telemetering speedometer for racing boat
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I would like to ask for ideas on how to improve a telemetering tachometer I am
building with the BS2.
The system is intended to help me tune the sails on a racing R/C sailboat.
Various servos on the boat can be
manipulated by R/C to make the boat go faster: I can change, for example, the
slot between the main and the jib;
alter the airfoil of the mainsail by subtly changing the curve of the mast, etc.
But the skipper, me, standing on shore, needs some instant feedback on how these
changes affect boatspeed. This is
the purpose of the telemetering tachometer.
A small boat is to be towed behind the racer. It has a freely spinning
propellor, and on the propellor shaft,
spinning along with the prop, is a magnet. A bipolar Hall detector/Schmitt
trigger chip (Allegro 3132) senses
the passage of the North and South poles.
The BS2 counts the pulses for about a quarter of a second, then multiplies the
count by a scaling factor. The
result is used to position the wiper of a DS 1267 digital pot. This 3-wire
digital pot is directly substituted,
with a little cutting and splicing, for the joystick pot of a lightweight R/C
transmitter. In short, the input
is a pulse count, and the output is PWM signal.
The BS2, Hall Detector, digital pot, stripped R/C transmitter and batteries are
all to be shoehorned into the
small towed boat. So far, it looks like it will all fit. And float.
I am using R/C gear for the telemetering function because it is designed to be
relatively immune to interference
from other R/C transmitters. There are are always quite a few boats active at
the pond where we sail, and the
system has to be immune, above all, to interference from the R/C system I am
using, on a different channel, to
control the sailboat.
Right now, the breadboarded tachometer system works. I can blow on the
propellor, monitor the pot output with an
ohmeter, and watch the needle go up and down with propellor speed. I can also
turn on the xmtr, blow on the prop,
and (across the room) move an R/C servo through an arc that roughly corresponds
to prop speed.
But at this point I am kind of stuck. Here are the problems. The servo is too
slow to follow the rapidly
changing data from the propellor. And it is clunky. I need an electronic
transducer of some kind on the receiving
end. This could produce an audio tone, in headphones, that goes up and down in
frequency as the boat speeds up
and slows down. (When you are sailing the boat, it is not convenient to read an
LCD or other visual indicator,
unless maybe you could pin one under the visor of a hat).
How do I get from a PWM signal, as output by the R/C receiver, to an audio tone
output? Do I need a second BS2 to
measure the incoming pulsewidths? Or is there some simpler, more succinct way to
do this? Or maybe some other
type of indicator?
Thank you for your insights.
Michael Gianturco
building with the BS2.
The system is intended to help me tune the sails on a racing R/C sailboat.
Various servos on the boat can be
manipulated by R/C to make the boat go faster: I can change, for example, the
slot between the main and the jib;
alter the airfoil of the mainsail by subtly changing the curve of the mast, etc.
But the skipper, me, standing on shore, needs some instant feedback on how these
changes affect boatspeed. This is
the purpose of the telemetering tachometer.
A small boat is to be towed behind the racer. It has a freely spinning
propellor, and on the propellor shaft,
spinning along with the prop, is a magnet. A bipolar Hall detector/Schmitt
trigger chip (Allegro 3132) senses
the passage of the North and South poles.
The BS2 counts the pulses for about a quarter of a second, then multiplies the
count by a scaling factor. The
result is used to position the wiper of a DS 1267 digital pot. This 3-wire
digital pot is directly substituted,
with a little cutting and splicing, for the joystick pot of a lightweight R/C
transmitter. In short, the input
is a pulse count, and the output is PWM signal.
The BS2, Hall Detector, digital pot, stripped R/C transmitter and batteries are
all to be shoehorned into the
small towed boat. So far, it looks like it will all fit. And float.
I am using R/C gear for the telemetering function because it is designed to be
relatively immune to interference
from other R/C transmitters. There are are always quite a few boats active at
the pond where we sail, and the
system has to be immune, above all, to interference from the R/C system I am
using, on a different channel, to
control the sailboat.
