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Notes from the Bikelab
Issue
#1 -- 12/9/90
by
Steven K. Roberts
Copyright (C) 1990, 2000 by Steven K. Roberts. All Rights
Reserved.
IN THIS ISSUE:
Introduction to the series
Brief overview of the BEHEMOTH
project
Bicycle-mobile HF dipole antenna
Microwave security sensor
(Discussion of 1990-era listserv mechanics deleted)
I had great dreams of starting this series with a complete
description of the new bike system, now renamed from Winnebiko
to BEHEMOTH (Big Electronic Human-Energized Machine... Only Too
Heavy). But the last time I wrote an overview, the file
exceeded 50K.
As you probably already know, BEHEMOTH is a computerized
recumbent bicycle that is getting completely out of hand. It's
about 350 pounds fully loaded, carries a whole suite of
networked computers, and provides extensive radio
communications ranging from a robust ham shack to cellular
phone modem and satcom. It has a heads-up display, binary
handlebar keyboard, and speech I/O. It uses GPS satellite
navigation for mapping and the highest level of security
response. It is becoming a unixycle, with an embedded
SPARCstation for mapping, CAD, and file serving. The GUI is
implemented in a Mac Portable on the console, driving a trio of
FORTH 68CH11s. There's a Peltier refrigerator, linked by a
fluid loop to a heat exchanger in the helmet for body cooling.
Power is provided by 82 watts of solar panels, and a
regenerative braking system. It has something like 330 Meg of
hard disk and at least 20 meg of RAM. And so on.
This project is obviously driven by passion, a recurring
theme. It's a blend of obsessions technoid and otherwise --
and has been going on for 7 years. I've already pedaled about
16,000 miles around the US, and my tires itch violently... I'll
be back on the road full time in July, starting in western Iowa
with the famed RAGBRAI madness (10,000 people pedaling across
the state) and then continuing on from there, somewhere...
About 130 sponsors are making the whole thing possible, along
with help from a wide variety of wizards, techies, machinists,
engineers, gurus, friends, and consultants. In a sense, I am
only project coordinator, though I do end up soldering into the
wee hours, coding, fiberglassing, hacking, staring at the wall,
piloting the CAD system, fashioning widgets, cussing at the
greasier jobs, and eventually, I hope, pedaling. The point is
that these updates should not be viewed as the techno-boasting
of a solo inventor, but instead as a succession of reports on
what this whole crazy industry can accomplish when the
objective is high-tech adventure and the bottom line is pure,
non-competitive FUN (though there may be a few commercial
spinoffs). I will also give hard technical data and access to
vendors wherever appropriate.
So. Rather than maunder on for the next hour trying to give
you a complete description of the system, I'll establish the
pattern of this series up front: focused commentary on
whatever I happen to be working on at the moment, followed
(beginning in July) by tales from the road. But first, I
suppose I should mention the basic design spec:
BEHEMOTH, whether moving or parked, must provide maximum
possible autonomy in power generation, computation capability,
file storage, communication, navigation, and maintainability --
anywhere in the world, all controlled via a flexible graphic
user interface. It must also be an elegant blend of art and
engineering... and very comfy to ride.
On with this week's details...
If
you're into ham radio and have ever operated mobile, you
know that it's not quite the same as flinging textbook-perfect
wire dipoles into the trees or erecting a beam on a tall
tower. There are all kinds of variables: imperfect grounds,
effects of nearby objects, vehicle noise, impedance changes
from wind-driven wiggling, etc. Move to a bicycle and it gets
even worse: there's not much of a counterpoise to work with,
making the SWR of a normal vertical whip at anything lower than
15 meters unacceptable.
I use a half-wave Larsen antenna for 2 meters, and will build
stacked J-poles for the Microsats. But the HF problem has
bugged me for quite a while. Stopping to erect wire dipoles
works, but eliminates the fun of mobile operation. Restricting
activity to the high bands is unacceptable. Making an
effective ground plane, even on a BIG bicycle like this, is
impossible. And the spectre of RF dancing around in my
microprocessors was almost enough to make me scrap the whole
idea.
The solution is an antenna that does not depend upon an
external ground. This boiled down to two choices: a dipole or
a loop. The loop I tried is really quite an astonishing
product -- the AEA IsoLoop, available for about $350 from
Amateur Electronic Supply (800-558-0411) or direct from AEA
(206-775-7373). It is about 32" across, and carries a big
black enclosure that houses an open-air variable capacitor
driven by a stepper motor. This is controlled from the shack
via a little box (which could easily be hacked to run under
software control), and requires constant vigilance since tuning
is VERY narrow. But performance is dramatic -- I've had the
IsoLoop outshine a wire dipole on some bands, even when mounted
only 10 feet off the ground. This is an ideal choice for an
attic antenna or someone with seriously limited space, but
packaging constraints on the bike made it impossible for me.
The dipole made of HF whips makes a lot of sense, and my first
experiments were with a whole thicket of Hustlers
(800-327-9076), using the shortened MO-4 mast and a little $8
steel dipole bracket from Burk Electronics (708-482-9310). The
Hustlers are notably broader band than the IsoLoop, but do
require accurate physical changes of tip rod position whenever
retuning is necessary (as well as resonator changes between
bands). Though I maintained an effective sked for some time
with these, the packaging problem got me again: the complete
system for 80-10 meters required 14 resonators as well as the
two masts. The back of the trailer would look like a
quiver...
