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

Sensor calibration: Custom method and calibration blob

In the last few days, I've been working on getting a basic sensor data filtering infrastructure set up. In addition to that, I've added support for getting and storing the calibration data that is saved on the controller (the axis naming is a bit different in the PS Move API compared to what you will find on that Wiki page). In addition to the factory-set calibration data, I've also implemented support for a "custom" calibration scheme where the user has to do a 6-point tumble test, which will be used as anchor points for calibration.

The custom calibration scheme works a bit like "mccalibrate" from linmctool, but has (at the moment) a bit simpler algorithm (taking the average over 200 sensor readings). The new calibration tool that I wrote (c/calibrate.c) can detect if you have moved your controller too much while the readings were taken, and will ask you to do the given position again. A custom calibration could look like this (I've moved the controller a lot for the first "buttons up" reading to demo the move detector code):

~S/psmove/psmoveapi% build/calibrate 
Serial number: 04:76:6e:XX:XX:XX
Put the controller in the position 'bulb up' and press the Move button
All readings done for bulb up.
bulb up:
a (avg:     1 |  4359 |   188)
a (dev:    20 |    13 |    43)
m (avg:     2 |    -8 |  -421)
m (dev:     4 |     8 |     5)

Put the controller in the position 'bulb down' and press the Move button
All readings done for bulb down.
bulb down:
a (avg:  -165 | -4379 |  -113)
a (dev:    30 |    20 |    48)
m (avg:   -69 |   287 |  -435)
m (dev:     5 |    10 |     5)

Put the controller in the position 'buttons up' and press the Move button
All readings done for buttons up.
buttons up:
a (avg:   177 |    62 |  4173)
a (dev:  3940 |  2079 |   987)
m (avg:   -34 |    57 |  -250)
m (dev:    22 |    16 |     6)



  DEVIATION TOO HIGH - PLEASE RETRY

Put the controller in the position 'buttons up' and press the Move button
All readings done for buttons up.
buttons up:
a (avg:   -41 |   358 |  4362)
a (dev:    22 |    19 |    19)
m (avg:   -29 |    77 |  -250)
m (dev:     5 |    10 |     5)

Put the controller in the position 'buttons down' and press the Move button
All readings done for buttons down.
buttons down:
a (avg:  -128 |   422 | -4343)
a (dev:    28 |    21 |    25)
m (avg:   -61 |    84 |  -515)
m (dev:     5 |    10 |     7)

Put the controller in the position 'buttons left' and press the Move button
All readings done for buttons left.
buttons left:
a (avg:  4252 |   188 |    63)
a (dev:    38 |    41 |    49)
m (avg:    96 |    76 |  -392)
m (dev:     4 |    13 |     8)

Put the controller in the position 'buttons right' and press the Move button
All readings done for buttons right.
buttons right:
a (avg: -4458 |   338 |   -82)
a (dev:    26 |    24 |    35)
m (avg:  -187 |    85 |  -369)
m (dev:     5 |    13 |     6)

Now that we have done a calibration run, we need a tool to display the results (also, we need a tool that reads the data from USB and stores it): Enter "dump_calibration". This tool will read and persist all calibration blobs of connected USB controllers (the "calibrate" tool will only store custom calibration, and only for Bluetooth controllers). When run with a Bluetooth controller (and again assuming that you have already done the USB fetching part), you can get output like this:

~S/psmove/psmoveapi% build/dump_calibration 
File: /Users/thp/.psmoveapi/04_76_6e_XX_XX_XX.calibration.txt
Flags: 3
Have USB calibration:
10 00 67 07 4f 7f a4 7f c2 90 68 6e 25 80 05 80
60 7f 10 80 bf 6e 75 90 c6 7f c5 7f c1 7f bb 90
33 80 47 7f c7 6e 90 7f d2 08 db 7f 57 80 47 80
d7 07 d2 7f 58 80 4b 80 00 00 00 00 00 00 00 00
00 01 ce 08 e0 01 04 97 53 80 5b 80 e0 01 cc 7f
7b 90 39 80 e0 01 dd 7f 4d 80 64 94 f4 07 d1 d7
12 41 72 fc d0 c0 c9 3e 0d c2 a4 1c 6f 3f a9 90
7b 3f 37 5c 71 3f 02 1d 32 3f 87 69 a1 3d 00 00
00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
# Orientation #0: ( -177 |   -92 |  4290)
# Orientation #1: (-4504 |    37 |     5)
# Orientation #2: ( -160 |    16 | -4417)
# Orientation #3: ( 4213 |   -58 |   -59)
# Orientation #4: (  -63 |  4283 |    51)
# Orientation #5: ( -185 | -4409 |  -112)
# Gyro X, 80 rpm: ( 5892 |    83 |    91)
# Gyro Y, 80 rpm: (  -52 |  4219 |    57)
# Gyro Z, 80 rpm: (  -35 |    77 |  5220)
# byte at 0x3F: 00

Have custom calibration:
         ax         ay         az         mx         my         mz
#0:       1.27    4359.10     187.74       2.04      -8.18    -421.33 
#1:    -164.57   -4378.57    -112.98     -69.21     286.53    -435.20 
#2:     -41.38     358.21    4361.73     -28.52      77.03    -249.96 
#3:    -127.78     421.94   -4342.93     -61.33      83.87    -514.74 
#4:    4251.81     187.99      62.83      95.57      75.67    -391.71 
#5:   -4458.25     338.40     -81.67    -187.27      85.35    -369.02 

This calibration file can be used by the new PSMoveCalibration API that wraps a PSMove object and provides calibration features on top of it. The function that users will probably use most is psmove_calibration_map() - it takes as input 3, 6 or 9 integer values and converts them into corresponding float values that have been normalized.

With the tumble test ("custom calibration"), we only get values for the accelerometer and magnetometer - for calibrating the gyro, we would need to have access to a turntable and control its speed - something that's not impossible to do, but very hard. Thanks to the research done by other MoveOnPC people, we can extract the information from the USB calibration blob - it stores the expected readings for 80 rotations/minute (according to the wiki page).

You can find the new code on github.com/thp/psmoveapi - expect some rough edges and more updates in the coming days and weeks :)