
---------------------- 
NOTES FROM THE BIKELAB 
Issue #4 -- 1/6/91
by Steven K. Roberts
----------------------

Copyright (C) 1990 by Steven K. Roberts.  All Rights Reserved.

	IN THIS ISSUE:
		RUMP Packaging
		CSPC:  The Poor Man's Composite
		Assorted Updates and a TV Appearance

	Art without engineering is dreaming;
	Engineering without art is calculating.
			-- SKR

RUMP Packaging
--------------

	RUMP packaging is something everybody thinks about at one time
	or another in their lives, and overweight BEHEMOTH is no
	exception.  The RUMP (Rear Unit of Many Purposes) is a
	cellulose-core, silicon-matrix, polyester-filled composite
	enclosure mounted to the Blackburn rack on the bike's rear --
	occupying the entire space a long-distance cyclist normally
	devotes to panniers and various lashed-on packs.  But all the
	usual touring gear lives in the trailer; the RUMP is the second
	of three major electronics bays.

	A quick overview:  the console, the most obvious repository of
	high-tech gizmology, is where most of the computers live.  It
	carries the Mac, the two main DOS systems, the FORTH
	bicycle-control processor, GPS board, head-mouse controller,
	modems and packet TNCs, diagnostic systems, Audapter speech
	synthesizer, Covox speech recognition board, RF datalink to the
	manpack, and so on -- in short, most of the computing and
	datacomm gear.

	The trailer (or WASU) is mostly for radio communications and
	power management, and the aft-most third of its volume is a
	commbay with flip-down door and operating table.  This is where
	the Icom 725 HF rig lives, along with the Yaesu 290 and 790
	multimode VHF and UHF transceivers for high-power packet and
	satellite operation, the AEA ATV unit, an audio filter, SWR
	bridge, antenna tuner, smart code keyer, cellular phone, and so
	on.  Since the lid of the trailer is the big solar panel, this
	is also where two of the three main batteries and all
	power-management hardware resides -- along with the trailer
	control processor to manage data collection, trailer security,
	cable minimization, audio routing, power control, etc.  The
	main antenna mast (BYP, or Big Yellow Pole) mounts on the left
	rear corner of the trailer, and the cellular whip emerges from
	the center of the solar array.

	The RUMP is in the middle, and has become a sort of nexus.  The
	BIU (helmet) whimsically featured last week plugs in here,
	along with the cable harnesses to console and trailer.  There
	are three equipment bays in the RUMP:  port, starboard, and
	main.

	The port RUMP-bay is where the SPARCstation will live, along
	with its hi-res LCD screen, 210 meg hard disk, CDROM drive,
	image processing tools, and associated interfaces (CellBlazer
	and local network).  The starboard bay is the refrigerator, a
	thermally-insulated space pumped by a pair of Melcor
	Peltier-effect modules -- taking advantage of excess solar or
	regenerative braking energy to cool my drinking water and, via
	a fluid loop, my head.  And the main RUMP-bay is what I've been
	working on all week.

	This enclosure (an integral part of the whole RUMP, but
	effectively a sealed space) carries the MIDI system (a hacked
	Yamaha DX-100 as well as a Casio CSM-1 and a Breakaway
	Vocalizer, all tied to the Mac via Apple's MIDI interface), the
	stereo amps and a pair of Blaupunkt speakers pointing at my
	head, the RUMP control processor, taillight controller, all
	major security system components including microwave sensor and
	UNGO box, paging system, the base unit of the Swintek
	full-duplex wireless intercom, an Ampro core-module stack for
	Private Eye control (on a LAN to the console), and the RUMP
	control processor to hold it all together and handle this
	site's audio and serial crosspoint matrices (replicated in
	console and trailer and linked by general purpose long-line
	buses).

	This whole unit is notched out to accommodate a Zero
	Halliburton case with solar lid, containing the laptop,
	business-band packet system, Icom dual-band HT, and other
	communication remotes.

