Compostie Questions about gliders

[Peter VanDerWal]

I'm no expert, but from what I've read Vacuum infusion can require a great
deal of trial and error to get the vacuum and infusion ports in the right
locations.  If you don't get them right, you end up with dry areas that
don't get any resin.

The larger, and more complex the part, the more trial and error.  Sounds
like a really expensive way to make a chasis.

As always, I could be wrong.  But I think it might be easier to do a wet
layup and vacuum bag it.

> I have been working on ideas for a composite chassis and I have a few
> questions that I hope some of the fabrication experts can answer.
>
> Gel coat
>     I keep hearing that you wait the 10-14 min until it passes the tack
> test, then continue the layup.
>     Since this is a big part, is it ok if the gel coat occurs days
> before the actual infusion.?
>     Is a gel coat suppose to be the final finish, or just a way of
> keeping fibers from printing out?
>
>     On one hand It would be nice for the part to pop out of the mold done.
>     But I can see where it would be great to be able to see the resin
> flow in this RTM-Lite or vacuum infusion process.
>     Does anyone ever use clear gel coat and colored resin?
>     I can also see where making all the composite parts with one color
> the using standard auto painting techniques could lower issues with
> color changes.
>
> Can I just paint a vacuum bagged surface.
>     If I made parts without using Gel Coat, what kind of surface would I
> have? Paintable?
>     I am trying to decide if it would be better to try to get my finish,
> color and "metal flake?" into a gel coat or just paint a surface.
>     What about a surface left by the vacuum infusion process, from the
> peal ply.
>     Is this possible? Can a peal ply surface on a compound shape be a
> good surface for automotive paints? or do you end up with lines where
> the peal ply sections overlap?
>
> Complex Molds.
>     All the demos I see for RTM-Lite are of really, really simple parts.
>     All the molds I see for car bodies are multiple part complexities.
>     The Heavy mold can be multiple sections, but anyone seen a multipart
> lite section?
>
> Sandwich construction
>     All demos I see for infusion processes including rtm-lite, are a
> single wall construction.
>     Can these techniques be used for a foam cored (or end grain balsa)
> sandwich.
>
>
> _______________________________________________
> For subscription options, see
> http://lists.sjsu.edu/mailman/listinfo/ev
>

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[Jeff Shanab]

I have been working on ideas for a composite chassis and I have a few
questions that I hope some of the fabrication experts can answer.

Gel coat
    I keep hearing that you wait the 10-14 min until it passes the tack
test, then continue the layup.
    Since this is a big part, is it ok if the gel coat occurs days
before the actual infusion.?
    Is a gel coat suppose to be the final finish, or just a way of
keeping fibers from printing out?

    On one hand It would be nice for the part to pop out of the mold done.
    But I can see where it would be great to be able to see the resin
flow in this RTM-Lite or vacuum infusion process.
    Does anyone ever use clear gel coat and colored resin?
    I can also see where making all the composite parts with one color
the using standard auto painting techniques could lower issues with
color changes.
 
Can I just paint a vacuum bagged surface.
    If I made parts without using Gel Coat, what kind of surface would I
have? Paintable?
    I am trying to decide if it would be better to try to get my finish,
color and "metal flake?" into a gel coat or just paint a surface.
    What about a surface left by the vacuum infusion process, from the
peal ply.
    Is this possible? Can a peal ply surface on a compound shape be a
good surface for automotive paints? or do you end up with lines where
the peal ply sections overlap?

Complex Molds.
    All the demos I see for RTM-Lite are of really, really simple parts.
    All the molds I see for car bodies are multiple part complexities.
    The Heavy mold can be multiple sections, but anyone seen a multipart
lite section?

Sandwich construction
    All demos I see for infusion processes including rtm-lite, are a
single wall construction.
    Can these techniques be used for a foam cored (or end grain balsa)
sandwich.


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[Roland Wiench]

Hello Jeff,

The mold may be a mirror finish, but it may be un-level.  The mirror finish
hides the un-levelness and waves in long panes, they be good for the average
person.  But for a experience body man, it will have to be block to
completely level the surfaces for show car quality.

This is where heavy metal flack and a lot of graphics hide the surfaces
imperfections.

I normally pickup all my fiberglass materials from a Custom Fiberglass Plant
which they do different types of lay up every day and these people can guild
you in how to lay out different materials, such as layering and lapping
different weights of cloth in the standard cloth and carbon cloth which uses
different types of resin.

