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Amature Rockey Flight Computer


#1

So here is the start of my new project. An on-board flight computer for an amateur rocket. I know that this has been done plenty of times before, but I am not the kind of person who likes to do things off-the-shelf so to speak.

I have a FEZ Mini which will be serving as the CPU for the computer

From SparkFun I have also ordered the following kit.
Triple Axis Accelerometer Breakout - ADXL345 : A 16g 3-axis accelerometer
Barometric Pressure Sensor - BMP085 Breakout : A pressure sensor for altitude measurement, good for about 9,100m (9km)
GPS Micro-Mini : Speed, Altitude, Location

I will be adding a Micro SDCard Expansion to my FEZ as soon as I can source one that won’t kill me with shipping costs. The Australian vendor I purchased the FEZ from didn’t stock the SDCard boards, SparkFun don’t stock them (huh!) and the shipping from TinyCLR/GHI Electronics to australia with FedEx is HUGE!

Once the parts from SparkFun arrive and I start Breadboarding the design, I will post some Photos and driver source code for the parts.


#2

Very interesting project. Do keep us updated.


#3

What kind of rocket are we talking about here? A cheap Estes rocket or a high powered hobby grade rocket? You may have issues with an Estes rocket.


#4

[quote]I will be adding a Micro SDCard Expansion to my FEZ as soon as I can source one that won’t kill me with shipping costs. The Australian vendor I purchased the FEZ from didn’t stock the SDCard boards, SparkFun don’t stock them (huh!) and the shipping from TinyCLR/GHI Electronics to australia with FedEx is HUGE!
[/quote]

We are into adding regular mail…very cheap. Actually, a USPS rep. is coming to our office today to talk about this :wink:


#5

Fun project! Keep us posted! :wink:


#6

Heffo, let me know if you don’t get another option - I am thinking I’ll be making a GHI order and shipment to Sydney shortly


#7

Hi Heffo,

I created a rocket flight computer out of the Spark Fun Package Tracker board they have. I made this rocket: http://www.apogeerockets.com/Quest_Magnum_Payloader.asp which had plenty room for the board and a LiPo battery wrapped in bubble wrap. There would be plenty room left for the GPS module also.

Looking forward to see what you create with a FEZ!


#8

Spark Fun does sell an SD card here: http://www.sparkfun.com/commerce/product_info.php?products_id=8163

Please note I am not affiliated with Spark fun except for being a happy customer for them. :slight_smile:


#9

Here are some more details on the rocket I am building.

The entire system is custom fabricated by myself. I have been building KNSU (Potassium Nitrate / Sucrose in a 65/35 ratio) propellant engines. To date I have launched a lot of small 25mm PVC engines, a lot more fun (and altitude) than the small Estes kit my brother paid over $100 for. I am in the process of building, refining and static testing a 40mm KNSU engine for use to launch my first generation PVC rocket.

The first generation rocket will last for a single flight as there will be no recovery system, it is mainly to verify the engine and my basic rocket building skills. Obviously no onboard electronics for this one. It consists of a 220mm long fin/engine section made from 50mm PVC pipe left-over from a plumbing job I done around my house. This fits into a body section 400mm long empty section of 50mm PVC, A 100mm long nose cone slots into the body section. There are four trapezoidal shape fins, laser cut from 3mm acrylic sheet (the upside of working for an engineering company is I can use the laser cutter whenever I want for free!)

The second generation rocket will be similar to the first, but this time with a single parachute recovery system to test the parachute and deployment system design. There will only be a basic 555 timer based deployment electronics to fire the deployment charge. If the rocket is recovered intact, I will have a second motor and deployment charge on standby to do an immediate re-load and re-launch to test re-usability.

The third generation rocket will have a larger engine, a drogue & main chute recovery system, which will be controlled by the flight computer (the FEZ will be in charge here). It is planned that upon detecting apogee, the drogue chute will deploy, allowing a quick but controlled descent, and once the computer is a preset distance above the ground, the main chute will deploy slowing the descent further, this way, the rocket will fall quick enough to keep the rocket close to the launch site, but still allow a soft landing under chute.

My eventual aim is to get to an altitude where the on board cameras will record both the curvature of the earth below it, and the blackness of space above it. And the biggest kick I will get from all this is knowing it was all my own work that got me there, no “off-the-shelf” components.

With the FEZ based flight computer, the design will also progress in three stages. The first is on a breadboard with the breakout components, in order to quickly refine the hardware and write the software.

