Retired DOD Electronics Engineer; ex-Navy & Los Alamos Electronics Tech; current Water Utility Authority Electronics Tech (soon to retire again)
Please tell us a bit about your UAV interest
Have a Q-Boat from OCEANSCIENCE with Trimble GPS & SonarLite SONAR from OHMEX controlled by FUTABA 7CAP transmitter, FUTABA FP-R1380P 8 Channel Receiver (4 are used) & Roboteq AX1500 Digital Motor Controller. The boat has 2 screws & a rudder; used to profile the buildup of mud & silt on the bottoms of some very large settling ponds and grit basins. An autopilot would be very handy to guide the boat in a pre-programmed grid to obtain repeatable position data which is stored on-board in a Brookhouse NMEA 0183 Data Logger.
Doug-- The Z-Boat and Q-Boat are very similar from what I have gathered - size, control, mission, etc. I currently have APM2.0 with the U-blox GPS. Don't even bother with MediaTek! Haven't gotten an accuracy measurement yet but +2.5meters would be great for my purposes. I am running into the same issue with twin screws. Just to get started with autonomy I routed the port motor through throttle control and stbd through "rudder" (ch2 in Rover). So when switched to Auto, for a left turn the stbd prop turns forward and for a right turn it goes in reverse, effectively assisting the turn in either direction. Haven't been able to fully test how this plays out on the water, but it is just until I figure out how to modify the code to give unified thrust.
I can relate to your frustration - it takes a while to learn how to navigate the site with so much information. I think the best place for APM2.5 info is in the ArduPlane Manual, Setup, APM2.x. Keep in mind that ArduRover was begun as a modification to the ArduPlane code. I can't recall where I found Ublox info- you pretty much have to just keep reading and following links to find some things.
Not sure I understand your switch question. Rover (and probably other firmware versions) uses a 3-position switch to ch8 and optional 2-pos to ch7, I think. So you set up your transmitter to send output from the switch to whatever spare channel you have on your receiver and then run a cable from that receiver output to the appropriate channel on your APM. The firmware is expecting the signal at that port and knows what to do with it. In the case of the 3-pos switch it will set your "flight" mode to Manual, Auto, or whatever else it is configured for in your configuration settings. A 1.5ms pulse is neutral, 1.0 low and 2.0 high. So 1.0ms might select Auto, 1.5ms Stabilize, and 2.0ms Manual. Your B-switch being only 2-pos skips the 1.5ms position. The settings are in Planner under Configuration>Flight Modes, but they don't show up until you are connected. When I started playing with things I didn't have a 3-pos switch so I just set everything to Manual.
Yes, if you only need two modes you could probably use your B switch fine, as long as it goes to ch8 input.
You're also right about APM passing through in Manual mode. In Manual, you could use whatever channel for any function as long as the output is same as the input. Of course in Auto mode APM expects things to be on specific channels.
I left my GPS inside the box in the boat and it works fine. Saves running cables and sealing holes, etc! You should give it a try before going to the trouble of relocating it with extension cable.
I can only tell you what I have gathered. I think you will find what you need here. I have the same thoughts on the second motor. I have looked over the code myself and had a programmer friend look at it but we couldn't find anything that looked like a throttle command. Seems like it should be fairly simple once we find it. You just have to give the opposite PWM value to the second motor. I have also left a couple of posts asking for direction but no good answer yet.
At one point I thought it might have been as easy as installing a Y servo cable off APM for the throttles. That works except that the motors are counter-rotating, so one turns forward and one backward all the time! (Hence the opposite PWM value above.) Let me know when you figure it out. :)
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