Hey,

I am building a robot for a competition (simple drag race on a dirt
road during a canadian winter).

I wanted to use a beacon transmitting in the RF range, and use a
directional antenna to correct the angle that the robot is travelling.
The robot would then travel forward towards the beacon (placed at the
end gate). So far I have no antenna experiance (havent taken the
antenna class yet).

Would a circular antenna work for this project? where can i learn more
about circular antennas?

Also are there any commercial (inexpensive, the competition only allows
a $100 budget), tranceivers I could use (preferably in the 433 Mhz
band). Since i only need a small signal to correct the course, it
doesnt have to be too powerful.

Thank you for your help,

G_dir

On 22 Sep 2006 11:09:52 -0700, "G_dir" wrote:


Thank you for your help,

Hi OM,

Skip antennas and transmitters and use a light beam, or several.

73's
Richard Clark, KB7QHC

The light beam idea is different but it does bring complications
For drag race you haven't got time to focus a light upon a small object
that is moving
Fior this purpose it would seem that a small verticle would suffice
such that the vehicle responds immediatly to commands I assume that as
a drag race range power is not a requirement. Richard was your aproach
based on a guided path control by light rays such that contact would
provide a direction correcting command?
Art

Richard Clark wrote:
On 22 Sep 2006 11:09:52 -0700, "G_dir" wrote:


Thank you for your help,

Hi OM,

Skip antennas and transmitters and use a light beam, or several.

73's
Richard Clark, KB7QHC

On 22 Sep 2006 12:25:42 -0700, "art" wrote:

The light beam idea is different but it does bring complications
For drag race you haven't got time to focus a light upon a small object
that is moving

Hi art,

If time is of the essence, it is of the essence for all applications
equally.

Fior this purpose it would seem that a small verticle would suffice
such that the vehicle responds immediatly to commands I assume that as
a drag race range power is not a requirement.

A vertical has no way to discriminate falling out of a path. UNLESS:

The aeronautical system of holding a flight path is with (or was with)
VOR. It's been a long time since I've maintained navigational
equipment, so my terminology may be way off. However, the concept is
there are two transmitters sending an Morse N and a Morse A, such that
if you are on the flight path, you obtain a constant carrier (the dits
and dahs overlap through carefully balanced antenna arrangement at the
transmitter).

If you should diverge from the flight path, there is an imbalance in
signal and one code predominates over the other. For the race car,
the burden would be on translating which code dominates, and what
course correction would be necessary.

Richard was your aproach
based on a guided path control by light rays such that contact would
provide a direction correcting command?

A light path can be resolved with hardware logic instead of software.
Faster performance.

73's
Richard Clark, KB7QHC

Richard Clark wrote:
On 22 Sep 2006 12:25:42 -0700, "art" wrote:

The light beam idea is different but it does bring complications
For drag race you haven't got time to focus a light upon a small object
that is moving

Hi art,

If time is of the essence, it is of the essence for all applications
equally.

Fior this purpose it would seem that a small verticle would suffice
such that the vehicle responds immediatly to commands I assume that as
a drag race range power is not a requirement.

A vertical has no way to discriminate falling out of a path. UNLESS:

The aeronautical system of holding a flight path is with (or was with)
VOR. It's been a long time since I've maintained navigational
equipment, so my terminology may be way off. However, the concept is
there are two transmitters sending an Morse N and a Morse A, such that
if you are on the flight path, you obtain a constant carrier (the dits
and dahs overlap through carefully balanced antenna arrangement at the
transmitter).

Yes I am aware of that but not for a flight path but for a destination
point
As a Londoner during the war, the big one that is. civilians were
constanly aware
that light emmissions allowed for night bombing but even when we got
rid of glass windows and replaced it with tar paper the dock area was
repeatedly pounded. Fortunately a bomber crashed somewhat intact and
the secret was opened. The germans had two widely separate transmitting
stations one with a continuos dot and another with a continuous dash
and where both transmissions was aimed at a required venue thus the
german bombers mnew when they were over the target when the dots and
dashes merged into a single drone. In relaliation british fighters were
able to anticape their arrival and finally drove them out from the
skies. My family house was knocked out in the early days when it was
like a carpet bombing but as time went on the raids became more
scattered and without the normal prewarningThe germans did not know
that their secret was broken so the British put out a rumour that their
pilots ate lots and lots of carrots which had ingredients that improved
night vision thus the german fighters obtained this addiction to
carrots. Unfortunately the battle continued later with the doodle bug
that I counted as they went over and then a short period of V2s
that fairly quickly stopped as the Allies advanced in France and
Belgium. Sort of something like the Yagi invention which was not
followed up by the Japanese military
because of inter secrecy of the invention between the services. On the
other side of the coin tho the british invented the jet engine it was
the germans who took advantage of it first with the jet fighter but
internal wrangling delayed its inaugeration. It all goes to show that
people reject change even tho it is inevitable and thus account for the
present resistance to the yagi being inefficient because most feel that
is the cat's wiskers and it takes a generation for change to take place
Art






If you should diverge from the flight path, there is an imbalance in
signal and one code predominates over the other. For the race car,
the burden would be on translating which code dominates, and what
course correction would be necessary.

Richard was your aproach
based on a guided path control by light rays such that contact would
provide a direction correcting command?

