Wednesday, November 11, 2020

SVL: Rebuilding Camera 3

Back in September, as we were gearing up for another full-blown socially-distanced ops session at Silicon Valley Lines, I quickly needed to build another camera car. I had already built a supplementary power supply for James' Dash9 dummy locomotive using a well car and a 10,000 mAh USB power bank. I wanted a self-contained camera car, so I decided to build a cradle for the second power bank I had, and mount the camera on the side of the power bank. That setup became Cam3.

This worked, and we used the car in ops sessions since. However, over time it became obvious that for some reason this car had worse wifi reception than Cam4, my original camera design. That's very curious since it's basically the same hardware ... with two exceptions: Cam4 is powered with a JuiceBoxZero connected to a Li-Ion battery, and Cam3 hugs a big hunk of metal. Side by side comparisons showed that Cam3 performed clearly worse than Cam4, even after reducing the network data requirements of the video streams as can be seen in the SVL operator training video.

After acquiring a power bank in a smaller form factor, as well as a low-profile, right-angle Micro-USB plug I was ready to replace the first design for mounting Cam3. I decided to install the PiZero horizontally, but since the USB plug is sticking out quite a bit, I mounted the PiZero on a styrene sheet and built a support structure into the well car with the PiZero mount sticking out about 1/4" on both sides of the car.  I verified with an NMRA gauge that the wider platform is still within the loading gauge. Next I built a camera mount over the board and was very satisfied with my work. Here is Cam3 on the well car next to Cam4 ...

That satisfaction lasted for about 5 minutes, when I remembered that we have a couple signal masts in Jacksonville that are mounted between the tracks and clearly this arrangement is not going to fit.

It was time for design number three, which I call "The Fin".

I rotated the camera 90 degrees, so that it stands on its side. The angled Micro USB plug is now at the top and the USB cable threaded through the support structure.

I was careful to make sure that the camera is well behind the lead truck. I needed to rotate the camera image, which is easily accomplished by passing -rot 90 to mjpg_streamer. I'd still like to find an actual low-profile Micro-USB plug. There are some variants of what I'm thinking of available from Chinese suppliers (e.g. reasonably cheap on, or very expensive on, but they all have lead times of about 4 weeks and the plugs look very finicky and prone to failure. It's probably easier, and definitely cheaper, to just solder the charging leads directly to the PiZero.

In either case, now that I liberated Cam3 from the hunk of metal, it seems to performs much more smoothly.

No comments: