Balsa/aluminum composite panels

[n1...@arrl.net]

In an effort to minimize vehicle weight, I'm considering trying a
balsa/aluminum sandwich construction for the hull of my first effort.
I've built test panels, and they're quite light and strong.

This structure is modeled on the aluminum honeycomb panels used on
space satellites, BTW. IIRC, the biggest consumer of balsa worldwide
is oil supertankers, which use an end-grain balsa/steel sandwich.

What you do is, make two copies of the panel you're building out of
thin aluminum sheet, and make a sandwich of the sheets and enough 1/4"
to 1'2" thick balsa planks to fill the space between them. Use a slow-
cure epoxy as the bonding agent. Place the sandwich between sheets of
wax paper (natch, it's a SANDWICH!), press between weighted flat
plywood sheets, and allow to cure.

The result is a very light, surprisingly strong panel that can be
drilled and bolted to (I recommend gluing bushings into the holes or
using reinforcing plates to spread the compressive load, as you CAN
crush the composite easily).

BTW, if you tediously cut the balsa into strips and orient the grain
so it's perpendicular to the aluminum sheets, you get a much stronger,
more crush-resistant panel.

This won't do away with the need for a strong frame for the axles
(lots of point loading there), but it SHOULD reduce overall weight
considerably. I'll have to think about whether I can use this for
roadwheels, but I have some doubts there.

Anyone familiar with this kind of structure? Has anyone used such a
structure for one of these tanks?

[Clark Ward Jr]

That's an interesting idea... How well does epoxy stick to the
aluminum sheets? I figure one would have to rough them up first with
sandpaper, but still it'd be good to have some data :)

--
_______
/ |O| \ Clark in Georgia
###=======### USMC M60A1
###=======### KI4GYT
### ###

[Frank Pittelli]

n1...@arrl.net wrote:
> In an effort to minimize vehicle weight, I'm considering trying a
> balsa/aluminum sandwich construction for the hull of my first effort.
> I've built test panels, and they're quite light and strong.
>
> This structure is modeled on the aluminum honeycomb panels used on
> space satellites, BTW. IIRC, the biggest consumer of balsa worldwide
> is oil supertankers, which use an end-grain balsa/steel sandwich.

Composite construction certainly does reduce weight, but using aluminum
for the skin instead of cloth results in a less "durable" solution.
Specifically, the aluminum skin is more easily dented and punctured.
That skin would also be more difficult to paint and repair over time.
Since you are using epoxy as the bonding agent, why not simply go with a
cloth composite (glass, kevlar or carbonfiber) on a filler?

Regardless of the skin used, balsa cores are being replaced more and
more by expanded foams or true honeycombs which are lighter, stronger
and easier to work with. Balsa cores are notorious for having dense
areas that don't bond properly to the skin, resulting in blisters over
time. Furthermore, as you stated, they have a grain, so they have
different structural properties in different directions. Other cores
don't suffer from these problems.

As you stated, when building composite structures, you have to be
painfully aware of the structural deficiencies. All through holes have
to be reinforced because the core is exposed along the sides of the hole
and therefore have no strength. In full size sailboats, you drill a
larger hole than needed, fill with epoxy+filler, then drill the actual
hole. You also have to use backing plates or large washers to prevent
crushing the composite walls or pulling the mounting bolt through the skin.

Composites *can* yield a lighter (and stronger) vehicle (if used
properly), but they definitely require (a) more tooling, (b) more man
hours, (c) more money and (d) more design time than traditional wooden
box construction. Over the last 15 years of building boats and tanks,
I've determined that the best overall value comes from a skin-on-frame
construction approach, using wooden or metal frames for structure, a
thin plywood for skin and a thin fiberglass covering for durability. A
good compromise across all dimensions, combining the best aspects of
wood and composite construction.

That said, I plan on making the S-Tank hull from composites (probably
carbon fiber on expanded foam), with a welded aluminum chassis, with
molded plastic wheels and tracks riding on composite axles. But, I'm
not doing it to save money or time ... I'm doing it for the "cool"
factor :-)

Frank P.

[Gettysb...@aol.com]

Well said Frank....I think...

Bobo

---

See AOL's top rated recipes and easy ways to stay in shape for winter.

