Saturday, October 27, 2018

Ground Station Setup For Converged IoT Platform



Antenna Cluster Planning

The mission scenario sketch example 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/obstructing signal line of sight.

RF Transmitter Setup



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. The flight video below shows long distance dive without any transmitter RF glitches, which would ma

nifest 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.

Video Receiver Setup

5.8GHz video receivers board based on the RX5808 module all have the pin-out in the diagram below, and the 6 terminals are connected with 3 AV cables.
The resistance of the AV cables varies among brands. In lower left picture, the thin conductors resulted in blackouts of video in the goggles. The picture on the right uses the brand product listed in material listing, which works properly.

In-Car Battery Charging

Fight batteries should be warmed/cooled with car vent optionally with a gardening wire hookup 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 

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. 

0. 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.
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.

Retractable USB-micro cable powers to the FPV receiver. Its host plug breaks out on the chassis column and is accessible for quick disconnect after craft landing to reduce heating of the receiver.
The FPV receiver explicitly based on the RX 5808 module 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 video output pin 6 is soldered to the AV yellow cable for video on the PCB. Pin 3 is ground. The tail end of the AV cable and the row of pins, including the pin base are encased together by the clear mounting tape. The male plug of the AV cable goes to FPV goggles. 



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.

The retractable USB coiling mechanism needs to be removed as the picture-in-picture below. 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 good in making the near vertical radiation pattern.


Optionally, the casing can be removed, 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 laptop's USB 3.0 port, which is spec'ed to output 0.9A . Optionally use a phone power bank that can output 2A current. 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 slash 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.


Below are considerations on the craft side.
The worst case noise interfering with FPV feed is with 12-16V direct battery power supply to the Caddx Turtle cameras (v1, v2, and Baby) in the following video if you watch the original feed video file https://drive.google.com/file/d/1nL07CPVMDrWu_w7SFtraSYZqxUejrDJr (download it then watch it on a video player instead of watching it online with online player because online video servers process out the noises to save their internet bandwidth).

The FPV feed is best clear of interference lines when using VTX's 5V aux power, which filters out low frequency ripples. 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". So, if voltage monitoring is desired, OSD on the ccraft is required. 

The following are the in-between options.

The Wolfwhoop MP2315-chip-based buck converter power supply, with 10uH inductor, has the video ripple noise level between direct battery power and VTX's aux power. The ripple noise can not be completely eliminated with a 10uH inductor LC filter because the ripple frequency itself is similar or lower than the 10uH inductor working frequency. The ripple noise can not be eliminated with a electrolyte audio A/C capacitor either because the ripple frequency, around 1MHz is much higher than the electrolyte capacitor's audio working frequency. The runcam system consumes 600mA, and can not be powered by VTX's aux power supply, which is limited to 360mA. For this reason, the run cam needs a separate power supply in the craft in parallel, such as the DROK buck converter. So, the caddx system is a better choice.

The MP1584 chip based buck converters are the worst for analog video applications, such as the Bluesky 5V power supply.



FPV Feed Flight Path Tracking

The raw FPV DVR recorded mp4 of the tail-spin crash with fishbowl optical illusion is saved at googledrive https://drive.google.com/file/d/1IchzErZsqhmW0qukS_ZLuJz3CpO4A27t .
When viewed in Android MX Player or the EV800D set, the last 3 frames used to track down the wreckage is not available frame-by-frame. A laptop with desktop Avidemux software is needed to step in the last 3 frames. Avidemux installation for Ubuntu laptops is the 2-step procedure seen in
http://ubuntuhandbook.org/index.php/2018/01/install-latest-avidemux-2-7-0-ubuntu-17-10-18-04/ .


Tuesday, October 16, 2018

Blade 180 - Oxy 210 Rotor Characteristics

Product source is ebay seller amain. Item "OXY2-081 OXY Heli Carbon Plastic Main Blade 210mm (Black) (2)"

The airfoil profile is (NASA predecessor)NACA0015. The symmetrical airfoil is generally known to have the center of pressure CP at quarter blade width from the leading edge during cruise flight when attack angle is smaller than 2-3 degrees in research paper. As shown in the picture below, the CP point is at 17.5mm/4 = 4.375mm from the leading edge but the bolting is at 4.3mm, so, when the attack angle is very small, it has perpetual pitch suppression. The research measurement also shows that the airfoil has perpetual up-pitching torque at cruise attack angle of 6 degrees because of "center of pressure moving forward of the quarter chord". 



When the mechanical margin of error is added between actuator servos and actual blade position, the blade angle shifts as the following time line.


This means that large slop gap can result in an unstable craft. And in the above example depiction, the slop should be improved from 3.2 degrees to 3 degrees to escape the perpetual pitch suppression slump. And to avoid over-correction, the slop needs to be smaller than 2.1 degrees.