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'[EE] Distance Measurement'
2006\02\17@104453 by Tim N9PUZ

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I'm researching options for measuring distances in a wet, outdoor
environment. The task is to measure the distance between two drive
units on a boat. The drives both propel and steer the boat.

Ideally I will end up with an indicator for the crew that sits at "0"
when the drives are a certain distance apart and will go positive or
negative from center if the drives are misaligned. The boat has
provisions for trimming the positions of each drive from the cockpit.

I'm looking for options to consider to do the actual distance sensing.
Water will occasionally splash around the sensor locations and since
the drives will be running there will be vibration. I do not know the
exact target distance right now but it is approximately 7.5 feet. The
drives have places where sensors, etc. could be mounted starting about
a foot behind the transom and out to about 5 feet or so on to the
drive assemblies.

Tim

2006\02\17@105645 by Bob Axtell

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Tim N9PUZ wrote:

>I'm researching options for measuring distances in a wet, outdoor
>environment. The task is to measure the distance between two drive
>units on a boat. The drives both propel and steer the boat.
>
>Ideally I will end up with an indicator for the crew that sits at "0"
>when the drives are a certain distance apart and will go positive or
>negative from center if the drives are misaligned. The boat has
>provisions for trimming the positions of each drive from the cockpit.
>
>I'm looking for options to consider to do the actual distance sensing.
>Water will occasionally splash around the sensor locations and since
>the drives will be running there will be vibration. I do not know the
>exact target distance right now but it is approximately 7.5 feet. The
>drives have places where sensors, etc. could be mounted starting about
>a foot behind the transom and out to about 5 feet or so on to the
>drive assemblies.
>
>Tim
>  
>
That should be easy with ultrasonic sound. The pulse is sent, and the
echo tells distance.
The sender/receiver modules are available commercially.

--Bob

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2006\02\17@110730 by Michael Rigby-Jones

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{Quote hidden}

I'm wondering if high frequency vibrations from the engines could play havoc with ultrasonics, and water splashing up will certainly cause problems with reflections, though those can probably be filtered out.

The only viable alternative I can think of would be a laser based system, which would also have problems with water splashes, but at least should be more immune to vibration.

Regards

Mike

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2006\02\17@120135 by Danny Sauer

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face
Michael wrote regarding 'RE: [EE] Distance Measurement' on Fri, Feb 17
at 10:12:
> I'm wondering if high frequency vibrations from the engines could
> play havoc with ultrasonics, and water splashing up will certainly
> cause problems with reflections, though those can probably be
> filtered out.
>
> The only viable alternative I can think of would be a laser based
> system, which would also have problems with water splashes, but at
> least should be more immune to vibration.

The motors shouldn't be vibrating in the ultrasonic range, should
they?  And wouldn't vibration be a bigger problem for a focused beam
of light than a high frequency sound wave?

Just thinking aloud here...

--Danny, hoping for a good suggestion he could also apply to a back-up
sensor on his car

2006\02\17@122300 by Michael Rigby-Jones
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{Quote hidden}

You can get get significant amounts of ultrasonic frequencies from an engine and it's ancilaries.  Even a humble ball race spinning produces ultrasonic vibration, as would any cavitation at the props.

Regards

Mike

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2006\02\17@122322 by Bob Blick

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> The task is to measure the distance between two drive
> units on a boat. The drives both propel and steer the boat.

I'm having trouble picturing what this is. The phrase "drive unit" brings
to mind an engine and transmission. Why would the distance between them
change, aren't they bolted down? This is a serious question, I'm not
kidding.

Thanks,

Bob


2006\02\17@123525 by alan smith

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Instead of trying to measure the distance between them, how about a sensor on each mount, that has a zero position.  Then the "controller" will look at each sensor independently and decide of either one is off the zero mark, and how far pos/neg from it and then they could be adjusted back to any distance.
 
 Question is...how close do you need to be aligned?  An array of sensors....maybe hall effect or proximity could be used perhaps...spread every quarter inch or however close you would need them to be aligned to.