	Now you see why the RUMP packaging is such an issue.  Here we
	have what essentially amounts to a fiberglass composite box on
	the back of a bicycle, subjected to rain, shock, direct
	sunlight, wrecks, sweat, and other forms of abuse that would
	give an industrial-control system designer bad dreams.  Yet it
	has to protect things as delicate as hard disks and CDROM
	drives.  (In case you're wondering, by the way, the Sony audio
	CD player and related stereo gear will live under the seat in
	its own enclosure for easy access... the NEC CDR-35
	dual-function CD turned out to be too sensitive for mobile
	audio use without extensive cushioning.)

	The floor of the main RUMP-bay is fiberglass-covered plywood,
	and it is bolted with stainless 1/4-20's down into an aluminum
	plate TIG-welded to the Blackburn rack.  A baseplate of .062
	angle-stiffened aluminum sheet is mounted to the floor via four
	shockmounts from Lord Manufacturing (essential tools for this
	sort of project -- catalog via 800-458-0456).  This is slowly
	becoming loaded with equipment, including one of the bike's
	three main Sonnenschein batteries (12 pounds) to allow
	uninterrupted system operation when on local rides without the
	trailer.

	But the internal stuff is pretty easy.  The hard part is
	keeping the water out, minimizing road noise amplification, and
	allowing at least a minor accident without having to do nasty
	fiberglass surgery.  Everything is gasketed, of course, a
	non-trivial problem in itself -- usually with EPDM rubber
	strips glued into all critical closures.  Gasket compression on
	the lid is achieved with Southco soft latches, lovely rubber
	assemblies that allow all sorts of imprecision while still
	looking clean and professional (Southco is at 215-459-4000).
	These are mounted with careful attention to the dangers of
	point-loads in fiberglass, and I machined in some adjustability
	slots with the aid of trusty Cecil.

	It's a bit hard to describe all this without pictures (which is
	why you should immediately hit a psychological control-S and
	send a $15 check to Nomadic Research Labs for the print edition
	of all this), but the manpack mounting introduces special
	problems of its own.  The idea here is to be able to grab it in
	a single quick motion whenever I leave the bike, and have with
	me a complete communication link back to the server, cellular
	gateway, security system, audio monitors, speech I/O, and so
	on.  This will let me turn my back on BEHEMOTH now and then to
	think about something else... but still be in touch.

	Two of the original Zero aluminum feet (which are noisy and
	rough on surfaces anyway) have been replaced by rubber ones,
	and the other two by little Z-shaped brackets cushioned with
	Permatex Color-Guard (a rubber dip coating often used for tool
	handles).  These are inserted into slots in the assemblies that
	make up half the RUMP-lid mounting system, the case is dropped
	onto its foam nest, and a single soft draw latch is used to
	cinch it down.

	The port and starboard RUMP-bay doors are a real problem, not
	yet entirely solved.  The original plan was for flush
	fiberglass doors, but the hardware overhead required to achieve
	reliable gasket compression was absurd.  The current plan is to
	mount a fabric bulkhead with riveted aluminum strips, with a
	hooded zipper providing flip-down access to the internals.
	This also allows addition of a pannier-style outer pocket,
	which will help absorb shock in accidents.  Fiberglass ALWAYS
	loses in an encounter with concrete.

	Finally, there is the problem of cables... entering the RUMP
	just behind my shoulders and leaving it down by the trailer
	hitch is the bike's cable harness, a rather bulky affair of
	various wire types all terminated by LEMO environmentally
	sealed connectors.  Again because of point-loading problems,
	these headers will be aluminum panels gasketed over large
	cutouts in the fiberglass.  Other fixtures that don't impart
	significant stress -- like speakers, the taillight, and so on
	-- require no special attention beyond sealing.

	It's a bit difficult to describe packaging details in a
	text-only publication, but I thought you might enjoy a bit more
	physical overview.  I get occasional letters asking what this
	looks like (and yes, there are two projects underway now to get
	image files that can be electronically distributed to anyone
	interested -- stand by!).

