Assembly (DFA)
Finite Element Analysis (FEA)
*Not guaranteed, but the opportunity is there!
Background Information
Let’s start at the basics, what is a trailing arm suspension? It’s commonly seen in the rear suspension of bikes as seen below.
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Now, back to the technical stuff. To answer a lot of these questions we need to set some design constraints.
Design Constraints
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You’ll probably learn some different terminology on this, but I’m using it as the values we know that we should design around. A big part of designing parts is finding number that you need to work around, but it’s very time consuming, so I’ve done the tedious stuff so you don’t! So, I’ll list them out here, and I’ll add in sections that show how I determined these values. You don’t need to know it, but I want to feed people’s curiosity where I can, and it stands to show a good example of documenting your design decisions.
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Feature | Dimension |
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Travel (distance between full compression and extension) | 2 15/16 inches 74.6125 mm |
Length at Max Compression | 12 3/4 inches 323.85 mm |
Eye Diameter (hole to bolt the shock) | 12 mm |
Design Criteria
Earlier we looked at constraints, specific numbers that limit what solutions are possible. Criteria are a bit more continuous rather than restricted. The best way to explain it is to apply them to this sprint.
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We’ll be using subtractive manufacturing methods (think sculpting, removing stuff to leave the part you want) on the parts of this car (additive we’ll need sponsorships, and we don’t have any secured). You’ll need to have more material than the part you want when you make a part with subtractive manufacturing. So finding a way to enclose your design, or a piece of your design, into the smallest volume possible. When you buy the blocks of stock (material that hasn’t been shaped) you’ll find that smaller blocks tend to be cheaper than larger blocks of metal (if you chose to go with metal). So, as a very rough starting point, you can “block out” the volumes that your design would need and roughly estimate cost by exclusively looking at material. |
Timeline
Week 1 - Concepting
Sept 11 - Sept 17
The idea’s pretty simple, come up with ideas! In concepting we want to come up with as many possible solutions as possible that can solve the problem we have. In our case, the problem is how do we support the wheel given all the information in Design Constraints.
What also might be useful to consider is how to make the part. If you take the best design possible that can’t be manufactured to a machinist, they still can’t make it. We won’t have the training/info session on manufacturing methods until later in the sprint, so only consider it at this stage if you have the time.
Deliverables
2 - 3 Concepts with Sketches (Digital or on Paper)
Week 2 - Computer-Aided Design (CAD)
Sept 18 - Sept 24
Now that we have some ideas on how to solve our problem, we need to pick one to develop further. Developing multiple ideas in parallel is very time consuming and not advised, but we won’t judge if you want the extra practice.
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An extension to this part of the design sprint would be to make your design parametric. A parametric design means that the dimensions of the part are defined “externally” from the file so it can automatically update if something needs to be changed. In essence, it makes it easier to tweak your design by not needing to dig through your feature tree to change a dimension.
Deliverables
1 Concept in SolidWorks Fully Defined
Week 3 - Manufacturing Design (DFM)
Sept 26 - Oct 1
With a design digitized, it time to start thinking about how it’s going to be made. Like I mentioned before, a great design is actually pretty bad if it can’t be made. Now that you’ve learned about different manufacturing techniques, it’s time to start specifying material and manufacturing techniques.
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A hint/idea I’ll throw out there is to see if your design can be made using multiple parts. I’ll try to bring example trailing arms during the presentation, but hopefully you can consider your design not as a single, solid piece of metal, but smaller more manageable chunks. Notices how this reduces costs as well, smaller blocks of metal are cheaper per unit volume than larger pieces of metal.
Deliverables
Bill of Materials with a manufacturing plan along with any changes to your design in CAD.
Week 4 - Static Structural Simulations (FEA)
Oct 2 - Oct 8
We have a design we can make, but will it hold up to the forces we need it to? Again, the idea is simple, but the execution is a lot harder. Hopefully you’ll understand the basics of SolidWorks FEA to run the simulation, but if you’re having any trouble with it, feel free to reach out!
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If through a thickness the part is failing, make the section thicker to increase the cross-sectional area.
Deliverables
A passing simulation with a stress distribution that makes sense along with any changes to CAD.
Final Review - Oct 22nd
This is where we get to put all your work together and see what others came up with! Everyone’s solution to the problem will be different, and their approach is something you can learn from. What we’ll do for the final review is combine the small groups on each time slot to see more solutions!
The date is not a typo, but it’s considering reading week and midterms for most of you. Which also means that you don’t need to finish the FEA for the 8th. But, I imagine during reading week and midterm week you have better things to do than figure out why a simulation isn’t working, but I let that be up to you to figure out.
Info Session Schedule
Date | Training Session Topic | Location |
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Sept 17th | *SolidWorks CAD | Rm 4417 |
Sept 24th | Manufacturing Methods | Rm 3052 |
Oct 1st | SolidWorks FEA | Rm 2004 |
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All will be happening from after Mech General (~1:15pm) to 2:30pm (hopefully). After the training session we’ll start doing reviews!
Review Schedule
We’ll be making small groups of around 3 people in which you will be paired up with either myself or Shangheethan. We’ll try to spend about 15 minutes on each of your designs, but we’re hoping it becomes a bit of a discussion on what the strengths were of designs and where there’s room for improvement.
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Jens is busy :( |
Sources
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Credits
This design sprint was heavily inspired by the one created by Aidan Lehal, Min Qian Lu, Kevin Bui, and Emily Guo! Big shoutout to them for the hard work they put in!
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