Introduction: Black Box
This black box tracker records magnetic and GPS heading as well as 3 axis GPS location, barametric altitude, and 3 axis tilt and acceleration. This allows for a wealth of information for both video overlays and for reviewing manoeuvres once you are on the ground.
Here is a video of the testing of an early prototype:
For this project you will require:
- A study container
- Paperbacked foam board
- MediaTek LinkIt
- GPS Antenna
- Standard LinkIt Battery
- 9-axis + barometric sensor "boodle"
A huge thank you to instructables, autodesk, MediaTek, and Penolopy Bulnick for sending me the Link It One used in this instructable.
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Step 1: Cutting the Base Plate
The first step is build a stable base to mount all of the components to. I used paper backed foam board left over from an architectural model but cardboard, balsa, or plastic board will also work.
I pressed the lid of my case into the foam to create an impression then cut it out with a utility knife. I made the piece of foam fit tight enough to friction fit into the lid.
Step 2: Wiring
Now connect the GPS antenna, Battery, 9-axis Sensor, trigger switch, and insert a blank FAT formatted microSD card into the LinkIt.
Step 3: Layout
Lay out all of the components neatly onto the foam board and trace the components as well as marking any screw holes. Then make pilot holes in the foam using a pin.
Step 4: Mounting
Select screws that will pass through the component without penetrating all of the way through the foam. I have found that the best place to find small screws for mounting components is electronics, I salvaged most of my screws off of old printers. For components without screw holes I used rubberized mesh, as it will not conduct electricity, and screwed the mesh down the the foam.
This rigid mounting will prevent false sensor readings due to movement of the components.
Step 5: Coding and Data
To read any of the data from the 9-axis sensor you will need to get the libraries from the git hub repository here:
Some general notes for setting up the sensors are:
The default I2C address is 0x68
Each of the value types (gyroscope, accelerometer, and magnetometer) are transmitted as their own 16bit integers
To find the vector of each value use the 3 dimensional pythagorean theorem to find the modules (m = (x^2 + y^2 + z^2)^1/2)
Things to keep in mind:
Barometric altitude will need to be calibrated in post (leave it raw), use your knee board values
GPS altitude is inaccurate an average of GPS and Barometric is advisable if calibration is unknown
Magnetometer data can be skewed by electronics (the alternator, magnetos, most everything electronic in the plane)
This sensor array is for informational purposes only and as you may note in the video at the start of the video is not always highly accurate
I will post a full source code file for this project on my website Just4FunMedia.TK under the "Apps" tab once I finish working out the bugs. Currently these bugs are inaccurate sensor data, randomly crashing, and corrupted text files. I believe this is due to inefficient coding and the large amount of data gathered during a flight.
I am currently working to find a balance in sensor update rate between quality and reliability, as I believe that my log rate is causing my errors.
The 9-axis sensor also logs x.y. and z axis magnetism which can yield some visually interesting results when graphed in 3 dimensions (see data above). NOTE: the graph is a "ball" because the sensor senses a certain magnetic declination that is broken down into a cartesian vector (X,Y,Z). Imagine the vector as the needle of a compass stemming from the origin to a point
Step 6: Finishing Touches and Use
All that is left is to secure the plastic cover and add some much needed stickers. To record cockpit audio I prefer to use a microphone placed in my headset. This way the recorder is fully electrically isolated from the plane, and the recorder can in no way interfere with radio system. Purpose made cables are also available to adapt the standard .25" and .206" headset plugs to 2.5mm audio jacks, although I prefer not to use them.
Just push the switch, Once the LED starts flashing, stow the tracker and forget it.
Feel free to post any comments, questions, or results in the comments.
Have a great day! :-)
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