Choosing a Camera

For the last few week we have been trying to make a final decision about what will be in the dome of the submersible, especially which cameras we will use. Originally we just had two pi cameras on a rod so they could be tilted up and down.

We then moved on to have the LEDs inside the submersible, putting them in between the two cameras. This worked well while we were planning on a 6" diameter submersible as the pi cameras were small enough, but once we changed to a 4" it didn't fit well.

Vertical LEDs between cameras

Thirdly we decided to have either two pi camera's or two webcams and no LEDs. The pi cameras fit more easily but didn't stream as nicely, so we thought about using webcams. Because most webcams are fairly long in one dimension they were going to have to stand up and would take most of the room. We then decided to buy a nice webcam and see how it fit. When it arrived we found that it was much bigger than the other (being about 3.25" long).

LED modules with two Pi-Cameras

With the new cameras and the decision to try and move the LEDs back inside the dome with the cameras we changed our plan entirely. We decided to have one nice webcam for streaming video, and having two pi cameras on board to do stereoscopic vision.

3 Cameras with LED strip

Another factor in choosing our cameras has been the video quality. After testing various different streaming methods (all can be found here) we settled on using a combination of cameras. For the live video feed we settled on using MJPG-Streamer on the BeagleBone with Logitech's C920. For the stereoscopic vision we decided to use two Raspi-Cameras. Both can be seen in the CAD images above (RPi are the small square ones, the C920 is the long one). While driving, the user will only be using the C920. The RPi cameras will only be used to take images and record video (and are specifically placed where they are for stereoscopic vision. An image of the C920 out of it's case is below:

MJPG-Streamer was chosen out of the various different streaming methods (GStreamer, Motion, FFMPEG, MPlayer w/ Netcat) because of its speed and compatibility. Not only can it handle 30 fps, but the stream can be picked up by OpenCV running on the OCU.

The last step with the cameras was potting them. We 3-D printed boxes for the cameras to fit inside of, as well as a place for a rod to go through the system so it could be tilted. The picture below is of the cameras epoxied into their boxes, and below that is a CAD model of the entire system in place.