A light path can be resolved with hardware logic instead of software.
Faster performance.

73's
Richard Clark, KB7QHC

On Sat, 23 Sep 2006 03:07:50 GMT, wrote:

VOR is very different.

Hi Alison,

Yes, I already admitted the term was probably pulled from an alphabet
soup of navigational equipment I've calibrated: TACAN, VOR, DME, ADF,
LORAN (although more commonly marine application) and on and on. The
mechanical phasing systems were a workable kludge. But what kludges
nonetheless. I've even navigated by the time differential between the
Naval Observatory encoded signal in LORAN stations and my atomic clock
aboard a sub tender (our LORAN was broke).

you decirbe the AN corridor scheme.

Which is eminently suited to the problem.

AN has 180degree ambiguity

Which is not an issue for the stated problem.

A light path can be resolved with hardware logic instead of software.
Faster performance.

Optical interferometry.

Hardly. This is gilding the Lily and painting the Rose. The optical
analog of the AN system is sufficient to the problem. Simpler beacon
methods would prevail even here.

The difficult issue is one of a closed feedback loop and maintaining
stability, not deciding if one is on or off the path. That is dirt
simple. What you DO with the information is the logical nightmare,
because errors compound quickly and information descends into
statistical nonsense in its out of phase application.

In a recent robotic car rally, the big name universities and
corporations with million dollar budgets, gizmos galore (multiple GPS,
radar, and what have you) and plenty of engineering talent were
literally blown off the road by an insurance broker who hobby funded a
garage crew outfit.

73's
Richard Clark, KB7QHC

Thank you for all your suggestions.

About the energy requirments... we do have one. 200 joules for a 21
meter race (its a small robot) and an allowed "production budget" of
CAN 100 (the robot, if mass produced, cannot cost more then $100 to
build).

I was thinking of having the robot o forward (with no control for
that), and using the beacon to correct my course.

The prefered solution is to build the bugger so well that it just
travells straight for the 21 meters... but alas, another requirmet is
that some sort of guidance system must be included (usually this
project involves obstacles the control system must avoid, the professor
took those out since the race is outside).

Cheers,

G_dir


wrote:
On Sat, 23 Sep 2006 01:12:12 -0700, Richard Clark
wrote:

On Sat, 23 Sep 2006 03:07:50 GMT, wrote:

VOR is very different.

Hi Alison,

Yes, I already admitted the term was probably pulled from an alphabet
soup of navigational equipment I've calibrated: TACAN, VOR, DME, ADF,
LORAN (although more commonly marine application) and on and on. The
mechanical phasing systems were a workable kludge. But what kludges
nonetheless. I've even navigated by the time differential between the
Naval Observatory encoded signal in LORAN stations and my atomic clock
aboard a sub tender (our LORAN was broke).

I flew the las AN and also all the other Alphasoup but as a civi pilot
and small boater. Even used LF ranges and DF off of broadcase
stations. There are a lot of electronic ways to navigate.

Which is eminently suited to the problem.

AN has 180degree ambiguity

Which is not an issue for the stated problem.

True, only noted it.

A light path can be resolved with hardware logic instead of software.
Faster performance.

Optical interferometry.

Hardly. This is gilding the Lily and painting the Rose. The optical
analog of the AN system is sufficient to the problem. Simpler beacon
methods would prevail even here.

I never said the hard way was best!

Me, I'd go with a beacon at UHF for small antennas and ease of
construction. Since the car has some control system I can resolve
where the front should point from there. A two antenna TODA can
provide enough phase info to generate an error signal. The real work
is the servo loop.

Of course a simple optical bangbang system using the same tricks
as heatseekers would work.


The difficult issue is one of a closed feedback loop and maintaining
stability, not deciding if one is on or off the path. That is dirt
simple. What you DO with the information is the logical nightmare,
because errors compound quickly and information descends into
statistical nonsense in its out of phase application.

Clasic servo problem. Classic answer, KISS!

In a recent robotic car rally, the big name universities and
corporations with million dollar budgets, gizmos galore (multiple GPS,
radar, and what have you) and plenty of engineering talent were
literally blown off the road by an insurance broker who hobby funded a
garage crew outfit.

Been there and done that in other areas. Nothing beats a few good
minds and a well stocked junkbox.


Allison

On 24 Sep 2006 18:14:14 -0700, "G_dir" wrote:

I was thinking of having the robot o forward (with no control for
that), and using the beacon to correct my course.

Hi OM,

Still very simple. A single, broad beam of light. A dual sensor that
is aimed "bore sight" to the direction of the robot's forward motion.
Even with RF at 5 GHz, the ability to discriminate is going to be very
poor. When both sensors see the light, equal displacement to the
steering (they cancel). When one sensor sees the light, then a
correction to steering until both see the light (they add).

If the robot thrashes (zig-zag) down a practice course, then reduce
the amount of steering the sensors add. If the robot loses track of
the beam, then turn up the amount of steering the sensors add. If the
correction makes slow looping curves, put horse blinders on the
sensors so they can only see a 10 degree field of view and turn up the
gain.

The best solution will always have some error in it (correction
circuits have to have something to work against). This means the
optimal design given your constraints will have some weave. It will
travel 22 to 24 meters to finish that 21 meter course.

73's
Richard Clark, KB7QHC