After you get the reversed mold to a mirror finish, which is normally done
with polish aluminum, you first spray it with a mold release compound, which
allows the material to break free from the mold.

It is best to lay down a tack coat of Gel Coat and then two full coats.  It
depends on the ambient temperature when the Gel is spray.  By the time you
spray a large surface, it is tacky enough to either spray in the fiber glass
and resin.  The fiber glass at these places, comes on single strands looking
like thin fish line which is chop up in the gun and mix with the resin.

The Gel Coat is actually a lacquer base pigment mix with fiber glass resin.
You can purchase this pigment in any colors you want and mix it yourself.
This base provides a good paint binder to the surface.

If you do a fiber cloth lay up, you first spray the tacky Gel Coat with the
resin you are going to do, and then roll in the lightest weight cloth there
is while adding more resins.  You must put in enough resin so the glass
actually floats away from the surface a bit.  Then you lay the next layer of
glass that is heaver and so forth.

I lay up 1/4 inch thick panels that took 4 layers of glass from very fine to
a very heavy weave.  I make flat panels by laying the glass up on sheet
metal.

For battery boxes, the finish was not too critical.  I finish the surfaces
by spraying on epoxy paint and did some block sanding.  Now for as a car
body panels which were all factory made, it still took me two years to block
sand the surfaces, paint and block sand, paint and block sand maybe more
than 10 times, and then color sand between sealers, primers, 6 color coats,
and 2 clear coats.

A body shop guy friend of mind took over a year to refinished and refit a
fiberglass body sports car for show, and he is still not satisfied with it,
but to a normal person it looks great.

Roland




----- Original Message -----
From: "Jeff Shanab" <jshanab@...>
To: <ev@...>
Sent: Sunday, June 29, 2008 8:50 AM
Subject: [EVDL] Compostie Questions about gliders

> I have been working on ideas for a composite chassis and I have a few
> questions that I hope some of the fabrication experts can answer.
>
> Gel coat
>     I keep hearing that you wait the 10-14 min until it passes the tack
> test, then continue the layup.
>     Since this is a big part, is it ok if the gel coat occurs days
> before the actual infusion.?
>     Is a gel coat suppose to be the final finish, or just a way of
> keeping fibers from printing out?
>
>     On one hand It would be nice for the part to pop out of the mold done.
>     But I can see where it would be great to be able to see the resin
> flow in this RTM-Lite or vacuum infusion process.
>     Does anyone ever use clear gel coat and colored resin?
>     I can also see where making all the composite parts with one color
> the using standard auto painting techniques could lower issues with
> color changes.
>
> Can I just paint a vacuum bagged surface.
>     If I made parts without using Gel Coat, what kind of surface would I
> have? Paintable?
>     I am trying to decide if it would be better to try to get my finish,
> color and "metal flake?" into a gel coat or just paint a surface.
>     What about a surface left by the vacuum infusion process, from the
> peal ply.
>     Is this possible? Can a peal ply surface on a compound shape be a
> good surface for automotive paints? or do you end up with lines where
> the peal ply sections overlap?
>
> Complex Molds.
>     All the demos I see for RTM-Lite are of really, really simple parts.
>     All the molds I see for car bodies are multiple part complexities.
>     The Heavy mold can be multiple sections, but anyone seen a multipart
> lite section?
>
> Sandwich construction
>     All demos I see for infusion processes including rtm-lite, are a
> single wall construction.
>     Can these techniques be used for a foam cored (or end grain balsa)
> sandwich.
>
>
> _______________________________________________
> For subscription options, see
> http://lists.sjsu.edu/mailman/listinfo/ev
>

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[Jeff Shanab]

Peter said...Comments interspersed
> I'm no expert,
I am not even a beginner, just advanced research, if my google skills count ;-)
>  but from what I've read Vacuum infusion can require a great
> deal of trial and error to get the vacuum and infusion ports in the right
> locations.  If you don't get them right, you end up with dry areas that
> don't get any resin.
True
> The larger, and more complex the part, the more trial and error.
True if nothing else changes. What is required her is sequencing of multiple fill tubes
        vacuum is pulled, and all tubes are opened.
        once the lines are all charged, all but 1 is clamped off,
        symetrically or one by one, the secondary inlets are opened so the fill is progressive.
>  Sounds
> like a really expensive way to make a chasis.
To make a chassis, yes But what about to make many of them?

> As always, I could be wrong.  But I think it might be easier to do a wet
> layup and vacuum bag it.
To labor intensive to be productive.
I am worried that the large wet layup can't be done fast enough to get it into the bag in time.
If I am going wet layup, vacumm bag is almost a waste. (Not going for minimum weight).

