CarBEN Model -- 1/24th scale model and 3D computer model for EV

[NeilBlanchard]

The CarBEN is just 5'- 4" inches wide. If I narrow it to 4'-4" wide I could not fit two seats side by side. And how can I fit a ~55kWh battery in with any less frontal area? The frontal area of the battery is 40" x 5.5" and there is no way to fit 768 cells in "inline" with any other part of the car; let alone with the best Cg possible.

Removing the middle foot reduces the interior volume by a huge amount: that is the tallest and longest portion. The widest interior dimension is about 4'-6" and the narrowest is ~2'-8" -- those drop to 3'-6" and 1'-8", which probably turn it into a 3 seat car. No thanks.

Even if you don't lower it a proportional amount (which you would have to, since a 5'-6" tall by 4'-4" wide vehicle looks a lot like the Tango!), you would lose 1/3 of the battery bay, dropping the capacity to ~37kWh.

The weight saving in the chassis would be minimal since the "perimeter" only would drop from 21'-8" to 19'-8".

The frontal area is just ~25 sq ft as it is. And if the Cd is between 0.11 and 0.14 (WAG) then the CdA is between 2.75 sq ft and 3.5 sq ft. Even saving 6 sq ft of area only drops that range to 2 - 2.66 sq ft.; as savings of a whopping 108 sq in or 12" x 9". That's a lot of sacrifice for a small result.

If I put in side doors, then the weight is probably increased and the strength in crashes is decreased. The shape of the CarBEN is based on the aerodynamic shape combined with a practical and usable space. I did not design it around the rear entry, though it does allow for the weight savings and greater crash protection.

Show me any other car under 14' long that holds five people and has aerodynamics as good as the CarBEN design. The Illuminati Seven holds 4 people, and "hides" the frontal area of the 52kWh battery in the middle of the passenger compartment -- but it is 21' long and weighs 3150 pounds.

How *specifically* would you design a better electric car, that has the general "specs" that CarBEN does?

Dave Cloud's Dolphin has a smaller frontal area (close to the 19 sq ft that Matt is asking for?) and maybe even better Cd, and while it might be made to fit four people, they would not be nearly as comfortable, and then fitting in an 11 cubic foot battery pack would be a trick. It has just the two side doors, and no hatch (so no access to storage).

It is not just the quantity of the frontal area, but also the layout of the frontal area. CarBEN is close to a square, so it encloses the just about the most volume possible for that frontal area. Take a foot away from the height, and make the width 1'-2" wider (6'-6" total) to keep the same area, and the seats must be reclined to fit people in, and then the length must be increased to still fit them. And the "perimeter is" now slightly greater, along with the added length, means more weight. How the seating is set up determines the comfort and you are still left with the question of where to put the 11 cu ft of battery.

Drop the height another foot and the width needs to be 8'-4" to get the same area...

[NeilBlanchard]

Originally Posted by euromodder

Design ideas :
- drop the huge hatch idea
- add side doors abeam/in front of the front passengers
- rearward sliding doors would hardly protrude from the body as the doors are at the widest section, and the design narrows going aft.
- move the rear seat to the right and further forward, though keeping the staggered layout as it reduces width.
- provide access to the rear seats between the front passenger seats (driver and front passengers already have to get in between these seats in the current design)
- the above will provide ample dedicated luggage space at the rear, and an even greater useful volume when the rear seats are made to be stowable in the sides or floor (could interfere with the batteries) ; alternatively, the design cold narrow or slope down even more at the rear if that's aerodynamically useful.

The key things to doing this would be:

Would angling the roof down more be aerodynamically helpful? Here's the most recent 2D drawing:


The overall angle is just ~9 degrees but the trailing edge is 15-16 degrees, so maybe a little bit? The sides are about 13 degrees but to increase this, the rear track would have to be narrowed more.

The hatch would still have to be there to use the storage area -- if it was shortened by half it's length, and the upper portion of the rear doors was joined to it?

The left side door would be only usable for the driver and the one passenger, while the right side door could be used by everybody. So, I would be inclined to only put in the right side door. The one side door would be roughly the same size as the reduced hatch, though it would add more weight; because the change in the hatch is just the length of the 2 sides, and the side door has at least 2X that perimeter length. The two side tubes would have to continue through the door and it has two hinges and at least two latches.