Right now, the breadboarded tachometer system works. I can blow on the
propellor, monitor the pot output with an
ohmeter, and watch the needle go up and down with propellor speed. I can also
turn on the xmtr, blow on the prop,
and (across the room) move an R/C servo through an arc that roughly corresponds
to prop speed.
But at this point I am kind of stuck. Here are the problems. The servo is too
slow to follow the rapidly
changing data from the propellor. And it is clunky. I need an electronic
transducer of some kind on the receiving
end. This could produce an audio tone, in headphones, that goes up and down in
frequency as the boat speeds up
and slows down. (When you are sailing the boat, it is not convenient to read an
LCD or other visual indicator,
unless maybe you could pin one under the visor of a hat).
How do I get from a PWM signal, as output by the R/C receiver, to an audio tone
output? Do I need a second BS2 to
measure the incoming pulsewidths? Or is there some simpler, more succinct way to
do this? Or maybe some other
type of indicator?
Thank you for your insights.
Michael Gianturco
Comments
Use a 2 or 5 amp RC ESC, (electronic speed control), to operate a small DC
motor strapped to your wrist or arm. Mount an offset weight on the motor
shaft to cause vibrations like they do with "silent" pagers. The ESC, as
you probably know, plugs into the receiver just like a servo. The faster
the boat goes, the faster the vibrations. You could probably use a surplus
pager motor with a dropping resistor. I frequently see ads for surplus
pager motors for a few dollars. www.balasp.com has GWS 2 amp ESCs for
around $20. With some twiddling, this approach may be practical.
Good luck,
Ray McArthur
> How do I get from a PWM signal, as output by the R/C receiver, to an audio
tone output? Do I need a second BS2 to
> measure the incoming pulsewidths? Or is there some simpler, more succinct
way to do this? Or maybe some other
> type of indicator?
oscillator to provide a difference so you can get a tone to hear.
Another method is to have the Stamp in the boat, convert the tach signal
into a tone to send to you over the radio.
To me it seems a bit complicated to put all that stuff in a little boat to
tow behind your sailboat. The extra drag may negate any performance
advantage you would get. Could you shoehorn the stuff into the sailboat
itself? I'd be worried about having it get bumped ot hit by another sailer.
The old "Oops, sorry about that, was that your boat?", right after the other
guy cuts across your stern.
Original Message
From: Michael Gianturco [noparse]/noparse]mailto:[url=http://forums.parallaxinc.com/group/basicstamps/post?postID=eKo7meryabFcRg-GyWa0A1kGaKCL8P6uLs1wNdoYyTrv2CfRegRPwUAnOOFrefXWib1BWNEYy8dTbHz7XBMpXw]michcg@m...[/url
Sent: Thursday, December 27, 2001 10:04 PM
To: basicstamps@yahoogroups.com
Subject: [noparse][[/noparse]basicstamps] telemetering speedometer for racing boat
I would like to ask for ideas on how to improve a telemetering tachometer I
am building with the BS2.
The system is intended to help me tune the sails on a racing R/C sailboat.
Various servos on the boat can be
manipulated by R/C to make the boat go faster: I can change, for example,
the slot between the main and the jib;
alter the airfoil of the mainsail by subtly changing the curve of the mast,
etc.
But the skipper, me, standing on shore, needs some instant feedback on how
these changes affect boatspeed. This is
the purpose of the telemetering tachometer.
A small boat is to be towed behind the racer. It has a freely spinning
propellor, and on the propellor shaft,
spinning along with the prop, is a magnet. A bipolar Hall detector/Schmitt
trigger chip (Allegro 3132) senses
the passage of the North and South poles.
The BS2 counts the pulses for about a quarter of a second, then multiplies
the count by a scaling factor. The
result is used to position the wiper of a DS 1267 digital pot. This 3-wire
digital pot is directly substituted,
with a little cutting and splicing, for the joystick pot of a lightweight
R/C transmitter. In short, the input
is a pulse count, and the output is PWM signal.