I want to be able to take a week of 4 hour evenings to lay up the mold and load all the investments.
 Then infuse it on saturday morning(late) and pop it out about 2 hours later.

If this works, I can get some kind of approval to make them, either crash test a few or kit car exemption,
then I can look into getting employees. 4 people loading takes my 20 hours and makes it probably less than 5 with practice.
The same 4 people Precut for the next shot while the first one cures then repeat. Potentially 2 chassis a day with low cost tooling.

Maybe I load these on a trailer and take them down to the local paint shop.(after post cure)

4 employess at $15/hr is more like $1000/day, If I can swing that, $550 of the chassis cost is just for the help.
        Epoxy glass and foam is another X dollars, I am working on that and hoping it is around a 1-2K (there are inserts)
        Then to keep going, there must be some profit. So we are probably looking at $3500 - $5500 for the chassis alone.

Unfortunately, I just got the price of the infusion machine for RTM-Lite and they are a lot more than I thought they would be(like 30K)

I think (if the mold is not too complicated) a pure vacuum infusion can work with the same tooling and more ports, RTM-lite machine then allows filing faster and more consistent results. I like the concept of changing the catylyst ratio to cure faster as you get towards the end of the shot so the first resin finishes curing at same time as final resin. ( Which I guess answers the other question of weather it goes in like a balloon flowing thru the center of a stationary skin like injection molding where the first resin in is closest to the fill point or weather it migrates in parallel so the first resin in is the first resin to hit the catch pot)

It would be great if I can make these 1 at a time in my garage and scale up later if necessary.

 


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[Lee Hart]

Jeff Shanab wrote:
> I have been working on ideas for a composite chassis and I have a few
> questions that I hope some of the fabrication experts can answer.

I'm just learning, too; but maybe I'm a rung or two up the ladder. I'll
take a stab at it, but others can chime in and correct me.

> Gel coat
>     Since this is a big part, is it ok if the gel coat occurs days
> before the actual infusion?

Yes, but if it's completely cured, you want to rough up the surface
first to get good bonding.

>     Is a gel coat suppose to be the final finish, or just a way of
> keeping fibers from printing out?

It can do both. You can use it as the final finish, or just as the
undercoating for a final coat of paint. To use the gelcoat as your final
finish, the mold has to be essentially perfect. Or, you can get by with
a less than perfect mold, and paint it normally after the parts are
removed from the mold.

>     But I can see where it would be great to be able to see the resin
> flow in this RTM-Lite or vacuum infusion process.
>     Does anyone ever use clear gel coat and colored resin?

You could for parts that won't be exposed to sunlight. The UV will break
down many resins.

> Can I just paint a vacuum bagged surface.

My understanding is that most bags have a good but not automotive grade
finish. It would work for interior parts, or parts that you're going to
hand sand before spraying the final coat of finish.

>     If I made parts without using Gel Coat, what kind of surface would I
> have? Paintable?

Slightly irregular. There may be bubbles, or patterns from the mold
release compound, bits of dirt or other material that got on the mold,
print-through from the cloth layup, etc.

>     I am trying to decide if it would be better to try to get my finish,
> color and "metal flake?" into a gel coat or just paint a surface.
>     What about a surface left by the vacuum infusion process, from the
> peal ply.
>     Is this possible? Can a peal ply surface on a compound shape be a
> good surface for automotive paints? or do you end up with lines where
> the peal ply sections overlap?

Don't know.

> Complex Molds.
>     All the demos I see for RTM-Lite are of really, really simple parts.
>     All the molds I see for car bodies are multiple part complexities.
>     The Heavy mold can be multiple sections, but anyone seen a multipart
> lite section?

Simple shapes are easier. That's why we are working to simplify the
shape of the Sunrise -- to make it easier to mold!

> Sandwich construction
>     Can these techniques be used for a foam cored (or end grain balsa)
> sandwich.

Yes. You can either layup the side against the mold, then apply the foam
or balsa, then the inner layup. Use a slow curing resin so you have time
to do it all, or work in sections, etc.

Or, you can do it in stages. You just have to be sure you have a good
bonding surface for the next day's layup.

--
Ring the bells that still can ring
Forget the perfect offering
There is a crack in everything
That's how the light gets in    --    Leonard Cohen
--
Lee A. Hart, 814 8th Ave N, Sartell MN 56377, leeahart_at_earthlink.net

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[Peter VanDerWal]

> leaning more towards most of the surface being solar panels anyway.  They
> could provide most of my power requirements.
-snip-
> concept in play is a six to seven passenger vehicle that is a minivan
> replacement.  Under the floor would be batteries.

A 6-7 passendger minivan powered by solar cells?  So you're planning on a
top speed of 25 mph and a range of perhaps 2-3 miles per day?

A typical small EV uses about 250WH per mile.

A typical solar panel of about 1 square meter, produces about 150 watts
when pointed directly at the sun, at noon, on a cold, clear day, in the
middle of summer, in Arizona (fwiw we don't get many cold days uring the
summer here).
In real life, when mounted on a vehicle and not pointing directly at the
sun, and generally kinda warm, you're looking at 1/2 to maybe 2/3 of that.
Given that most places north of Arizona get somewhere between 1 to 4 hours
of usuable sunshing a day.  Then you loose somewhere between 10-25% of
that converting it to the proper charge voltage, and then another 20-30%
in battery charging efficiency.

So every square meter of solar panels produces enough in one day to move a
small car maybe 1 mile.  Perhaps 2 miles during the summertime.




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[Dave King]

Jeff

This is based on doing aircraft parts so some might not apply.

Gel coat isn't used too heavy and subject to cracking.

Infusion is only used on hyper critical i.e. expensive parts.
Vacuum bagging is a good process and easily and cheaply done at
home.

You don't peal ply surfaces to be painted only surfaces that
are going to be used to have more layers added. The peal ply
is just Dacron (or polyester) cloth from the fabric shop. 1-2
oz weight think is usually for lining things. (don't sew , don't care ;-])
Also no sizing/coating on it. Coloured is ok as you can actually
find it after things cure up. White tends to blend in and you
will spend hours hunting for the #$%#$% edges to pull on if you use it.
The epoxy doesn't stick to it as it has no sizing. Same thing happens
to fibreglass when you get it wet and wash off the sizing. Anyway
when you yank it off the layup the surface is very rough. The idea being
to knock down the worst with some 80-120 and do the next layer. If
you plan to paint over you need to prep it ending up with say 220.

When you paint composites the prep starts at the epoxy. You need to use
a good system or the paint and primer will just come off in dinner plate
sized scabs within a year or so. Any wax or pva (or even handprint oils)
left on for example and you will have blisters and bubbles.

I've done a fair amount of panels for cargo floors in a few of the aircraft
we converted to cargo. Those were aluminum faced balsa cored panels. Those
are pretty heavy duty being capable of supported over 1000 lbs per sqr foot.
They are also pretty heavy. These were also only about 5/8 thick. For
smaller
loads you can easily use a much lighter foam core with just a few layers of
glass. When you do this right they are very light and unbelievably strong.
One demo I saw was a set or car ramps. Both easily carried in one and full
sized truck didn't even make them flex. That's almost as interesting as
using
the weather radar on the ground to pop balloons ;-]

Since you are in Kalefurnia try aircraft spruce and specialty and see if
they
still have a book called moldless composite construction by Burt Rutan,
that's
the same guy who designed the Voyager and Spaceship 1. You should also have
a chat with a fibreglass supply place about doing the layups and then a
paint shop to get that end sorted out. Two separate process's but they have
to be compatible to get it to work long term. Write me off list if you have
any questions.

Dave



-----Original Message-----


I have been working on ideas for a composite chassis and I have a few
questions that I hope some of the fabrication experts can answer.

Gel coat
    I keep hearing that you wait the 10-14 min until it passes the tack
test, then continue the layup.
    Since this is a big part, is it ok if the gel coat occurs days
before the actual infusion.?
    Is a gel coat suppose to be the final finish, or just a way of
keeping fibers from printing out?

    On one hand It would be nice for the part to pop out of the mold done.
    But I can see where it would be great to be able to see the resin
flow in this RTM-Lite or vacuum infusion process.
    Does anyone ever use clear gel coat and colored resin?
    I can also see where making all the composite parts with one color
the using standard auto painting techniques could lower issues with
color changes.
 
Can I just paint a vacuum bagged surface.
    If I made parts without using Gel Coat, what kind of surface would I
have? Paintable?
    I am trying to decide if it would be better to try to get my finish,
color and "metal flake?" into a gel coat or just paint a surface.
    What about a surface left by the vacuum infusion process, from the
peal ply.
    Is this possible? Can a peal ply surface on a compound shape be a
good surface for automotive paints? or do you end up with lines where
the peal ply sections overlap?