	Back at the beginning of this article, I mentioned that the
	RUMP is a cellulose-core, silicon-matrix, polyester-filled
	composite enclosure.  If you wondered what on earth I meant by
	that, read on.......

CSPC:  The Poor Man's Composite
-------------------------------
(first published in _Nomadness_ issue #8)

	Have you ever wanted to build a custom enclosure, oddly shaped
	structure, waterproof canopy, camper shell, or special box --
	only to be frustrated by the cost and effort involved in
	fabrication?  You know the scenario:  without facilities for
	this kind of work, you end up spending far too much,
	compromising your design with scrounged junk, or simply
	forgetting the whole damn thing.

	This is the mode I was in when designing BEHEMOTH's new trailer
	(or WASU, for Wheeled Auxiliary Storage Unit).  I knew what I
	wanted -- a lightweight, waterproof, aerodynamic structure with
	wheel wells, special flanges for equipment and antenna
	mounting, sealed access panels, a 72-watt solar lid, and so
	on.  But how would I build such a thing?  I even considered
	hacking up one of those hideous black plastic tool bins they
	sell for pickup-truck beds.

	I described the whole problem to Dave Berkstresser one
	evening.  Dave is one of those wizards who can sketch a dozen
	unique solutions to any mechanical problem that seemed
	impossible only moments before, and is the designer of the
	eccentric, agile, and swift Vacuum Velocipede human-powered
	vehicle.  He also did the CAD work on my folding console,
	machined the Private Eye mounting, designed the new steering
	system, and added various other artistic engineering touches to
	BEHEMOTH.  (As of this week, he's in the consulting business:
	for truly inspired mechanical design, call 408-257-2937.)

	"Build it with cardboard," Dave told me, taking a sip of beer.

	"No, seriously," I replied.

	"I AM serious," he insisted.  "Take a hot-glue gun, throw
	together your basic shape out of an old refrigerator box, then
	fiberglass over it.   I made a kayak out of cardboard once."

	The elegance of his suggestion was instantly obvious.  All
	sorts of structures ranging from airplane wings to transit
	boxes for delicate equipment are made of composites,
	structures that consist of two walls separated by a "matrix."
	Usually some kind of foam or honeycomb, this core is what keeps
	the thin walls at a constant distance and provides the
	dimensionality and moment that keeps them from collapsing.
	Some of these materials, such as Hexcel, are among the most
	high-tech structural materials available.

	And garden-variety corrugated cardboard is a close analogue!
	It is used everywhere you look for very good reasons:  it's
	strong, light, and cheap.  Covered with fiberglass, it's
	waterproof, good-looking, and stronger still.  And best of all,
	it is infinitely hackable... if you screw the design up, you
	can always scrounge more cardboard and brush on some more goo.

	Needing a name for this wonderful discovery, Dave and I puzzled
	for a while and finally came up with CSPC... or Cellulose-core,
	Silicon-matrix, Polyester-filled Composite.  And now, a few
	months later, I'm building BEHEMOTH's communication and power
	systems into a blazing-yellow custom trailer that looks like a
	cross between a '56 Buick and a solar-panel-encrusted
	satellite.

CARDBOARD CONSTRUCTION

	The first step in building anything using this method is to
	noodle over it for awhile, sketching and perhaps even making
	models until you know what you really want.  Then buy a
	hot-glue gun (typically about $15) and lay in a good supply of
	cardboard.

	A note here about materials.  Corrugated cardboard comes in all
	sorts of styles (never thought about this before, did you?),
	ranging from heavy thick mushy stuff to thin, brittle material
	that cracks when you bend it.  Somewhere in between is the
	right stuff -- look for a good stiff feel, thin walls, and
	consistent corrugations.  There's no reason to go with heavy
	cardboard for strength:   all we're trying to do here is hold
	the two fiberglass layers in a fixed relationship.  Get
	material that feels clean and light, and hasn't been walked on
	or creased.

