Once you’ve selected an FPV camera, video transmitter, motor, speed controller, and airframe, the next big task is to hook all of this gear up so that the FPV video is clear and free from interference and that RC control won’t be a limiting factor.
A few things need to be taken into consideration before forging ahead and cutting holes in foam and soldering wires together. The placement of components, voltage and current requirements, and potential electromagnetic and radio frequency interference sources are important factors in the design and wiring scheme of your FPV aircraft.
Component Placement in an FPV Setup
Where you install the components that make up the FPV system – battery, camera, transmitter, etc. – is a large factor in the amount of radio-frequency interference (RFI) you’ll have in video output, and consequently, how far you’ll be able to fly.
Spacing the components as far from each other as possible on your given airframe is an ideal start to minimizing RFI. Using many of the less effective noise reduction methods post-install won’t make up for a cluster of wire and electronics crammed into a tiny space.
Of course, the choice of antenna and frequency matters a great deal, but let’s first look at how the placement of components and certain wiring tricks can reduce the interference in your FPV setup.
FPV Setup on a Flying Wing.
Ways to Reduce EM Interference in Your FPV Setup
RFI comes from two sources, the electronics and wiring on your aircraft and the environment. Placing components as far as possible from one another, and especially the video transmitter and RC receiver, will greatly help in achieving solid RC control and a good quality FPV video feed.
Once you decide on a general component layout, several additional actions will reduce RFI further.
Positioning of Components
Many FPV setups are possible, but usually it’s recommended to place the video transmitter on one side (left or right) of the wing, and the RC receiver on the other. Placing these two core components on either side of the wing will help balance the plane, and allow for easy access to wire connections.
Another idea is to place the transmitter on the tail of the plane, and the receiver toward the nose. However, noise from a high definition recording camera, such as a GoPro, or an FPV camera can reduce the usefulness of this setup.
Configuring your layout on a flying wing is a bit more difficult, and there are fewer options for placement. In the above image of an FPV flying wing, the RC receiver is on the far right hand side of the wing, and the video transmitter is on the other side.
The antennas are connected directly to the receiver per the manufacturer’s recommendation to limit signal loss. The RC receiver could be moved even farther out on the wing, but this will require more wire between components and the receiver. More wire will cause an increase in noise generation, added weight to the plane, and more work in the event of repair or alteration of the wiring scheme.
You’ll have to find a balance between ‘spaced far enough away’ and ‘too far for comfort.’ With an 8 channel receiver, extending the position 1 foot farther to the wing tip would require 6 or 7 additional feet of servo wire in this particular FPV setup.
UBEC – Universal Battery Elimination Circuit.
“Dirty” Power and Power Filters
Another source of interference, especially for those of us who use only one battery or battery network to power the entire aircraft, is interference from the electric brushless motors.
This interference is caused by the current spikes generated during normal brushless motor commutation.
With the fluctuating frequency of the noise with throttle setting, you could get some nasty interference at half power and above. This interference shows up as wavy lines moving across the video screen. As the throttle is increased, the interference worsens.
To prevent or limit this source of interference, it’s a good idea to install a power filter. A power filter is essential if you run off of one flight battery, and should be installed on the lead that enters the camera – video-transmitter circuit.
UBEC – Universal Battery Elimination Circuit
A nice way to use one battery to power both the motors and the electronics while minimizing noise is to use a UBEC. A UBEC steps down the battery voltage and regulates the power so that servos, cameras, OSD systems, and any other electronics have a stable and clean power source.
UBECs are also helpful if your camera and video transmitter operate at a lower voltage than the nominal voltage of the main flight battery, or if you have more than a few servos. UBECs can be built in to the speed controller, but separate UBECs typically provide greater amps and will provide redundancy if the speed controller stops working in flight.
The UBEC input is determined by the main flight battery characteristics, and the output is usually 5 or 6 V and several amps. Pictured is a 7.5 A UBEC suitable for larger aircraft with standard size servos. A toroid choke is installed on the output end of the pictured UBEC.
A toroid choke is simply a donut of iron with wire wrapped around the outer ring that reduces RFI. The toroid choke helps prevent wires from acting as antennas, and from generating RFI that will interfere with other components on your aircraft.
You can see a toroid, or ferrite choke, in the top left of the UBEC picture. Besides the toroids that come stock with some equipment, such as a UBEC, I haven’t added these to my planes, and the theory behind their function is complex.
For the purpose of a general FPV setup, the toroid chokes sold online at a store such as ReadyMadeRC should work fine.
Advanced Technology and Long Range Systems (LRS)
Others may have differing views, but I believe a LRS or UHF system should be used with any FPV setup. Using UHF for RC control will allow for a solid video feed on the 1.3 GHz frequency.
Using 1.3 GHz for video with a 2.4 GHz RC frequency, however, can cause control problems if filters are not used. Spread spectrum technology, such as Futaba’s 2.4 GHz FASST system, has improved basic RC control, but LRSs remain an ideal choice for FPV setups.
For example, if you use the 1.3 GHz frequency for video and 2.4 GHz for RC control, your video feed will greatly out-distance your control range. With an LRS, control range is again bumped pass video range.
Depending on location, your options for video transmitter power and frequency may be limited. It may be a worthwhile idea to look into taking an ARRL license test.
High Pass, Low Pass, and SAW Filters
A variety of filters are available depending on the frequency used for video and RC transmission. These filters can be pre-installed on some higher-end video receivers-transmitters and UHF LRS systems.
It’s best to consult the message boards for specific applications of filters to your desired FPV setup.