Hi Tom,

thank you for your quick response. what i am trying to do is to implement an external GPS onto APM2 via the I2C port that locates closet to the on-board GPS. the reason for this is because the ext. GPS i have only takes 3.3V or else it fries. And the existing ext. GPS port that is closer to the SD card exerting 5V to the port.

due to the lack of EM406 connector i am not able to use the port directly which force me to the idea of using the group of 4 pin holes that is right next to/behind it. I use the multimeter to check the voltage at the holes behind these ports and found them to have the same voltage as their respected VIN.i powered it up and it seems to work except i dont know where to obtain the data.  on the DIY site with the manual, i am able to disconnect the on-board GPS but i failed to tell APM2 that the new GPS is at the I2C port not the GPS port. do you know what i can do?  is there any different between using TX/RX and SCL SDA to transfer GPS data?

Tom--

I Googled Z-Boat and the pics look like a full sized boat!  My Q-Boat is maybe 6 ft. long and carries no passengers.  Right now it maneuvers via Radio Control.  I think I've decided on the ArduRover APM 2.5, but I'm a bit concerned about the Ublox LEA-6 GPS.  If I read the specs right, its accuracy is +/- 2.5 meters.  That's quite an area.  Anyway, next step is to order the hardware and get started. 

Tom--

I received my APM2.5 with LEAS-6 today.  Problem:  No manual, user or otherwise, and I can't find it on 3DR.  I've seen references to it, and really need something in-depth so I know where to go, what to do to get this boat running.  My major burning question is, what kind of signal does the RC/Autopilot input require?  My only spare FUTABA channel is from the "B" switch, which changes the 70Hz pulses from 1ms to 2ms width.  Does the APM2.5 recognize that, or is a solid level required?  Lotsa questions here!!

Doug, all the APM manuals are linked in the product listing.

Tom--

I'm learning a lot about my system setup and about the APM2.5!  The receiver (Futaba FP-R138DP PCM1024) uses only 3 channels, 2 thru 4.  As I mentioned, #5 is connected to the B switch.  #2 is the Elevator & 3 is the Throttle.  These are connected to a ROBOTEQ AX1500 Dual Channel Digital Motor Controller.  #4 runs directly to the Rudder.  This may help you with your twin screws.  Apparently, the AX1500 is programmed so the right screw is controlled by the Elevator (the right joystick), and the left screw is controlled by the throttle (left joystick).  I tried to communicate with it via RS232 Com1, but there were comm errors.  I'll try again.  I don't think I'll need the 3-position switch (G), since I need only 2 modes.

I'm assuming that in RC mode, the APM2.5 passes signals straight thru to the outputs, but in Autopilot mode, the outputs are controlled by the waypoint programming.  I'm gonna need to buy some servo extension cables for connecting receiver outputs to the APM2.5.  Also, since the receiver & ROBOTEQ are in a box inside the boat, I'll need an extension for the GPS unit since it has to see the sky from the deck of the boat.

Chris Anderson left a comment that the manuals are linked in the Product Listing.  What I've seen there isn't quite enough.  What are the Eagle Files?  I downloaded them (2) but don't have an app to open them.

Tom--

Last Friday I connected my APM 2.5 to my laptop and oggled the flashing lights!  The APM came to life.  Using Mission Planner, I looked thru a list of parameters & commands.  Mission Planner now has an ArduRover configuration, with some new commands.  Now I need to reprogram one channel to operate the Right Throttle, which comes from the RX channel 2 (normally Elevator).  Intuitively, any APM channel can be reprogrammed to do that by copying the code from APM channel 2.  APM 3 is the Elevator chanel, but I don't think that must be used; there are optional channels that might be easier to program.  But what is used to change programming in the APM channels, Arduino, Flip, what?  And where can I find the individual channel coding (I assume it's in C or C++)?  One final question:  What is Git???  Thanks for your help.  I feel a bit lost and need a clear roadmap.