	Now you can start construction.  Using a metal yardstick and a
	good sharp knife (X-acto or retractible), cut the pieces as you
	need them, being conscious of "grain" wherever you have to make
	a bend.  At every junction, run a bead of hot-melt glue, on
	both sides if necessary.  Don't let the glue glob up -- it's a
	pain to work lumps down to a smooth curve that won't bubble the
	fiberglass.

	There are a few tricks that make later work easier...

	First, fiberglass doesn't like abrupt sharp angles -- it will
	gap and leave ugly air spaces.  Don't make any angles sharper
	than 45 degrees, or any right angles with a bend radius of less
	than a half-inch or so.  You can usually get away with using a
	circular sander or rasp to brutally round the edges, but if you
	can add a long strip to break right-angle joints into a couple
	of 45s you'll be better off.

	Gentle simple curves, like the front of my trailer, can be
	distributed uniformly over a large surface by pre-bending the
	cardboard over a table edge, parallel with the corrugations,
	one step at a time.  By carefully creasing the material at
	every wave, it will hold a smooth curve -- though the inside
	surface will be rippled and cause lots of tiny air gaps.  It
	turns out that this doesn't matter much.

	Dave swears that he has made compound curves by carefully
	analyzing the corrugation pattern and making tiny, well-placed
	incisions with a sharp knife.  I find this astonishing, but
	knowing Dave, it's probably true.  Experiment.

	Edges can be messy.  They became in issue in two parts of the
	trailer:  the outside, exposed rim of the solar lid; and the
	edges of the long stabilizing strips that add strength to
	walls.  Details in a moment, but be aware that every exposed
	edge will take extra effort and try to keep them to a minimum.

	Don't create any situations where you won't have easy access
	later during the glassing process.  Over time, you'll
	intuitively recognize the behavior of the stuff, but for now
	just make everything as open as possible.  Really tight spots
	may be better approached using two or more parts that are later
	joined -- it will keep resin off your elbows, and probably look
	better.

	Once you have the cardboard structure intact, stare at it, play
	with it, and think through all the ramifications of the
	design.  It will be hackable later if you forget something, but
	it's a lot more so now.  If there's anyplace you will have a
	bolt compressing the surface, mash the cardboard flat or hog it
	out and fill with cloth so it won't collapse and loosen later;
	wherever there will be major stress, add reinforcement.
	Smooth off all the blobs of glue, round the corners (I did the
	outside edge of the solar lid by gluing on half-round pine,
	sculpted smooth on the corners), and mentally run through the
	glassing process.

	Like it?  Time to make it permanent.

CLOTH AND GOO

	When you go out looking for fiberglass material, you'll find
	yourself deluged with options (unless you go to the local
	hardware store, in which case you'll have too few).  In
	California, the best supplier is Tap Plastics (415-829-4889 for
	a catalog and info on local stores), and the personnel are
	quite knowledgeable about the fiberglass cloth and resins they
	sell.  There are a couple of basic choices...

	First, polyester resin versus epoxy.  Polyester is cheaper and
	much less nasty to work with, but is less strong.  Your
	application will determine which makes more sense -- I used
	polyester.  Also, be aware of the meaning of "surface curing
	agent" -- a waxy additive that seals the layup to help it
	cure.  Problem is, it also interferes with adding additional
	layers.  Avoid this entirely, and use structural layup resin or
	bond coat, not surfacing resin.  My personal preference is the
	thixotropic structural layup resin -- it's easy to brush on,
	doesn't sag or puddle, and cures quickly.  You'll also need
	catalyst, which is the highly poisonous Methyl Ethyl Ketone
	Peroxide.  If weight is critical, you can add millions of tiny
	air pockets by mixing "micro balloons" with the resin.

