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Roof

Single Sliding Bar Mechanism

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• 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

  • There are different system architectures to achieve this and these will be discussed below

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

• Roof Prop

• Roof Hinge

• Prop Mounting (to Roof and Chassis)

Note: For clarity the the areas highlighted in red and yellow are the potential Roof Hinge mounting areas, while the areas highlighted in blue and green are the potential areas where the Prop Mount (to the chassis) could be located

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Roof Prop

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

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

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    • 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

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    • 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

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  • 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:

• Eye bolt

  • The prop itself will have an “eye bolt” on its end while the roof will have an mounting brackets with threaded holes for the bolt to run through

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

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    • 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

    • This system is generally quite simple and straightforward

      • Which should make manufacturing and design easier/faster

• J Bolt

  • The prop will have a “J Bolt” while a shoulder bolt that runs through two brackets will be mounted to the roof

    • The “J bolt” will then latch onto the shoulder bolt (see below)

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    • 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 is easier to use than the “Eye bolt” as the prop only needs to be lifted up to unlock, as opposed to sliding out

    • The flanges on the mounting brackets must be sufficiently long enough to allow for enough clearance space to engage and disengage the “J Bolt” from the shoulder bolt

      • These flanges are essentially cantilevered beams so the longer they are the greater potential they have to deflect / deform

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

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  • 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)

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  • 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

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  • 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)

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

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

• Roof Prop

  • One acts as a hinge replacement

  • Other retains the same functionality as before (changes length to alter angle of roof)

• Prop Mounting (to Roof and Chassis)

See video below for clarification

• Top rectangle represents the roof

• “Hinge replacement” prop is the one on the right

Note: For clarity the the areas highlighted in red are where the roof props could potentially be mounted on the B Panel Bulkhead

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Pros of this architecture:

• No hinge design is required, this simplifies both the operation and manufacturing

• This would be an entirely closed system, and would not require the prop to be removable

• Roof could be opened while remaining within the vehicle

Cons of this architecture:

• The “hinge replacement” prop must be restricted from rotating

• May be issues with ensuring the roof’s motion is purely vertical in the beginning stages

• Will need to create an enclosure for the props so that the occupants will not come into contact with them in the event of an impact

• The mounts to the chassis will need to have flanges long enough such that the prop will not interfere with the motion of the roof

  • The longer these flanges are, the greater the potential for them to yield/fail (essentially a cantilever beam)

Selected Concepts

Trunk

Selected Concepts

Trunk

Roof

Preliminary Design

Trunk

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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 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

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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 bracketsbe 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