@YamahaForMe -
Steve - Thanks for your input. You certainly have the correct terms where I do not and I am sure I could learn a lot from you. You are spot on with the over correction occurring. This is a result of 200 rpm steps. I assume an integrator uses a predicative model. I could certainly create a predicative model in fact by examining the actual speed curve over the last second and rate of turn I have a fairly simple one already. Of course I could bump that to 10 seconds but I think you are referring to using the observed delta and other variables over a long history of previous runs. What I think I will run into though is all of the other variables that will affect speed that would require inputs prior to a given run. These would include people weight, water ballast, fuel weight, ambient temperature, relative humidity, elevation, water temperature, skier weight, skier aggressiveness, windspeed, wind direction relative to the boat course, beer weight, and so forth.
Currently the target speed is set once the target speed is reached by the user observing the target speed from the built in boat GPS speedometer and then pressing and holding the cancel button. This means we are starting from a somewhat steady state. I am able to read in GPS speed into my micro controller every tenth of a second and it take less than a tenth of a second for it to compute wether or not to bump the rpms up or down by one or two 200 rpm steps. The boat recognizes this and reacts in less than a tenth of a second once the command is sent. So the loop delay is less than 0.2 seconds. The boat then takes time to get to it fully realized speed correction but of course the skier is still impacting that. I have also found that when manually controlling speed when towing a wakeboarder it is harder at 18 mph then at 20 mph because of the natural planning speed of the hull. This will matter when there is more chop in the water as I want 20-21 mph on glass but 18 mph when conditions are not ideal.
I really want this to work. The idea of having a one plug and done system for under 100 bucks in parts is great in theory. Perhaps it is even possible if instead of using the built in rpm steps ( I still think this is something that can't be fully accounted for without some sort of annoyance in operation) someone could figure out the commands to send directly over the engine can bus to regulate the rpms without using the cruise control steps (Not something I want to try spending the time on as I think that would be far more difficult to figure out never mind that would almost certainly void the warranty on the engine ecus and the motors). I know it is theoretically possible as the e and x series throttles are just potentiometers that send control voltages to a independent control unit that then interprets the control voltage into an command to send to the ECU (my opinion based upon the wiring diagrams and parts listings available online). The I/O on the ECU from the wiring diagrams is certainly different and possible the firmware in the ECU as well.
As previously mentioned I have no doubt that I could clone the perfect pass method to overcome the 200 rom steps but would have to fabricate the bracket system on top of figuring out a whole bunch of code and the cost of the parts would easily exceed $300. Even if I bought the brackets from perfect pass I am still looking at a boat load of time to get it all working even just using a set button without a display. Perfect Pass of course allows the user to enter a target speed prior to starting the run get the boat up to a certain rpm and then it takes over. This is better and in order to do that some method of input prior to the run would be needed such as a smartphone but a dedicated water proof lcd and a couple of buttons is better in my opinion. So in the end that is a whole lot of development time and for arguments sake lets say my time is worth only $1 a minute. Even at that rate the time alone would cost me more than just buying a system that is fully ready to go. I bought the boat to enjoy my time and while this is could be a fun project for someone I just don't want to put my time towards it anymore (1 wife, 3 teenage kids, 1 dog, 2 cats, relocating next year, etc). I need a working system by next spring and testing is out of the question with my boat shrink wrapped for the winter.
If you want to give this a try I can point you in the right direction and I bet you could get to the same point I did or further. I won't just deliver the project in its current state though as I am very timid about any perceived gain in something that is patented. This also means I won't give any explicit or implicit advice/directions when it comes to the finer details.
I really do appreciate you input Steve, and perhaps if we connected earlier on I would not be giving up on it. Perhaps we can connect on this or another project someday. Feel free to pm me if you would like to connect further.
On another topic .. I am jealous of what you do for a living and I bet you could give great advice on a lot of different questions/projects here. Granted don't need to reinvent the wheel on 12vdc but you must know your stuff.
Chris
Most control loops are PI (Proportional - Integral). The proportional gain controls how quickly your system responds and the integrator helps smooth out the error. Feedback control loops can be difficult to tune, but don't give up.
