CarBEN EV concept open source design

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CarBEN EV concept open source design

NeilBlanchard
Hello folks,

I've started to design what I hope will be an uber-efficient electric car, I'm calling the CarBEN EV.  I made a 1/24th scale (aka 1/2" = 1'-0") wooden model first, and then traced photos of it in DataCAD.  Then I did orthographic projection from 5 views to make 15 section profiles; separated by 1 foot in Z-height.  Then I used the ruled surface tool to connect as much as possible, and then I exported this to SketchUp, using a DWG file.  Then, in SketchUp, I built the rest of the surface.

I then revised it several times and simplified the number of polygons, and ended up with a decent looking model, if I say so myself.  I've written an entry in my blog, describing the design, and I've included photos of the model, the DataCAD drawing I did, and image captures -- and an animation from SketchUp.  Here's my blog entry (updated periodically):

http://neilblanchard.vox.com/library/post/carben-concept-ev-an-open-source-project.html

And here's the YouTube URL where the animation video is:

http://www.youtube.com/watch?v=C7jbqgCvx8U

My main idea is to have it be as low aerodynamic drag as possible.  So, the wheels are fully enclosed, and in order to keep the width of the front as narrow as possible, this will require having the front wheel skirts be articulated  -- i.e. when steering sharply, they will move with the steering.  At highway speeds though, there will be enough space around the wheels to allow the wheels to move without having to move the skirts.  The skirts will not move with the suspension, as this would be too much unsprung weight, and it would create more problems then it solves.

My hope is to do some CFD testing on a computer, but so far, I have not found a way to get the SketchUp model into a CFD program.  They require a "solid" type model; as opposed to a surface model that SketchUp creates.  My blog entry goes into how I hope to build it (similar to a monocoque airplane,); though composite construction would lend itself well, too, I think.

I'm hoping to eventually use a supercapacitor for regenerative braking (like the Carnegie Mellon "Charge Car" project).  And I'm hoping to use regenerative shock absorbers, like the ones that were just announced from a company called Levant Power:  http://green.autoblog.com/2010/03/27/shocks-that-can-save-fuel-charge-batteries-and-propel-vehicles/#comments

If and when I get the rolling chassis built, I'm sure I'll be looking for lots of input on the battery pack and the drive system.  I'd appreciate any and all comments you may have on the overall concept, as well.

Sincerely, Neil
http://neilblanchard.vox.com/library/posts/




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Re: CarBEN EV concept open source design

Roland Wiench
Hello Neil,

It may be possible to keep the front wheels fully enclose all the time
without any wheel skirts to be articulated.

The front suspension will have two parallel steering arms and pivot points
for the wheels instead of one.  Using this method, the wheels will never
extend beyond the fenders.  Turning the wheels, the wheel that turns toward
the fender, the rear steering control arm pulls the wheel while the front
steering arm maintains a fix position.

The other wheel does the opposite movement.  The front of the wheel axis
point is pull in while the rear is held in a fix position.

The steering mechanism could be a electric rack and pinion unit they use on
hot rods or modified custom cars, except you use two of them.

To access the wheels for maintenance, have the entire fenders hinge up and
maybe in two sections where it can double fold for side clearance.  All four
fender sections on the vehicle could be identical where one panel will fit
in any of the four positions.

The doors could have this opening action too.

Another material that could be use to make the body, is to use a highly
temper alloy call magnesium steel which is use on some of the small light
weight aircraft. Is very thin and can take a good impact without denting.
To form this material, you do not have to stamp it out. It can be roll and
must have a radius bends that is not too sharp.

To form this type of material into a curve in to two different directions, a
pattern is made out of card paper with cut segments out of it.  Then it is
roll very slightly and bend as needed.  The cut segments edges are then push
together with a jig and the cut edges are the welded together with a
heli-arc machine.

All the edges of this material is flange which is the fastening points for
this type of panel, there is no rivets on the expose surfaces.

