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Old Jul 02, 2015, 04:15 PM
RoanokeJim is offline
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Joined Jul 2015
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Build Log
Dual Operator: S900-Lightbridge-T14SG

Greetings fellow inmates. I was recently asked to help make a recalcitrant S900 fly. I have never done this before and I don't own any multicopters. What I do have is a special set of skill... oh wait, all I have is one of those little double rotor mini-copter things you fly into your television screen and it leaves a mark. Despite the plethora of advice available online, I was able to get an S900/HD-3D/GH4 to fly using a dual Pilot/Cameraman setup on Futaba T14SG controllers, Lightbridge, and an A2 flight control system. This is the condensed version my personal hel... of our quest for flight! Also, combining both pilot/camera operations on a single T14SG is mentioned in passing.

For the record, the major components are:
DJI S900 hexarotor
Full DJI A2 flight control suite
DJI Lightbridge air and ground systems
Futaba T14SG flight controllers for pilot and cameraman

The stuff incidental to this presentation:
Any HDMI monitor that is compatible with Lightbridge for viewing real time video and flight parameters
Any gimbal and camera system compatible with the S900 and Lightbridge. We used a Zenmuse HD-3D gimbal and a Lumix GH4 camera

First things first; verify your bird is assembled correctly. Double check ALL connections. If you have to be reminded of this process with aircraft, you probably should find another hobby.

Update everything. I don't care what you read, nothing will make sense if all the software is not on the same page version-wise. Bricked controllers are not the end of the world. After the software updates are finished, click on the resultant flashing warning in A2 Assistant and choose Verify to make it go away. Make sure you have good wi-fi or internet access to your PC when updating. There is a lot of RF interference with the bird up and running. Need good Intertubes to keep hacking at the updates to take hold.

Magic Talisman
When in doubt; Reboot. Seriously. Follow your favorite path-dependent restart of everything (I turn on Camera, T14SGs, Lightbridge, S900), not just a USB plug/unplug or by cycling the bird. Reboot everything. Software up-date not showing up? Reboot everything, including the computer, and try again. A2 Assistant will not read the current A2 flight control parameters after you changed them? Reboot it all. I'm guessing registers get read from CMOS on bootup and if you don't let it rediscover the data on its own terms, lost it be, frustration reigns. Must control, fist of death! Re. Boot.

Next up; screen shots of: software versions, T14SG channel assignments (both devices), Lightbridge mapping assignments, A2 Assistant View screen and more! All leading to this story's happy conclusion; you, flying that magnificent bastard, alone, unfettered and free, and dayum, battery alarm, again!

What You Should Know
You should know how to access the Futaba T14SG menu of programming functions. Seriously. The manual is dense. Find a mentor.
You should know how to use the various Assistant software packages (free download) from the DJI support site. Specifically, the A2 Assistant for modifying the parameters of the onboard A2 flight control system on the S900, and the Lightbridge Assistant for mapping Lightbridge channel assignments.

Our A2 Assistant summary (View) screen is reproduced below. Notice the IMU and GPS location data. I assume you have balanced the Bird around the three opposing rotor arms. This places the center of mass along a line drawn vertically through the center of the bird, straight down the GPS shaft on our installation. The third coordinate (Z axis) is located along this line. The mass of the battery, camera, and gimbal, on our installation, pulls the CG down to about the center of the battery pack. This is the elusive “Center of Gravity (CG)” (0, 0, 0).

The IMU, positioned on the lower structural plate of the S900 appears as (-9cm, 0, -7cm), behind and up from the the CG in the A2's coordinate system (consult the screen in the A2 Assistant for the coordinate reference). The GPS ends up at (0, 0, -28cm), directly above the CG.

Insert A2 Assistant View Screenshot here

Here is the software version lineup in our A2 flight controller (from A2 Assistant).

Insert A2 Flight Control Software Versions Screenshot here

Here are the A2 flight control mappings. Notice only flight controls show mapped. This will be come clear in a moment. The A2 is used only for flight control. The onboard A2 radio transceiver and the A2 gimbal control features are not used when Lightbridge is present and active. The A2 internal comms unit is disabled when you plug the D-BUS cable from the Lightbridge onboard transceiver into the X2 port on the A2 Flight Control unit. We also don't use the A2 gimbal control stuff either. Bad boys, bad buoys!
Warning: Leave the unused A2 radio antennas plugged into the A2 unit. If you accidentally activate it without an antenna load, baaaaaad things (I'm told) will happen to your A2. Don't risk it.

Insert A2 Channel Assignments Screenshot here

Lightbridge Air Station software versions (from Lightbridge Assistant plugged into LB Air Unit). Some times it will read from the ground unit. Sometimes.

Insert Lightbridge Air System Software Versions Screenshot here

Lightbridge Ground Station software versions (from Lightbridge Assistant plugged into LB Ground Unit).

Insert Lightbridge Ground System Software Versions Screenshot here

Before we go further, let's look at this from a systems point of view. There are three systems, three!: (1) the Ground System (GS) consisting of two Futaba T14SG controllers plugged into the Futaba Training Cable for use with; (2) Lightbridge (LB) the communications system that manages two-way digital data transfer between the GS and the (3) Air System (AS), which is everything up there flying around and taking pictures.

Ground Control to Major Tom
Configured as we have them, the Futaba T14SG controllers will give you up to twelve data channels you can signal over using the various buttons, sliders and joysticks built-in. Five are pretty much reserved for the Pilot; 1-4 and U (which is usually assigned channel 7). Use the menu buttons on the Futaba controller to match (map) a switch to a particular signal you want to send over the LB comm link. You should know how to program your T14SG controller before you go any further. No more warnings.

Controller Settings
Below is the Pilot T14SG setting list. Always start with both T14SG controller's power switched to off. Plug the Training Cable into the Operator T14SG, then the Pilot T14SG. The act of plugging the Training Cable into the back of a T14SG turns the device on and disables the internal RF transmitter/receiver that would have been used to communicate with the A2's onboard transceiver, which was disabled, remember?; 'cuz Lightbridge? With LB in the loop, T14SG communications go over the Training Cable to the the LB GS and thence to the LB AS on the bird (I finally got to use thence in a sentence.)

Insert Futaba T14SG PILOT Controller Settings Screenshot here

Notice in the spreadsheet above that the TRAINER columns have non-zero entries. More on that in a second. The Futaba T14SG Training Cable protocol requires one controller as Master and the other as Student. That relationship be decided by where the controller appears on the two available Training Cable plugs. Setup the two controllers as Student (Operator) plugged into Master (Pilot) and then Lightbridge ground station.

On the Master controller you get to choose which channels from the Student controller are allowed through the Training Cable to the bird. Looking at the spreadsheet above, follow the TRAINER channel with a non-zero entry across to the left and you get the Student channel being let through. To the right is the Master channel it is mapped to. The Master controller has this power. It's good to be King. I was never able to get partial or scalar control over the Student signal, so the four functions we have chosen to pass through are disabled on the Master with 100% pass-through of signal from the Student to the LB signal stream. Also, when the Student controller is not plugged into the Training Cable, like with Single Pilot/Operator, the TRAINER function is disabled (Remember this Padewon).

Below is the Camera Operator T14SG setting list. Here we usurp the function of the primary flight control sticks to control the camera gimbal TILT and PAN and assign two switches for Shutter and Norm/C.lock/H.lock. Note to self: Remember to tell them to begin programming the respective T14SG channels from the bottom up, 'cuz it resets in mysterious ways if you do it otherwise. Plays like whacka-mole.

Insert Futaba T14SG OPERATOR Controller Settings Screenshot here

I really don't want to get into ENDPOINT settings on the Futaba controller here. Suffice to say that when you play with your switch and watch the little marker move in the A2 Assistant mappings screen, you can control the extent to which the little bugger moves in the A2 Assistant using the T14SG setup menus. Useful, say, when you want to get that pesky MODE switch to fall into those narrow bands...

DJI A2 flight controllers have an onboard, and more importantly, not-turned-off when you plug a D-BUS transceiver (like LB) into the A2 X2 port, automatic fail-safe system that you setup in A2 Assistant. FAILSAFE settings in the T14SG controller are unnecessary. Trust me. The 20m minimum return height is scary, so be careful.

Back to our Systems chat
The control signals you enter into the T14SGs flow through the Training Cable to the LB GS, thence through the aether to the LB AS, and then, and then, AND THEN!, they split. Go figure. The flight control information runs back and forth from the LB AS over a cable to the A2 X2 D-BUS port where the A2 works it. The gimbal and camera control information flows back and forth from the LB AS over a cable plugged into the gimbal, where everything goes swimmingly. Not getting into gimbal setup. Just update the software and keep it sane.

You have some control over how information is mapped in Lightbridge. Lightbridge "sees" the bird at one end, and both controllers at the other end of its two ended communication stream. LB works to match the controller signal-channels with the corresponding signal-channels on the bird to reflect the A2 flight control and Zenmuse gimbal programming. Think of LB as a more proficient third party translator between the bird and the controllers, and it gets you 16chs too! The Futabas are only 12ch individually!

Here are the channels available to LB on the bird. Look at some of those high numbered channel mappings from a 12ch system. Very suspicious.

Insert Lightbridge Channel Mappings Screenshot here

Here's why!
In the LB channel mapping function (not the screen below, sorry), LB can "see" the physical channels of both the Pilot and Operator T14SG controllers. You use LB Assistant to map the respective controller channels to the corresponding flight and gimbal control channels on the bird.

Insert Lightbridge Channel Map for Futaba T14SG Controller here

Remember "Remember Padewon?" When you choose to not plug the Student controller into the Training Cable, the TRAINER function is disabled in the Pilot controller. Camera and gimbal control are then mapped on the Pilot T14SG as per the spreadsheet for Pilot alone.

HOWEVER, LB still "sees" the old high numbered mapping for gimbal control from when the Student was connected. You need to change this mapping in LB Assistant; remapping the requisite Pilot control signals in Lightbridge to the functions on the bird previously controlled by the Student controller.

Remember to reboot everything, including the PC, and reset the LB AS transceiver for good measure. Do this a lot during this process, especially the updating.

The end. I hate Multicopters now.
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