It looks like I have found the solution, however, and yesterday
morning's tests pretty well convinced me. The antenna of
choice is the Outbacker, made in Australia and available in the
US via Outbacker Antenna Sales ($169 to $259, depending on
model -- 615-899-3390). This odd-looking thing is a
brightly-colored fiberglass lance, either 4 or 6 feet long
(mine are 4, the "Jr." model), studded with 8 female banana
jacks in streamlined nacelles. There is a "wander lead" that
begins near the base, is coiled counterclockwise around the
body, and is plugged into the socket for the band you want.
This sounds arcane, but is really quite elegant. I took two of
the all-band 4-foot units and mounted them as a dipole atop the
BYP (Big Yellow Pole) that rises from the back of the trailer
(this is nominally 6 feet long, but can be extended to 12 when
conditions permit). No tuner or balun is required -- I just
drive the array directly from my Icom 725 transceiver. And
performance is unmistakably HOT: band changing is easy,
bandwidth is quite acceptable with only occasional tweaks of
the tip rods, and overall weight is minimal (sorry, I don't
have a scale). This morning's tests in the Sun MTV-4 parking
lot yielded QSOs with 17 states and two provinces on 10 meters
(mostly east coast), as well as easy voice and code chats on
12, 15, and 40. On 10 meters, anyone I could hear could also
hear me, and signal reports were symmetrical even if they were
relatively big guns. I was running 50 watts from the bike's
solar panels with the micro-dipole up 12 feet... and all in
all, the experience was every bit as gratifying as ham radio
should be.
A future article in this series will detail the mounting scheme
that will let the Outbackers and the stacked J-poles fold out
from a tight cluster on the BYP. Ham radio is becoming a very
large part of this project, and a lot of the system engineering
is devoted to making it effective in a variety of
environments. You'll be hearing more about all this as the
weeks pass. (N4RVE here, by the way, pleased to meetcha!)
One of the most common questions I hear about the bike, now
worth somewhere near $1 million, is: "Mah gawd, man, how do
you LOCK that thing?"
Well, I do have a cable lock, but it is seldom used. Instead,
there is a very robust security system that includes 7 levels
of sensors, opens voice and data links to my backpack during an
alert, and even beacons latitude and longitude on ham packet
frequencies if the Trimble GPS satellite navigation receiver
starts reporting changes in coordinates without the right
password. It can lock its own wheel, call 911 and deliver a
synthesized message if it thinks it's being stolen, and even do
a few things I probably shouldn't write about. Like ham radio,
security is a complex subsystem that will appear in these
reports often.
The most recent security project involved the "level-1" sensor
-- a microwave doppler motion detector made by Alpha Industries
(617-935-5150). The model number is MSM10200, available direct
as a developer's kit for $195. With a power drain of only 10
mA from a 10-26V source, this device provides a closure to
ground in response to movement within its field of view (which
depends on choice of antenna -- two come with the unit). Four
trimpots let you set sensitivity and other operating
characteristics... and coverage of an unobstructed area out to
100 feet or more is no problem.
The motion sensor is very sensitive, but there was one catch.
I want BEHEMOTH to know when someone has moved within 8-10
feet. This is not necessarily an alarm condition (consider a
restaurant parking lot), but it can be... or it may simply help
eliminate falsing of other sensors due to wind or rumbling
trucks. So how do we take a narrow 10 GHz microwave beam and
turn it into a tight 360 degree pattern that surrounds a
12-foot-long bicycle?
Behind the seat of the recumbent, there is an area known as the
RUMP (Rear Unit of Many Purposes). This is reasonably central,
including the trailer, and also one of the highest points on
the bike. The sensor is mounted inside the RUMP, with its
feedhorn pointing straight up through a PVC fitting designed to
interface a gutter downspout with 4" pipe. This penetrates the
fiberglass body, with a good seal to keep water out of other
electronics in the enclosure.
Glued into the downspout part is a PVC 4"-to-2" adapter, and
inside that there is a copper cone made from Micaply (thin
flexible PC board material). The cross-section of the cone is
90 degrees, and its apex is roughly even with the exit aperture
of the microwave feedhorn. Atop all this is a 2" cap, carrying
the 7" yellow barricade flasher (see future story on the
lighting system).
Outdoor tests last week demonstrated that I got lucky (working
with microwaves involves either great expertise on the subject
-- which I lack -- or a healthy dose of luck). The radiation
pattern appears to extend 360 degrees from the RUMP, spreading
24 degrees on either side of a horizontal plane even with the
top of the seat. I was unable to get close enough to the bike
to touch it without being noticed.
This output will be available to the RUMP Control Processor
(one of the New Micros 68HC11 FORTH machines that handle all
the real-time control) along with the UNGO system, optical
sensors on all access panels, and various other inputs. The
action taken in response to an alert depends entirely on
software, and will be the subject of a future story...
I hate to stop, but there will be plenty of other opportunities
to do this. No sense burning out on issue #1. Next week, I'll
tell you about making bicycle taillights out of high-brightness
LEDs, a non-trivial task that was well worth the effort.