Saturday, October 27, 2018

Ground Station Setup For Converged IoT Platform

Antenna Cluster Planning

The mission scenario sketch example with Blender 3-D modeling is in the picture on the right. The small matchbox at the lower left corner is the base station. And, based on the mission scenario, the RF-control/FPV antennas are arranged to prevent internal interference and obstructions.
The computerized equipment needs to be carefully integrated. Recent car models have computerized battery management and shuts electric circuit after 20-30 minutes of parking the car. If a base station video receiver is powered from a car and gets shut off in the middle of a flight, it poses a serious danger. The solution is to stop the car in N neutral gear and engage manual brake manually.  After arrival on site, put transmission on N gear (not D gear) and stop engine. Wire up ground station. Start FPV receiver and goggles and start recording.

RF Transmitter Setup

The alternative micro sized transmitter module wiring pictured here.
The alternative Frsky R9M module can be set to output 500mW using alternative Taranis QX7's transmitter's regular power pins without external power source, as shown in this video,

This flight sequence rehearses the mission plan, diving from 330 feet east, 440 feet north, ground distance 550 feet, air distance 1000 feet, relative to ground station. 3 flips above the landing patch area. Level traversal between 330 feet east, 440 feet north, and 330 feet straight east.

Video Receiver Setup

The Hyper Tough cigarette power plug is specifically chosen because it has a very tight fitting to fix suspected causes of crashes, such as the pilot's knee knocking the plug during flight, video recorded below on the left. The FPV receiver explicitly made for racing is chosen because experiments on the FXT Triversity receiver had video "blue outs," video below on the right.

The real fault point, including all previous blackouts, was the FXT Triversity receiver overheating in the product casing, not the FPV goggles.

LCD TV monitor also has a blue screen of death when an input signal is very noisy for aesthetic purposes and should not be used. The latency is about 50ms "glass-to-glass," as shown in the following test with an LCD TV monitor, where a stopwatch time was simultaneously photographed directly and through the FPV video capture and transmitted through the alternative Furious True-D 4.0 VTX and displayed on the Pisichen monitor. The time difference was 58.88s - 58.83s = 0.05s = 50ms.

5.8GHz video receivers board based on the RX5808 module all have the pin-out in the diagram below. 

The resistance of alternative RCA AV cables varies among brands. In the picture (crossed out), the thin conductors resulted in video blackouts in the goggles. Also, it would be dangerous if 3 RCA connectors were connected incorrectly in the field, resulting in short-circuiting. RCA cables shall not be used. The 22-gauge ribbon cable setup is pictured here.

The right angle SMA adapter for the mushroom antenna needs to reverse the polarity with the inner core pin on both sides because both the mushroom antenna and the receiver side have the inner core pin hole. Manufacturers of both the VRX and the antenna prefer not to have the inner core pin because that would introduce vulnerability to their product. The patch antenna with 9.4dBi is the directional antenna projecting the craft's diving trajectory. 

The latency of Cobra S with nano 3 camera is about 30ms glass-to-glass, as follows. Here below, the goggle is tracking from 25.29  to 25.30 seconds while the original stopwatch object is turning to 25.33 seconds. This is expected as Drone Mesh's YouTube channel shows non-racing cameras with about 20ms delay, and a 60 Hz refreshing rate adds another 16ms delay, here .

In-Car Battery Charging

Fight batteries should be warmed/cooled with car vent 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 1A maximum, to prevent low voltage cut-off during charging.

Alternative Video Receiver Setup 

The retractable USB coiling mechanism needs to be removed as the picture-in-picture below. And the retractable soft cable is good for use with the flight computer of the craft to avoid pulling the flight computer off the craft with hard cables. Both the Eachine Pro58 (white) and the Furious TrueD (red) have the same pinout, utilizing ping 1, 3, and 6, as VCC, GND, and Video, as is the case for all analog VTX based on the RX5808 module. Using AV cables to connect to the VRX in this setup is OK because the two combined AV GND wires reduced the resistance. The 45 degree SMA adapter is good in making the near vertical radiation pattern.

It is incorrect to use the 3/4 inch velcro strip to wrap around because that traps heat especially with black velcro, and also pulling back the Velcro also pull open the RF cavity. It should be a habit of disconnecting USB cable from the chassis column right after landing the craft.

Optionally, the casing can be removed to make the ground station operation low-key, which also removes the joystick of the receiver module. The True-D receiver can be made to auto-search and tune to VTX's frequency without the joystick. 

In any case, the video receiver should be powered from a 0.9A-capable outlet or higher, such as a car cigarette port with switching buck converter or a laptop's USB 3.0 port ,which is spec'ed to output 0.9A. Standard USB is only spec'ed to output 0.5A, which is insufficient. 

Alternative FPV Goggles

The FatShark Recon3 goggles' Velcro sticker does not need to be removed. Just use an art class knife to cut a cross on the 4 outer bore holes, and the Hypertough #1 driver can unscrew the screws. For the inner 2 shallow holes, one wedge of the crosscut needs to be sliced off to give room for the driver. Before mod grinding begins, tape over the optical cavity and the MicroSD opening to block saw dust.
The small 15mm diameter rotary cuuting disk can grind out the glass fiber of the RF module. You can notice that the nearest surface mount components have at least 15mm clearance. Hollow out the fiber glass between the top and bottom header leads first, then polish away the solder until the art class knife can slide in between the RF module and the main board from the left edge to the center.
To prepare the AV cable, stick a piece of transparent mounting tape on the main board to temporary fasten the cable and adjust the cable leads. The ground lead goes to pin 3; Signal wire goes to pin 6, same as diversity receiver's pin-out order. Stick a piece of insulation underneath pin 1 and pin 2 of the RF module to block power supply to the module. Shown below are a pink piece of paper and a piece of clear tape.

Use the 1mm milling bit to notch the SMA antenna hole for the AV cable and thread the cable through the hole before soldering as above picture-in-picture. Then permanently tape the cable one on top of the temporary mount and another taping next to the SMA antenna base after soldering. 
After reassembly, to adjust the fitting, use cuticle scissors to incision the cushion tube and the foam laterally. Real human faces are not completely symmetrical and I need to remove the left side cushion to align my pupils to the center. Also removing the side cushion sections flattens the curve.

Pre-failure Video Receiver Check

When the received video loses color or proper dynamic range, it is actually an indicator that the ground station's video receiver is failing. Ignoring the re-failure signs resulted in a catastrophic fly-away when the video blacks out in the middle of a flight. A good receiver is swapped in at 0:10 of the video here. No change to the video transmitter or camera during the short time gap of merely 1 second between flight time 3:13 and 3:14 without changing the camera angle and position. 

FPV Feed Flight Path Tracking

The raw FPV DVR recorded mp4 of the tail-spin crash with fishbowl optical illusion is saved at googledrive .
When viewed in Android MX Player or the FPV headset, the last 3 frames used to track down the wreckage is not available frame-by-frame. A laptop or Chromebook with Avidemux.AppImage is needed to step in the last 3 frames. 

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