Two side doors would be a lot heavier than the hatch reduction. Having seen the Edison2 cars up close and over a 6 day period, I saw how a 700 pound rolling chassis is built. Their doors are not structural in that they have no frames. The tubes of the chassis are covered with the FRP skin and the doors are hinges and latch at one place; so they are "covers". The seating in the VLC's is low to the floor of the car, and the sides are protected by the tubes of the chassis; and you have to step over them and sit down in beside them. Getting in and out is not equivalent to a conventional car.

Personally, I find upright seating much more comfortable, and riding a little higher than a typical car helps the visibility. I've already discussed the space requirements for reclined vs upright seating. *Protecting* an upright seat requires that the structure also be higher. If you penetrate this structure with a door opening, then the door itself must be structural, and so it will weigh more.

The hatch and rear doors on CarBEN do have to be structural and latched in multiple places, so this is a weigh penalty. But if there is just one door that covers all the functions, and if that door is the lowest risk in crashes (~3% of all crashes involve the rear end), then this saves on the overall weight. And the sides (which are much more likely to be crashed into) are much stronger and much lighter than they would be otherwise.

We are talking convenience vs weight/efficiency+safety. I'm willing to give up a little convenience if the payoff is the highest possible efficiency and still excellent safety.

Sliding doors are hard to do and heavier than swing doors. The shoulders of the CarBEN drop down a lot as they go back, so a sliding track would be extraordinarily difficult to pull off.

The seats are going to be quite slim and light weight, so they could either fold up to the side, or detach and store in the rear most part of the floor. If I end up doing solid/non-inflatable tires, there is no need for a spare or a jack.

And guys -- this is a prototype! I think it is well worth trying this out, and seeing how it works. I'll bet getting in and out of the CarBEN is faster and easier than putting on a motorcycle helmet and crash suit and gloves?

[RobertSmalls]

Here's an illustration with about 17% reduction in width, and a larger % reduction in trailing area and aerodynamic drag.

The battery problem is actually easier than you think. The next step is going to save you even more frontal area, so I'm going to target a battery 2/3 the size of yours to achieve the same range.

There are lots of places to stash batteries without having 100% of their volume add to the frontal area of the car. You could emulate the Leaf, and stash them under the seats. Or emulate the EV1, and if you leave space between the driver and passenger seats, wedge some batteries in there. There's room all around the rearmost seat.

Maybe some of my Photoshop (okay, MSPaint) won't work out, but you have to try. There's SO MUCH ROOM for aerodynamic improvement here.

Originally Posted by NeilBlanchard

How *specifically* would you design a better electric car, that has the general "specs" that CarBEN does?

A lot like the CarBEN, but with as great an emphasis on Cd as A. So: longer, less tall, and narrower. It would have three doors: one for the front row, one for the rear row, and a hatch at the back.

The driver would sit near the left edge of the car, so he can better judge his position in his lane. Read up on RHD vs LHD cars on Italian mountain roads. Having the driver on center is best on the track, unless it's NASCAR and you only turn left. But not on the road.

I would also include a MUCH longer front crumple zone, especially if my crash test budget was small. And I'd give it a full boat tail. A Crown Vic is 17.7' long, so you can go at least as long as that.

But I've been saying so since the second page of this thread.

Have fun, Neil!

[euromodder]

Originally Posted by NeilBlanchard

The sides are about 13 degrees but to increase this, the rear track would have to be narrowed more.

Then I'd say it's better not to reduce width at the rear, as a narrower track will also lead to a less stable vehicle.

The hatch would still have to be there to use the storage area -- if it was shortened by half it's length, and the upper portion of the rear doors was joined to it?

While keeping the height, the hatch could be reduced to just (a) vertical rear door(s), fitting within/onto an efficient ringlike structure (C/D-pillar) - much like it is on a near-vertical hatchback or station-wagon design.

Reducing rear height would likely require a roof cut-out to get proper access to the luggage area.
As this also reduces luggage space and overall volume - practical things really worth having - it's probably better to keep the current size of the rear end and put the available volume to good use.

The one side door would be roughly the same size as the reduced hatch, though it would add more weight;

It'd take a structural engineer to calculate the weight impact of both options on your design, but I really don't think you can get away with the (full sized) roof hatch very lightly.

because the change in the hatch is just the length of the 2 sides, and the side door has at least 2X that perimeter length.

Adding multiple small holes to a design doesn't have the impact of adding one larger hole of equal area.

Even going with one side door would still double the access options of the design.

The two side tubes would have to continue through the door and it has two hinges and at least two latches.

It'd still require structural stiffening - any opening will require that - but efficient car door design is nothing out of the ordinary, as there's a lot of expertise in that area.

