Sensors

From PaparazziUAV
Revision as of 08:55, 9 August 2007 by Ghattenb (talk | contribs) (instruction to modify the vertical fma sensor)

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Infrared Sensors

Paparazzi x-y IR sensor board

The paparazzi autopilot uses infrared thermopiles for primary attitude sensing. The theory is that at zero bank or pitch angle, the difference in the heat between the two sensors should be zero, and at 90 degrees it should be maximum. From this relationship a linear regression is made and angles are calculated during flight. Each pair of sensors measures one axis, a minimum of 2 pairs must be used to measure pitch and roll but best results are obtained thru the use of a 3rd pair on the vertical axis. Since the output signal from each sensor pair is proportional to both the attitude and the weather/terrain, systems with only x-y sensors require a ground calibration and may not provide accurate angle calculations as the aircraft travels over terrain with different IR radiation.

Architecture

IR Sensor Board Architecture.jpg

Dual Axis Board Pinout

Component Side View


Single Axis Board Pinout

Component Side View


Below is a product designed by FMA Direct and is a replacement for their Flight Stabilization system. With a simple resistor swap, this module is suitable for use in the Paparazzi UAV.

CPD4SENUNIT

FMA Direct CoPilot Sensor Head

Fmairsensor.jpg

IR Sensor Board Bottom
IR Sensor Board Top

Stock FMA Components

The stock FMA resistors R2/R3 and R5/R6 (0.8 Mohm/510 ohm) set the op amp gain to approximately 1600. Since this unit is designed to run on 5V and we are running it on 3.3V, it is advised to change R3 and R6 from 510 ohm to 1K ohm for an approximate gain of approximately 800. Without the change, it is theoretically possible to overdrive the Op Amp in extreme hot regions/seasons.

Another resistor swap option for this board is to replace R2 and R5 with 560 Kohm resistors, generating an output gain of approximately 1100; a gain which is practically identical to that of the Paparazzi board.

R1 200 ohm
R2 0.8 Mohm
R3 510 ohm
R4 200 ohm
R5 0.8 Mohm
R6 510 ohm
R7 600 ohm
R8 600 ohm
C1 0.026 uF
C2 0.026 uF
C3 0.026 uF
C4 0.026 uF
C5 0.01 uF
C6 0.026 uF

FMA Direct Vertical Sensor

Fmavertsensor.gif

IR Vertical Sensor Board Bottom
IR Vertical Sensor Board Top

The same operation can be done with the vertical sensor (single axis). The resistor R3 should be changed from a 510 ohm to a 1K ohm.


Inertial Measurement

Work is underway to create a complete 17 state Kalman filtered inertial navigation solution! Watch the demonstration video of the current 7-state system.

The IMU features the following hardware:

  • Analog Devices AXDRS150 5V 150 deg/s gyros (top left)
  • MMA7260 3-axis 1.5 - 6g accelerometer (center left)
  • 3.3V LDO regulator (lower left)
  • Micromag 3-axis SPI magnetometer (right)
  • MAX1167 Multichannel, 16-Bit, 200ksps Analog-to-Digital Converter (below Micromag)
  • LPC2148 ARM7 microcontroller (below Micromag)