Roland






----- Original Message -----
From: "Neil Blanchard" <[hidden email]>
To: "Electric Vehicle Discussion List" <[hidden email]>
Sent: Tuesday, March 30, 2010 2:55 AM
Subject: [EVDL] CarBEN EV concept open source design


> Hello folks,
>
> I've started to design what I hope will be an uber-efficient electric car,
> I'm calling the CarBEN EV.  I made a 1/24th scale (aka 1/2" = 1'-0")
> wooden model first, and then traced photos of it in DataCAD.  Then I did
> orthographic projection from 5 views to make 15 section profiles;
> separated by 1 foot in Z-height.  Then I used the ruled surface tool to
> connect as much as possible, and then I exported this to SketchUp, using a
> DWG file.  Then, in SketchUp, I built the rest of the surface.
>
> I then revised it several times and simplified the number of polygons, and
> ended up with a decent looking model, if I say so myself.  I've written an
> entry in my blog, describing the design, and I've included photos of the
> model, the DataCAD drawing I did, and image captures -- and an animation
> from SketchUp.  Here's my blog entry (updated periodically):
>
> http://neilblanchard.vox.com/library/post/carben-concept-ev-an-open-source-project.html
>
> And here's the YouTube URL where the animation video is:
>
> http://www.youtube.com/watch?v=C7jbqgCvx8U
>
> My main idea is to have it be as low aerodynamic drag as possible.  So,
> the wheels are fully enclosed, and in order to keep the width of the front
> as narrow as possible, this will require having the front wheel skirts be
> articulated  -- i.e. when steering sharply, they will move with the
> steering.  At highway speeds though, there will be enough space around the
> wheels to allow the wheels to move without having to move the skirts.  The
> skirts will not move with the suspension, as this would be too much
> unsprung weight, and it would create more problems then it solves.
>
> My hope is to do some CFD testing on a computer, but so far, I have not
> found a way to get the SketchUp model into a CFD program.  They require a
> "solid" type model; as opposed to a surface model that SketchUp creates.
> My blog entry goes into how I hope to build it (similar to a monocoque
> airplane,); though composite construction would lend itself well, too, I
> think.
>
> I'm hoping to eventually use a supercapacitor for regenerative braking
> (like the Carnegie Mellon "Charge Car" project).  And I'm hoping to use
> regenerative shock absorbers, like the ones that were just announced from
> a company called Levant Power:
> http://green.autoblog.com/2010/03/27/shocks-that-can-save-fuel-charge-batteries-and-propel-vehicles/#comments
>
> If and when I get the rolling chassis built, I'm sure I'll be looking for
> lots of input on the battery pack and the drive system.  I'd appreciate
> any and all comments you may have on the overall concept, as well.
>
> Sincerely, Neil
> http://neilblanchard.vox.com/library/posts/
>
>
>
>
> _______________________________________________
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>

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Re: CarBEN EV concept open source design

Lee Hart
Roland Wiench wrote:

> It may be possible to keep the front wheels fully enclose all the time
> without any wheel skirts to be articulated.
>
> The front suspension will have two parallel steering arms and pivot points
> for the wheels instead of one.  Using this method, the wheels will never
> extend beyond the fenders.  Turning the wheels, the wheel that turns toward
> the fender, the rear steering control arm pulls the wheel while the front
> steering arm maintains a fix position.
>
> The other wheel does the opposite movement.  The front of the wheel axis
> point is pull in while the rear is held in a fix position.

Possible; but it adds steering effort and rolling resistance. The track
of the front tires decreases when you turn; in effect you are dragging
the contact points on the pavement sideways, toward each other.

Wheel skirts and the aerodynamics of wheel wells is an area of hot
debate. Some feel that open wheels are the best; others that they need
to be covered. Some favor large wheel wells with lots of room for the
air; others say to keep the wheel wells a close fit to the tire.

A big part of the complication is the tread on the tires. It acts as the
vanes of a blower. Big wide aggressive tread, lots of airflow in the
wheel wells.

