For those who have been following this post I recently updated the project with some improvements that result in much improved video quality.
This project has to fall under the category of stoopid quadcopter tricks but I wanted to try flying FPV indoors and I had a Syma X5 on hand so, yeah.
The body shell of the X5 looks kind of like a ‘mini me’ version of the DJI Phantom which makes it ideal for this kind of hack. It’s hollow body has lots of interior space to play with and it’s able to lift the added weight of the FPV gear without much complaint.
My goals for the project were simple:
- Keep the budget close to the cost of the copter (around $60)
- Use 1.3GHz video for good through-the-wall penetration
- Ultra wide-angle video camera
- One-day build time
- Use off-the-shelf components
- Make minimal mods to the copter
Component selection was initially frustrating because the only hobby outlet that sold everything I wanted has been out of stock for months. That left eBay (i.e. hit-and-miss quality) and more expensive US hobby outlets but eventually I found what I needed and within my budget.
The video transmitter came from the good folks over at Ready Made RC and is one of their 1.3GHz ‘Pico’ transmitters rated at around 40mW. A nice feature is the inclusion of a gain control located opposite the connector side of the circuit board (you can get a look at it in this photo.) The Tx ships with its gain pretty much bang-on but I found I still had to dial it back a bit to keep whites from appearing blown-out. The Tx operates at 5V but being a typical toy copter the Syma uses a tiny 3.7V 1S LiPo for power. To get around that I added a 3V to 5V DC-to-DC upconverter I found on eBay.
The upconverter provides the Syma with a 5V supply that’s stable right up to the point where the copter’s battery is too low to keep it in the air. An added bonus of using a DC-to-DC converter is that nearly all noise on the battery side gets filtered out during the conversion, thus eliminating the need for a heavy LC filter. And while the output of the upconverter is relatively clean, I decided to add a 470uF capacitor on the output to remove any remnants of the regulator’s switching frequency and stabilize the voltage even further.
One thing I found that I couldn’t work with was the large half-wave dipole antenna that comes with the Tx so I made my own quarter-wave monopole (shown here prior to applying shrink tubing). This is half the size and weight of the original antenna but still has adequate signal strength for my purposes. Indoor performance of the modified Tx isn’t bad and I’m still able to maintain a picture through a wall.
If you’ve never made your own quarter-wave antenna before it’s very straightforward. You start with a length of coaxial cable — RG316 in this case — then calculate the wavelength of your frequency and divide that number by four. The quotient is the length of cable that needs be exposed from the shield. The actual frequency of the video transmitter I’m using is 1258MHz which works out to a wavelength of 238.47 mm. That number is based upon the velocity factor of radio waves in a vacuum but, when traveling through metal those waves slow by about 5%. To compensate for this the wavelength needs to be multiplied by 0.95 which gives a corrected wavelength of 226.55 mm. Dividing that value by four gives us 56.6 mm which is exactly how much of the cable’s center conductor needs to be exposed to create a quarter-wave antenna.
An advantage of moving to a simple monopole is the antenna can now be easily positioned outside the aircraft by drilling a small hole in the body shell. I initially chose to exit the body shell sideways to protect the antenna in the event of a crash but, doing this makes the antenna horizontally polarized which means the receiver antenna must also be positioned on its side for optimal reception. That worked okay but after some experimentation I decided to just orient the antenna vertically up though the body shell. It’s easier and the Syma X5 really doesn’t crash with enough force to worry about.
The camera I initially selected is a tiny little unit I found at SurveilZone and has an ultra-wide 120-degree FOV that is near perfect for indoor FPV. It also weighs a mere 3g and draws only 50mA which are huge advantages for an underpowered machine like the X5.
On the performance side, colors aren’t terribly saturated but the sensor is very sensitive so low light performance is surprisingly impressive. My only complaints is that there is no UI to make adjustments to the gain (it’s way too high and I suspect my camera doesn’t have an IR filter) and at 600TVL the resolution falls slightly below VGA which means the image is a tad on the soft side but hey, it’s an under $20 camera so, yeah.
The only ‘gotcha’ is its operational voltage range. SurveilZone says it will operate from 3V to 5V but in my testing 5V is just a bit too high, causing the image to become bleached out, while much below 3V and the camera struggles to maintain a signal. The solution was to insert a 22 ohm 1/4-watt carbon resistor between the 5V supply and the camera, effectively dropping the voltage to just over 3V which keep the gains in its sweet spot while also protecting the camera (note: any value from 15 ohms to 22 ohms will work nicely). The video signal from the camera is AC-coupled to the video transmitter via a 10uF capacitor to eliminate any DC offset.
If you think the above camera’s FOV is a bit too wide and you don’t mind a minor weight penalty then I’d give this camera a try. It’s the one I’m currently using and can be had for under $20. It shares the same electronics as the smaller camera but the image quality is slightly better plus it has an optional IR-blocking filter and a lens that you can re-focus. Note that if you do go this route be sure the seller’s product photo is identical to this one and that they state it has an IR-blocking filter. There are several models of this camera out there with the same enclosure and cables but the one shown in the photo is the only version with a wide-angle lens. To prep the camera for installation you must first cut the cable just above the voltage regulator (it’s that large rectangle molded into the cable) then carefully strip the cover from the remaining cable to reveal the four wires inside: Black (ground), red (+3V to +5V), yellow (video), and white (audio).