Indoor Pool Test

(Video by Hannah Simpson)

This past weekend Hannah and I took AMOS to the After School Pool Club in Fredericton for a quick one hour test. This was the first time that the new surfboard design had been tested in the water. The pool measured 40 ft x 20 ft, so we had to be a bit careful with the driving to avoid smashing into the walls too much. Steering with the air rudder was a bit sluggish, and took some practice to get the boat moving and turning in the desired direction. Also, the coat hanger cross-piece that joined the two rudders slipped out of its mounting hole a few times, which required some manual intervention with a pair of pliers to set it back into place.

As can be seen in the short video, the boat is quite buoyant; the rockered front and back pieces don't even touch the water. Probably the boat could have been constructed from a single piece of foam insulation, rather than the double-layer that was used in this build.

After bumping into the wall at one point, wireless communications was lost, and this required a reboot and an inspection of the main compartment, which revealed that a USB power cable had slipped out slightly. After re-inserting the cable, the wireless still seemed pretty spotty for a few minutes, but then seemed to somehow magically fix itself and work well again. Not sure what happened there, I'll have to go over the ship log files to see if they offer any clues.

The difficulty with the rudder prompted a re-design of how AMOS steers. Rather than use a pair of rudders to control the direction of air flow, it was decided to just rotate the propeller itself and dispense with the rudders altogether. Today, I 3-D printed a bracket for attaching the propeller assembly to the same servo motor that was used for the rudders. The servo is fairly powerful, so should have no trouble rotating the rudder I think. The servo offers +/- 90 degrees of rotation, which should allow for tighter turns vs. what could be achieved previously with the rudders. I'll need to lengthen the power cables going to the propeller though before trying it out, to avoid straining them too much for large rotation angles.

A nice little bug was also found and fixed this week. When testing out the Boat Captain PC software, I noticed that the GPS timestamps shown on the PC screen seemed to be a few minutes off. The discrepancy was traced back to some code for reading in the streaming GPS data, which was delaying for too long in a loop, so that GPS data was not being read in as fast as it was arriving, resulting in old, buffered data being used for the "current" position. This bug has been present since almost day 1, but may have only become an issue after testing for a while (say half an hour or more). It very likely was responsible for some of the odd navigational behavior that I observed during some of last summer's tests.