Ultimately, I think you need to do wind tunnel tests to find out what is
best with the specific tires type being used.
--
Lee A. Hart | Ring the bells that still can ring
814 8th Ave N | Forget the perfect offering
Sartell MN 56377 | There is a crack in everything
leeahart earthlink.net | That's how the light gets in -- Leonard Cohen

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Re: CarBEN EV concept open source design

NeilBlanchard
Hello Roland and Lee,

> Roland Wiench wrote:
>> It may be possible to keep the front wheels fully enclose all the time
>> without any wheel skirts to be articulated.
>>
>> The front suspension will have two parallel steering arms and pivot points
>> for the wheels instead of one.  Using this method, the wheels will never
>> extend beyond the fenders.  Turning the wheels, the wheel that turns toward
>> the fender, the rear steering control arm pulls the wheel while the front
>> steering arm maintains a fix position.
>>
>> The other wheel does the opposite movement.  The front of the wheel axis
>> point is pull in while the rear is held in a fix position.
>
> Possible; but it adds steering effort and rolling resistance. The track
> of the front tires decreases when you turn; in effect you are dragging
> the contact points on the pavement sideways, toward each other.
>
> Wheel skirts and the aerodynamics of wheel wells is an area of hot
> debate. Some feel that open wheels are the best; others that they need
> to be covered. Some favor large wheel wells with lots of room for the
> air; others say to keep the wheel wells a close fit to the tire.
>
> A big part of the complication is the tread on the tires. It acts as the
> vanes of a blower. Big wide aggressive tread, lots of airflow in the
> wheel wells.
>
> Ultimately, I think you need to do wind tunnel tests to find out what is
> best with the specific tires type being used.

Lee, I think you are on the right point about the scrub friction.  I was recently enlightened about using Ackermann steering geometry:

http://en.wikipedia.org/wiki/Ackermann_steering_geometry

In a nutshell, the two steering tires must try to pivot around the same turning circle *center* to avoid scrub friction.

As to the best aerodynamics, I have read enough of the Hucho "Aerodynamics of Road Vehicles" book on this to know that having as little air space around the spinning tires is best.  So, not only is covering the wheel better, and and having a smooth wheel (with no holes through it) and having the inner fender be as close to the tire tread as possible -- all will help reduce aerodynamic drag.  The tires and wheel openings can contribute up to 30% of the overall drag.

You want to maintain smooth, attached air flow.  Turbulence is always bad.  Basically, I want to build a modified version of the 1938 Schlörwagen "Pillbug", and reduce the width and shrink the size of the air space around the front tires.  Here are some pictures of the Schlörwagen, which is one of the most low drag cars ever made with a Cd of ~0.18:

http://smg.photobucket.com/albums/v724/NeilBlanchard/?action=view&current=Schlr-SideProfile.jpg
http://smg.photobucket.com/albums/v724/NeilBlanchard/?action=view&current=Schlor-FrontView.jpg

>From the front view (the second link), you can see that the front wheels are inset quite a ways, and the overall width of the car was substantial.  Another inspiration for my CarBEN design is an early model of the Mercedes Bionic (aka "Boxfish") car, with it Cd of a measly 0.095:

http://smg.photobucket.com/albums/v724/NeilBlanchard/?action=view&current=Boxfish.jpg

Since they ended up by building it with the wheels uncovered, the Cd ended up at a still excellent 0.19:

http://img.photobucket.com/albums/v724/NeilBlanchard/Mercedes-bionic-fish-concept-1.jpg

I appreciate your feedback.  And check out my blog entry on the CarBEN EV design.

Sincerely, Neil
http://neilblanchard.vox.com/library/posts/




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Re: CarBEN EV concept open source design

nicklogan
Neil,
     The design is somewhat reminiscent of Buckminster fuller's Dymaxion Car :

 http://www.slashseconds.org/issues/002/003/articles/jhight2/image003.jpg

http://www.youtube.com/watch?v=YlLZE23EJKs

The design was supposedly unjustly forced off the road as unsafe after a Chicago pol collided with it and used his influence to blame the car.