Complex Molds.
    All the demos I see for RTM-Lite are of really, really simple parts.
    All the molds I see for car bodies are multiple part complexities.
    The Heavy mold can be multiple sections, but anyone seen a multipart
lite section?

Sandwich construction
    All demos I see for infusion processes including rtm-lite, are a
single wall construction.
    Can these techniques be used for a foam cored (or end grain balsa)
sandwich.


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[jerryd]

             Hi Jeff, Peter and All,

----- Original Message Follows -----
From: Jeff Shanab <jshanab@...>
To: ev@...
Subject: Re: [EVDL] Compostie Questions about gliders
Date: Sun, 29 Jun 2008 15:06:49 -0700

>Peter said...Comments interspersed
>> I'm no expert,
>I am not even a beginner, just advanced research, if my
>>  google skills count ;-) but from what I've read Vacuum
>> infusion can require a great deal of trial and error to
>> get the vacuum and infusion ports in the right locations.
> If you don't get them right, you end up with dry areas
>> that don't get any resin.
>True

         Very true!! I personally don't see the advantage as
these take about as much work as hand layup.
         A FG body production line can make as many bodies
as number of molds x's 2-4/8hr shift using hand layup, resin
guns and precut FG sheets.
         A RTM would be just a couple molds because they are
too expensive, making nany fewer parts/shift.
         Using peelply or vacuum bags has a labor intensive
surface to finish afterward where as a good worker with a
putty spreader will leave it smooth with only filling maybe
needed. The hand layup will be some to a lot lighter due to
RTM tolerances.
         A continuous line with waxers, gelcoat people, FG
placers, resin/spreaders, core, FG placers, resin finishers,
8 people could do 1/hr without a problem. About 1/2 that
doing thew chassis part so 12hrs/unibody.
        Let's say FG/resins are now $3/lb, labor about $3/lb
 you are only $8/lb for everything. The Freedom EV is a
250lb composite part, the Sunrise should be about 600 and a
Rabbit size about 450 lbs. So it's costs doing hand layup in
production is quite good compared to steel and you can break
even on 1/week/1 person vs 50-100,000/yr needed for steel
cars.  
        I should say I'd never do my own FG production but
farm it out instead, just assembling the parts into an EV.


>> The larger, and more complex the part, the more trial and
>error.  True if nothing else changes. What is required her
>is sequencing of multiple fill tubes
>    vacuum is pulled, and all tubes are opened.
>    once the lines are all charged, all but 1 is clamped
>off,
>    symetrically or one by one, the secondary inlets are
>>  opened so the fill is progressive. Sounds
>> like a really expensive way to make a chasis.

          You are going to make a lot of them before you get
ones good enough to use and  too many bad ones using RTM
besides the heavy cost of the double molds.

>To make a chassis, yes But what about to make many of them?
>
>> As always, I could be wrong.  But I think it might be
>> easier to do a wet layup and vacuum bag it.
>To labor intensive to be productive.
>I am worried that the large wet layup can't be done fast
>enough to get it into the bag in time. If I am going wet
>layup, vacumm bag is almost a waste. (Not going for minimum
>weight).
>
>I want to be able to take a week of 4 hour evenings to lay
>up the mold and load all the investments.
> Then infuse it on saturday morning(late) and pop it out
>about 2 hours later.

        I hand laid up the Freedom EV the first time in
about 10hrs about complete body/chassis bonded together. And
I have a bad back!!  In mass production it could be cut to
4-5hrs/unibody or less. My materials averaged $1.75/lb but
have increased I'd bet  about 50% since then.


>
>If this works, I can get some kind of approval to make them
>, either crash test a few or kit car exemption, then I can
>look into getting employees. 4 people loading takes my 20
>hours and makes it probably less than 5 with practice. The
>same 4 people Precut for the next shot while the first one
>cures then repeat. Potentially 2 chassis a day with low
>cost tooling.

          FG companies will deliver precut FG saving you
that employee. Just place, wet out and go!


>
>Maybe I load these on a trailer and take them down to the
>local paint shop.(after post cure)

           Painting saves weight, about 20+lbs/cars vs
gelcoat.

