Tuesday, 23 September 2014

The Camera

The choice of the camera to be used in the flight was once again preceded by examining previous HAB projects. A lot of them used the GoPro cameras and, after seeing the quality of the footage, I too would ideally liked to use one. Unfortunately, the GoPro cameras were beyond my budget. (Recently, I came across a Mobius ActionCam camera that seems to provide comparable video quality for a fraction of the GoPro's price. Definitely the one I would consider for a future flight.) So I continued looking and found a very neat solution in using a Canon camera combined with a CHDK script.Canon Hack Development Kit is a special firmware you upload to your Canon camera which allows you to control a lot more functions than the standard firmware does. Plus as a bonus, it makes using custom scripts possible.
Being decided for a Canon camera, I made a list of models that allow CHDK use and searched Aukro (a sort of a Czech version of Ebay) for an acceptable offer. Eventually, I bought a Canon A2200 with a 16GB SD card.



After familiarizing myself with the CHDK environment, I began testing the camera's battery endurance and working on my script. I wanted the camera to take both pictures and videos during the flight. I tested different combinations of video length and picture frequency and finally decided for a 1 minute long video every 11 minutes and as many pictures as possible in between. The reason is that the battery in this mode managed to power the camera for 2 hours and 40 minutes whereas in a mode with a 1 minute video every 11 minutes and just 5 photos in between, it lasted for 2 hours and 47 minutes. For comparison, taking only photos every 51 seconds, the battery managed 3 hours and 4 minutes. With such a minimal battery savings compared to a much better documentation (in the chosen mode the camera managed 16 videos and about 1300 photos in 2 hours and 40 minutes taking up 4.6GB on the SD card), the decision was simple.



The script turns off the camera's monitor as well to safe the battery, but with every shot it automatically turns on again, so the end result is a periodic switching off and on. I am not sure how much battery that might safe, but I left it in the script anyway. Just be careful when manually turning off the script, do so during the time the monitor is on, otherwise, it will stay off an you will have to restart the camera to be able to see something on it again. Here is the script I used in my flight.

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@title Rapid Balloon Final

sleep 3000
a=get_mode
print "Mode " a
sleep 3000
if a=1 then set_record 2
if a=0 then set_capture_mode 9
sleep 3000
a=get_mode
print "Changed to Mode " a
sleep 3000

b=get_capture_mode
print "Changed to Capture Mode " b
sleep 3000

rem 15 sec

for m = 1 to 1000

   set_backlight 0

   sleep 3000
   print "Loop starts"  

   set_capture_mode 9
   sleep 3000

   set_backlight 0

   b=get_capture_mode
   print "Capture Mode set to " b
   sleep 3000
  
   press "shoot_full"
   sleep 3000
   release "shoot_full"

   set_backlight 0

   sleep 60000
   click "shoot_full"
   sleep 5000

   set_backlight 0

   print "Video finished"
   sleep 5000
  
rem 82 sec - 1 min 22 sec

   set_capture_mode 2
   sleep 3000

   set_backlight 0

   b=get_capture_mode
   print "Capture Mode set to " b
   sleep 5000
  
rem nove

   t=get_tick_count
   l=t+540000

   do

   shoot

   sleep 1000
   set_backlight 0
   sleep 500

   s=get_tick_count

   until s>l

rem  konec noveho

   a=get_mode
   b=get_capture_mode
   print "Done shooting with Mode " a
   print "and Capture Mode " b
   sleep 5000

next m

set_backlight 1

print "Ending..."
sleep 3000
end

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