Archive for July, 2017

June Autonomous Test

Posted by Pierce Nichols on 15 July 2017

On June 11, we took the boat out for another autonomous test. We fixed the earlier issues with the rudder, so it steered more or less in the right direction. Here's what our course looked like:

2017 Jun 11 Test

2017 Jun 11 Test

The blue placemarks are the position and speed reports while the red stars are our waypoints. Our first mission of the day was to film our chase boat repeatedly approaching the test boat with the onboard 360 degree camera. This is to support our work developing optical obstacle dodging so we can let the boat out in the busy waters of the Puget Sound without a chase boat shadowing it. While I think this is the right approach, it's the wrong camera. At the point where the test boat needs to take evasive action, the chase boat is only a dozen or so pixels wide. This isn't enough to generate a good signal out of any algorithm, so we're going to take a different approach and use multiple cameras.

After we did all of our video test cases, we did a circuit of the waypoints from last time. That went well, although we did discover that we still have issues with our compass steering. There are three things wrong that caused use to make those curved courses.

  1. I forgot to add the call to the function that sets the magnetic declination. The result was a westward error of ~16 degrees
  2. The compass was installed about two degrees right of the boat centerline.
  3. There is a small heading dependent error

After that, we did a test of our virtual anchoring (the waypoint marked 'ANCHOR'). We can't really call it dynamic positioning, because we don't have that kind of control authority. The boat did its best to maintain the designated point, which is good enough for now. Once we were satisfied with that, I set it to make another circuit of the waypoints. However, shortly before reaching the third waypoint, we noticed that the boat was slowing markedly. Rather than risk a breakdown in the water, I took over manual control and brought the boat back into shore.

Looking at the data, it looks like we had a couple of problems. First, our little trolling motor is designed to propel a heavier boat at a lower speed. As a result, it's not drawing full current and we're getting less speed out of it than we would have with the right prop. Second, our batteries are nine years old (beggars can't be choosers) and are weak. The fact that we're not drawing full current covered this up until this test because it was longer and faster than our previous ones.

We were looking into buying a new set of batteries, but that would take money away from the sail demonstrator, which is closer to our real intended path. Our original battery donor offered us a new set, so that will put the power boat back in action without much in the way of money or time. However, we will probably not put it back into the water until we're ready to test the obstacle avoidance stuff we've been working on.


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