I got out Monday for a first flight for my digital flight control system. Overall it was a big success! The one thing I cut corners on to get out there was fully waterproofing the servo. I felt that the likelihood of a turtle capsize was low (my last one was months ago). Of course, what did I do after 90 minutes out there? Turtled the boat and killed the servo--HAHA! But still a great day with lots of learning and successes:
1) Being able to "arm" the system at the press of a button was a major convenience. When the system is "not armed" it is as if the wand is all the way up and in non-foiling mode. In the armed state, the boat will try to fly at the desired altitude set point. Sailing off the dock and around the marina where you really don't want to foil is super easy. No more swimming out to the spirit to adjust ride height! Furthermore, adjusting altitude and other parameters was easy with the key fob switch. The LCD could have been easier to read, but it worked.
2) The electronics enclosure really is waterproof! After a tough turtle recovery, the electronics survived DRY after 3-4 minutes submerged in about 12 inches of water!
3) The servo is NOT as waterproof. After the same submersion the servo continued to work for another 5-10 minutes before water ingress fried the circuit board in the servo. Thankfully these are $40 parts and available with 2-day shipping. There are lots of tutorials on how to waterproof servos. I plan on doing so prior to my next flight test.
4) Control loops need tuning. Things worked out on the water but the control loops felt like they were always behind where they should have been. I can see it in my data collected and it can be seen in the videos (below). After an hour of tuning with the wireless key fob, I was starting to get close to the performance I wanted. Thinking more about the wand if it were a PID controller (Proportional, Integral, Differential), it will have a P = infinity and I = D = 0 (yes, I know I'm ignoring the mode where the wand is just fluttering on top of the water, but let's keep this simple folks). That leads me to believe, I will need to really crank up my P constant (currently set at 9.0). I think the I and D constants will be helpful for improving performance beyond the wand, but I'd like to duplicate what I have first.
5) Epic data collection! After 90 minutes of floating and foiling I have 5MB of CSV data on heel angle, pitch angle, altitude, smoothing params, PID params, acceleration in X, Y and Z axes, battery cell voltages, etc. This data will help me tune control loops on shore. My first guess at constants was made by watching our UFO videos frame-by-frame and estimating elevation and rise/sink rates. My new data is at 20ms resolution and will give me a much better shot at getting things very close on shore before I head out next!
6) Battery life will NOT be an issue. After 1.5 hours of foiling I had better than 85% of the battery left. On prototype #2 I will definitely go with a smaller battery to cut costs and reduce size / weight). Either way, I have hard numbers on cell voltages vs. time and will accurately be able to calculate how much battery capacity will give me how much time on the water.
7) I need a hard-reset switch on the boat. The ultrasonic altimeter I am using is a cheap one from a car bumper. Occasionally it gets noisy and needs a reset. Having a way to do a full power cycle on the water short of taking the lid off the enclosure would make resetting the altimeter easier. In the long run, I will be looking for a higher reliability part for prototype 2.