>
>4 employess at $15/hr is more like $1000/day, If I can
>swing that, $550 of the chassis cost is just for the help.
>    Epoxy glass and foam is another X dollars, I am working
>on that and hoping it is around a 1-2K (there are inserts)
>    Then to keep going, there must be some profit. So we
>are probably looking at $3500 - $5500 for the chassis
>alone.
>
>Unfortunately, I just got the price of the infusion machine
>for RTM-Lite and they are a lot more than I thought they
>would be(like 30K)

      A vacuum pump will work with gas valves for much less.
With the right resin, 10lb vacuum should do the trick.
Probably a fridge compressor would work or an A/C vacuum
pump would.


>
>I think (if the mold is not too complicated) a pure vacuum
>infusion can work with the same tooling and more ports,
>RTM-lite machine then allows filing faster and more
>consistent results.

          Not likely in real life.

I like the concept of changing the

>catylyst ratio to cure faster as you get towards the end of
>the shot so the first resin finishes curing at same time as
>final resin. ( Which I guess answers the other question of
>weather it goes in like a balloon flowing thru the center
>of a stationary skin like injection molding where the first
>resin in is closest to the fill point or weather it
>migrates in parallel so the first resin in is the first
>resin to hit the catch pot)
>
>It would be great if I can make these 1 at a time in my
>garage and scale up later if necessary.

           I do, you can too.

                             Jerry Dycus

>
>
>
>
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[Jeff Miller-12]

I am certainly considering similar things but I didn't plan to use Gel coat
due to cost and weight constraints.  Also as my thoughts have evolved I am
leaning more towards most of the surface being solar panels anyway.  They
could provide most of my power requirements.  Naturally somebody on here
will explain to me that I am really out to lunch which is why I am here!

I was thinking the "back" of the car would be all panels for traction motor
power.  The "hood" would provide power on the 12 volt side as it probably
won't be large enough to generate significant amps at the correct voltage.
I would still have a DCtoDC converter for those hot summer nights but I
should be able to run most of the time on solar for the accessories.  The
concept in play is a six to seven passenger vehicle that is a minivan
replacement.  Under the floor would be batteries.
So the driver would be up high like a minivan.  The two rear most passengers
aren't going to be very tall but who cares about those short rear
passengers.  It could just as easily be eight passengers.  Still early in
the idea cycle here.  A composite and foam core body is pretty well
insulated and as such should require less energy to keep cool or warm.

Composites
If you were to manage to construct the entire structure's core first then
you could lay up the whole job without doing molds but the surface finish
will be at best the texture of the upper layer of fabric.   The possibility
exists of gel coating it after the fact but that isn't what most people do
obviously.  It comes down to your personal requirements.  For me surface
finish isn't critical yet.  I am a function over looks kind of guy.

The way that seems to be work best for doing the above layup is attach the
core to a giant rotisserie so you can set the angle of the part so you
aren't fighting gravity.

if the core is simple to create and you have nice open corners you could lay
it up in four days depending on how big it is.  The above minivan is
complexly shaped so that it will take me a while to do it.  Some of my
smaller 2 passenger idea's are basically bathtups on wheels and those could
be done in 1.5 to 2 days once you had the core done.


-----Original Message-----
From: Jeff Shanab [mailto:jshanab@...]
Sent: Sunday, June 29, 2008 8:50 AM
To: ev@...
Subject: [EVDL] Compostie Questions about gliders


I have been working on ideas for a composite chassis and I have a few
questions that I hope some of the fabrication experts can answer.

Gel coat
    I keep hearing that you wait the 10-14 min until it passes the tack
test, then continue the layup.
    Since this is a big part, is it ok if the gel coat occurs days
before the actual infusion.?
    Is a gel coat suppose to be the final finish, or just a way of
keeping fibers from printing out?

    On one hand It would be nice for the part to pop out of the mold done.
    But I can see where it would be great to be able to see the resin
flow in this RTM-Lite or vacuum infusion process.
    Does anyone ever use clear gel coat and colored resin?
    I can also see where making all the composite parts with one color
the using standard auto painting techniques could lower issues with
color changes.

Can I just paint a vacuum bagged surface.
    If I made parts without using Gel Coat, what kind of surface would I
have? Paintable?
    I am trying to decide if it would be better to try to get my finish,
color and "metal flake?" into a gel coat or just paint a surface.
    What about a surface left by the vacuum infusion process, from the
peal ply.
    Is this possible? Can a peal ply surface on a compound shape be a
good surface for automotive paints? or do you end up with lines where
the peal ply sections overlap?

Complex Molds.
    All the demos I see for RTM-Lite are of really, really simple parts.
    All the molds I see for car bodies are multiple part complexities.
    The Heavy mold can be multiple sections, but anyone seen a multipart
lite section?

