ImuCalibration/Gyroscopes

Pictures

• 

  Turntable rig

• 

  IMU cradle view 1.0

• 

  IMU cradle view 1.1

• 

  Encoder mount base

• 

  Olimex LPC H2148

• 

  Omron rotary encoder

Components

• audio-technica AT-LP120_USB Direct Drive Professional Turntable
• Olimex LPC H2148
• Omron rotary encoder
• Lisa/L+IMU, Xbee 2.4Ghz modem set, fibreglass mounting plates and general wiring components
• Encoder mount hoop - engineering shop?

Wiring

Encoder to LPC

• Black (common) to EXT2 GND

• Red 5~12 VDC to EXT2 Vin(5v)

• White OUTA to EXT1 PO.22

LPC to LPC

• EXT2 3.3v to EXT1 PO.22 (pull up resistor)

LPC Code Modifications

In case of USB 2.0 A-B cable operation, ~/conf/airframes/Poine/turntable.xml has to be amended, as follows, and saved as ~/turntable_dev_usb.xml:

File: conf/airframes/Poine/turntable_dev_usb.xml

main.CFLAGS += -DUSE_USB_SERIAL main.srcs += $(SRC_ARCH)/usb_ser_hw.c main.srcs += $(SRC_ARCH)/lpcusb/usbhw_lpc.c $(SRC_ARCH)/lpcusb/usbinit.c main.srcs += $(SRC_ARCH)/lpcusb/usbcontrol.c $(SRC_ARCH)/lpcusb/usbstdreq.c main.CFLAGS += -DDOWNLINK -DDOWNLINK_TRANSPORT=PprzTransport -DDOWNLINK_DEVICE=UsbS #main.CFLAGS += -DUSE_UART0 -DUART0_BAUD=B115200 #main.srcs += mcu_periph/uart.c #main.srcs += $(SRC_ARCH)/mcu_periph/uart_arch.c #main.CFLAGS += -DDOWNLINK -DDOWNLINK_TRANSPORT=PprzTransport -DDOWNLINK_DEVICE=Uart0 main.srcs += subsystems/datalink/downlink.c subsystems/datalink/pprz_transport.c #main.CFLAGS += -DMB_TACHO #main.srcs += $(MB)/mb_tacho.c </makefile> </airframe>

A new turntable session has to be added to ~/conf/control_panel.xml:

File: conf/control_panel.xml

<session name="Flight with USB-serial_TT modem"> <program name="Data Link"> <arg flag="-d" constant="/dev/ttyACM0"/> <arg flag="-nouplink" constant=""/> <arg flag="-s" constant="115200"/> </program> <program name="Server"/> <program name="GCS"/> </session>

A new aircraft (A/C) named "TT" has to be built using the paparazzi centre:

File: conf/conf.xml

<aircraft name="TT" ac_id="3" airframe="airframes/Poine/turntable_dev_usb.xml" radio="radios/cockpitSX.xml" telemetry="telemetry/default_rotorcraft.xml" flight_plan="flight_plans/dummy.xml" settings=" settings/rotorcraft_basic.xml" gui_color="blue" /> <aircraft

IMU Code Modifications

Similar files have to be created for the IMU cradle unit:

File: conf/control_panel.xml

<session name="Flight USB-serial_TT @57600"> <program name="Data Link"> <arg flag="-d" constant="/dev/ttyUSB0"/> <arg flag="-s" constant="57600"/> </program> </session>

The airframe is a standard rotorcraft file with the appropriate IMU defined.

File: conf/conf.xml

<aircraft name="TTIMU" ac_id="4" airframe="airframes/Audax/slh_lisa_mkk_i2c_indoor_tt_asp1.0.xml" radio="radios/cockpitSX.xml" telemetry="telemetry/default_rotorcraft.xml" flight_plan="flight_plans/rotorcraft_basic.xml" settings=" settings/rotorcraft_basic.xml" gui_color="blue" /> <aircraft

Encoder Code Modifications

Line 43 in ~/sw/airborne/firmwares/motor_bench/main_turntable.c has to be amended to reflect the encoder's factory pulses per revolution (P/R) setting from default "#define NB_STEP 256". The encoder above has a factory resolution set at "300" (P/R). The resolution setting has to reflect turntable velocity message outputs of ~200deg/s (3.49065rad/s) and ~270deg/s (4.71239rad/s) for 33rpm and 45rpm respectively.

File: sw/airborne/firmwares/motor_bench/main_turntable.c

#define NB_STEP 300

Data Collection Setup

In Paparazzi Centre:

• Build A/C "TT" using "main" target and the USB A-B lead detached from PC.
• Attach USB A-B lead to both LPC & PC and upload code.
• Start "Flight with USB-serial_TT modem" "Session".
• Open default "Message" box and "Real-time Plotter" from the "Tools" menu. Choose "IMU_TURNTABLE" readout.
• Switch to A/C "TTIMU" in same "Paparazzi Centre" window. Build and upload code.
• Start "Flight USB-serial_TT @57600" "Session".
• In original "GCS" window change "Telemetry" to "raw_sensors".
• Open a new "Message" box and choose "IMU_GYRO_RAW" readout.
• Arrange placement of IMU cradle, for the chosen axis (p, q, r), on the side which reports the highest or positive reading.
• Start turntable @ 33rpm and drag "IMU_TURNTABLE" data from "Message" box to "Real-time Plotter".
• Restart "Server" 1 second before a full minute readout and record for four minutes.
• Halt "Data Link" for both A/Cs "TT" and "TTIMU" and change turntable speed to 45rpm.
• Restart - click both "Data Link" boxes and record for a further four minutes.
• Stop "Server".

Data Analysis

• The captured turntable velocity and gyro axis data can be found date and time stamped at:

File: var/logs/xx_xx_xx__xx_xx_xx.data

~/var/logs/12_06_05__18_11_00.data

• Right click the file and open with "LibreOfficeCalc". Click column D and elect "Sort Ascending".
• Choose "Extend selection" box. Note the time stamps of the IMU_TURNTABLE outlier data in column A.
• Insert them in the search box of a separate open editor version of the log file and delete the offending prints.
• Save the file and run the following:

File: ~/paparazzi/sw/tools/calibration$

./calibrate_gyro.py --id 4 --tt_id 3 --axis r /home/stephen/paparazzi/var/logs/12_06_05__18_11_00.data Linear regression using stats.linregress regression: a=824.56 b=16.03, std error= 0.048 <define name="GYRO_X_NEUTRAL" value="16"/> <define name="GYRO_X_SENS" value="4.967519" integer="16"/>

• These accompanying plots are also generated: