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Single Sliding Bar Mechanism

  • 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

  • Instead of having a mechanism that is placed within the car even when the roof is closed, an “add-on” roof prop mechanism was chosen

Logic for above decision is as follows:

  • Roof would/should never open while car is travelling, thus there does not need to be a roof prop mechanism that is integrated within the roof/chassis

    • Where (as seen above) there was not enough space

  • An “add-on” roof prop mechanism can achieve the same goal (propping up the roof when the car is stationary) while avoiding the limited space issue

    • However, some components of this mechanism/system will have to remain integrated within the car

      • (potential) Roof Hinges

      • Prop Mount

    • Roof prop itself will be removable

Note: For clarity the the areas highlighted in red are the potential Roof Hinge mounting areas, while the areas highlighted in blue are the potential areas where the Prop Mount could be located

The rest of this section will now cover the concepting and researching behind the following components of this “add-on” roof prop mechanism:

  • Roof Prop

  • Roof Hinge

  • Prop Mounting (to Roof and Chassis)

Roof Hinge

It is important to note that the top of the roof panel will be flush with the tops/edges of the side panels

Thus, any hinge design considered must be able to lift the roof panel to be cleared/above the side panels. (i.e. the roof panel does not collide/interfere with the side panels during opening and closing)

Four Bar Multi-point Hinge

Pop up Hinge

  • Similar to https://www.youtube.com/watch?v=kh252HOZrqc

    • Seems like this will take up more mounting room

    • Concern with the top peg being constantly forced against the top of the slot

      • Would need to ensure the mounting plate (that has the slot) is adhered on properly to provide a sufficient reaction force to the peg’s upward force

    • Motion is also not necessarily smooth and continuous, could be a cause for concern

    • Will have to mount this system flush against the bulkhead

Four Bar Hinge

  • This design seems to be utilized in other solar cars as well

    • Four Bar Linkage Roof Hinge.wmv

    • Simpler than the multi-point hinge variant

    • Mounting space is larger than multi-point hinge but less than pop up

      • In MSXIV would have to mount this against the bulkhead panels in order to be feasible

      • Block with two threaded holes could be adhered to the bulkhead panel

        • Shoulder bolts threaded into those holes would then support the moving linkages seen in video above

Roof Prop

Two types of roof props will exist: fixed length or variable length

Fixed length roof props will be:

  • Lighter

  • Have more simple construction

    • No moving parts and thus (theoretically) will require less maintenance

Variable length roof props will be:

  • More flexible

    • Allowing for the angle of the roof to be variable

    • Roof solar array will be more efficient at a wider variety of angles

    • Will take up less storage space within the car

  • Will likely be heavier

    • Though by how much depends on the specific variable length rod type

Fixed length:

  • Standard rod

    • Essentially a metal or composite rod of a fixed length

Variable Length:

  • “Snap Lock”

    • Telescoping rod with a snap on lock, very similar mechanism to those found on telescoping tripod legs

      • Once the lock is “snapped on”, it induces a compressive force onto the outer tube

        • Which then induces a compressive force onto the inner tube

        • This causes the two tubes to be in contact with one another and therefore frictional force prevents movement of the inner tube

      • Quite user friendly

        • Does not require a lot of input

      • Making the locking mechanism may be quite complicated

        • Need to research applicable manufacturing processes' as well as materials

        • Note: locking mechanisms can be purchased separately and this may allow us to circumnavigate the potential manufacturing issues of this

  • Spring Loaded Pin

    • Pin that is attached to an internal spring

      • In the spring’s unstretched position the pin protrudes out

      • User depresses pin and then moves inner rod to desired length

        • Spring will naturally extend back to its unstretched position and pin will protrude out into holes drilled into outer rod, thus locking it in place

      • Assembly may be quite intricate

        • Making sure the spring and pin are properly assembled within inner rod

      • Restricted to set positions

        • Based on holes drilled into outer rod

      • Not user friendly

        • Sometimes is hard to depress the pin enough while moving the inner rod

  • Internal CAM Lock

    • A cam is attached to the inner rod, it is shaped such that when the inner rod is twisted a certain number of degrees, it will push out on a set of plastic/metal halves