[n1...@arrl.net]

Many thanks, Frank. You've clearly thought this one out well and have
more experience than I in this regard. You make good points. I shall
profit from this advice...;-)

[Frank Pittelli]

n1...@arrl.net wrote:
> You make good points. I shall profit from this advice...;-)

Whoa there ... hold on ... any "profits" made from this mailing list are
taxable under the legal terms that you agreed to when you originally
joined the group. (I'm sure you saw the legal agreement in 0.2pt font
streaming past at 6,250 words per second when you joined.) Please be
sure to fill out the proper paperwork (in triplicate) and send your
advanced payment in advance to the Office of Advanced Payments before we
have to turn this matter over to our Office of Collections and Mass
Destruction.

Frank "Good Advice Is Never Free" Pittelli

[n1...@arrl.net]

> streaming past at 6,250 words per second when you joined.) Please be
> sure to fill out the proper paperwork (in triplicate) and send your
> advanced payment in advance to the Office of Advanced Payments before we
> have to turn this matter over to our Office of Collections and Mass
> Destruction.
>
> Frank "Good Advice Is Never Free" Pittelli

Ah, I think I may have to refer this to my staff Panzerkapitan,
Theodor von Rinnstein, for, um, disbursement at an appropriate
time... ;-)

BTW, anyone know of a grouping in the Boston area?

Steve

[Odyssey...@aol.com]

In a message dated 12/21/2007 5:11:50 P.M. Eastern Standard Time, fr...@rctankcombat.com writes:

That said, I plan on making the S-Tank hull from composites (probably
carbon fiber on expanded foam), with a welded aluminum chassis, with
molded plastic wheels and tracks riding on composite axles.  But, I'm
not doing it to save money or time ... I'm doing it for the "cool"
factor :-)

    Frank P.

okay, if your using expanding foam for the core to glass over, what are you putting the expanding foam onto to make the basic hull shape or are you just going to use pink foam board and glass over that?

 

chris

[Odyssey...@aol.com]

isn't there a hobby grade plywood? i think it has thinner layers of wood, and the sheeting is thinner too (not sure what a sheet size might be...........) wouldn't this be ideal for some things like upper hull construction (with some ribbing for extra strength) to help aid in saving weight?

[Chrysanthos Kanellopoulos]

http://www.youtube.com/watch?v=RmPbLRDwuGY&NR=1

http://www.youtube.com/watch?v=_Oxt8Myjv4c&NR=1

Have you seen this kind of movement? Goes to teh side
Impressive
C

[Mike Lyons]

The chassis is from Vex Robotics, but the wheels are not the Vex Omni-
Directional Wheels (see http://www.robotcombat.com/images/store_vexomni_lg.jpg).
They could be the Multidirectional Acetal wheels carried by McMaster
(see http://www.mcmaster.com/ and search for "skate wheels").

On Dec 22, 12:21 am, "Chrysanthos Kanellopoulos" <xchr...@otenet.gr>
wrote:
...

[Clark Ward Jr]

For the freakish curves of the M60 turret, I'm using 1/64" hobby
plywood on a 1/4" framework, covered by a few layers of 10oz
fiberglass. The 1/64" can hold nearly any curve you ask it to, with a
little persuading...

[SmithD]

----- Original Message -----
From: <n1...@arrl.net>
To: "R/C Tank Combat" <rctank...@googlegroups.com>
Sent: Friday, December 21, 2007 3:19 PM
Subject: [TANKS] Balsa/aluminum composite panels

>
> In an effort to minimize vehicle weight, I'm considering trying a
> balsa/aluminum sandwich construction for the hull of my first effort.
> I've built test panels, and they're quite light and strong.

Aircraft style construction for a tank! If you can bond the AL to the balsa
it will be impressively strong for its weight. If you try this, keep us
informed. What works? What doesn't? DSmith

[Odyssey...@aol.com]

someone just spoke about this honeycomb (filler?) that could be covered with wood/glass. did you say it can be bought at home depot, and if so, what area so i can go look at it next time i'm in there

[Jud...@aol.com]

I have used cardboard cut into 3/8 strips, stacked side by side and sandwiched between masonite sheets with contact cement to make lightweight panels for puppet show stages. I also inserted a strip of wood around the edges so there was something to screw the hinges to. The cardboard was the thicker stuff they pack appliances in. A four foot panel would hold about 150lbs with minimal deflection.  

 

Another way I have seen used is to make a wood frame, cover it with cardboard and then fill it with expanding foam. The same type you get from Home Depot. Maybe it would work with the aluminum instead of the cardboard?

[Chris. b]

Google a product called "diabond" its a plastic/aluminium composite
panel, I use it all the time at work, it can be routed and bent very
easily, and its very very light, its also very rigid. I plan on making
a tank out of it one day, after I finish my current 3, lol.

Chris. b

On Dec 24, 3:31 am, Jud...@aol.com wrote:
> I have used cardboard cut into 3/8 strips, stacked side by side and  
> sandwiched between masonite sheets with contact cement to make lightweight  panels for
> puppet show stages. I also inserted a strip of wood around the edges  so
> there was something to screw the hinges to. The cardboard was  the thicker stuff
> they pack appliances in. A four foot panel  would hold about 150lbs with
> minimal deflection.  
>
> Another way I have seen used is to make a wood frame, cover it with  
> cardboard and then fill it with expanding foam. The same type you get from Home  
> Depot. Maybe it would work with the aluminum instead of the  cardboard?
>

> **************************************See AOL's top rated recipes
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[Odyssey...@aol.com]

In a message dated 12/23/2007 11:26:00 P.M. Eastern Standard Time, barthe...@hotmail.com writes:

Google a product called "diabond" its a plastic/aluminium composite
panel, I use it all the time at work, it can be routed and bent very
easily, and its very very light, its also very rigid. I plan on making
a tank out of it one day, after I finish my current 3, lol.

Chris. b

mmmmm .... sounds interesting, i wonder how it would hold up as the metal cleats in track links (like the ones i'll be casting).

 

i'll have to see if there is any dealers around in my area........... and as you say, it could be something for making hulls will, but how would you fill in seams and such? how does it take paint?

[Odyssey...@aol.com]

well, the first site i am looking at makes it sound like it is a sandwiched material, with a thin, double wall aluminum sheet with a foam core. once this is cut, then the foam core would be exposed. i thought it was more of a composite as in a mixture of resin and aluminum (flakes/powder).

 

this place is in UK:

http://www.multipaneluk.co.uk/?gclid=CMn7sPKMwJACFQiSHgodKU4PPg

 

 

 

this company is offering 4' x 8' sheets (sold in a lot of 5)

http://store.foamboardsource.com/medium---heavy-duty-board--dibond.html

 

2mm $1,303.00

 

3mm $1,475.00

 

a bit too pricey for me

 

another company

http://www.alcancompositesusa.com/product_detail.html?uid=gd40c8daac51170

 

now i see this site sells by the sheet - prices listed at bottom

http://www.tri-dee.com/Dibond%20Aluminium%20Composite%20Panels.htm

 

 

 

this doesn't look like anything i'd be looking into anytime soon (or if ever)

 

chris

[Chris. b]

I have never seen or used the foam core one, only the thermoplastic
core one, paint has no affect on it, you dont need to fill the ends as
its totally water/paint proof. I think it would be good for a fram/
skin type build.

Make a nice frame then just rivet diabond onto it, be very light if
you used an aluminium frame.

Chris. b

On Dec 24, 2:53 pm, OdysseySlipw...@aol.com wrote:
> well, the first site i am looking at makes it sound like it is a sandwiched  
> material, with a thin, double wall aluminum sheet with a foam core. once this
> is  cut, then the foam core would be exposed. i thought it was more of a
> composite  as in a mixture of resin and aluminum (flakes/powder).
>
> this place is in UK:

> _http://www.multipaneluk.co.uk/?gclid=CMn7sPKMwJACFQiSHgodKU4PPg_
> (http://www.multipaneluk.co.uk/?gclid=CMn7sPKMwJACFQiSHgodKU4PPg)

>
> this company is offering 4' x 8' sheets (sold in a lot of 5)

> _http://store.foamboardsource.com/medium---heavy-duty-board--dibond.html_
> (http://store.foamboardsource.com/medium---heavy-duty-board--dibond.html)

>
> 2mm $1,303.00
>
> 3mm $1,475.00
>
> a bit too pricey for me
>
> another company

> _http://www.alcancompositesusa.com/product_detail.html?uid=gd40c8daac5...
> (http://www.alcancompositesusa.com/product_detail.html?uid=gd40c8daac5...)

>
> now i see this site sells by the sheet - prices listed at bottom

> _http://www.tri-dee.com/Dibond%20Aluminium%20Composite%20Panels.htm_
> (http://www.tri-dee.com/Dibond%20Aluminium%20Composite%20Panels.htm)

>
> this doesn't look like anything i'd be looking into anytime soon (or if  ever)
>
> chris
>

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