Through the entire car-era, side-opening doors are very much a constant feature. None of the alternatives so far have stood the test of time.
Last rumour I heard about Loremo, they were considering reverting to conventional doors.

I can feel it's a pet-feature on your design, but IMHO it introduces too many undesireable effects to be really viable
- single entry/exit point for all passengers and any cargo
- seating arrangement (bus-like, i.e. none too cosy)
- severely limited headroom for aft passenger
- large % of wasted floor area by requiring a free aisle all through the vehicle
- voluminous loads would block entry and access completely (no van-variant would be possible)
- huge single-opening for a small design

I know of no vehicles with only a rear-entry option.
This in itself is not a good argument, but it should get the alarm bells ringing as to why it hasn't been done (more often) before ...

The seating in the VLC's is low to the floor of the car, and the sides are protected by the tubes of the chassis; and you have to step over them and sit down in beside them. Getting in and out is not equivalent to a conventional car.

Sounds a lot like a Lotus Elise.

Such design options also severely limit a design's usefullness to many people - the fast growing crowd of elderly people who aren't as nimble as a youngster.

That said, CarBEN's rear-entry design could be easily adapted to transport wheelchair users - if the driver can still get in after the wheelchair is rolled in, that is.

Personally, I find upright seating much more comfortable, and riding a little higher than a typical car helps the visibility.

A lot of people feel that way, and it's a design option used in just about every European MPV design (Renault Espace, Scenic, Modus, Opel/Vauxhall Meriva, ...) as it allows the designs to be shorter while still giving plenty of leg room.

Sliding doors are hard to do and heavier than swing doors.

Agreed, but they're also highly practical in confined spaces.

If I end up doing solid/non-inflatable tires

Something like Michelin's Twheel ?

And guys -- this is a prototype! I think it is well worth trying this out, and seeing how it works.

Sure, but it's very useful to think out the practical side of a design before prototyping it.
It's easier to change the design than it is to change the prototype

I'll bet getting in and out of the CarBEN is faster and easier than putting on a motorcycle helmet and crash suit and gloves?

It sure would be.

[NeilBlanchard]

Matt, you think two people can sit side by side in 3'-7"? My friend's Sonex airplane is about that wide -- it would be incredibly tight. And your drawing crams the legs of the front passengers in an around the front wheels. There is suspension parts that have to fit in there, too. I think that plan is unworkable.

You should start with the Dolphin -- it fits your criteria. ~17.3 sq ft frontal area, and I'd guess a Cd of ~0.15? (Open front wheels) That gives a CdA of ~2.6 sq ft; slightly better than the CarBEN. The Metro is a small 4 seat 2 door car to begin with, and Dave Cloud added 18" of foam in the nose. He chopped and lowered the roof (so less headroom than stock), and the back seat got significantly narrower (if there were no batteries there).

And I'll bet is about 17' long. For what it's worth, the Dolphin sans it's batteries is about 1,220 pounds, IIRC.

Where would you put the batteries? If you use the same EiG cells I am assuming, they are 10" x 5.5" x 0.375" -- how many can you fit? What about the fifth person?

[dbc1218]

Can you post all the dimensions for the 768 cell battery pack. How many batteries in each row, gap between rows, overall length and width, relation to the rear axle, etc. Also do you want to be able to install/remove cells individually, or all together, or rows together? I'm working on the chassis and suspension and am starting with the location of the tires and the battery.

[NeilBlanchard]

Sure, I'm basing it on the EiG cells that FVT uses: each cell is 3/8" thick x 10" x 5 1/2". There is 24 lineal feet of these cells in CarBEN's floor battery bay: two long rows 7'-8" long and two short rows 4'-4" long. The spaces for the wiring (and they use small gauge wires -- see these pictures: FVT eVaro :: FVT eVaro battery pack picture by NeilBlanchard - Photobucket are 2" in the center (where the terminals on the long rows are) and 1 1/2" where the terminals of each short row is.

I've got new 2D drawings underway, so the dimensions of the up to date CarBEN EV Mk 3.8 will be available.

[NeilBlanchard]

I've been working on HLR (hidden line removal) views of the SketchUp model, using DataCAD X3, and at long last I've got something pretty close to reality:



Now, I have to draw in the battery pack, structure, seats, etc.

[Bicycle Bob]

Have a look at
Photos: 50+ years of Japanese concept cars ::: Pink Tentacle

About picture #30, see the Mistubishi ESR, 1993.

[NeilBlanchard]

Thanks for that link, Bob. There is a lot of cars there I have never seen. Here's that Mitsubishi:



I can see a couple of similarities with CarBEN, for sure.