Selecting the equipment - RC Groups
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This thread is privately moderated by klaw81, who may elect to delete unwanted replies.
Aug 22, 2012, 12:02 AM
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Selecting the equipment

Thankfully for my wallet, I already had all the needed equipment for a radio controlled aircraft, since I’d been in the game for a while. This made my entry into the hobby a little cheaper. - I didn’t need to buy batteries or a charger, and my Turnigy 9x was pretty much perfect for an FPV beginner since it can be easily and cheaply upgraded for longer range if I want to.

I also had a decent collection of tools and other supplies - a soldering iron and solder, spare wires and servos and all those handy bits and pieces that come in handy occasionally. There were still a bunch of things I needed to buy though...

Video transmitter and receiver
Having researched my options for video frequencies, it very quickly became apparent that 2 of the common FPV frequencies were definitely not an option. There’s a mobile phone tower operating on 900Mhz just a few kilometers from my favourite flying field, so 900Mhz was definitely out. I use a ER9X-modded Turnigy 9X radio for all my aircraft so 2.4Ghz wasn’t an option either. Some deeper research suggested that all of the lower-frequency options would probably be rather illegal in Australia without a ham radio license, although I understand some longer-range pilots are risking it and using 1.2Ghz gear.

5.8Ghz was emerging as my best (legal) option, The main limitations of this frequency are signal multi-pathing (causing poor image quality) and the inability to penetrate solid objects. Since I would be generally flying within visible range in semi-rural areas where obstacles are rare, and I was already planning on using circularly polarised antennas to avoid multi-pathing issues, neither of these limitations would present any problems for my intended use.

To keep costs low, I decided to go for a relatively low-power video transmitter. With good antennas, a 200mw 5.8Ghz transmitter should be sufficient for over 1km of range, which is the safe limit of my Turnigy RC system anyway. I ended buying the 200mw 5.8Ghz transmitter/receiver combo from HobbyKing.

While I was buying from HobbyKing, I also ordered a 1000mah 2-cell battery for $5 - this will be used to power my video receiver and should be sufficient for a couple of hours’ continuous use. The video transmitter will be powered by the plane’s 3-cell battery for simplicity’s sake, although I may need to use some sort of “filter” to ensure noise from the plane’s ESC won’t interfere with the video signal.

Selecting a camera was surprisingly easy. The Sony SuperHAD PZ0420 was getting rave reviews all over the internet, and a thumbs-up from Bruce at RCModelReviews was good enough for me. There are better cameras available, but this one appeared to offer the best bank for my buck, and the camera’s ability to handle sudden changes in brightness without distorting colours is very impressive. Information about how to get the best performance from this camera is plentiful, and the HobbyKing video transmitter has a 12V output that suits this camera nicely.

After some deliberation and reading a few online arguments over what was best, I ended up getting the very slightly more expensive 2.8 lens version, rather than the more common 3.6 lens. I don’t have any preconceived expectations about how the picture should look, and given that I’m not going to use tilt/pan, a slightly fish-eye wide angle lens seemed to be the wisest choice. SecurityCamera2000 speed of delivery and after-sales service was top-notch.

Selecting a suitable viewing screen was by far the hardest thing to do. I didn’t have anything vaguely suitable at home (that could be used in the middle of a paddock) so I would need to buy a viewing screen of some sort. My first idea was to buy all-in-one goggles (AIO or Fatshark) with an integrated video receiver and head-tracker. The compactness and simplicity of this arrangement was very appealing, but the price was well outside my budget and I couldn’t find an affordable alternative.

Instead, I decided I would make a DIY head-mounted ground station, with a small sun-shaded screen, battery and video receiver on a welding helmet or hard-hat. I had seen several setups using this arrangement on forums, and it didn’t look too hard to achieve. I searched eBay obsessively for generic screens and video glasses, looking for something that had the right combination of low price and minimum VGA resolution. I found screens with the right specs as low as $20 (posted) for 4.3”, and about $60 (posted) for 8” screens.

I was about to pull the trigger on a screen when a pair of used Fatshark Base goggles came up for sale at a reasonable price, and I bought them immediately. Having not tried video goggles of any kind before, I was a little worried that they would not be sure what they’d be like to wear and use. Happily, they turned out to be quite comfortable and reasonably light. The picture was clear, bright and respectably big, although not as massively wide as I thought it might be - roughly equivalent to a 24” PC moniter at 30cm or so, at a guess. I was expecting an IMAX style picture, somewhat over-optimistically.

It only takes a few minutes of reading to realise that circularly polarised antennas (and the clover-leaf and sker-planar wheel in particular) offer significant performance benefits over standard “rubber ducky” aerials, and the obvious choice for my application. I ended up buying a set from eBay to start me off, but I also intend to try making my own (for bonus street cred) in the near future. My thanks to IBCrazy and many others for their helpful explanations and tutorials on how to make these and get good results.

Other bits and pieces:
Just a couple days after buying the goggles, I managed to obtain an old portable DVD player for free. The device came with a 6” screen, extended 3000mah battery, RCA inputs and cabling, making it absolutely ideal for bench-testing my video setup. After some trials to make sure it was reliable, I set the DVD player up as a “passenger” screen. The screen resolution is quite low so I wouldn’t like to try flying from it exclusively, but it should suffice as a backup if the goggles die mid-flight for some reason.

I also decided to invest in a couple of other cheap safe-guards:

1. A low-battery alarm - this will be plugged into the battery powering my receiver, and alert me if the battery voltage is getting low. If the receiver loses power, I will lose my video feed to the goggles and probably crash. An alarm will hopefully give me time to land, or at least get the plane to where I can see it, before the video drops out.

2. A lost-plane siren - this will be mounted somewhere on my training plane, and I will program the landing gear switch to trigger it. If the plane crashes in long grass or into trees where it can’t be seen, I should be able to trigger the siren from my radio and the noise will guide me to the plane.

Hopefully these little gadgets will help me stay out of trouble, and at $5 for the pair from HobbyKing, they are very cheap insurance.

In the interests of keeping things cheap and simple, I didn’t buy an on-screen display (OSD) unit, or a video recorder. Since my radio has an audible countdown timer to keep track of flying time (to battery exhaustion) and I will be using a spotter and flying line-of-sight only (to prevent plane loss through poor orientation/interference) I don’t see the need for these expensive add-ons at this stage. I might consider getting them later, if I feel the need.

Here's my entire parts list, with pricing:

200mw 5.8Ghz transmitter/receiver combo $65 from HobbyKing link
Sony SuperHAD PZ0420 camera, 2.8 lens $50 from SecurityCamera2000 link
Screens - Fatshark Base goggles $195 second-hand
- portable DVD player with AV in $0
CL & SPW antennas $20 from eBay
Ground station battery (2 cell 1000mah) $5 from HobbyKing link
Low-battery alarm $2 from HobbyKing link
Lost-plane siren (to be mounted in plane) $3 from HobbyKing link

Total outlay: $340 AUD, including postage of all items.

In my next blog entry, I'll give a rough explanation of how all of these items can be connected together to create a working system.
Last edited by klaw81; Sep 04, 2012 at 02:06 AM. Reason: added links to bought components
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