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PICList Thread
'Water Rockets'
1999\06\27@142537 by Greg Hastings

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<x-flowed>Hi all,
 Back in High school we built water rockets from 2 liter bottles
and shot them into the air with an air compressor.

 I am going to build some more, this time adding a PIC to it to
record its highest altitude.  Does anyone have any ideas on how
the altitude can be determined?

 Also if anyone has done any projects involving rockets and
microchips please email me.  I would be very interested to hear
what you have done..

Thanks,
 Greg H. (spam_OUTghpoeTakeThisOuTspamhotmail.com)



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</x-flowed>

1999\06\27@152507 by Dave Johnson

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Greg Hastings wrote:

>  Also if anyone has done any projects involving rockets and
>microchips please email me.  I would be very interested to hear
>what you have done.
I haven't done any combinations of the two yet, but I've been playing
with water rockets for a couple years now
(http://www.geocities.com/CapeCanaveral/Lab/5403/), and programming PICs for
work (http://www.imagiworks.com), so I'm also thinking of making a rocket
instrumentation package.

There are commercially available altimeters for rockets that use a
pressure sensor. The one that I've seen (made by a company called Adept,
http://www.diac.com/~adept/) worked like this: you turn it on with the rocket
stationary on the launch pad, and it samples and records the pressure as
a baseline, then it tracks pressure throughout the flight, saving the
minimum (max. altitude). When you're done you push a button and it beeps
out the altitude repeatedly until you turn it off. Nice and simple.

I haven't yet identified an appropriate pressure sensor for this (and
honestly I haven't tried yet), but if you find one (or if anyone else has
ideas for one) please let me know.

It also occurred to me that you could build a pitot tube airspeed
indicater with a pressure sensor as well. My dream device measures
acceleration, airspeed, and altitude, and saves the curves for all three
for later download into a PC.

Dave Johnson

1999\06\27@172925 by Shaun Wilson

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<x-flowed>Greg,

Im am in the process of making a alitimeter myself. So far im pretty much in
the  designing stages. I am going to be interface it to a stamp but it would
be just as easy to use a PIC. I am waiting for my pressure sensor in the
mail. I used a MPX4115, the data sheet is available from
http://mot-sps.com/cgi-bin/get?/books/dl200/pdf/mpx4115a*.pdf
I aslo found another source http://www.novasensor.com/
They offer a free sample pressure sensor but i didnt want to wait around for
it to come so i got the MPX4115. I bought the MPX4115 from peter anderson.
They are $20 http://www.phanderson.com/

The pressure sensor outputs a voltage so you will need a ADC. I chose
a MAX187 because i could get it for free but any would do.
http://www.maxim-ic.com

The next thing you need is a way to isolate the sensor from the ADC and get
rid of noise.
This is done by using a op amp. Any old opamp will do Maxium has some or you
could use a 741.

Here are some sites i found with some info on alitimeter.
http://www.tfs.net/~petek/altimeter/begin.html really good site.
http://www.h2net.net/p/jkarp/altim.htm


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</x-flowed>

1999\06\27@183716 by Sean Breheny

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Sounds like a really neat idea!

I haven't tried this, but considering the small flight duration, maybe it
would be possible to just use an accelerometer,subtract out gravity's
acceleration value, and then just integrate twice up until the point where
it drops below 1G (indicating that it is now falling)?

Sean


At 11:23 AM 6/27/99 PDT, you wrote:
{Quote hidden}

| Sean Breheny
| Amateur Radio Callsign: KA3YXM
| Electrical Engineering Student
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1999\06\27@184316 by Sean Breheny

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Oops, I should have thought a bit more before sending that last message.
Actually, the acceleration would be negative way before it reached apogee.
Hmmmm, I think you could still detect apogee by seeing when the
acceleration was downward and exactly equal to 1 G.


I think the accel curve would look like this:

Initially 1 G downward.
High acceleration upward at liftoff.
Gradually decreasing due to air resistance.
When engine shuts off, it suddenly goes to >1G downward (air resistance +
gravity)
Gradually goes to exactly 1G downward (as air resistance decreases)
then gradually decreases (due ro air resistance in the descent) until
striking the ground.

Sean


At 11:23 AM 6/27/99 PDT, you wrote:
{Quote hidden}

| Sean Breheny
| Amateur Radio Callsign: KA3YXM
| Electrical Engineering Student
\--------------=----------------
Save lives, please look at http://www.all.org
Personal page: http://www.people.cornell.edu/pages/shb7
RemoveMEshb7TakeThisOuTspamcornell.edu ICQ #: 3329174
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1999\06\27@215303 by Des Bromilow

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Building a PIC based Altimieter for model rockets.......

Here's what advice  I've got to offer.

launch detect...  Software detected, OR lanyard, or G Switch, or electrical switch. All have inherent faults, and benefits. Barometric drift is an issue with software, whereas weight and reliability are issues with the others.

Alt sensing. It's up to you, but most common methods involve a 0-15 psi barometric sensor (Absolute or differential) Offset and baseline need to be factored in and the equation relating pressure to altitude is an exponential one, so the best way to implement it is in a lookup table (abbreviated with a little effort) OR don't evaluate the pressure/ altitude relationship in the PIC, but rather have the altimeter report pressure and then get the relationship worked out on the ground later (in a PC or chart) (My design does the calc in the PIC after the flight has finished, thus keeping the PIC processing free to monitor the flight, and saving the intensive "number crunching" until later)
Other sensing methods are typically based on accelleration and will require maths functions for analysis (again.. could be downloaded to a PC) Both barometric and accelleration sensors require an Instrumentation amp and ADC. (I use 12 bit serial)

reporting... In the first instance I'm using a Piezo beeper to "beep out" the max altitude, but others can use LCDs (beware of the weight penalties and size restrictions) I use DIP switches for entering a few programmable variables.

If the altimeter is to perform actions (other than recording) then suitable devices need to be added such as logic level FETs. or software features such as "mach timeouts" or timers.


>From what I've seen, most of the cost is in the sensors. I have sample requests waitng with about 4-5 companies, but as yet, no samples have arrived. I manged to get apart an automotive acelleration sensor (for airbags) and am trying to design a smaller version for use as a launch detect switch. Most of my efforts have been aimed at reducing the sensor prices by looking at reusing other devices (liek medical sensors) or building my own...... Unfortunately I will never be able to compare to the standard of a micromachined silicon device.


Hope this helps,
Des Bromilow




>>> Shaun Wilson <spamBeGoneshaunwilsonspamBeGonespamHOTMAIL.COM> 6/27/99 6:27:51 pm >>>
Greg,

Im am in the process of making a alitimeter myself. So far im pretty much in
the  designing stages. I am going to be interface it to a stamp but it would
be just as easy to use a PIC. I am waiting for my pressure sensor in the
mail. I used a MPX4115, the data sheet is available from
http://mot-sps.com/cgi-bin/get?/books/dl200/pdf/mpx4115a*.pdf
I aslo found another source http://www.novasensor.com/
They offer a free sample pressure sensor but i didnt want to wait around for
it to come so i got the MPX4115. I bought the MPX4115 from peter anderson.
They are $20 http://www.phanderson.com/

The pressure sensor outputs a voltage so you will need a ADC. I chose
a MAX187 because i could get it for free but any would do.
http://www.maxim-ic.com

The next thing you need is a way to isolate the sensor from the ADC and get
rid of noise.
This is done by using a op amp. Any old opamp will do Maxium has some or you
could use a 741.

Here are some sites i found with some info on alitimeter.
http://www.tfs.net/~petek/altimeter/begin.html really good site.
http://www.h2net.net/p/jkarp/altim.htm


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1999\06\28@100818 by John Pfaff

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I haven't personally done this, but in researching solid-state gyros and
accelerometers, I came across the Danish Amateur Rocket Club
http://inet.uni2.dk/~dark/ ).  Looks like they've done a lot of neat stuff.
It seems that a lot of the gyro and accelerometer applications are for R/C
helicopters, airplanes, and model rockets.  You can do an Internet search
for 'solid state gyro' and see several other applications.  DARK is the only
one I remember finding specific to model rockets.

{Original Message removed}

1999\06\28@115915 by Tom Handley

picon face
  Greg, I've wanted to do a complete payload package for a long time.
Several already exist and there have been many articles. One source is
Circuit Cellar #98 (Sept 98). Though they were measuring acceleration to
record the performance of standard Estes engines using an Analog Devices
ADXL50, there is a lot of good info in the article. It's based on a
PIC16C73, stores data in a serial flash memory, and sends data to a PC.

     http://www.circuitcellar.com

  I've never tried water rockets but I have years of experience with Estes
and other model rockets. I'm still trying to imagine a 2 liter bottle taking
off with all the issues of stability, drag, center of gravity, center of
pressure, etc. This seems more like an artillery round than a rocket ;-)

  I did take a look at the site Dave Johnson mentioned. Since you are only
going up to around 300 feet, you could just use simple trig like those cheap
or home-made altitude trackers. Stand back a fixed distance from the launch
pad, site the rocket at it's apogee, and note the angle from horizontal. You
can make the thing out of cardboard and a straw. Ok, that's no fun ;-)

  You will need a 0-15 PSI absolute pressure sensor and a 12-Bit A/D to get
any decent resolution. I'd use at least a temperature compensated sensor,
preferably calibrated. These are bridge transducers and require a stable
excitation voltage. 5V is typical. You also need an instrumentation amp. The
best deal now days appears to be Motorola's MPX4115 which includes the above
and costs about the same but there are other considerations.

  Of course one of the main concerns is weight. Most sensors come in a
variety of packages. Other issues are response time, sensitivity, linearity,
hysteresis, and repeatability. It all depends on how accurate you want to
get. Since these sensors use piezoresistive elements, you will get `garbage'
during the `violent' launch and will have to look at the data near apogee.
If you use a parachute recovery system, you can take readings on the way
down to evaluate chutes.

  In your case, I'd recommend the Motorola MPX4115 and a serial 12-Bit A/D.
You could use a PIC12508 and send the results to a PC. Wait for a fixed
period of time and then start reading the sensor.

  For info on pressure sensors, check the following sites:

     Motorola: mot-sps.com/products/sensors/pressure/index.html
     Sensym  : http://www.sensym.com
     Lucas   : http://www.novasensor.com/

  - Tom

At 11:23 AM 6/27/99 PDT, Greg Hastings wrote:
{Quote hidden}

1999\06\28@120750 by John Pfaff

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face
I haven't personally done this, but in researching solid-state gyros and
accelerometers, I came across the Danish Amateur Rocket Club
http://inet.uni2.dk/~dark/ ).  Looks like they've done a lot of neat stuff.
It seems that a lot of the gyro and accelerometer applications are for R/C
helicopters, airplanes, and model rockets.  You can do an Internet search
for 'solid state gyro' and see several other applications.  DARK is the only
one I remember finding specific to model rockets.

{Original Message removed}

1999\06\29@061644 by Mark Willis

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face
"Inquiring Minds have to know":  How does one LAUNCH a water rocket?
(Reply off-list or on, I just want to know <G>)  Hopefully it's
electrical & attached to a PIC.

I've seen Magnetic and optoelectronic "Launch" detectors in model
rockets, btw.  A piece of electrical tape can serve to interrupt the
opto, so long as it's not IR - then you want to add a piece of aluminum
foil inside the tape <G>

Admin note:  We're getting duplicate messages & some people are getting
"You shouldn't send duplicates to the PICList" error messages, known
problem, should be solved soon.  Someone's ISP is messed up, I'm being
patient.

 Mark

1999\06\29@145507 by w. v. ooijen / f. hanneman

picon face
>    Greg, I've wanted to do a complete payload package for a long time.
> Several already exist and there have been many articles. One source is
> Circuit Cellar #98 (Sept 98). Though they were measuring acceleration to
> record the performance of standard Estes engines using an Analog Devices
> ADXL50, there is a lot of good info in the article. It's based on a
> PIC16C73, stores data in a serial flash memory, and sends data to a PC.
>

Note that they found a strange oscillation in their reading which I think
is caused by the flash drawing a large current during writing.

Wouter.

1999\06\29@172059 by Des Bromilow

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face
water rockets work on compressed gas (normally air) which sits in a "pressure vessel" (normally a PET bottle) with an amount of water between the gas and the nozzle. the pressure of the gas forces the water out of the nozzle, and the reaction force is the thrust.
The controlling parameters in the design and performance of the water rocket are:
the amount of water, the nozzle dimensions, gas pressure, and aerodynamic properties of the rocket body.

Multi staging is acheivable, but the real "R&D" of water rockets seems to be directed towards the development of recovery systems.

Hope this helps,
Des

>>> Mark Willis <RemoveMEmwillisspam_OUTspamKILLspamNWLINK.COM> 6/29/99 8:15:03 pm >>>
"Inquiring Minds have to know":  How does one LAUNCH a water rocket?
(Reply off-list or on, I just want to know <G>)  Hopefully it's
electrical & attached to a PIC.

I've seen Magnetic and optoelectronic "Launch" detectors in model
rockets, btw.  A piece of electrical tape can serve to interrupt the
opto, so long as it's not IR - then you want to add a piece of aluminum
foil inside the tape <G>

Admin note:  We're getting duplicate messages & some people are getting
"You shouldn't send duplicates to the PICList" error messages, known
problem, should be solved soon.  Someone's ISP is messed up, I'm being
patient.

 Mark

1999\06\29@193148 by Brian Kraut

picon face
When I was a teenager I used to have all kinds of fun with an air
compressor and 2 liter plastic bottles.  I used to launch them accross
my basement, etc.  They amazingly never popped at 180 PSI.  The one time
I filled one half full with water to make a super squirt gun it blew up
at under 100 PSI.  Luckilly I wasn't next to it.  From the looks of the
shrapnell there would have been some nasty injuries.

Greg Hastings wrote:

{Quote hidden}

1999\06\29@204158 by l.allen

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> Hi all,
>   Back in High school we built water rockets from 2 liter bottles
> and shot them into the air with an air compressor.
>
>   I am going to build some more, this time adding a PIC to it to
> record its highest altitude.  Does anyone have any ideas on how
> the altitude can be determined?
>
>   Also if anyone has done any projects involving rockets and
> microchips please email me.  I would be very interested to hear
> what you have done..
>

One way of detecting point of apogee could be visual detection of the
horizon, or better the sun. Recessed light to voltage sensors e.g.
TSL250 by Texas Instruments could be along the cone. When the rocket
is on its side apogee is detected.
A PIC such as 12c672 (a favourite of mine) could detect the highest
value on a detector and take this as the level to look for moving
through the other sensors.
I intend to give this a go so I will report my results.
I know optical horizon sensors have been used with model aircraft for
years.
Actual height?  acceleration and a detected apogee would be a start.

Lance Allen

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