Sunny vs. Cloudy

A few things were accomplished this past week. Firstly, AMOS set a couple of new single-outing distance records. On May 23, it traveled 5.35 km in 1 hour and 12 minutes, going back and forth on my usual Woolastook GPS course:

The day started off well weather-wise, but quickly became overcast, and at the 1 hour 12 minute mark, the battery gave out. I'm not certain that it was completely charged prior to the test though.

Today the weather was nice and sunny, and AMOS got a new distance record of 6.12 km on the same course, before I noticed that the screws were loose on the propeller mount causing it to bang around like crazy inside the cage. I'll need to find a more secure way of fastening the screws; perhaps use Loctite or something. For this second test, AMOS was a bit slower; possibly because the weather was a bit windier, but also because I had accidentally sheared off a plastic clip on the side of the boat when loading it into the van, causing a long plastic piece of conduit holding some wires to periodically dip into the water, producing drag. It was encouraging to notice after this second test that the battery voltage (when not running) was the same 13.2 V that it was before the test. Since voltage was recorded every minute in the ship log, I was able to plot a comparison of the voltage levels for the cloudy vs. sunny tests:

As can be seen from the above graph, the fall-off in voltage under high load can be pretty steep if the sun isn't around to keep the battery charged up. At present the software in AMOS is not making any decisions based on voltage, but probably there should be something to put the boat into a low-power state once the voltage gets down to ~ 11 V.

The other big accomplishment this week was that I finally got serial wireless communications from the Android phone (or PC) to Bluetooth (or a USB serial cable) to the RFU220 transmitter to AMOS and back again working much faster, so that it is now actually feasible to download a small image file from the boat. This actually required a few weeks to get right, and up until a few days ago I was semi-convinced that there must have been serious hardware problems impeding correct communications. But the issues were all software. Once the timeouts, flushing, buffering, etc. were finally set properly it just worked. 😸

Edit: Here are the pictures of the screws (indicated by thin red arrows) that came loose:

The stainless steel M3 screw in the top picture is used to hold down the arm mechanism for the servo motor that controls the direction of the propeller. When I noticed that the two black screws were loose (lower picture) there were no screws whatsoever in the other two holes on the same mounting plate. I don't remember if I forgot to screw them in, or more likely they vibrated out at some point and were forever lost. So I'm using a couple of stainless screws now in those holes instead.