Regards,
John Nicholson

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Re: CarBEN EV concept open source design

Kelly Hales-2
In reply to this post by NeilBlanchard
Neil,
Pretty cool.  I was surprised to see you used DataCAD since it is an
architectural package.  I have used it also.  Then I wondered if you were
the same Neil on the old Dbug list.  Small world.  Looks like a great
project, keep us informed on your progress.
Kelly

Hello folks,

I've started to design what I hope will be an uber-efficient electric car,
I'm calling the CarBEN EV.  I made a 1/24th scale (aka 1/2" = 1'-0") wooden
model first, and then traced photos of it in DataCAD.  Then I did
orthographic projection from 5 views to make 15 section profiles; separated
by 1 foot in Z-height.  Then I used the ruled surface tool to connect as
much as possible, and then I exported this to SketchUp, using a DWG file.
 Then, in SketchUp, I built the rest of the surface.

I then revised it several times and simplified the number of polygons, and
ended up with a decent looking model, if I say so myself.  I've written an
entry in my blog, describing the design, and I've included photos of the
model, the DataCAD drawing I did, and image captures -- and an animation
from SketchUp.  Here's my blog entry (updated periodically):

http://neilblanchard.vox.com/library/post/carben-concept-ev-an-open-source-project.html

And here's the YouTube URL where the animation video is:

http://www.youtube.com/watch?v=C7jbqgCvx8U

My main idea is to have it be as low aerodynamic drag as possible.  So, the
wheels are fully enclosed, and in order to keep the width of the front as
narrow as possible, this will require having the front wheel skirts be
articulated  -- i.e. when steering sharply, they will move with the
steering.  At highway speeds though, there will be enough space around the
wheels to allow the wheels to move without having to move the skirts.  The
skirts will not move with the suspension, as this would be too much unsprung
weight, and it would create more problems then it solves.

My hope is to do some CFD testing on a computer, but so far, I have not
found a way to get the SketchUp model into a CFD program.  They require a
"solid" type model; as opposed to a surface model that SketchUp creates.  My
blog entry goes into how I hope to build it (similar to a monocoque
airplane,); though composite construction would lend itself well, too, I
think.

I'm hoping to eventually use a supercapacitor for regenerative braking (like
the Carnegie Mellon "Charge Car" project).  And I'm hoping to use
regenerative shock absorbers, like the ones that were just announced from a
company called Levant Power:
http://green.autoblog.com/2010/03/27/shocks-that-can-save-fuel-charge-batteries-and-propel-vehicles/#comments

If and when I get the rolling chassis built, I'm sure I'll be looking for
lots of input on the battery pack and the drive system.  I'd appreciate any
and all comments you may have on the overall concept, as well.

Sincerely, Neil
http://neilblanchard.vox.com/library/posts/




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Re: CarBEN EV concept open source design

NeilBlanchard
Hi Kelly,

> Pretty cool.  I was surprised to see you used DataCAD since it is an
> architectural package.  I have used it also.  Then I wondered if you were
> the same Neil on the old Dbug list.  Small world.  Looks like a great
> project, keep us informed on your progress.


The same -- it is a small world.  Thanks!

Sincerely, Neil
http://neilblanchard.vox.com/library/posts/



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Re: CarBEN EV concept open source design

NeilBlanchard
In reply to this post by nicklogan
Hi John

> The design is somewhat reminiscent of Buckminster fuller's Dymaxion Car:
>
> http://www.slashseconds.org/issues/002/003/articles/jhight2/image003.jpg
>
> http://www.youtube.com/watch?v=YlLZE23EJKs
>
> The design was supposedly unjustly forced off the road as unsafe after a
> Chicago pol collided with it and used his influence to blame the car.


Well, steering in the rear at highway speeds would be a tricky thing!

This has been remarked on before.  The CarBEN is similar in some ways, but significantly different in others.  The CarBEN's size is only a bit bigger than my Scion xA, which puts it in a different league from the Dymaxion.  Having four wheels and steering in the front also make it much more conventional.  They share front wheel drive and similar general shapes.  Being designed as an EV, the CarBEN can easily fit the motor in the front.  

Actually, the Schlörwagen (I posted links in an earlier post on this thread) had a rear engine -- another big advantage EV's have is very little need for cooling the drivetrain; which in turn helps the aerodynamics a lot.

