Lighting – CAD Model

The lights in our newly designed submersible will hopefully look much nicer than previously. Our previous lighting solution was a little ugly and didn't work well in practice. The problem we had faced was fitting the LEDs, three cameras, and all the mounts inside of a 4" diameter PVC pipe. The switch to a 5" cuboid makes mounting the lights much easier. It not only gives us much more room, but also makes for an easier mounting surface.

Below are the three major iterations that the new sub's lighting design went through. The last design is the one we decided to use.

Version 2.1

Our first idea was to mount the lights on strips across the top and bottom using acrylic and aluminum.

LED Slabs

The problems with this idea were numerous. It limited the space for the camera and greatly diminished the angle of illumination from the LEDs. It also increased the coefficient of drag when moving forward because flat plates are much worse than either domes or cylinders. Having three lights in one packages also made each of the light slabs $100 which would make replacement costly. The only pro was the ease of production. After weighing the pros and cons we felt there was enough reason to revamp the design.

Version 2.2

After discussing a few other ideas we settled on this design. This design (pictured below) incorporates the LEDs and heat-sinks into the form factor of the sub. This gives us all of the function of the previous design, while illuminating much more space.

LED Heat-sinks w/ LEDs

We decided on grouping the LEDs across from one another. We have one set of lights centered, two sets aimed downwards, and one set aimed upwards. The decision on the placement of the LEDs stemmed from three places. The first is that we wanted to have at least one set looking almost directly forward to ensure enough light for navigation. The second was that we wanted to save some money and have 8 and not 10 total LEDs. Thirdly, due to the last two constraints, we decided to have two sets facing down and only one facing up because we expect users to spend more time looking down at the sea floor rather than the surface of the water.

We then had to create a case for the LEDs. Our first idea was to mount them directly to the heatsink with epoxy so that they would be completely waterproof. Unfortunately this solution is not very good for replacing burnt out LEDs, as we would have to replace both good and bad LEDs as well as the entire heat-sink.

Our solution was to make a separate case for each LED. The first case design had four sides closed by a 3D printed piece of plastic. The fith side we left open and the  sixth side will be made from a 1/16" piece of aluminum to give us a larger area of contact between the LED and the curved heat-sinks. An important aspect to this design was a 12mmx12mm PCB for our high power LEDs. This small PCB allowed us to make the cases small, but we still ran into problems. If you'd like to read more about our small PCB adventure read this post.

We went through a few different version of the small 3D printed case. Below is the old design we used to test the printer accuracy with:

Old 3D Printed Case (4 sides)

Entire LED Module (old)

We then moved onto the real print, only changing few parts of the case. The changes we made were closing the 5th edge of the case and curving the mounting edge to better fit the form factor of the aluminum heat-sink. The light, however, fits the same into the case.

Updated LED Case

Although this design is effective, it is costly and time consuming. We have to buy 8 LEDs are re-solder them onto the correct size PCB.  The aluminum is also expensive and time consuming to make. Therefore we decided to work on a third and final light design. 

Version 2.3

Our third design uses only 4 LEDs and takes advantage of the rotation of the camera by mounting to the same servo as the camera. We originally decided to stay away from this type of light setup because of the reflection back into the camera, but when using bent polycarbonate the light is not reflected back into the camera (this has been tested empirically). We also kept the LEDs on the star PCBs they come on, sinking them into a piece of aluminum (in the future we will buy the individual LEDs, but as we said in this post, it wasn't an option this summer). Below is an image of an LED module. 

LED Array

We then mounted the array above on either side of the camera using 3M bolts (refer to this post for color scheme).

Lights Straddling Cam

This is the design we finally settled on. Not only does it provide ample light for our camera, but it allows us to minimize the size and cost of our system. By allowing the lights to rotate with the camera we keep our illumination at a maximum while keeping our design simple. Stay tuned to find out how the building of this section goes!