>{Original Message removed}

2006\02\17@125216 by blackcat

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How often do you have to measure ?  How
much do the motors move relative to each other ?
Do they also vary in parallel alignment ?  Do
they twist around their axis ?  Since each motor
can be adjusted are you asking for distance from
a center point for each motor ?

My first thought was to use a PSD ( position sensing
diode ) which would not work too well if the motors
do not stay parallel.  You could certainly take a lot
of samples quickly and massage them.

If you could look down on them, a cheap video camera
could measure position.

AGSC

On 2006-Feb 17, at 8:45 AM, Tim N9PUZ wrote:

I'm researching options for measuring distances in a wet, outdoor
environment. The task is to measure the distance between two drive
units on a boat. The drives both propel and steer the boat.

Ideally I will end up with an indicator for the crew that sits at "0"
when the drives are a certain distance apart and will go positive or
negative from center if the drives are misaligned. The boat has
provisions for trimming the positions of each drive from the cockpit.

I'm looking for options to consider to do the actual distance sensing.
Water will occasionally splash around the sensor locations and since
the drives will be running there will be vibration. I do not know the
exact target distance right now but it is approximately 7.5 feet. The
drives have places where sensors, etc. could be mounted starting about
a foot behind the transom and out to about 5 feet or so on to the
drive assemblies.

Tim

2006\02\17@145347 by David VanHorn

picon face
I'd be looking at low frequency magnetics, maybe 1kHz - 1MHz.
Signal strength is inverse square of distance, so this can be pretty
sensitive.
Not sure what the proportions are here though. Movement vs distance, vs
mechanical vibration

2006\02\17@160621 by Tim N9PUZ

picon face
Bob Blick wrote:
>>The task is to measure the distance between two drive
>>units on a boat. The drives both propel and steer the boat.
>
>
> I'm having trouble picturing what this is. The phrase "drive unit" brings
> to mind an engine and transmission. Why would the distance between them
> change, aren't they bolted down? This is a serious question, I'm not
> kidding.
>
> Thanks,
>
> Bob

The boat has 4 engines coupled to a pair of drive units. The owner
tells me that the two individual drives are not solidly linked
together by design (I do not know a lot about the mechanics and/or
boats.) Each drive unit moves and/or can be adjusted to both steer and
set the trim of the boat. The distance between them out near the props
can change based on their position. The measurement and adjustment
function will be more of a trimming feature and is not a part of a
real-time control. It just needs to be done at speed instead of
statically when the boat is not moving.

With regard specifically to ultrasonic sensors don't they typically
have elements that would be open and hence adversely effected by the
water? I had looked at literature for a couple. It seemed like sealing
them up would render them inoperable.

As far as problems from spalshing goes for either ultrasonic or laser
based sensors I believe that sort of interference could be filtered
out since this isn't a control system and the nature of the
adjustments rules out big changes in a short period of time.

Tim

2006\02\17@162210 by Jinx

face picon face
> With regard specifically to ultrasonic sensors don't they typically
> have elements that would be open and hence adversely effected
> by the water?

Ultrasonic depth sounders don't......

2006\02\17@173604 by Jinx

face picon face
BTW, just on the subject of ultrasonics, I came across
this the other day whilst Googling

"Ultrasound beyond the speed of light"

http://www.acoustics.org/press/150th/Mobley.html

"So it may be hard to believe that by sprinkling in some small plastic
beads, water can be made to support ultrasonic pulses with speeds
faster than light. Not only can ultrasound pulses outrun light in this
watery mixture, they can also propagate in negative time, apparently
reaching a more distant point before a closer one. How is this possible?
What does it mean? How does it fit within the known laws of physics?"

2006\02\17@191609 by Juan Cubillo

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face
ultrasonics with a lot of averaging... If a measure goes way apart from the average just discard it.