The BS2, Hall Detector, digital pot, stripped R/C transmitter and batteries
are all to be shoehorned into the
small towed boat. So far, it looks like it will all fit. And float.
I am using R/C gear for the telemetering function because it is designed to
be relatively immune to interference
from other R/C transmitters. There are are always quite a few boats active
at the pond where we sail, and the
system has to be immune, above all, to interference from the R/C system I
am using, on a different channel, to
control the sailboat.
Right now, the breadboarded tachometer system works. I can blow on the
propellor, monitor the pot output with an
ohmeter, and watch the needle go up and down with propellor speed. I can
also turn on the xmtr, blow on the prop,
and (across the room) move an R/C servo through an arc that roughly
corresponds to prop speed.
But at this point I am kind of stuck. Here are the problems. The servo is
too slow to follow the rapidly
changing data from the propellor. And it is clunky. I need an electronic
transducer of some kind on the receiving
end. This could produce an audio tone, in headphones, that goes up and
down in frequency as the boat speeds up
and slows down. (When you are sailing the boat, it is not convenient to
read an LCD or other visual indicator,
unless maybe you could pin one under the visor of a hat).
How do I get from a PWM signal, as output by the R/C receiver, to an audio
tone output? Do I need a second BS2 to
measure the incoming pulsewidths? Or is there some simpler, more succinct
way to do this? Or maybe some other
type of indicator?
Thank you for your insights.
Michael Gianturco
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they can keep the eyes outside. The speed of the beeping changes with
the rate of climb. Since the length of the period in the Pause
command can be controlled by an expression, it would be easy to use
the incoming pulse width to do something similiar.
Good luck,
Bruce
all of them just to see what works.
Re the vibrator, It occurs to me that an electronic speed controller for an R/C
application might be PWM on both
input and output. The simplicity and directness of this idea is just great. But
if somebody spottted me in the
act of taping a motor to my arm, er, how would I explain this?
For the glider style beep system, I guess I should use PULSIN to measure the
incoming PWM pulse width, and then
generate PAUSE intervals to correspond. And FREQOUT for the tone? It seems the
Stamp could do the whole job in
this application, without any other electronics.
It is interesting that the only other R/C telemetry system I have come across
was developed for R/C sailplanes.
It was called the "thermic sniffer" and was marketed through ACE. Possibly it
still is. The designer used two
thermisters mounted in a pitot tube to (somehow) detect when the glider had
found its way into a thermal. The
telemetry radio was a two or three transister FM xmtr that sent a beep stream
back to the pilot on the ground. He
was then supposed to maneuver to keep the aircraft in the updraft.
The BFO system seems a little sophisticated for me. I can't quite see how to do
it. Maybe use the stamps inherent
PWM capability and then mix the signal with the R/C receiver output? If I
correctly remember the BFO, maybe from
a pretty long time ago, it was used to develop a tone, at the receiver, from a
keyed CW transmission, that is, an
unmodulated carrier.
It would be best to put the tachometer sensor, Stamp and xmtr aboard the racing
boat, I agree, but it is not
legal under our racing rules to carry an xmtr on a boat when it is in
competition.
With the tachometer aboard a small towed boat, you can use it to tune up the
sails on race morning, then unhook it
and go race. Also, I sail in a club, and the towed tachometer "dinghy" will be
used by many of us. Um, if it
works. The racing boat is 50 inches at the waterline. The dinghy is 13 inches.
Best, Michael
brucgar wrote:
> Glider pilots use a beeping tone to indicate their rate of climb so
> they can keep the eyes outside. The speed of the beeping changes with
> the rate of climb. Since the length of the period in the Pause
> command can be controlled by an expression, it would be easy to use
> the incoming pulse width to do something similiar.
> Good luck,
> Bruce
>
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