Gyro calibration experiments with a turntable

Last weekend, I've dug out an old turntable to see how well the gyroscope of the Move can be calibrated with the USB-based calibration blob. The turntable has the advantage that it has a known rotation speed (two modes: 33 RPM and 45 RPM), so this can be used to see if the values we get back from one of the gyro axes somehow relates to real-world values.

Before I tried the turntable method, I just played around with the raw Gyro values to see what I can get out of them. I wrote a very simple QGraphicsView-based GUI to see the output visually, and this is what came out of that example:



As you see, that was not really anything to write home about, so next up was the turntable experiment. With that, I could scale the raw gyro readings so that "1.0" (in my case) corresponds to e.g. 45 RPM. Coupling that with an audio player using Qt MultimediaKit, one can translate the turntable movements into playback rate values and control the media player just as if it were a vinyl record:



In this week, I've been working on perfecting the calibration algorithm, cleaning up the API for the calibration part of the library and hooking everything up to Sebastian Madgwick's AHRS algorithm and visualizing the result with Qt3D.

New labs application: Sensorfilter

If you've been watching the PS Move API repository recently, you might have noticed the new "labs/" subdirectory. In there, I'll push some small utilities that I use for debugging and visualization of the current inner workings of the library. The first tool to be put there is "sensorfilter", which is a quick visualization utility that I wrote for testing the new sensor filtering and calibration APIs. It makes use of both PSMoveFilter and PSMoveCalibration, as well as the original PSMove API. With a properly calibrated controller, you can get good readings (again, I've moved the controller a lot for this screenshot):

The slider at the left controls the current low-pass filter implementation's alpha value (i.e. how quickly should the sensor values converge to the newly-read value). As the sensor filter API is kept modular, it's possible to try to stick other sensor implementations in there without having to change client applications (of course, if there are tweakable settings, the client application has to know about these). With the Sensor Filter utility, it's easy to try out new filters and to sanity-check the calibration code.

The utility is available on github.com/thp/psmoveapi in the "labs/sensorfilter" subdirectory. Have a look at the README file to find out how you can build it. It depends on Qt 4 (tested with 4.8).

Plans for the next few days:

• Have a look at the OpenCV status, provide feedback to Benjamin
• Try improved sensor filtering algorithms and compare them
• Finish the calibration backend code, supporting USB "calibration blob" modes
• Clean up and document the code, extend the Python and Java bindings