Just Sharing Knowledge on Robotics, Electronics and Programming

Wednesday, November 16, 2011

Global Positioning System ( GPS ) for UAV Autopilot



At the end of my project, I use a GPS with a brand Leadtek LR9805, with the following specifications


  1. SiRF chipset single StarII
  2. Compact module size for easy
  3. integration: 24 x 20 x 2.9 mm
  4. Multiple I / O pins reserved for
  5. customizing special user applications
  6. RoHS compliance

Features :

Hardware and Software

  1.    Based on the high performance features of the SiRFstarII single chipset
  2.    Compact module size for easy integration: 24x20x2.9 mm (0.94x0.79x0.11 in)
  3.    Fully automatic assembly: solder reflow assembly ready
  4.    Hardware compatible with software SiRFXTrac
  5.    Multiple I / O pins reserved for customizing special user applications
  6.    RoHS compliance
Performance
  1.    Cold / Warm / Hot Start Time: 45/38/4 sec at open sky and stationary environments
  2.    Reacquisition Time: 0.1 second
  3.    RF Metal Shield for best performance in noisy environments
  4.    Multi-path Mitigation Hardware

Interface

  1.    TTL level serial port for GPS communications interface
  2.    Protocol: NMEA-0183 / SiRF Binary (default NMEA)
  3.    Baud Rate: 4800, 9600, 19200, 38400 or 57600 bps (default 4800)
Advantages
  1.    Ideal for high volume mass production (Taping reel package)
  2.    Cost saving through elimination of RF and board to board digital connectors
  3.    Flexible and cost effective hardware design for different application needs
  4.    Secure SMD PCB mounting method
Accuracy
  1. 10 meters, 2D RMS
  2. 5 meters 2D RMS, WAAS corrected
  3. Position
  4. <5meters(50%), DGPS corrected
  5. Velocity 0.1 meters/second
  6. Accuracy
  7. Time 1 microsecond synchronized to GPS time 
General Spec
  1. Frequency  L1, 1575.42 MHz
  2. C/A code  1.023 MHz chip rate 
  3. Channels  12
  4. Update Rate : 1 Hz
but keep in mind is that the gps data update frequency of 1 Hz or 1 packet of data in 1 second, and baudrate 4800 bit / s. with updates like this could have the plane on autopilot, but I still do not dare to fly fast, there are concerns with the speed of the plane will crash.
but it seems this is not a big problem, because based on the references of some projects to others, they use the GPS 1 Hz and are still able to fly,

GPS Accuracy for this brand is 10m, but when I try and I got a very amazing accuracy, I was in position A without moving (stationary), but the device that I have though with the appearance of ground segment, I get the inaccuracies of more than 30 meters . did I test with a little cloudy conditions, and also I try to light conditions (excessive heat during the day) but the results are not much different.
I think this system should be made formula like PID to overcome this error. for the results of its testing I will soon upload a video.

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