Dynamic Data Gathering – Calibso!
This process is identical for all Autoquad boards, AIMU or DIMU based.
In this step we are aiming to gather scale and offset data for gyros, accels and magnetometers. We do that by a series of coordinated moves, affectionately known as the dance calibration dance “Calibso”.
AIMU compass compensation
To make sure the AIMU compass is correctly compensated for soft and hard iron magnetic effects in the frame and electronics, the Calibso MUST ALWAYS be performed with the AIMU board installed in the powered airframe in a completely flight ready condition except for propellors.
Ideally, you should have all gimbals, cameras, Video transmitters and telemetry running, but that can be hard to deal with so keep it to the main airframe, battery and telemetry to begin with.
DIMU Compass compensation
It is recommended to do the Calibso in the fully configured and powered frame like for an AIMU to make sure that you are compensating the compass for hard and soft iron effects in the frame and electronics.
However, DIMU is not succeptible to compass vector distortion in flight, since the compass is only used to estimate initial craft heading on the ground. In flight, the heading is purely maintained by the gyros and corrected by GPS (when available).
So, with a DIMU, you can worry less about calibrating the board exactly to the frame, or you can do the calibso off frame. If you still have a good heading estimate when the board is mounted in the frame, powered and disarmed, you are still good.
Also, with the DIMU you can consider to use the Onboard Compass calibration to calibrate the compass to a new frame in a quick way. This means you can easily move boards between frames without having to do a full recalibration.
If you plan to later use the Onboard compass calibration, you can just perform the Calibso with the board off frame and skip step 3 and 6 in the calculations.
Introducing the Calibso
The “Calibso” is a specific sequence of rotations (hence the ‘dance’). Consider that the frame has 6 “faces” like a cube:
- Top face
- Bottom face
- Right face
- Left face
- Front face
- Rear (back) face
Start with any face pointing up (opposite of gravity’s pull) and then slowly rotate 90 degrees to an adjacent face and back up. Repeat until all 4 adjacant faces have been covered. (Front, back, right, left).
Then rotate craft slowly to bring a new face up and repeat the 4 rotations to the adjacent faces.
While this is going on, slowly rotate your body on your own yaw axis. Repeat until all 6 faces of the craft have been covered.
The videos below show the procedure in details. Part one just shows how how to move the craft for reference. Part 2 shows the whole sequence with the body rotation included:
Dynamic Calibration Movie, part 1
Dynamic Calibration Movie, part 2 (complete sequence)
Complete Calibso dance sequence
- Place your craft on a level surface, and power it up.
- You can wait for GPS 3D fix, but its not needed. However it will make sure that your log files are time stamped.
- When board is booted (Green LED blinks 2 times per second) and you have a GPS fix (blue LED on solid), insert the card (green LED blinks 5 times a second when logging) and let the craft sit still for at least 10-15 seconds.
- Pick up your craft GENTLY and begin the dance we call “Calibso” (If you don’t know what Calibso is, go back and watch the videos with the dancing lessons again).
- Start with any face pointing up (opposite of gravity’s pull) and then slowly rotate 90 degrees to an adjacent face and back up. Repeat until all 4 adjacent faces have been covered. (Front, back, right, left). While this is going on, slowly spin your body in place (yaw) like a slow waltz (but without swaying!).
- Then rotate craft slowly to bring a new face up and repeat the 4 rotations to the adjacent faces, still turning slowly on your own yaw axis.
- Repeat until all 6 faces of the craft have been covered and return your craft gently to a level surface and let it log for at least another 10-15 seconds.
- Unplug power and remove the uSD card.
The whole sequence should take at least 5 minutes – time yourself and if it’s shorter than 5 mins, you are going too fast.
The micro SD card will now contain a number of log files that can be used for the calculations. You should now a number of large log files containing the static data (around 200-250Mb) and 1 or more smaller log files containing the dynamic data (around 22-28Mb).
Back up these files to a local storage on your computer. You could rename them to help you keep track of them, but its not mandatory.
Just like the static files, you should check the files in the log viewer and possibly also clip away the noise in the beginning and end of your files. More on this in the Dynamic Log file analysis page.