Sandwich construction
    All demos I see for infusion processes including rtm-lite, are a
single wall construction.
    Can these techniques be used for a foam cored (or end grain balsa)
sandwich.


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[Jeff Shanab]

Thanks everyone on the real world info.
Jerry, The one think that confuses me about a hand layup is how to get
an "automotive grade" finish on the out side of the part.
The current concept that I may have to give up on is 1 multipart mold
makes the rolling chassis, the other molds just make doors, hoods, and
the front fenders.
The main chassis could have the drivetrain mounted and drive away. So
either the core is the mold surface and I depend on the skill of the
layup person with a squegee on the outside finish, or the outside is the
mold and they have to work inside.


Jeff miller said
...
> The way that seems to be work best for doing the above layup is attach the
> core to a giant rotisserie so you can set the angle of the part so you
> aren't fighting gravity.
>  
I actually thought of that at first but decided against it for a
practical reason. (convex hull constraint) It is however always in my mind.

If any of you have ever used one of those shrinkwrap machines like
http://www.ferret.com.au/c/Alpha-Racking/Pallet-Film-shrink-Wrap-Machine-p12787
The carriage has a roll of material under tension and as the pallet
spins the carriage goes up and down.
A double 45 weave would have enough flexability to conform if the shape
was completely convex. even could put a pressurized nozzle the fabric is
pulled thru to load with resin. :-)

One thing I want to try is 3D reinforcement. Some way of minimizing
catastrophic skin failures. I have multiple ideas on that.


-=-=-=-==-=-
Another idea is to do an assembly. Outer skin, inner skin and expoxy
coated core.

Here is a wild idea, What if the inner and outer skin formed the two
surfaces of a mold, the mold gets the foam core injected into it.
kinda like those 7-11 super big gulp insulated cups, Would the foam
stick to the skins?
But this dictates the ability to assemble, no reentrants allowed.

In all honesty, as I work on the design, I come accross details that
can't be handled by these grandios automation ideas.  Too many
reentrant  or changes in  direction are needed.
-=-=-=--=--=-=-=-

Today I bought some 3/16 poaster board and glue and 1/10 scale wheels
and rims. I am gonna print out the body designs and glue the slices
togather to get a feel for the shape and imagining the layup and mold
parting lines.

One last question. Lets say you have a parting line of a mold , like we
are making a fender and the mold must split on the apex of the fender to
get it apart.
No matter how good the mold is, you are gonna have a parting line. right?
Do you close the mold and spray on the gel coat, or us it better to put
on gelcoat and then assemble mold halves.
I think I will use gelgoat, I am not as concerned about the last few
pounds as someone in racing or aircraft may need to be., I forgot about
the UV protection it can provide, and it will provide some stock for
sanding prior to painting. I will probably treat the gelcoat
conceptually like a primer. white for bright colors, grey for the blues
and red for the reds and blacks.


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[Nick Drouin]

Just to add a bit of real-life experience to the solar-car comments.
I raced McGill's second generation solar car in Canada, Australia and
the US.  This was back in 1996-1997, so all of this is from memory,
hopefully not too embelished with the years!


We are talking about a 2m wide by 6m long by 1.2m high, tear-dropped
shaped Kevlar bodied, carbon-fibre monocoque-frame single-seater
race-car.  The car had an amazing CdA and rolled on tandem bicycle
tires pumped to 110psi.
The back 2m x 4m  was covered in solar cells rated at 16% efficiency
which ran at over 320VDC in 6 'areas' and many diode protected
sub-areas (to optimise for the directionality of the sun and cell
failure) brought down to a 120VCD bus using multiple Vicors and other
power electronics. Apart from having a few too many plys of carbon and
Kevlar, and using lead batteries, it would have been really hard to
make a more a aerodynamic lightweight (~1200lbs with driver?) car.

That being said, the top speed was 111km/hr (69mph) using the 120VDC
Gel batteries, the system wasn't maxed out, just the drivers nerves:
70mph on bicycle tires has a sobering effect.

The fastest 'solar only' speed was 64km/hr (40mph) in Australia on a
cooler, partly-cloudy day, in the desert, in the early summer.
Race-speed was around 60km/hr and could be maintained (except for on
hills) from 8am to 4pm for days at a time; in all three countries.
Charging was solar-only from sunrise to 8am and 4pm to sunset.

It should be noted that solar-cells were NOT aerodynamic, we used
half-cells in a 3M-film sandwich but there were still irregularities
in the surface which forced us to conclude that we had turbulent flow
over the entire cell area.  The only way to make a curved, smooth,
cell-surface was to lay-up the cells in resin: they loose even more
power behind the resin; however they are more robust and much smoother
-- other teams did this.

The conclusion that I have from my three years of slaving over this
student project: solar-cars are NOT practical.  Great student project,
but this is simply not usable in real life.  The cost-benefit,
weight-benefit, aerodynamics, electrical complexity and system
robustness just don't pan out.

If you really insist on solar, you might be able to use it to
maintain/charge your accessory loads while parked (forget the traction
pack); use the back-half of your vehicle for cells: where you are
likely to already have turbulent flow over the surface.

Do your calculations:

Solar power per unit area in W/m2 (assume 1000W/m2 if you don't have
local data, adjust up to 60% downward for poor air quality, high
humidity, haze and most cloud conditions; adjust up to 30% upwards for
snow on the ground, cold temperatures, the 'right' partially cloudy
conditions) x cell efficiency (a factor of cell-mounting technology,
surface-temperature and cell type) x sine of the angle of incidence of
the sun x a factor for electrical losses x solar-cell area in m2


In my humble opinion, I would look at solar-power as a nice-to-have
add-on; not a design element; it seems to me there are already enough
design elements to worry about before bringing solar-power into the
mix.

Best of luck,

-Nick



On 6/29/08, Peter VanDerWal <evdl@...> wrote:

> > leaning more towards most of the surface being solar panels anyway.  They
> > could provide most of my power requirements.
> -snip-
> > concept in play is a six to seven passenger vehicle that is a minivan
> > replacement.  Under the floor would be batteries.
>
> A 6-7 passendger minivan powered by solar cells?  So you're planning on a
> top speed of 25 mph and a range of perhaps 2-3 miles per day?
>
> A typical small EV uses about 250WH per mile.
>
> A typical solar panel of about 1 square meter, produces about 150 watts
> when pointed directly at the sun, at noon, on a cold, clear day, in the
> middle of summer, in Arizona (fwiw we don't get many cold days uring the
> summer here).
> In real life, when mounted on a vehicle and not pointing directly at the
> sun, and generally kinda warm, you're looking at 1/2 to maybe 2/3 of that.
> Given that most places north of Arizona get somewhere between 1 to 4 hours
> of usuable sunshing a day.  Then you loose somewhere between 10-25% of
> that converting it to the proper charge voltage, and then another 20-30%
> in battery charging efficiency.
>
> So every square meter of solar panels produces enough in one day to move a
> small car maybe 1 mile.  Perhaps 2 miles during the summertime.
>
>
>
>
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[Lee Hart]

Jeff Shanab wrote:
> The one think that confuses me about a hand layup is how to get
> an "automotive grade" finish on the out side of the part.

With lots and lots of work. :-)

I wish I could think of some way to wean people away from requiring this
kind of finish. It has the potential to save a *lot* of time and money!

For instance, I loved Jerry Dycus's "Ewoody" EV with its beautiful wood
body. Or, we accept matte finishes on all sorts of outdoor equipment. Or
the painted pictures most often used for advertising signs on vehicles.

> The current concept that I may have to give up on is 1 multipart mold
> makes the rolling chassis

The chassis doesn't require that mirror-smooth finish. It *can* be made
with print-through from the fabric, etc.

> If any of you have ever used one of those shrinkwrap machines...

One of the techniques I want to play with works somewhat like that. But
because the molds for your outer body panels are concave, I'm thinking
of using vacuum forming to suck the plastic sheet in against the mold.
Then do the layup, and when the resin cures, the plastic serves as your
mold release. It also provides a "pretty good" surface finish.

--
Ring the bells that still can ring
Forget the perfect offering
There is a crack in everything
That's how the light gets in    --    Leonard Cohen
--
Lee A. Hart, 814 8th Ave N, Sartell MN 56377, leeahart_at_earthlink.net

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[EVDL Administrator]

On 30 Jun 2008 at 11:55, Lee Hart wrote:

> I wish I could think of some way to wean people away from requiring
> this kind of finish. It has the potential to save a *lot* of time and
> money! ... we accept matte finishes on all sorts of outdoor equipment.

Let's see how well consumers accept the matte finish on the Think EVs.  I've
heard only minor gripes about the earlier versions from a few years ago, and
only from automotive writers, not from real customers (though I might have
missed some).

David Roden - Akron, Ohio, USA
EVDL Administrator

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