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https://docs.google.com/document/d/1CCwGOWY7R8nmJOKmoRsVYOPtctsRLJMWH11a8YYiBiw/edit?usp=sharing960

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The Google Doc linked below contains all the following content for this section. This was done as doing it within Confluence’s built-in word processing was getting messy and unorganized.

Google drive docs
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Selected Concepts

Trunk

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  • Selected concept based on further research and feasibility analysis: Compressed air struts

Main reasons:

  1. Ease of use

  2. Ease of implementation

  3. Manufacturing time

Ease of Use (1)

Based on the research done in the previous section, it was evident that the user interaction would be much easier and streamlined with the compressed air struts compared to the 2 bar linkage system.

Compressed Air Strut:

  • Opening the trunk: User unlocks trunk latch and lifts trunk. Compressed air struts prop trunk and keep it open (no user interaction needed beyond lifting of trunk)

  • Closing of trunk: User pulls down to close trunk panel, locks trunk latch

2 Bar Linkage System:

  • Opening the trunk: User unlocks trunk latch and must lift trunk for entirety of its range of motion. User then needs to slightly lower the trunk to engage the “Bird’s Mouth” Lock

  • Closing the trunk: User needs to raise the trunk panel slightly to disengage the “Bird’s Mouth” Lock. User then pulls down to close trunk panel, locks trunk latch

2 Bar linkage system’s process is: lengthy, not intuitive and cumbersome

Ease of Implementation (2)

As can be seen in the previous section, there were notable concerns with the 2 bar linkage system.

2 Bar Linkage system - Locking (to keep Trunk open):

  • Basic assembly did not account for gravity. Therefore hard to verify if the “Bird’s Mouth” Lock could easilybe engaged.

    • There were some cases where the top bar may not translate diagonally and could instead rotate. This would not properly engage the “Bird’s Mouth” lock

    • In the end more testing would be required

2 Bar Linkage system - Unlocking (to close Trunk):

  • Basic assembly did not account for gravity. Hard to verify if gravity would pull bottom bar down and for the entire assembly to fold into itself (like how it was shown in the video)

    • Again more testing would be required if this would happen in real life

2 Bar Linkage system - Summary:

  • Need to conduct more testing, making design process longer

    • Could use SolidWorks motion study to account for gravity

      • But the slot mate used to connect top and bottom bars was not compatible with motion study

    • Could build scaled down model

Compressed Air strut - Summary:

  • “Back of the envelope” calculations verified struts could keep the trunk open (official calculations can be seen in the Detailed Design phase)

    • To be safe, each one of the struts can keep the trunk open

      • Therefore even if one fails, the other will be enough to ensure trunk stays open

  • “Back of the envelope” calculations verified users could easily close trunk

  • Overall more confident that it can work as intended as opposed to 2 Bar Linkage system which still had major uncertainties

Manufacturing Time (3)

2 Bar Linkage system:

  • Simple geometry but would still require manufacturing and assembly time

  • Would also take up manufacturing resources

    • Regardless of if we do it in-house or outsource it, it is a manufacturing resource that is being used

Compressed Air strut:

  • Would not need to be manufactured

    • Only the mounts need to be manufactured

      • But those need to be manufactured for 2 Bar Linkage system as well

  • Frees up manufacturing resources

  • Was reasonably priced (approximately $63.00 CAD for a set of two from McMaster-Carr)

    • Therefore price was not an issue

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  • Overall Concept Selected: Add on Roof Prop System

Main Reasons:

  1. Weight

  2. Size / Volume

  3. Loading Conditions

Overview

As the Hinge-less Roof Prop System would be mounted onto the B Panel Bulkhead, the prop itself would need to be quite long to:

  • Reach the roof panel itself

  • Be long enough to angle the roof to the desired position

This would lead to an increase in both weight as well as overall size / volume.

With regards to the size / volume, it would also be taking up a significant amount of space within the interior of the car. Given that the interior space of the car was already tight, this would only make matters worse

Finally, while the “hinge replacement” roof prop in the Hinge-less Roof Prop System would undergo compression (which most materials are fairly strong in), the other one would be undergoing bending as well. Due to their very long and thin nature of the rods, this may require rods made of high(er) strength materials which may drive up costs and/or weight

Selected Components of Add-on Roof Prop System

This section will now cover which components of the system architecture for the Add-on Roof Prop System were chosen.

Hinge Mounting: Supplementary Panel and Direct Attachment

For the rear hinge (behind the C Panel Bulkhead) the direct attachment method was the most straight forward, with little to no additional hardware required. This would reduce both manufacturing time and cost.

For the front hinge (behind the B Panel Bulkhead) the supplementary panel was chosen as it achieves the same functionality (providing a mounting area for hinges) as the Weld Tab while retaining more flexibility in how it is mounted (can be adhered, fastened or welded). This allows for more flexibility in the manufacturing and design process.

Roof Hinge: Four Bar Hinge

This was the simplest, smallest and most feasible hinge design option. This reduces risk, while also reducing design and manufacturing time and cost. In addition, its usage by other solar car teams is a vote of confidence that this mechanism is well suited for use as a hinge for tilting roof mechanisms.

Roof Prop: Snap Lock

Among the considered concepts this was the safest (can have multiple snap locks along the prop), most robust (if a lock fails can easily reinstall a new one as they only interact with the outside of the outer tube), and simplest. This reduces risk and is a solution that is appropriate to the rigorous nature of our application.

Prop Mounting - to Roof: Eye Bolt

Based on the concepts for Prop Mounting to the Roof, the Eye Bolt was the safest, most reliable and most feasible concept. Its straightforward construction and operation reduce risk and reduce manufacturing and design time. That being said, it isn’t as user friendly as other options since the user has to screw / unscrew the shoulder bolt but this also makes it the safest option.

Prop Mounting - to Chassis

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  • Configuration 3 for the Trunk Prop was chosen due to its manufacturability and ease of assembly

Important to note is that due to design changes to the chassis, chassis tubes extending to the trunk area were included and these will be used as a mounting area for the brackets

This is preferable to using the bottom panel as the bottom panel is no longer structural (due to manufacturing constraints the honeycomb core was not placed between the carbon fibre plies). Mounting to the chassis tubes provides a more stable base for the trunk prop

Regular L brackets can be used in the mounting of the compressed air strut as Configuration 3 was chosen

Compressed Air Strut

As mentioned earlier McMaster-Carr Gas Struts were chosen. This was due to their: reliability, variability (many sizes to choose from) and cost

Below will be how the specific size and force of McMaster-Carr Gas strut was selected

Force

To determine the required force the gas strut must exert we must determine the mass it must hold

  • Weight of Trunk Panel itself: Maximum 9kg

  • Weight of Solar Cells and Encapsulation: Calculated via - Solar Cell Surface Density * Surface Area

    • Solar Cell Surface Density = 1000g/m2

    • Surface Area Total = 1.4770m2

    • Therefore Weight of Solar Cells and Encapsulation = 1447g or 1.447kg

  • Total Weight = 10.447 kg or 23.03 lbs