Project Goals
Get leads accustomed to designing relevant components and critiquing each other’s work.
Making self-driven decisions throughout the entire process, starting from basic requirements + constraints, to selecting OTS components, all the way to sim validation.
This is very important as we anticipate to be designing with little direct supervision (i.e we can rely on prev leads so much; being able to think critically for ourselves is huge).
Getting comfortable with holding each other accountable to our own deadlines.
Documenting our progress and decisions.
Topics to be Covered
Force Analysis (hand calculations)
Off the Shelf Part Selection
Concept → Design
Material and Manufacturing Selection
Finite Element Analysis
Drafting
Project Introduction
We are challenged with designing the bellcrank, bellcrank clevis, and pushrod for the inboard suspension pictured below. The given parameters are as follows. Requirements and constraints will be at the discretion of each person.
...
Purpose of Inboard Suspension: “The main advantages of a push/pull-rod suspension system on a track-focused race car have to do primarily with the ability to move suspension components closer to the ground, lower the chassis of the vehicle, and lower the centre of gravity to improve efficiency in cornering, body-roll, and high-speed stability.” - Wikipedia
For the purposes of this project, we want to maximize the force output of the shock, in doing so, the force vector needs to be directly in line with the coilover shock. We will accomplish this using a clevis to redirect the angled bump/gravity force and translate it into the shock along the axis required. [See Appendix for visual explanation]
The given dimensions and component specifications are in the table below:
Specification | Value | ||||
|---|---|---|---|---|---|
Shocks from MSXIV | Spring Force: https://www.ridefox.com/family.php?m=bike&family=floatx2 | ||||
Chassis and Suspension Geometry |
| ||||
Mass of Vehicle | 192kg | ||||
Center of Gravity Location |  | ||||
Loading Conditions |  | ||||
Assembly Max Height | Cannot exceed 100mm past top chassis member. |
Timeline
Phase 1 [Jan 3-14; 2 weeks]
Conceptual Design: Sketches of design concepts, with labels and descriptions where needed to effectively communicate design ideas.
Force analysis: Using the diagram of force locations on the model car above, find the center of mass/gravity (CG) for the vehicle, use the CG to determine the load distribution between axles, use the load distribution to find out how much load each independent suspension assembly needs to withstand, calculate how much load each component in your design undergoes based on the front left independent suspension load force.
Off the Shelf Part Selection: Ensure that your sketches and designs include what types of off the shelf (OTS) parts you would like to use (e.g. You want to join two components together without welding? What type of fastener will it be? Will you use a pin? Shoulder Bolt? Zip tie?). In Phase 1, the selection process does not need to be specific (diameter, thread length, head type, etc.), but these factors should be considered when designing.
Phase 2 [Jan 17 - 28; 2 weeks]
Detailed Design: Concepts should be finalized at this point and moved into CAD. An accurate model containing all properly dimensioned components and OTS parts should be drafted (to be done in SolidWorks). Ensure proper modelling techniques are used, each component is a different part, proper naming of each component, properly mated assemblies, CAD files/mock replacements for OTS parts. The final CAD model should look exactly how it is expected to look in real life.
Material Selection: Each component should have a material assigned to it based on the requirements of your design. Use past experiences and intuition to select materials for a component (e.g. glass shouldn’t be used as the chassis material of a car because it will shatter upon impact) and refer to the material’s properties to make an accurate selection.
Resources to help with material selection: https://www.engineeringtoolbox.com/material-properties-t_24.html, http://www.matweb.com/
Manufacturing Method: How will your part be made? Consider the tools we have in the bay and in the machine shop. Will this part need to be outsourced for manufacture? Ensure you determine one or more methods of manufacture (waterjetting, CNC Mill, injection mould, etc.) for each component.
Refined OTS Part Selection: With your OTS parts selected, it is time to specify the exact parts you need for your design to work (with safety factors included). Use websites and catalogues to determine what exists out there and try to select a cost effective part for your design. Try to be consistent and use standard sizes where possible (e.g. A bolt size M6.789 is very specific and unlikely to find, try designing with M8 instead). For example, say you want to fasten two brackets together using a nut and bolt:
Refined Bolt Specifications: Bolt size, bolt material, tensile strength, shear strength, grade (needs to comply with ASC 2024 regs), etc.
Refined Nut Specifications: Nut size (should fit on bolt), nut material, grade (needs to comply with ASC 2024 regs), etc.
Resources to help with OTS parts: https://www.mcmaster.com/ is a great tool to find OTS parts to fit your design needs (and most of them have CAD files too!), it can be a more expensive option though so once you have a part selected, try to find a cheaper one of equal quality.
Phase 3 [Jan 31 - Feb 18; 3 weeks]
Finite Element Analysis (FEA): Using your SolidWorks model, analyze how the load forces (calculated in phase 1) for each part will impact your design. Setup the model with accurate constraints, load forces , load force locations, environmental impacts (gravity, atmospheric pressure, etc.), and simulation refinements (mesh size, fastener implementation, etc.) for the best results. Use the FEA results as a comparison point to how you thought your design would react under the conditions. Check and recheck your setup to ensure the results from the FEA are as accurate as can be.
Redesign (if needed) based on FEA: Strengthen, stiffen, reinforce, reduce, or resize the components in the model as needed to make it work under the load conditions established. Midnight Sun uses a safety factor of 2 on all components as a personal standard and to comply with ASC 2024 Regulations. Safety Factor is calculated with the formula [Part Yield Stress/Part Max Stress >= 2]. Return to Phase 2 as many times as needed to achieve the desired results from the FEA.
Drafting: Once the model is adequately designed, compile all OTS parts and raw materials required into a Bill of Materials (BOM), and make a orthographic drawing of each component with proper General Dimensioning and Tolerancing (GD&T) annotations so it can be manufactured.
Project Deliverables
After each phase, a review will be held to share ideas, get feedback, and inspire your teammates! The following deliverables should be presented in a Slide Deck** (MAX 5 minutes per presentation with 10 minutes for feedback/questions):
Phase 1: 3 Concepts sketched and labelled (1,3), load distribution calculated (2)
Phase 2: Detailed design of one concept in SolidWorks (1), and all required specifications for components (2,3,4)
Phase 3: FEA summary (visuals and short description of changes made)(1,2), BOM and orthographic drawings of each component (3)
**it is recommended to keep a design log (in google slides format) throughout this project of all decisions/choices made, the log will make finding the content to present easier come review day!
Proposed Phases/Reviews:
The primary goal is for the mech leads to receive feedback and iterate as many times as possible within ~1 month. To do this, two review periods will be set.
...
Phase 1: Pre-review. This is time for the designer to
Analyze the problem at hand
Come up with concept sketches
Perform force analysis
Come up with initial designs + justifications
Material selection + manufacturing method selection
Propose an initial design in the form of a design log, going through the key decisions that were made, etc.
Phase 2: Post-leads review
Based on the feedback from each other, the designer will have time to rethink their approach and patch up any problems that they may encounter.
This will also help with both giving and receiving feedback; a critical skill moving forward into the design of the car.
Phase 3: Post-advisors review
Based on feedback from the advisors, final design changes can be made, as well as reflecting on the approach taken throughout this process.
Potentially a secondary advisor review to get some kind of closure on the iteration made after the advisor review? This can be discussed in further detail
Appendix
...