Stage two is taking the breadboard design and packing it into the rocket using stripboard as a breadboard substitute, testing it in-flight.

Stage Three is designing as small a PCB as physically possible and soldering a computer together in the final configuration, and building a dedicated “avionics bay” section I can slot into the rocket body for flight.

I will be documenting Stage One of this process, and possibly (depending on interest) making available finished Stage Three boards to anyone who wants one.


#10

Hi Heffo,

Sounds like you know where you were going! The reason I asked about the rocket was because I saw someone trying to do some microcontroller project with an estes rocket and it turned out very badly.


#11

@ Brett

If you are making an order, contact me (robheffo att live dawt com dawt au) and we can work something out about getting hold of the MicroSD card board.


#12

Chris, yeah I can imagine a homebrew microcontroller project would be a problem in an estes, the one my brother bought would barely fit the engine and chute. so trying to put almost any electronics inside it would not be easy.

Then there is the software development environment for a PIC or AVR, this is where I love the FEZ and being able to use the .NET MF and C#. I write commercial software in my spare time and am already fluent and comfortable using Visual Studio and C#. Fire up Visual Studio, jack the FEZ into USB and ready to rock! no need for hex files, flaky serial programmers, and obscure feature-limited free compilers with little documentation.


#13

Are you also going to try for an RF link to the ground?


#14

Eventually, but it’ll probably be via an X-Bee link or something providing a basic telemetry stream.


#15

Very cool. Have you ever measured the acceleration of one of those rockets?


#16

Hey Huffo, I’ve been tinkering with the Primer2 STM32 device to be a portable launch control and tracker. I was going to implement the DIgi XBee modules to do this also. I would imaging the FEZ Cobra with LCD and enclosure would work for this application also. I know here in the US, you need FAA clearance for the type of rockets your planning on building. Do they have those sort of regulations there? What is the expected apogee altitude for your rocket?

Chris, my little rocket had about 3G thrust measured with the Package Tracker device. I’m sure Huffo’s will be much more!


#17

In australia there are similar laws to the FAA, I cannot launch more than 400ft within 5 Nautical miles of an airport. I can launch up to 400ft without notifying CASA (the Commercial Aviation Safety Authority, Australia’s FAA) Above this requires permits.

I ran some simulations on an older design of my 40mm engine, and the current rocket design and I got an expected apogee of a little over 1,100m. The fuel load has since been decreased due to an additional inner layer of PVC to stop burn-through, and the extra weight of a cement nozzle with a steel throat section, to avoid the excessive throat erosion I was experiencing.

Just go give an idea of my current engine design, here is an image of a SolidWorks model I made of the engine


#18

Hi Huffo,

I’m wondering how PVC would hold up to the temperatures afflicted on it from repeated firings. Do you have an idea how hot the inside temperature would be and how it would affect the PVC integrity? Sounds like a FEZ could be used to monitor temperatures at various points with some thermocouplers. I know from building my kit rocket how heart breaking it would be for my rocket to simply explode on the pad after ignition. I had a miss fire of my double engine rocket and it scared the heck out of me. Fortunately, it just went a couple yards popped and popped its top for the chute to somewhat reduce the impact speed. I wired the engines in parallel instead of in series so only one engine fired.


#19

Logitechs,

The PVC engines are single-firing only. In order to hold the pressure of combustion, the parts need to be glued together with regular plumbing PVC adhesive, making it so you can’t get it apart again. The components are extremely cheap to buy from local discount hardware stores (Think Wal-Mart but for hardware, timber, tools, etc), I would estimate about AU$7 for an “I” class motor (including propellants)

Heat-wise the PVC holds up well as the fuel grain itself acts as an ablative insulator and it only gets exposed to the 1500degC combustion gasses for a fraction of a second right at the end of the burn as the fuel is finally consumed. It is enough to soften the PVC so it is flexible in your hand, by the time this happens in flight there is no thrust left and the airflow cools and re-solidifies the pipe extremely quickly.

My last engine test involved a double-wall of PVC where I glued one PVC tube inside another for additional strength and after the test burn the tube was still perfectly solid and if it wasn’t for the fact that the end caps were glued on, I could quite possibly reloaded and reused the casing.

If you google around for PVC Rocket engines there is plenty of information about them. Richard Nakka and Jimmy Yawn are both rather good sources of information on these kinds of engine and are pretty much required reading on the subject.


#20

I have uploaded a (poor quality) video of the last firing of my 40mm motor design to Youtube.

You can check it out here… http://www.youtube.com/watch?v=VMP_m1esIzk