3" Diameter Arduino Controlled Two Stage E-Bay

Hi everyone,

I have been playing a lot with arduino accelerometers and gyroscopes. There are some pretty cool projects that can be done when data can be read off those sensors. I've been playing with the idea of building a two stage out of some spare 3" blue tube I have laying around from my level 2 project and wanted to get opinions on my bay design. I did a 3" bay for my level 2 project and disliked how cramped everything felt. My way around this was to simply make the bay much longer than I did last time, 10" as opposed to 7".



When powered on the arduino would wait for an acceleration equivalent to the 7g's expected at launch. At that point it would wait for burn out, light an e-match in the staging bay to separate the booster/sustainer, and read the gyroscope. If the rocket tips more than 23 degrees from launch orientation, the arduino will not fire the second stage igniter. Stratologger CF altimeter's operate independently in both stages.

This is my first solo two stage project and am starting at the electronics bays to make sure that everything will be safe. I'll need to do testing to see if the arduino uno can even light e-matches and small igniters. I also have a pet GPS tracker on board with a pre-paid sim card for tracking in the sustainer. It still looks pretty packed but I think the layout of this bay is much smarter than my cramped level-2 project electronics bay. If I find I need more batteries I have plenty of room, as well as room for an 808 camera for on board video.

I've been toying around with a similar thing for my 2 stage.

What CAD program is that?

Also, what accelerometer/gyroscope are you using?

I will be watching with great interest.

Matt

I'm using these two sparkfun breakout boards for the gyroscope and accelormeter:
gyro: https://www.sparkfun.com/products/11977
accelormeter: https://www.sparkfun.com/products/9269

I've used both of them for acceleration and roll data on a 100,000 foot balloon satellite project recently and they work pretty good. The CAD program is SolidWorks. I'm also going to try putting a smoke flare in the interstage coupler to be lit at separation so I don't have to use a tracker in the booster stage. That part is the prototype for a bigger project to be built later on .

I left a couple of notes in your post back in the HPR forum, but... a couple more here. Firstly, don't even try to light an e-match with the Arduino without some sort of external driver. A low-current solution will need a bare minimum of 100mA ( even the fabled Quest Q2G2 needs more than that ), and outputs on the Arduino are limited to 20mA if you don't want to risk damaging it. However, a low-side transistor, darlington or MOSFET switch would solve that quickly. By the same token, a small igniter ( at least a couple of Amperes ) is impossible without a driver. Some option should be pretty easy to lash up however. The trick is going to be making sure that it's safe when you don't want the igniter/e-match to light.

As it stands, the e-bay looks good to me. I only have a couple of concerns with it. I mentioned the first above, power drivers. The other is, how are you hoping to connect wires to the Arduino. It's an easy board to play with, but it's not really well suited to wiring in high-vibration/high-acceleration environments. I could easily see the wires working their way out. In that case, there could be no staging or, if the driver isn't properly designed, worse -- random stage ignition. You have plenty of room there, and everything looks nicely mounted both for function and access. What makes sense to me is to simply remove the headers on the Arduino and solder directly to the board. Another option would be to design a shield ( PCB and circuitry ) to mount on top that would hold the drivers and the connections for the breakout boards. Then, it would be possible to bolt the shield and the Arduino down to the sled. It looks like there should be sufficient height in the e-bay for a shield.

How are you planning to deal with the drift of the angle due to the gyroscope bias? And, are you using your own libraries to interface to the sensors, or something you found ( like those that Sparkfun has available )?

Again, great project!

Cheers,
Martin Jay McKee

One option to get around the header connections on the Arduino is to make an "off board" Arduino. You could make your own board and have access to all the Arduino functions with the connectors of your choice or even soldered connections to you gyro's etc. The attached breadboard picture is all that is required. The red FTDI board is used to power and upload programs to the ATMega chip. The LED's are used just for indicators that the Arduino chip is working and can be left off the board. If you strip it down to the basics all that is required are the ATMega328, 2 22pf capacitors, 1 10K resistor and the 16mhz crystal. I have also included a "off board" Arduino I use for a game called "Reaction Timer". The benefits are light weight, solid connections, inexpensive, small footprint. I think I bought the ATMega chip preloaded with the Arduino bootstrapper, 16mhz crystal,resistor and capacitors for around $6.50.

Here is the pin layout for the ATMega328.

Modern Device sells a small Arduino using the 28-pin DIP that you could simply solder wires to, and you can get it in a 3.3V version too so you don't need to mess with level converters for your sensors. I've bought a few of them, I use them for things like device programming where it's not worth the time to make a PCB for a one-off build.

Actually, I started thinking about the "non-uno" form factor Arduinos. Something like an Arduino Mini or Micro without mounted pins could be used to good effect here, or even mount pins and simply solder it onto a prototyping PCB that holds the rest of the circuitry. One additional advantage, beyond the smaller size, that you can get a Chinese clone for about $2.50 shipped.

Martin Jay McKee

I have read before about the limits of the arduino in terms of output current and voltage and was researching ways to get around that problem. Your advice about the driver is really helpful.

I didn't have time for this post to show the shield that I'm putting together to fit onto the arduino. It will have headers on it to plug directly into the arduino, with the gyroscope, accelormeter, and any other sensor I can fit on soldered down to prevent the violence of the launch from tearing about the board.

In terms of the drift on the gyroscope I plan to test fly the bay on an old rocket and calibrate the sensor over 2-3 flights. Depending on how bad the drift is (the one I'm using for my balloon satellite project only deviates about 1-3 degrees when not moving. Most of the time it stays constant) I'll consider multiple gyro's for redundancy. I will probably use the sparkfun library that is pre-written. I'll post the code once I get that far. I have to make the shield first

amarillo_rocket said:

One option to get around the header connections on the Arduino is to make an "off board" Arduino. You could make your own board and have access to all the Arduino functions with the connectors of your choice or even soldered connections to you gyro's etc. The attached breadboard picture is all that is required. The red FTDI board is used to power and upload programs to the ATMega chip. The LED's are used just for indicators that the Arduino chip is working and can be left off the board. If you strip it down to the basics all that is required are the ATMega328, 2 22pf capacitors, 1 10K resistor and the 16mhz crystal. I have also included a "off board" Arduino I use for a game called "Reaction Timer". The benefits are light weight, solid connections, inexpensive, small footprint. I think I bought the ATMega chip preloaded with the Arduino bootstrapper, 16mhz crystal,resistor and capacitors for around $6.50.

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This is a really cool idea. It would save a lot of room or even let me add more/redundant sensors. Maybe even a piezo speaker to scream for help once the rocket lands. Thanks for the advice and for the pin layout.

The March 2015 Nuts and Volts magazine has a lot more detail. They did several articles about this setup last year. I have used it many times in places I did not want to put the entire Arduino board. I have not had one problem with the setup. You can use a regular Arduino for programming your ATMega chip. Just upload the code to the ATMega remove it from the Arduino and plug into the socket of your board. I buy most of my ATMega's from Jameco. I think the chips are $4.75. Jameco has the other components you will need. There are several places to source your hardware I like Jameco's service. Sparkfun and AdaFruit are my other 2 primary sources.