    • These plastic/metal halves contact the outer rod

      • Frictional force prevents movement of the outer and inner rods

    • Assembly of this may be quite complicated

      • Ensuring plastic/metal halves are positioned properly

      • Needing to ensure cam is mounted/positioned properly

      • May be more efficient to purchase this item

    • Quite user friendly

      • Locking/unlocking motion is done by twisting one of the rods

    • NOTE: This may be require additional features to be compatible with some of the mounting methods discussed below

Prop Mounting

The roof prop will need to be mounted to both the roof and chassis of the car in order to properly support the roof

It is also important to note that as the roof prop may need to be removed, the mounting hardware should allow for this as well

Roof Mount:

  • Fisheye Hook and Bolt

    • The prop itself will have a fish eye hook while the roof will have an L bracket with a stationary bolt running through

      • The fish eye hook will be placed such that the bolt runs through it as well (see picture below)

      • Image RemovedImage Added

      • NOTE: To be compatible with the twisting motion of the internal cam lock system, the prop would have to be able to ROTATE INDEPENDENTLY of the fish eye hook

        • For the other prop mechanisms discussed above, this mounting method works directly as is

      • Would need a nut on the end to secure the system

        • Unless the bolt is glued/adhered to stay in

        • Above maybe unlikely thus constantly loosening and tightening the nut is not user friendly

      • This system is generally quite simple and straightforward

        • Which should make manufacturing and design easier/faster

  • Hook and Pin

    • The prop will have a standard “C-shaped” hook while a pin/dowel that is press-fit between two brackets will be on the roof

      • The hook on the prop will then latch onto this pin/dowel (see below)

      • NOTE: To be compatible with the twisting motion of the internal cam lock system, the prop would have to be able to ROTATE INDEPENDENTLY of the fish eye hook

        • For the other prop mechanisms discussed above, this mounting method works directly as is

      • System has more components than the “Fisheye Hook and Bolt” method but is still relatively straightforward

        • Press fitting pin/dowel could be a cause for concern

        • Could easily replace this with a shoulder bolt and nut however

      • System is easier to use than the “Fisheye Hook and Bolt” as the prop only needs to be lifted up to unlock, as opposed to sliding out

Chassis Mount:

  • Hook to Chassis Tube

    • A hook on the end of the prop would rest directly on the chassis bar in the previously mentioned blue highlighted area

    • Image RemovedImage Added

    • No additional mounting hardware needed, so this theoretically simplifies manufacturing process

    • However, will need to manufacture a hook/integrate a purchased solution such that it will be in this orientation

  • Hook and Pin

    • General concept remains the same as how it is applied in the roof mounting scenario

    • Due to the geometry in the mounting area, a pin would potentially be press-fit into a block which would then be adhered onto the bulkhead panel (see below)

    • This concept requires more mounting hardware

      • Overall more manufacturing work and also adds a bit more weight to the car

    • In addition the concern with how to press-fit the pin/dowel remains

    • May be easier to integrate the end piece (hook) onto a rod than the “Hook to Chassis Tube” method

  • Hook and Pin (C-Bracket Variant)

    • Same general concept as above, but instead of a dowel press-fitted within a block, it is placed within a C-bracket

    • Image RemovedImage Added

    • If an adhesive is being used to connect the C-bracket to the bulkhead, then the contact area between the two must be sufficient to allow the bracket to stay in place

      • Would need to calculate this area based on the adhesive and specific material of the C-bracket

  • Hook and Pin (Platform Variant)

    • If the required contact area between the bracket and bulkhead is too large, an oversize C-bracket would have to be used, which may take up an unnecessary amount of space

    • In this case an L-bracket (or just an L-shaped piece of sheet metal) is used to obtain whatever necessary contact area is needed

      • On the flange of this L-bracket is a smaller L-bracket with a dowel/shoulder bolt through it that runs through it and to a hole into the larger L-bracket (see image below)

      • Compared to other methods this is more cumbersome and utilizes more parts

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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:

  • Used hand calculations to verify “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

  • Used hand calculations to verify user “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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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

Mounting Brackets:

As the chosen 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)

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

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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

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: