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Mar 28 2012

Forest Fire Videos Captured with a Hexakopter

Here are links to two videos we collected of the forest fire we flew in early March in New Jersery.  Stephen had posted previously, post here, about our experiences getting the payload to fly on the Hexakopter, a repeat of similar work from last year.

Taking video was an afterthought for the project so we only had an SD4000 on hand for filming.  I think the video quality would have been a lot better if we had the GoPro.  Despite the wiggle and bluriness of the video, it is still possible to see the smoke lines set by the fire managers (see images at left) and there are places in the afternoon video where I think you can even see fire.  Note that these videos were taken pointing about due west, so I believe the shots from later in the day appear darker due to exposure compensation.

Video from about 12:45 - 12:55 local time: http://youtu.be/q3S3V3212bo?hd=1

Video from about 15:45 - 15:55 local time: http://youtu.be/GQHh2LX_ad8?hd=1

Aug 03 2011

Pentax WG-1 GPS camera–too slow for scanning

I loved the Pentax WG-1 GPS camera when it first arrived.  It looked cool, had a non-extending lens, and offered the potential for GPS tagging our photos during flight – a feature that could be very time-saving for reconstructions.

But out of the box I quickly noted some major drawbacks.  The first was that the GPS only updates every 15 seconds.  At the average speed of 5 m/s of a Hexakopter, that meant that GPS logs would be something like 75m apart!  The unit also has a slower continuous shooting mode than the SD4000, about 1 fps.  The biggest drawback by far though was the lag, which I can only assume is a memory write lag.

I set up the camera to the maximum image quality settings, in continuous shooting mode, and with 15 second GPS refresh.  I was using a brand new Sandisk Extreme 16GB memory card, which would provide professional grade write speeds.  I strapped down the shutter button by lightly taping a plastic nut over the button and wrapping the unit with a velcro strap, just like we do with the SD4000s.  The Pentax WG-1 would take a continuous stream of about 30 photos then stop.  It would show the ‘number of images remaining’ counting down and just hung out.  After sometimes 10-15 seconds it would then resume taking photos continuously, but then repeat the same thing after another 30 photos.  The camera was not taking photos for 10-15 seconds while in continuous shooting mode.  At a flying speed of 5 m/s that means that for 50-75 meters in the air, no pictures would be taken!

I repeated this test with increasingly lower camera settings until I got down to the lowest possible settings of maximum compression and 640x480 resolution.  This time the camera took lots more photos  (~100 or so) but still had a long lag of no photos.

It was this that finally made us decide to send the Pentax WG-1 back.

Based on my research this GPS camera has the fastest GPS refresh time of any other point and shoot style camera, but the continuous shooting ‘lag’ was a deal breaker.

Oct 29 2010

Testing the Scanning Camera

  Flashback to a couple of weeks ago- this shot was taken with the scanning camera when the Hexakopter believed that it had flown its intended route and was waiting for someone to tell it to land. While the flight itself was a disaster we did gain some valuable information from the photos it took.

  As you can see from the picture we did get some good quality photos, even though it’s mostly parking lots… However what was most concerning was that the pictures taken were not consistent in terms. You can clearly see the difference between the two pictures taken less than three minutes apart.


  What I wanted to know was why the second shot blurred, at the time of this shot the Hexakopter was hovering in the same spot for about 5 minutes with little movement. At first I thought that the vibration caused by the motors or the gyro reaction to the swinging mass had affected the shots.

  So in the lab, with Jonathan’s help, we came up with a way to test my theories. We suspended a Hexakopter from a pipe and mounted the scanning camera on the Hexakopter, in the  same fashion as the previous flight. We started by turning on the scanning camera without the Hexakopter on, in other words this was our control test. We quickly found out that the swinging motion did not cause the Hexakopter to move at all, putting some doubt on one of my theories.  After close examination of the setup in action, I noticed a small vibration occurred on the camera mount whenever the camera moved to the front or back. Noting this, we continued the test except with the Hexakopter powered and the motors on. With the motors on, the Hexakopter reacted no differently than with the motors off. We did observe a cool damping effect whenever you pushed the Hexakopter.

  After the testing was completed, I decided to take a look at the pictures that were taken by the scanning camera throughout the entire test. I found that the small vibrations from the camera moving forward did in fact cause the photos to come out blurred. In addition, I found that making the mounting the scanning camera on a more stable base reduced the vibrations, resulting in sharper images.

Much later I found out that the two above images were taken at different shutter speeds. The above left photo was taken at a shutter speed of 1/320 sec, while the one right was taken at a shutter speed of 1/100 sec. Upon checking the rest of the photos taken by the camera that day, I saw that alot of the images had varying shutter speeds. I tried to compare these photos with the ones taken in the lab and found out that the two sets were incomparable due to different lighting conditions and consequently much different shutter speeds (the lab photos were taken arround 1/60 sec).

  In the end, Jonathan found out that the scanning camera setup would still sweep back and forth without the camera attached. Using the fact that the scanning camera had inconsistent shutter speeds, he attached the Cannon SD4000 to the setup.