Sincerely, Neil
http://neilblanchard.vox.com/library/posts/




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Re: CarBEN EV concept open source design

Doug Weathers
In reply to this post by NeilBlanchard

On Mar 30, 2010, at 5:36 PM, Neil Blanchard wrote:

> You want to maintain smooth, attached air flow.  Turbulence is  
> always bad.

Absolute statements are always wrong ;)

There are two types of aero drag - skin-friction drag and pressure drag.

There are two types of boundary layer flows - laminar and turbulent.

It turns out that laminar flow lowers the skin friction drag, but  
since it has a tendency to separate from the body sooner than  
turbulent flow, it can cause a large low-pressure area behind the body.

Turbulent flow has higher skin friction drag, but it doesn't separate  
from the body as easily, so it hugs the body longer.  When it  
eventually separates, the low pressure area behind the body is  
smaller, so there's less pressure drag.

So which is better, laminar or turbulent?  The answer is, as usual,  
is "it depends".  On the shape of the body, the surface roughness,  
air density, and the speed of the airflow.

A long, smooth, slender shape will probably do better with laminar  
flow, while a short, blunt shape will have probably have less drag  
with turbulent flow.  This is why golf balls are covered in dimples,  
because the designer wanted turbulent flow around the blunt spherical  
shape.

Here's a good page, with pictures showing the difference between a  
smooth and dimpled sphere.

<http://www.aerospaceweb.org/question/aerodynamics/q0215.shtml>

Often a designer will deliberately "trip" the boundary layer from  
laminar to turbulent at a strategic point (before the laminar flow  
will separate from the body), to keep the flow laminar as long as  
possible (lower skin friction drag).  After the trip point, the flow  
is turbulent and is more resistant to separating, so the pressure  
drag is lowered.

Here are a couple of classic pictures showing the effect of tripping  
the boundary layer.  They're in both of my aero textbooks.

Laminar flow around a sphere, with large wake region causing lots of  
pressure drag:

<http://www.engineering.uiowa.edu/~cfd/gallery/images/turb4.jpg>

Laminar flow tripped by a wire wrapped around the sphere, becoming  
turbulent and causing a smaller wake region:

<http://www.engineering.uiowa.edu/~cfd/gallery/images/lim2.jpg>

(Note that the source page labeled them backwards.  You can see the  
trip wire in the second picture.)

Too bad that golf balls spin in flight, or they'd be smooth except  
for a trip wire :)

Actually predicting where the boundary layer will detach is  
essentially impossible in the real world.  The math is messy and the  
real world is so imperfect - one dead bug can ruin your carefully-
modeled fluid flow.  Engineers tend to do a lot of experiments to  
figure out the details.

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Re: CarBEN EV concept open source design

Jeff Shanab
In reply to this post by NeilBlanchard
May want to be a little careful going to far on the front wheel aero,
you will overheat the brakes!

A workaround is to duct the brakes into the front grill and then you can
control the amount of air, even help pressurize the wheel well to
support he air going over it.

A slighly furthor out front edge than rear and a nice smooth trailing
edge is also used.
Narrower tires helps, but at what cost? it is all compromise.

look at front wheel wells of honda insight.
http://en.wikipedia.org/wiki/Honda_Insight

