Fwd: Re: Folding liquid fiberglass bicycles

[Kragen Javier Sitaker]

Forwarding conversation on the bicycle idea.

From: Kragen Javier Sitaker <kragen at pobox.com>
To: Michael Leonhard <michael206 at gmail.com>
Subject: Re: Folding liquid fiberglass bicycles
MIME-Version: 1.0
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You write:
> Hi Kragen,
> This is an interesting idea.  What kind of material did you have in
> mind?  Glass fibers can be embedded in many kinds of materials, some
> flexible and others stiff.  I've used very light weight fiberglass in
> radio controlled models.  First, I must cut the fiberglass cloth and
> lay it over a form.  Then I apply epoxy, which soaks into the cloth.
> For added strength, several layers of cloth may be applied
> successively and soaked in epoxy.  After the epoxy hardens, I destroy
> the form, leaving a thin fiberglass-epoxy composite shell.  The
> flexibility of this shell depends on the kind of epoxy and the number
> of layers of fiberglass cloth.  A single layer of very light weight
> cloth can yield a part that is about as flexible as the cardboard from
> a cereal box.  It's not the kind of thing you would roll up and stick
> in your pocket.

Thanks for your thoughts!

It doesn't sound impossible to roll up the single-layer material and
stick in your pocket (especially with a dowel or something to roll it
around) but it does sound difficult --- and that's only a single
layer, which presumably has very little strength.  (I think I
calculated that the glass part of the thing would need to be 0.12 mm
thick --- roughly how many layers of glass cloth is that, before you
apply the epoxy?)

To keep it flexible with greater thickness, the material holding the
layers of fiberglass together would have to be one of the following:
- very yielding to shear (say, rubber) which implies that it would be
  thick or heavy;
- nonexistent --- maybe you'd wrap the glass sheet around the water
  many times
- very thin indeed (although I think the required thickness of the
  glass alone would prevent this)

> I suppose there must be some very flexible plastics that could be
> mixed with fiberglass to make very strong and flexible cloth.  Have
> you heard of anything in particular?

Indeed not; I know very little about the material, just what my
ex-co-worker Matt told me about his airplane models.

> If the frame will be filled with water, perhaps osmosis create the
> necessary pressure?  According to Wikipedia, ocean water has 27 atm of
> osmotic pressure.  That is about 400 pascals, three orders of
> magnitude less than you estimate is needed.  But I suppose it would be
> difficult to make a semipermiable membrane that is strong enough to
> contain the 300-650 kpsi necessary for the structure.

That's the tensile strength of the glass, not the necessary pressure
of the water.  I think I calculated the pressure needed in the water,
but apparently I failed to translate that into the electronic version
of the post.  A 46 cm^2 cross-section is 7 in^2, and I was saying we
could probably get by with 300 pounds of bending strength (i.e. being
able to support 300 lbs. in the middle of a strut), which gives means
we need 1100 lbs. of pressure to prevent the "under compression" side
of the glass from going below zero tension when it's under bending
stress.  That's almost 160 psi, which is about 10.6 atm.  Achievable
with a bicycle pump, and if most of the internal space is full of
water, it won't even be that much work.

> How about a scooter?  The wheels could be shaped like shallow bowls
> that fit together, holding the deflated frame and axels inside.

That's a great idea!

> Have you read Neal Stephenson's book The_Diamond_Age?

No, although I've read a lot of the extropian and Foresight source
literature it's based on.  But Neal's writing is a lot more riveting
than Drexler's or Merkle's, so people read him more.

> He describes a future where nanotechnology facilitates cheap and
> perfectly recyclable machines.  An automated manufacturing machine
> is called a 'matter compiler'.  While the automated recycler is a
> 'decompiler'.  Recycling is then 'deking'.

Suppose the technology described above comes to pass.  What
institutions are needed to allow human beings to continue to enjoy
some kind of privacy and day-to-day security?

> A common mode of transportation is the 'velociped'.  It's a pair of
>  robotic stilts or bionic leg extensions.  They allow the person to
>  walk comfortably while taking enormous strides to travel very fast.

Powerisers are a non-computerized version of this that go about 30mph.

> One character in the book uses a new velociped for every commute.
> His home compiler produces them every morning for him to take to
> work.  When he gets to work, he dekes them.  At the end of the day,
> he compiles a new pair for the trip home.  The velociped is created
> by a computer so each one is identical.  It is very enticing to
> always have perfectly new machines.  Dropped your PDA?  Just deke it
> and compile a new one!

Better make sure you have a backup of the data, though.

> I dunno about fiberglass though...

Presumably, in the glorious molecular nanotech future, we'll be able
to use diamond fibers, anchored together into sheets with more diamond
fibers, instead of settling for glass and epoxy.

By the way, may I forward your comments to the kragen-discuss mailing
list?