	Second, you'll need to select the kind of cloth you want.  This
	is very important, for it will determine weight, flexibility,
	cost, and appearance.  It's also very much a function of the
	job.  On the trailer, I used Tap "A" and "C" weight cloth, the
	latter being lighter (5.85 oz per square yard, .01" thick).
	Considering that your base material is cardboard, going with
	super heavy cloth, thick mat, or woven roving is generally
	overkill.  At the other end of the spectrum is light "deck
	cloth," which cures almost transparent.  Again, think through
	the project, decide where the stresses are and where you just
	want to waterproof the surface, then choose accordingly.  In my
	case, the trailer floor and lid structures are mostly "A"
	cloth, and the sidewalls are covered with "C."

	Other materials for the job are mixing cups (start with the
	graduated paper measuring cups, then once you get the hang of
	it you can switch to old tin cans), stirring sticks, cheap
	brushes, acetone for cleanup, paper towels, and scissors.  You
	also need to decide how you want to keep the stuff off your
	hands, and TAKE THIS ISSUE SERIOUSLY!  These chemicals have a
	cumulative effect when absorbed through the skin, and you may
	get away with sloppiness for years then suddenly develop an
	agonizing, lifelong allergic reaction to resin and catalyst.
	The homebuilt aircraft world is full of sad stories about
	people who sold their partially-built planes after careless
	habits made dealing with fiberglass impossible.

	When I started this project, I used rubber gloves and kept a
	bar of Neutrogena handy.  The gloves were loose and sloppy, and
	led to more of a mess than doing it barehanded -- but it took a
	while to develop techniques of dealing with the brush and
	mixing can (like always wiping at the seam so you know where
	not to touch).  After a few sessions, I abandoned the sticky
	gloves and tried to be careful, washing after every batch.  Now
	I use Glove Cote, which is a lanolin-based cream that's
	supposed to keep you safe.  I'm careful anyway.

	OK, ready to start?  Take the phone off the hook.  A batch
	under normal thermal conditions will only last about 10-15
	minutes, so you don't want interruptions.  Mix the stuff
	according to directions (around 5 drops of catalyst per ounce
	of resin, more if it's cold or you want a fast cure) and lay
	down a preliminary coat on the cardboard surfaces you'll be
	working on first -- this helps adhesion and is quite
	necessary.  When the batch starts to thicken, STOP -- it won't
	soak in, and will have the opposite effect instead.

	Now cut your first pieces of cloth and lay them on the
	cardboard, which should be tacky.  The wrinkles will brush
	out.  Start laying up the structure, adding layers where you
	think the major stresses will concentrate (corners, support
	points, etc).  This is where the art comes in -- after a while
	you'll just know how much cloth to use and how thickly to brush
	on the resin.  In general, you want to use just enough to make
	the cloth transparent, but not enough to puddle.  The strength
	lies in bonded cloth, not globs of brittle resin.

	Take successive passes at the work, never mixing more than 5
	ounces of resin or so unless you're covering a large area with
	a large brush.  Overlap the cloth by a few inches, and keep
	working at it until you feel that the coverage is complete.
	Notice the material's reluctance to take sharp bends... this is
	how you gradually home in on the constraints that affect the
	initial cardboard design.  On exposed edges, let the wetted
	cloth hang off -- don't try to wrap it around.

	Finishing the edges is easy if you do this.  After it's all
	dry, you can slice the excess cloth with a sharp knife, then
	use a file to remove any sharp points.  It will look terrible.
	But now mix up a small batch of Tap 500 plastic filler and work
	it into the exposed corrugations with a plastic squeegee, then
	file and sand after it dries.  The result will be a smooth,
	waterproof edge that takes paint easily and completely conceals
	the truth -- that the core of this beautiful structure is an
	old cardboard box!

FINISHING

	How pretty do you want this?  If you've come this far, you'll
	have a rather ugly brown material, with lots of ragged overlaps
	and texture variations.  If the need is purely structural, this
	may be the place to stop.

	There are two ways to add color.  First, as I did on the
	trailer's underside, you can mix special concentrated pigments
	with the resin (I used black).  This in no way alters the
	surface texture, but it does hide the big Hotpoint logo which
	would otherwise show through the fiberglass.

