Subtle changes: front fenders are slightly elliptical, window corners are fillets, 'C' pillars "lean" rearward slightly more, rear exhaust vents are now in buttressed fins, the rear doors have thickness, all the marker lights are slightly proud (so they show better in the renderings).
[see my blog for more pictures]
[see my blog for more pictures]
I'm refining and adding some of the important elements; modeling in SketchUp and I've settled back to where I started: I think it will be a fiberglass shell, with tube steel as the chassis and safety structure. Here's my updated blog entry:
My next step is to model the mesh seats. And I need to buy a (used) bandsaw to cut plywood ribs, and start fiberglassing!
If I use the EiG prismatic cells from FVT (like they use in their own eVaro), I can fit ~48kWh pack in the floor of the CarBEN. I'd like it to be 50-60kWh.
I am hoping to have the Cd between 0.1 and 0.14 which would put the CdA between 2.5 sq ft and 3.5 sq ft. (the frontal area is just under 25 sq ft). I based the design on the early Mercedes model of the Bionic, which has a Cd of 0.095 -- which is the lowest drag form with 4 wheels as I have seen.
I'm hoping that the total vehicle weight will be ~1,600-1,800 pounds -- the Edison2 Very Light Car is ~830 pounds, including the ~100 pound ICE drivetrain. The electric motor(s) will be similar (or 50 pounds heavier) to that, and the battery pack will be about 800 pounds.
My goal is to build the CarBEN EV and get it <100wH/mile, and so I hope the range can be >400 miles. The early Aptera prototypes were reported to be able to do this, and Dave Cloud's Dolphin comes very close, with a total weight of ~3,200 pounds. So, it is doable; though certainly challenging.
I'd be happy to send you, or anybody who is interested, the SketchUp model, and you can use the free version of SketchUp to view it and to work on it as well.
...I am hoping to have the Cd between 0.1 and 0.14 which would put the CdA
between 2.5 sq ft and 3.5 sq ft. (the frontal area is just under 25 sq ft). I
based the design on the early Mercedes model of the Bionic, which has a Cd of
0.095 -- which is the lowest drag form with 4 wheels as I have seen...
Sounds like you want to first build a cheap and cheerful shape-correct initial
rolling prototype to check this out in full scale.
How I'm not sure.
Roll down tests on a little travelled country road?
The diffuser fins are probably the last thing that would get put on the car; if they ever go on. They are meant to reduce drag, and if they "help" the air exit the underside of the car, then they would decrease drag. I would have to do tuft testing to see what direction(s) the air is flowing before they go on, so as to not cause drag.
Yes, the idea is to build a full size fiberglass shell, so I can do testing, and verify all sorts of important aspects, and show actual building progress, in particular. I can section the SketchUp model in DataCAD X3, and plot full size templates for the construction ribs. The ribs may be plywood, or possibly aluminum -- I have an offer to use a plasma cutter, which would be an incredible time saver.
Latest video of CarBEN EV open source project Mk 3.7 (yes I skipped a video of Mk 3.6, in case you were wondering!)
Please notice the open doors! This design is open source, too! Hmmm...
Would you like a copy of the SketchUp model?
Besides some smoothing in the hood (leading up to the windshield wipers), I have now figured out how to show the doors open and closed in the same model, so this video "animates" that -- or at least it show the car from various angles with the doors open and closed.
...wonder how "stiff" (not) the side body panels will be with that roof opening arrangement? Certainly negates the "aircraft monocoque" design originally mentioned.
...but, I *do* like the utilitarian aspect of the roof opening.
I am planning to have at least 2 latches each on the rear doors and at least 3 latches on the hatch; including connecting the hatch firmly to both rear doors.
Also, the driver's seat would be supported off of two (more or less) vertical steel tubes that connect the floor with the roof and a roll bar; just ahead of the hatch door's hinges. The sides of the CarBEN are uninterrupted by door openings, so they are acting like very deep web beams; and the floor structure is a flattened box beam, as well. So, torsional stiffness I think will be excellent.
The crash protection on the front and sides are helped by a continuous wraparound structure. And for rear crashes, the floor structure and the shallow 'V' of the rear doors (when viewed from above), which are backed up by a stop behind them on the underside of the hatch, should be very strong. The two rear doors are not very large: they are each no larger than 14" wide and about 35" tall. The "license plate" on the rear is a standard 12" x 6" automobile size.
The analogy of a cube is fine as far as it goes, but the top and sides of the CarBEN are closer to being a truncated pyramid laying on it's side, with slightly curved surfaces. The floor is double thick, as it were, and the sides have only the window openings. The hatch opening has the curved "lip" at the two long sides that extend all the way down to the back. So with the doors open, there could be some flexing, but when they are closed and latched, I think/hope it will be negligible.
I've now modeled the 5 seats, and reworked the interior, now the headlights "light" up in the renderings! Hooray!
[see my blog for more pictures]
If the top of the sides at the rear need to be strengthened, I can add a sliding rod at the top corner of each door at the hinge side that adds a 3rd anchor point (the 2 hinges plus the rod) that forms a box corner? The two rear doors will also latch together and form an end gusset and if the hatch door has 5 or 7 anchor points (2 hinges plus 3 or 5 latches!) it will all lock together pretty well, I think. If this is the only issue I have, I'll be ecstatic!
There could be an emergency hatch in the roof above the driver (like a school bus, sort of), and/or the side windows.
The rear doors could be closed just after the last person enters, and then the hatch door gets closed/open by a remote release. The struts could slide on tracks on the sides, and let the hatch close, or push it open; not unlike a power sliding door on a van.
Here's two more images; a plan and longitudinal sections:
And I have a new video animation of the CarBEN EV Mk 3.8 model:
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