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titleDifferent concepts and Research for the Trunk Roof Props

  • SINGLE SLIDING BAR MECHANISM

  • 2 BAR LINKAGE SYSTEM

    • Similar to one described for the Trunk

      • Could have second mounting point on the existing chassis tubes

...

Feasibility Analysis and Further Research

Trunk

      • Must consider if this will potentially damage solar cells

        • We know pressure should not be exerted onto the solar cells from the top - but could pressure from the bottom be an issue?

Expand
titleFurther research and analysis done on the selected trunk concepts

2 Bar Linkage Mechanism with “Bird’s Mouth” Lock

  • Bird’s Mouth Lock system shown in research section above can be simplified down

    • Simplified version utilizes only a flange to keep the two bars from rotating (thus locking them in place and propping the trunk)

      • Above image shows an exploded view of the simplified mechanism

      • Below is a video of the theoretical motion of the system

        • NOTE: GRAVITY IS NOT SIMULATED IN THE VIDEO SHOWN - THIS MAY AFFECT THE FINAL MOTION OF THE SYSTEM

        • 2 Bar Linkage with Bird's Mouth Lock Motion (3).wmv

          • Considerations:

            • When locking (i.e. pushing down on the top linkage to engage with the flange), steps must be taken so the linkage translates diagonally down (as opposed to rotating about its mounting point) so that it properly engages the flange

            • To do so: the rotation point could be tightly secured

            • When closing, the two linkages should fold into each other, we are assuming gravity will pull the bottom linkage down and thus provide this motion but this is an assumption

Compressed Air Support Strut

  • Considerations

    • Generally support struts are used in pairs

      • This will result in even distribution of force (as both sides of whatever item is being supported are receiving the force exerted by the support struts)

    • Support strut will exert a force that is When the trunk is in the open position, the compressed air struts will be exerting a force greater than the force exerted by from the mass of the trunk

      • When closed the compressed air support strut is constantly exerting a force that will try to open up the trunk

        • Latch must be able to withstand this force (though this shouldn’t really be an issue unless the support struts being used are overspecc'ed by a large amount - which should not happen)

        • This constant force will result in a residual stress buildup in the mounting area of the trunk

          • Must consider if this will cause elastic / plastic deformation of the trunk panel

            • While this shouldn’t happen (as the magnitude of force is quite low) it should still be considered

          • Must consider if this will potentially damage solar cells

            • We know pressure should not be exerted onto the solar cells from the top - but could pressure from the bottom be an issue?

Purchasing Link

Rated Force

Compressed Length

Extended Length

Purchasing Link

Rated Force

Compressed Length

Extended Length

Price

Notes

https://www.mcmaster.com/gas-struts/gas-springs-7/extension-force~range~~-11682713872416/

Smallest: 66N

128.016mm - 300.99mm

(centre to centre)

178.054mm - 511.048mm

(centre to centre)

$25.19 (converted from USD)

(potential shipping costs not included

Note: This encompasses a wide selection of gas struts

This is a link to their American website

Note: These do not include mounts, but they include a ball stud so making the ball socket is not necessary

https://www.amazon.ca/10inch-Supports-Gas-Struts-Screws-ARANA/dp/B07S6GFCXB/ref=sr_1_12?dchild=1&keywords=10lb+strut&qid=1603594722&sr=8-12

45N (each)

90N (for set of 2)

165mm (Centre to Centre)

250mm (Centre to Centre)

$63.99

($22.31 for shipping)

Comes in a set of two

https://www.amazon.ca/OTUAYAUTO-45N-10Lbs-Gas-Strut/dp/B088NLN4LV/ref=sr_1_1?dchild=1&keywords=10lb+strut&qid=1603593527&sr=8-1

45N (each)

90N (for set of 2)

165mm (Centre to Centre)

250mm (Centre to Centre)

$39.99

($6.85 for shipping)

Comes in set of two

No reviews

https://www.amazon.ca/FURNICA-Close-Telescopic-Spring-Support/dp/B075KV5XCX/ref=sr_1_5?crid=3YC4RIXRSJWQ&dchild=1&keywords=40n%2Bgas%2Bstrut&qid=1603384346&sprefix=40n%2B%2Caps%2C204&sr=8-5&th=1