	The other way is with paint, and this is another one of those
	areas where time, money, skill, experience, and luck all
	conspire to yield either beauty or a giant mess.  I did the
	trailer lid with yellow Copon epoxy paint and had all sorts of
	problems -- now I need to sandblast it off and try again.  The
	body is another story:  Maggie put her old auto-body skills to
	work during a full week of applying Tap 500 (like Bondo, but
	much more flexible) and sandpaper, finally perfecting the
	surface with glazing putty.  We then took it to Charles Tripp
	in Los Gatos, who did a beautiful job of spraying on DuPont
	Imron (a fiesty thoroughbred of paints, not for the poor or
	fainthearted).  The stuff is over $100 a gallon and can cause
	respiratory failure if you spray without breathing apparatus,
	but it looks great.  It's pretty, but is still a bit fragile
	when abused... and inside, where there is no bodywork,
	adhesive-based cable tie downs can easily detach a circle of
	paint.

	And there you have it.  The trailer, for a moderate amount of
	time and money, looks professional enough to prompt people to
	ask where I bought it.  I grin and tell them it's just some old
	cardboard boxes, glass, goo, and Imron paint, all mounted on a
	custom chrome-moly frame built by Rock Lobster and painted by
	Dr.  Deltron.  They don't believe me.

	I do have one final suggestion if you try this on your own
	structural fabrication problems.  Do an unimportant test
	project first to get most of the mistakes out of the way.  That
	first layup will seem awkward and messy, with the cloth
	buckling and resin dripping down your chin.  But give it a
	chance... it works!

Assorted Updates and a TV Appearance
------------------------------------

	In the continuing saga of power management, I have an update
	from last week's lament.  You may recall that I was complaining
	about finding a simple, standalone solar charge controller for
	the sealed lead-acid batteries (one that works even if the
	computers are all down).  I had objected to the Sonnenschein
	pair's uneven current distribution and the SCI's dark current.

	Thinking again, I've decided to stick with the SCI (the
	Automatic Sequencing Controller from Specialty Concepts --
	818-998-5238).  The dark current is 5.6 mA, which will kill my
	batteries in about 8,000 hours of dark storage (assuming a
	perfect world, lumped constants, and no self-discharge...).
	The unit is actually quite clever, and the fix for the
	oscillation was to simply eliminate the schottky diode and let
	it sit on the battery bus where it belongs.  It now switches
	neatly and quietly, harmlessly shorting the solar panels when
	the battery is at or above setpoint (and it doesn't care about
	the presence of other charge sources).

	In ham radio news, I did another Outbacker test last weekend:
	worked a sked on 40 meters, along with a nice handful of
	stateside stations, Japan, and Chatham Island on 10 meters.  It
	is very satisfying to do that bicycle-mobile, since one of the
	design specs for this whole thing is achieving near-100%
	probability of making contact with someone, somewhere, at any
	time from anywhere.  Piece o' cake.

	Finally, if you are in the SF Bay Area and would like to see
	BEHEMOTH and its bio-controller, tune into the new "Silicon
	Valley Report" show on public television KTEH, channel 54.
	I'll be doing a biweekly series from the road starting in July,
	and to help lay the groundwork, producer/anchor John Crump has
	put together a 5.5-minute intro piece filmed here in the
	bikelab.  The new series premieres this week; I will be on NEXT
	week at the following times:

		Jan 17 at 9:00 PM
		Jan 18 at 7:30 PM
		Jan 19 at 5:30 PM

	Back to a night of packaging and wrestling with balky
	adhesives...

	Cheers from the bikelab!!!

		Steven K. Roberts 
		Nomadic Research Labs 
		P.O. Box 2390 
		Santa Cruz, CA 95063

		wordy@bikelab.Sun.com 
		wordy@cup.portal.com
		GEnie, MCI, or AOL:  wordy