{Original Message removed}

2006\02\20@035411 by Michael Rigby-Jones

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>-----Original Message-----
>From: piclist-bouncesspamspam_OUTmit.edu [@spam@piclist-bouncesKILLspamspammit.edu]
>Sent: 17 February 2006 21:07
>To: Microcontroller discussion list - Public.
>Subject: Re: [EE] Distance Measurement
>
>The boat has 4 engines coupled to a pair of drive units. The owner
>tells me that the two individual drives are not solidly linked
>together by design (I do not know a lot about the mechanics and/or
>boats.) Each drive unit moves and/or can be adjusted to both steer and
>set the trim of the boat. The distance between them out near the props
>can change based on their position. The measurement and adjustment
>function will be more of a trimming feature and is not a part of a
>real-time control. It just needs to be done at speed instead of
>statically when the boat is not moving.

Would it be possible to use angular sensors at the point where the drive units pivot?

Regards

Mike

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not make any use of this information, or copy or show it to any
person. Please contact us immediately to tell us that you have
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2006\02\20@081000 by Vasile Surducan

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On 2/17/06, Bob Axtell <KILLspamengineerKILLspamspamcotse.net> wrote:
{Quote hidden}

And the wind speed and with a little struggle the wind direction as I saw on
one of my friends project. Not talking about temperature and humidity
which are included in the distance...

Vasile

2006\02\20@093048 by Tim N9PUZ

picon face
Michael Rigby-Jones wrote:
>
> Would it be possible to use angular sensors at the point where the drive units pivot?
>

The pivot point is inside a piece that's about 18 inches wide so it
may be very difficult to get to.

An option (this will be hard to describe) might be to create kind of a
parallelogram that swings with the drive and measure the angle at a
more convenient spot.

I'll have to take some measurements and get a better definition of the
amount of change in distance to be measured. For example, if a
half-inch is important out near the prop that will be a very small
angular change at the pivot point.

Good idea -- thanks.

Tim

2006\02\20@113843 by Alan B. Pearce

face picon face
>I'll have to take some measurements and get a better
>definition of the amount of change in distance to be
>measured. For example, if a half-inch is important
>out near the prop that will be a very small angular
>change at the pivot point.

Is it the prop to prop distance that is important, or the angle of each
relative to the hull? You may be best to sort out some form of linear
transducer that can be bolted between the prop units, and then a single
measurement of one unit relative to the hull. Computing power could then
calculate any other measurements deemed necessary.

>From this a couple of questions arise

- how much do the prop units move relative to each other (obviously they
cannot be allowed to come that close that the props try and mangle each
other).

- How much do they move relative to the boat hull? This will obviously be a
reasonable amount to effect the steering of the whole assembly, unless there
are separate rudder units for this purpose.

2006\02\20@141939 by Tim N9PUZ

picon face
Alan B. Pearce wrote:

> Is it the prop to prop distance that is important, or the angle of each
> relative to the hull? You may be best to sort out some form of linear
> transducer that can be bolted between the prop units, and then a single
> measurement of one unit relative to the hull. Computing power could then
> calculate any other measurements deemed necessary.

The owner says the prop to prop distance is what's important. He does
not need to know whether they are inline with the hull.

> - how much do the prop units move relative to each other (obviously they
> cannot be allowed to come that close that the props try and mangle each
> other).

I've asked for clarification but there is no danger of them actually
striking one another unless something has gone wrong that's a much
more serious problem to worry about.

> - How much do they move relative to the boat hull? This will obviously be a
> reasonable amount to effect the steering of the whole assembly, unless there
> are separate rudder units for this purpose.

Unkown (by me) right now.

Tim



2006\02\22@091951 by Tim N9PUZ

picon face
A short update for those following the distance measurement discussion...

I've now had an opportunity to see the boat with the drives mounted as
it's being built. The drives are steered (and trimmed) by hydraulic
actuators which travel about 8 inches from stop to stop. Initially, I
was told these were internal to the drive housings and not accessible.
I believe the most reliable method of indicating the distance between
the two props will be to measure the position of the cylinder ram and
calculate based on that. The positions of the rest of the steering
system are fixed when everything is aligned during installation.

I appreciate all the suggestions and discussions from the list.

Thanks,

Tim

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