40N

Through calculation based on drawing: 171mm (End to End)

247mm (Centre to Centre)

269mm (End to End)

$35.60 CAD

These are not soft close - only soft open
-Unlike the description given

Some reviews mention metal mounts are starting to buckle

-Could purchase the struts but make our own mounts

-Gas struts have ball and socket mounting system (will be hard to produce the ball mount)

-May have to just reinforce existing mounts

https://www.amazon.ca/Spring-Strut-Heavy-Compatible-Mounts/dp/B00Y3H2MSY/ref=sr_1_6?dchild=1&keywords=10lb%2Bstrut&qid=1603594722&sr=8-6&th=1

45N (each)

304.8mm (did not specify whether or not it was centre to centre or end to end)

508mm (did not specify whether or not it was centre to centre or end to end)

$33.86

($9.99 for shipping)

Set of 2 costs $39.97 (only costs $6.11 more?)

DOES NOT COME WITH MOUNTS

-would have to purchase our own

Compatible with 10mm ball socket

  • Preliminary Motion Analysis

    • Conducted using McMaster-Carr gas strut (12.2” extended length, 8.26” compressed length), with placeholder trunk and side panels

    • Note: This initial test was done with a flat trunk panel placeholder, the actual trunk panel is not flat

    • Early results:

      • Gas struts can be mounted within our vehicle architecture and still produce desired results

        • Compressed Air Strut Motion.wmv

          • Note: The compressed air strut should be PARALLEL to the trunk in the closed position. This should be done so that when the trunk is unlocked it does not immediately open (because force of the strut will be acting parallel to the trunk)

            • This will avoid any potential accidents where the trunk is unlocked while there is an obstruction above the trunk and hits it while opening - which would result in serious damage to the solar cells

  • Unconventional Mounting (if needed)

    • If the the mounting point of the trunk is not in line with the rotation point of the trunk (unlike how it is in the test above) the strut must be slightly extended when the trunk is closed

      • This will allow for the necessary slight compression of the strut when the trunk first opens up

        • The circle represents the path of the mounting point. When the trunk first opens up, it will travel up and away from the pivot point, thus requiring the strut to compress

        • Also note how the strut is slightly extended when the trunk is in its closed position (as described previously)

Roof

Expand

Single Sliding Bar Mechanism

Image Removed

As seen in the image above, there is (at a minimum), 5mm of clearance between the top of the chassis tube and the bottom of the roof panel

This does not provide sufficient space for the single bar sliding mechanism

Unless an unconventional, super low-profile design is utilized

This may present manufacturing issues however

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.

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

Selected Concepts

Trunk

Expand
  • 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

Roof

Expand
  • 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

Preliminary Design

Trunk

Expand

Compressed Air Strut with Mounting Brackets

Two compressed air struts will be mounted on either side of the trunk to keep the trunk supported when it is in the open position. The potential location of these mounting brackets is highlighted by the red circles in the images below

Image AddedImage AddedImage Added

Mounting Brackets:

As the most suitable compressed air struts (McMaster-Carr ones) have a M8 thread on their ball studs, M8 threaded nuts will be used to secure the struts to the bracket.

Note that due to the ball end, the strut and ball stud can rotate independently of one another. Therefore even though the ball stud is fixed and cannot rotate (due to the nut), the strut can still rotate about the ball end. (See picture below)

Image Added

In the picture above, an L-bracket is utilized as the mounting bracket of choice. For mounting to the trunk and in configuration 3, this is appropriate as the contact area of between the bracket and the mount is relatively flat.

However, in configuration 1 and 2, as there would be no perpendicular surface for the mount to be placed on, similar designs to those discussed in the Chassis Mount of the Roof Prop will need to be used.

In addition, the side/bottom mounting area has a curvature that must be taken into account. Here the following options can be pursued:

  • Manufacture the bracket such that the contact area has the same curvature as the panel

    • This will almost certainly require CNC machining and does not seem like the best allocation of time on a CNC machine

  • Manufacture the bracket such that the contact area has an angled cut that approximates the curvature at the panel

    • Then use a more flexible material as an “intermediate”

      • Need to research feasibility of this

Detailed Design

Trunk

Expand
  • 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

Image Added

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