> Hello Roland and Lee,
>
>  
>> > Roland Wiench wrote:
>>    
>>> >> It may be possible to keep the front wheels fully enclose all the time
>>> >> without any wheel skirts to be articulated.
>>> >>
>>> >> The front suspension will have two parallel steering arms and pivot points
>>> >> for the wheels instead of one.  Using this method, the wheels will never
>>> >> extend beyond the fenders.  Turning the wheels, the wheel that turns toward
>>> >> the fender, the rear steering control arm pulls the wheel while the front
>>> >> steering arm maintains a fix position.
>>> >>
>>> >> The other wheel does the opposite movement.  The front of the wheel axis
>>> >> point is pull in while the rear is held in a fix position.
>>>      
>> >
>> > Possible; but it adds steering effort and rolling resistance. The track
>> > of the front tires decreases when you turn; in effect you are dragging
>> > the contact points on the pavement sideways, toward each other.
>> >
>> > Wheel skirts and the aerodynamics of wheel wells is an area of hot
>> > debate. Some feel that open wheels are the best; others that they need
>> > to be covered. Some favor large wheel wells with lots of room for the
>> > air; others say to keep the wheel wells a close fit to the tire.
>> >
>> > A big part of the complication is the tread on the tires. It acts as the
>> > vanes of a blower. Big wide aggressive tread, lots of airflow in the
>> > wheel wells.
>> >
>> > Ultimately, I think you need to do wind tunnel tests to find out what is
>> > best with the specific tires type being used.
>>    
>
> Lee, I think you are on the right point about the scrub friction.  I was recently enlightened about using Ackermann steering geometry:
>
> http://en.wikipedia.org/wiki/Ackermann_steering_geometry
>
> In a nutshell, the two steering tires must try to pivot around the same turning circle *center* to avoid scrub friction.
>
> As to the best aerodynamics, I have read enough of the Hucho "Aerodynamics of Road Vehicles" book on this to know that having as little air space around the spinning tires is best.  So, not only is covering the wheel better, and and having a smooth wheel (with no holes through it) and having the inner fender be as close to the tire tread as possible -- all will help reduce aerodynamic drag.  The tires and wheel openings can contribute up to 30% of the overall drag.
>
> You want to maintain smooth, attached air flow.  Turbulence is always bad.  Basically, I want to build a modified version of the 1938 Schlörwagen "Pillbug", and reduce the width and shrink the size of the air space around the front tires.  Here are some pictures of the Schlörwagen, which is one of the most low drag cars ever made with a Cd of ~0.18:
>
> http://smg.photobucket.com/albums/v724/NeilBlanchard/?action=view&current=Schlr-SideProfile.jpg
> http://smg.photobucket.com/albums/v724/NeilBlanchard/?action=view&current=Schlor-FrontView.jpg
>
> >From the front view (the second link), you can see that the front wheels are inset quite a ways, and the overall width of the car was substantial.  Another inspiration for my CarBEN design is an early model of the Mercedes Bionic (aka "Boxfish") car, with it Cd of a measly 0.095:
>
> http://smg.photobucket.com/albums/v724/NeilBlanchard/?action=view&current=Boxfish.jpg
>
> Since they ended up by building it with the wheels uncovered, the Cd ended up at a still excellent 0.19:
>
> http://img.photobucket.com/albums/v724/NeilBlanchard/Mercedes-bionic-fish-concept-1.jpg
>
> I appreciate your feedback.  And check out my blog entry on the CarBEN EV design.
>
> Sincerely, Neil
> http://neilblanchard.vox.com/library/posts/
>
>
>
>
>
>  

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Re: CarBEN EV concept open source design

NeilBlanchard
In reply to this post by Doug Weathers
Hi Doug,

>> You want to maintain smooth, attached air flow.  Turbulence is  
>> always bad.
>
> Absolute statements are always wrong ;)
>
> There are two types of aero drag - skin-friction drag and pressure drag.
>
> There are two types of boundary layer flows - laminar and turbulent.
>
> It turns out that laminar flow lowers the skin friction drag, but  
> since it has a tendency to separate from the body sooner than  
> turbulent flow, it can cause a large low-pressure area behind the body.
>
> Turbulent flow has higher skin friction drag, but it doesn't separate  
> from the body as easily, so it hugs the body longer.  When it  
> eventually separates, the low pressure area behind the body is  
> smaller, so there's less pressure drag.

I guess I should have specified "large scale turbulence" is bad?  Thanks for your clarifications -- I'll check out your links, as well.  I just order a copy of the Hucho book...

Sincerely, Neil
http://neilblanchard.vox.com/library/posts/




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Re: CarBEN EV concept open source design

Dave Hymers
what about this approach ?

http://www.carstyling.ru/resources/studio/1970_Colani_C-112_10.jpg

Nice looking car if it wasn't pink :)
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