|Aug 22, 2012, 12:06 AM|
Australia, QLD, Toowoomba
Joined Jul 2012
Putting it all together
For a noob, the most daunting and tricky part of building an FPV system out of disparate parts from a variety of vendors is making it all work together - especially in a world where manuals and instructions are often missing, unclear or written by people with a poor understanding of the language. This is the price we pay for cheap electronic equipment sometimes, and the information is usually only a Google search away. I was pleased to find that the majority of the setup was actually straightforward and stress-free. Even a complete noob has little to fear here.
The aircraft-mounted parts were the first to go together. Both the camera and video transmitter (VTx) require a nominal 12V power source to operate, which works well with the 3-cell LiPo battery which most of my planes run. In addition, the colour-coding on the wires for the camera and Vtx use an identical colour code - yellow for video signal, red for positive, black for earth. This made connecting the 2 items together very simple; I only had to cut off the standard camera power/signal cable supplied with the camera (it has security-camera-oriented connectors, which are both bulky and heavy) and connect them to the VTx’s bare wiring harness - 5 minutes with a soldering iron, some heat-shrink and it was complete. RCModelReviews has an excellent Youtube video of how to make these connections, and also recommends the adaption of a servo extension cord to allow the 2 items to be easily unplugged. I didn’t bother, but it’s a great idea nonetheless.
The Sony camera comes with a 5-button “control board” which plugs into the main camera board. Plugging in the control board allows the user to adjust the camera’s various settings and change settings, using a simple on-screen display and the 5 buttons for navigation and selection. Once the camera is configured in the desired manner, the settings are saved to the camera and the control board can be disconnected. This handy arrangement means the control board can stay on the ground, saving weight in the aircraft and preventing damage to the controller. Settings can easily be adjusted in the field by plugging the control board in and using a screen or goggles to navigate through the menus. I found a couple of very informative videos on Youtube which helped me to configure the camera for optimal FPV use.
The ground-station wiring was even easier - all of the connections had standard cables and plugs so no soldering was required. The video receiver (VRx) has a power lead with a common JST plug, which could be connected directly into a 2-cell LiPo battery. I actually used a 9V battery from a smoke alarm to start off with - it lasted for several hours, which demonstrates how little power the VTx actually uses. The A/V-out cord from the VTx uses industry-standard triple RCA plugs (the yellow/red/white plugs commonly used for DVD players, game consoles etc) which connected directly into my portable DVD player’s AV-in cable for bench testing.
Both the video transmitter and receiver were supplied with small “rubber-ducky” whip antennas, but I didn’t use them. The circularly-polarised antennas screwed directly onto the VTx and VRx using the slightly unusual RP-SMA connector. Fortunately I was already aware that the HobbyKing 5.8Ghz FPV equipment comes with RP-SMA antenna ports, rather than the more common SMA plug, and had ordered my CP antennas with this plug accordingly. RP-SMA and SMA connections are not compatible with each other - a common trap for young players apparently.
When they arrived in the post, the Fatshark goggles proved to be equally simple to set up. They are supplied with both power and A/V via a single cord which plugs into the right-hand side via a proprietary plug. The other end of the cord has triple-RCA plugs for audio and video signals, and a barrel-type power-in jack which apparently accepts 6-12V - perfect for 2 or 3 cell LiPo battieries. The Fatshark cable also includes a power-out plug, so I used a spare barrel-type plug (cut from the PZ0420 camera’s original cord) to create an adaptor harness which allows the VTx and goggles to be powered from a single 2-cell LiPo with a JST plug. I soldered the low-battery alarm into the adaptor harness as well, to ensure it would always be online while my battery was connected.
My biggest headache turned out to be setting the channels on the video transmitter and receiver. Both the VTx and VRX have a selection of 8 channels - this allows the user to choose the most interference-free channel for best picture quality, or to allow the use of 2 sets of Tx/Rx equipment concurrently without interference. Both the transmitter and receiver must be set to the same channel for the video link to work.
The channels are selected by toggling 4 small switches on the circuit boards to pre-defined patterns, which would normally be a simple matter of following the supplied diagrams - however, the diagram on the manual and the diagram on the VRx sticker didn’t match at all. I didn’t know which one was correct, so I tried both - the sticker turned out to be the right one. Also, the switches on the VTx are tiny- so small that I didn’t even see them at first. They are covered by a clear heat-shrink, so I used scissors to cut away a small area, and the point of a toothpick to toggle the switches.
My final job was to create the “backpack” mount for the camera and VTx. It had to be light, compact and as strong and aerodynamic as possible. It also needed a flat underside for a large velcro patch, it had to allow access to the camera’s connection ports (including the control board’s connection plug) and ensure that the VTx heatsink would be properly cooled by the passing air. After a couple of sketches and some rough origami, I constructed a prototype from a couple small pieces of 3mm depron and used double-sided tape and a few spots of hot glue to hold the camera and VTx in position. They are easily removable if needed, and the whole backpack weighs less than 100 grams, ready to fly.
By the way, I know I haven't even mentioned the aircraft yet....I will get to that part in the next blog entry, I promise.
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