The reason of using HD cameras on the multicopters is to make videos from above in high quality. As the multicopter is continuously moving, the footage is always worse than if the camera was stands on the ground, steady mounted. There are a few factors that have to be aware of when using HD cameras for making videos.
- type of image sensor (CMOS/CCD)
- prone to vibrations
- powering (inbuilt battery, powering from outer source)
- AV out (live video out port)
- inbuilt features (wifi, gps)
Let’s check the most important of these factors:
* sensor type
Most HD cameras use CMOS sensor. This kind of sensor allows much higher resolution that a CCD one but is very prone to the rolling shutter effect (see later). The dynamic light handling of the CMOS sensors is getting better every day, so this is not an issue anymore. However, picture made in low light is still very bad with these.
HD cameras with CCD sensors are very expensive and are not commonly used in AP applications (at least on hobby level).
The less the better is not always true on multicopters. Of course the flight time gets better with easier cameras but they can get more prone to vibrations, because the mass inertia is lesser as well.
* prone to vibrations
There are more factors, making a camera vulnerable to vibrations, and these are mostly the sensor type, weight, optics. Generally, we use to mark some types of cameras as ‘copter friendly’, while some not. The effect the video suffers from is the so-called ‘rolling shutter effect’, that looks like a waves in the picture, when excessive high frequency vibrations get to the camera. the reason is the method how the picture is created on a CMOS sensor (line by line).
To avoid the problem, there are a few methods. The simplest is to mount some weight to the camera, so the mass inertia is bigger. the best practice for it is to mount the camera to the battery, that is heavy enough to avoid the vibrations. Another method is to use a so-called ‘ND filter’, that is a simple optical dimmer, that allows less light to the CMOS sensor so the shutter speed gets higher. Third method is to use a gimbal, that’s weight itself helps, plus it can correct some of the micro movements. The best and widespread used solution is to use special ‘rubber balls’. These are available in different hardness, thus, dampening different frequency vibrations.
The better quality these are of, the better is the picture. Some cameras have very good shape, electronics, firmware and very good priced but are still unusable, because of the cheap and bad lense. (typically the Xiaomi Yi)
Fortunately all the HD cameras today have inbuilt batteries. The problem is that some are simply of too small capacity for using a camera for its normal purpose. On the other side, smaller battery means smaller weight. One have to decide whether it is better to use a camera from an outer power source or from the inbuilt battery. When using outer power source, the camera is drawing power from the system (flight time decrease). When using the inbuilt battery, when it gets exhausted we are not able to do pictures anymore.
* AV out
More and more cameras are getting to have an AV out port recently. This is a very handy feature, allowing us to use one camera only, when flying FPV. In this case we do not need the FPV camera so we gain more flight time and simplicity in build. On the other side, as I mentioned most of the cameras are of CMOS type and this type can not always handle the changing light conditions fast enough, end even they ‘see’ very bad in low light conditions. Beside of that, there is one more factor, a bit of lagging (about 0,1-0,3s) where the video signal gets from the camera to vTX a bit later, and this can cause troubles when doing fast, proximity flying.
Many cameras today use builtin WIFI transceivers. This is rather a bad feature than a useful one, as the Wifi signal (2,4G) can sometimes disrupt RC link.