Frame Design Early Research

Owned by Joshua Miksits
Last updated: Sep 14, 2024
4 min read

1) Early Design Considerations of the Frame

2) Define main goals for the competition and create a chassis around that. i.e., solar car competitions are endurance-driven

  • Light weight to reduce work on the battery and rolling resistance

  • High stability to prevent roll overs (i.e., a low center of gravity is more stable)

  • Ergonomic comfort (i.e.,roll cage and occupant space must have enough clearence so driver can seat comfortably for 1,000s of miles

3) Generate and decide on high-level design choices that effect the team as a whole. (Body shape, wheel configuration, and frame type)

  • Body shape - important for aerodynamic performance and locations of driver/battery box. Ensure there are enough clearences for these major systems

    • Monohull

      • More suitable for cross-country races

      • Tend to be very rear-biassed in weight (due to the solar array and battery box)

      • Long and narrow, arrow-like shape

      • Suspension geometry must be narrow enough to fit the track width and within the aeroshell package

      • Challenging to keep stable because of its shape

    • Catamaran

      • Wider and bulkier

      • Weight is distrubuted front to back

      • More interior room

      • More stable and can’t roll over as easily

  • Wheel configuration - important for not only energy efficiency but vehicle stability

    • 4-wheeled

      • Slightly less energy efficient than 3 wheels

      • More dynamically stable

      • Asymmetrical design with motor biassing left or right rear wheel

      • Simple suspension design

      • Wheels are consistently in contact with the ground, which permits even tire wear

      • Simple, stable handling

      • Traditional design with lots of design resources

    • 3-Wheeled

      • More energy efficient, with less drag and rolling resistance

      • Less dynamically stable, especially at corners because of the lateral load transfer and rear wheel slippage

      • Symmetric design with simple rear wheel alignment

      • Complex suspension design for rear wheel (trailng/swing arm)

      • Aerodynamic package could be better with a narrower tear-drop profile

      • Need a wider track width and wheel base for stability

      • Need to balance COG and the position of driver/battery so that 60-70% of the weight shifts to front wheels during braking. I.e., we need to make sure most weight nearer to front axle

      • Vehicle handling is difficult

      • More innovative with less design resources

  • Frame Configuration - Important for weight-savings and strength, but must also take into account complexity, design time, manufacturing time, etc.

    • Tubular Space Frame

      • Quick design and development

      • Cheap and less time-consuming to manufacture

      • Heavy with more rolling resistance

      • Design is adaptable and can be reiterated relatively easily

      • Mounting is less complex

      • Simulation is less complex (or should be) because of the consistent material properties of tubes

      • More jigging during manufacturing

    • Composite Monocoque

      • Extensive time designing and developing

      • More expensive and time-consuming to manufacture

      • More lightweight and energy-efficient

      • Design must be completely finalized before manufacturing

      • Mounting suspension is complex

      • Simulation is complex because of the inconsitent material properties of composites

      • Less jigging during manufacturing

    • Hybrid Monocoque

      • Relatively simple to design, but composite panelling adds complexity which adds research, adds time, etc

      • Can switch structural areas of heavy tubing with lightweight and rigid panels, decreasing weight

      • Complicates validation of load cases (i.e., empirical testing, FEA, both…?)

      • Kickstarts development of composite monocoque which drives the team forward from failed past designs

4) Define main goals for the team and create a chassis around that i.e., the chassis exists to meet the design and packaging requirements for all the major systems

  • Design to integrate with suspension

    • Form the chassis around the hardpoints

    • Settle on the desired chassis width and height based on what vehicle kinematics the team wants

  • Design to integrate with driver area/ergonomics

    • Leave enough interior room for driver area and roll cage clearences, while still fully enveloping the driver safely (free movement of head)

    • Enough room for the legs of the driver to fit in the car (maybe do a 3 level frame to seperate design contraints of suspension from the design constraints of ergonomics so frame height is not fixed

    • Enough room for ergo components, including pedal box, dashboard, steering, ballasts, driver seat

  • Design to integrate with battery and motor controller

    • Leave adequate space for the motor controller and battery box, including insertion and removal of battery, modularity of electrical components, etc.

  • Design to integrate with aeroshell

    • Ensure the canopy and roll cage are designed in tandem so that the car is balanced and there is enough room for the driver

    • Work with aeroshell when determinig the thickness of the chassis in various locations, where will it be more narrow and where will it be wider

5) Define performance targets

  • Locate major systems to optimize vehicle stability

    • Use weight estimates to determine a target center of gravity based on a predetermined track width and wheel base

      • For 3-wheeled, COG should be longitudinally located nearer to front axle so as to balance 60-70% of weight on front wheels during braking

      • Find ways to lower the COG height, i.e., suspension components lower to the ground, a lower frame height, type of driver we are aiming to design around, etc

      • Where along the chassis should the driver and battery/array area be so that the car is the most dynamically stable during driving, cornering, and braking conditions.

 

 

Resources:

https://drive.google.com/file/d/1LSd4Qrnsn590R89NNFfRHFjNbKEwbnv1/view?usp=sharing

https://michaelsri.wordpress.com/2021/06/28/ku-solar-car-history-part-2-5-astras-car-design/

https://engineerdog.com/2015/09/09/engineering-a-3-wheel-vehicle-chassis/

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