Saturday, October 27, 2018

Ground Station Setup For Converged IoT Platform

Antenna Cluster Planning

The mission scenario sketch is in the following picture. The small matchbox at the lower left corner is the base station. The modeling is made in Blender. And, based on the mission scenario, the transmitter/FPV antennas are arranged without internal interference or obscuring/blocking signal line of sight.

Antenna/Transmitter/Receiver Setup

FrSky R9M 900mhz Long Range module is chosen as a substitute of TBS micro module to save modification in the QX7 transmitter itself. 10-pin, 1-meter ribbon cable connects TX pins to module. Breadboard jumpers tethers the module. The USB extension cable connects car cigarette power, and a retractable USB-micro cable connects the power to the FPV receiver.

The Hyper Tough cigarette power plug is specifically chosen because it has very tight fitting to fix a suspected cause of crash of pilot's knee knocking the plug during flight.

In the following picture montage, from the top right picture, clockwise, the soft, retractable USB-micro cable is wedged behind the sun shield board. 2 large paper clips are bent and coil to form hooks to hang the TX and the FPV goggles when all cables are hooked up pre-flight. The cigarette plug and USB extension cable are duct taped on the lower peddle firewall and out on to the chassis column. The USB extension cable and USB-micro cables are installed into the chassis column.

The FPV receiver based on the RX 5808 chipset is chosen because experiments on the FXT Triversity receiver had video "blueouts". The real fault point, including all previous blackouts, is the FXT Triversity receiver, not the FPV goggles.

The 3/4 inch velcro strip wraps around the lower corner LED as an anchor, then  goes over the bottom side of the receiver and up. The antenna plugs make a natural tilt angle for the velcro strip to slide down on the RF cavity cover. The video output pin 6 is soldered to the AV yellow cable for video on the PCB. The tail end of the AV cable and the row of pins are encased together by the clear mounting tape. The head end of the AV cable goes toward FPV goggles.

The right angle SMA adapter for the mushroom antenna needs to reverse the polarity with the inner core pin stem on both sides because both the mushroom antenna and the receiver side has the inner core pin hole. The patch antenna with 9.4dBi is the directional antenna projecting the craft's diving trajectory. The 45 degree SMA adapter is essential in making the near vertical radiation pattern.

The receiver antennas allow quick release folding. Just loosen up the lower antenna's 90 angle connector with 5-6 counter-clockwise twists, then fold the upper antenna backward 90 degrees and fold the the lower antenna backward 180 degrees.

The worst case noise interfering with FPV feed is with 12-16V power supply to the Caddx Turtle cameras (v1, v2, and Baby) in the following video if you watch the original feed video file (download it then watch it on a video player instead of watching it online with online player) 

The FPV feed is clear of interference lines when 5V power is supplied. But, the voltage sensor of the camera only operates between 10.0 and 12.0 volts. Any voltage outside the range has the idle display of "12V".

The FPV goggles should not be Eachine EV800D, which has video quality cutoffs that blanks the entire screen when the craft is behind strong obstacles. The original Makerfire off-brand EV800D skips the quality circuits and continues video feed transmission in all conditions. The original version has the circuit board seen in the picture on the right. The newer versions of the Makerfire goggles do include the video quality cut-off circuit and become a generic production, hence multiple branding , including DMKR. Though, the cut-off circuit is not as stringent as Eachine and hence fewer black-out occurrences.

The Frsky R9M module can be set to output 500mW using Taranis transmitter's regular power pins without external power source. The flight video shows long distance dive without any transmitter RF glitches, which would manifest itself in fail safe mode level free-fall aborting diving.
This flight sequence rehearses the mission plan, diving from 333 feet east, 444 feet north, ground distance 555 feet, air distance 1000 feet, relative to ground station. 3 flips above the landing patch area. Level traversal between 333 feet east, 444 feet north, and 333 feet straight east.

In-Car Battery Charging

The EV800D micro USB charging port is delicate and fragile. It can be modified it to use direct USB power outlets. 
To start the modification, scrap the enamel of the copper strands of the USB cable cores. Solder on XT30 terminals on the battery cables and the USB cable. For the monitor screen, only peel back the packaging film, not the screen matte film. The matte film is very tough, and removing it damages the monitor itself.

The EV800D board can be further modified to fit in the FXT Viper periscope, as above pictures. The mounting foam does not need to surround the entire monitor screen because the monitor is much brighter than leaked light during operation.

Fight batteries should be warmed/cooled with car vent using a gardening wire to hook up the charging plug before charging in cold/hot temperatures. 

When the car engine is offline, the car battery voltage has a slight drop, so the flight battery charger needs to be set to output 1.2A instead of the usual 2A, to prevent low voltage cut-off during charging, which can happen in the middle of a mission.

FPV Goggles Setup

For focal point correction, a small positive or negative diopter can be added by opening the camera box and repositioning the lens. To move the lens closer to the eyes, stick 2 strips of clear mounting tape at the bottom and 2 squares on the ceiling wall, then stand the lens on the bottom strips and balance it by tilting the box until the lens is parallel to the original lens frame before closing the ceiling wall.

The AV input is connected to the RCA video cable via the yellow video adapter cable included in EV800D package.

Radio Transmitter Antenna

TBS Crossfire Stock TX Antenna allows bending radiation pattern for better diversity. The straight polarity-reversing adapter is needed to connect this antenna to R9M module. The consumer general-purpose 900MHz antenna that comes with R9M sale reduces range by a good margin as reviewed by CurryKitten on Youtube.

FPV Feed Reviewing

The SD Card needs the SD-Card-USB reader connected with OTG cable to an Android phone for craft recovery path tracking. Use the MX video player App to review and backtrack the flight path after a crash.   

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