Airboat Revisited?

On Wednesday of last week I took AMOS out to Woolastook to try out the new navigation software, and see if perhaps it could collect a test sample grid of temperature and pH points in a 200 x 300 m area of the river. Unfortunately the new software for getting faster updates of the yaw angle (from the magnetometer) proved to be too noisy for the boat's simple turn function, so it would usually tend to fire the thrusters somewhat randomly trying to do a stationary turn. This function worked fine in the pool, but under real world conditions it was no good. To compound difficulties, I had also keyed in the GPS coordinates for the corners of the sampling grid incorrectly, so that the boat was always attempting to drive itself back to shore.

That night, the software was modified to use a filtered average yaw angle from the magnetometer, based on the previous second's worth of data. This restored the original functionality of the simple turn function. The coordinates of the sample grid were also fixed, and the following day, the test was re-attempted. Things started off well and AMOS proceeded into the wind towards the northwest corner of the sample grid. It then proceeded eastward to complete the first row of sampling, but started behaving quite erratically as can be seen in the GPS track shown below:

After about an hour of this, it mysteriously died. I think that possibly the software crashed, although there was no record in the ship's log file or any of the Raspberry Pi log files to indicate what might have caused the crash. The ship's log file indicated that the battery level was OK before the crash, so presumably power was not an issue. One possibility is that some wires might have shorted out inside AMOS, causing the Pi to stop running. There is some reason to suspect this, since it was discovered after the fact that the compass module had pulled out of its enclosure and was free to float around inside the boat. It was this floating compass that was responsible for the erratic navigation during the eastward sampling stage. The next day, Velcro was applied to the compass module to hold it in place within its enclosure, and a second log file was created for the shell software that starts the main AMOS program, to hopefully save the exit code if a crash occurs.

The next couple of days (Thanksgiving) were spent at Mom and Dad's cottage, wiring up the new A to D board that arrived from ControlEverything.com. It was pretty close to what I had before in terms of parts, just professionally soldered and put together, so I'm sure it will be more reliable. There were some minor software changes to make for it too... some of the configuration commands were slightly different, and I needed to do some averaging in software to achieve an 18-bit level of precision. So far it seems to be working quite well. The weather didn't cooperate for most of the weekend, but on Monday, the waves were not too bad, so I released AMOS for what was planned to be a short 1 km test. Unfortunately AMOS only went about 75 m north from the shore, and then struggled to move anywhere... eventually the wind (which was coming from the north) pushed it back to shore where I retrieved it and discovered that the thrusters had both become fouled with seaweed, the leftmost one worse than the right. Below are a picture of the thruster with the seaweed in it and the clump of seaweed by itself after I picked it out by hand:

So apparently the new propeller shield is not very effective, at least not for this common variety of seaweed. So today I spent some time googling various types of airboat designs. This one (https://www.cim.mcgill.ca/~mrl/pubs/anqixu/iros2011_boat.pdf) seemed intriguing, and indicated that a vessel of a size similar to AMOS could be driven using air propellers. I ordered some inexpensive drone equipment from Amazon (https://www.amazon.ca/dp/B07C5KYNY7/ref=pe_3034960_236394800_TE_dp_1) so once that arrives I'll attach it to AMOS and see whether or not it can actually push the boat through the water.