This time it is time for something slightly different: not enough P gain. Usually this problem can be identified without any log analysis. Symptoms are quite visible: multirotor is sluggish during maneuvers, has a tendency to change attitude on its own, constant course corrections are required. In worse cases, it is unflyable. But how does it look like on Blackbox logs.
First of all, symptoms are not so clearly visible. There are no huge oscillations for example. Zoomed out log might event look good on a first glance. For example like this:
Welcome to second part of Blackbox PID tuning tutorial. Last time I have showed few examples how excess P gain might look like. Today I will write few words about next common PID tuning problem: too much D. Derivative (future) part of PID controller is very useful, since it allows to smoothen control loop output when it is reaching the target. So, at the end of move (roll, pitch, yaw, anything else) multicopter will start to “slow down” before target is reached. It’s just like accelerator pedal in a car. When you want to reach 50 you start to release it before you reach 50, and not in the exact moment you reached target speed. If you would, you would have to use brake to slow down to 50. Derivative part helps not to overshoot. Without it, movement would be shaky, not smooth.
Unfortunately, D is tricky. Like everything that tries to see the future, it is unreliable and can introduce noise. We do not like noise. Not enough D = shaky, mechanical, movement and overshooting. Too much D = extra noise, vibrations, damped response.
How excess D would look like in Blackbox logs? Like this:
You can buy almost everything from China. Including 2 axis gimbal for less than 50 Euro. Websites like BangGood and Aliexpress sell them worldwide. The only question is: are they any good? I’ve decided to check that out and I have purchased Eachine Light-2D Brushless Gimbal w/Motor&Controller For DJI Phantom. Of course, it is not only for Phantom. If you can mount it on your multicopter, you can use it. Why not, it is a clone of BaseCam SimpleBGC 8-bit. The most general purpose gimbal controller there is!
My FPV acrobatic skills are low. Very, very low. I try to practice and at least I’m not crashing as often as I used to crash, but still, my skills are low. But I’ve learned few things: trees are the enemy, and I really should stop flying near them. Because when I fly near then, this is happening:
I think all popular computerized DIY devices like Arduino, Raspberry Pi or any other microprocessor/microcontroller based boards has one common drawback: low output current. Few miliamps per pin. While this is enough to light a single LED or provide input to other electronics device, it is far from enough to run a motor or power a LED strip. It’s all about current.
Good thing this problem can be solved with two additional devices: resistor and bipolar transistor. Together they can act as a switch. Idea is simple: low current (and voltage if you wish) applied to transistor base causes bigger current (and voltage) to be passed between collector and emmiter. We have two choices: NPN or PNP bipolar transistor. Switch that uses NPN transistor is open/enabled when positive voltage is applied to base. In other words, base is connected to plus.
When camera and minimOSD are connected to video transmitter, minimOSD is not overlaying OSD data. If camera is disconnected, OSD data is transmitted. After connecting camera, only camera image is transmitted.
Check if camera and minimOSD are using the same display system. Usually monitor/goggles and video transmitter does not care very much about used display system. Transmitter just transmits, and monitor/goggles very often can detect if signal is PAL or NTSC. But if camera is sending PAL signal, minimOSD has be overlaying imag using PAL subroutine. If it will try to use NTSC mode, it will fail. In case on MW OSD software (Scarab OSD), OSD display system is configured in GUI. Set it to the same system as camera.
Both electrical motor and ESC are source of electrical noise that influences all devices connected to the same battery. This is why, very often, on airplanes or big multirotors FPV circuit is powered from separate battery. On small or medium drones this can be hard to archive: additional weight will influence both flight performance and flight time. So, when your setup is suffering from a power noise manifesting itself as vertical bars or other image distortions on goggles/monitor, you can do 3 things:
use separate battery to power camera and video TX,
cut the noise using LC low-pass power filter.
I would choose low-pass filter. Cheaper and lighter. You can buy one for a few dollars/euros or make 10 by yourself for the same price.