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Wanted: Plans for three-axis accelerometer data capture

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Tetrahedron

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Hello,

I have been thinking about this lately and with readily available Arduino board and three-axis accelerometer boards I would think that It would be possible to get this done for around $30-$40.
What I am interested in is a unit that would only record the three-axis accelerometer data, no deployment or anything else, just recording. I have seen you tube videos where they connect
the ADXL345 three-axis accelerometer (or 9 df IMU etc.) to an Arduino board. However, I would need a stand alone memory chip to record data and the software (e.g. after turned on it
won't start record until 2G for at least 0.5 seconds or something like that when rocket is on pad). I also think the Arduino board can be stripped to only keep the necessary components like
the main chip and some interfaces (USB port) etc. All powered by a 2S Lipo or so. Any ideas and thoughts are appreciated.
I think there was an article in Sport Rocketry some time ago about some similar unit.:cool:

-John
 

ttabbal

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I don't know of any plans, but it's not too complex or expensive. For the arduino, start with a smaller board like the nano. It doesn't have compatibility with the shield format, but it's already very small. Add a IMU breakout, just 4 pins for most of them. And something for storage. A simple Dataflash chip on a breakout is one option, or micro-SD. There are already arduino libraries for all that, so really you're just putting it together. There are some pre-made data loggers out there, Sparkfun sells a couple types.

Just a couple possibly useful bits...

https://www.sparkfun.com/products/13712
https://www.sparkfun.com/products/11113
https://www.sparkfun.com/products/9716
https://www.sparkfun.com/search/results?term=imu

Picking on Sparkfun as I'm more familiar with their website, lots of places have similar boards. They are a good vendor though.
 

soopirV

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I've had similar ideas, but am tied up in some other arduino-based projects at the moment. My only recommendation would be to use the modules to breadboard the design, but plan to build a board (perf/vero or etched PCB if you've got the equipment (I can help with that if you're interested)) so you have a smaller form factor, less weight but most importantly, solid connections. I bought a bunch of non-bootloaded ATMega328P from Ebay for ~$1 each, so I can build something permanently. So far I've designed and built a lightning trigger for my camera, a deployment/airstart timer (breadboard only at this point), an ultrasonic liquid level sensor for my home brewery, a 2 sided UV PCB exposure box, and am now working on an intervalometer and dolly for my camera to do timelapse. I'm not a programmer or an EE, but working with this stuff is just so much fun!
Have another idea for rocketry: use an LED as a sensor, and measure light input during flight to assess air quality at different altitudes. Need to characterize my LEDs to see which are receptive to the right wavelengths, and need to figure out which wavelength to measure for dust...right now just a cerebral exercise.
 

cerving

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When you get to the point that you want to make your own PC boards, it's much easier to use a PC board CAD program such as Eagle (free for personal hobby use!) and use a shared PC board fab service like OshPark to make your boards. OshPark is $5 per square inch for three double-sided boards, turnaround is about 3 weeks, so a 4" x 1" board will cost you $20 for three of them. Eagle is a decent program, but there's a pretty good learning curve, especially if you have to create your own part libraries. SparkFun has part libraries available for Eagle with almost all of the parts that they sell, so if you're using them then you'd be wise to go with Eagle.
 

Tetrahedron

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This is all very good information, thank you.

-John
 

radiohound

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I did a similar project, but using RF telemetry. The great thing about Arduino is there are so many libraries available for all the sensors you could ever want. I like the Teensy 3.2, but the new Teensy 3.5 and 3.6 have a micro SD card slot. I used the PJRC Prop Shield 9dof sensor. This board has a bonus MPL3115 pressure sensor, as well as a 8meg flash for storage in addition to the 9dof sensors. So for $40 you could mate the Teensy 3.2 and the Prop Shield together for altimeter and orientation recording.

I should point out that if you are interested in using the 3d accelerometer for acceleration data vs orientation, the accelerometer on this 9dof only goes up to 8g's. But a separate i2c accelerometer could be used separately to sense vertical g's.

propshield.jpg

Here is a link to the telemetry project site if you are interested:
https://hackaday.io/project/15425-rocket-real-time-transponder-and-gui
 

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