power suply for flight controler to multirotor  - Page 1
Forum section: electronics / projects

author: BZQ
author_rank: Newbie
timestamp: March 19, 2020, 08:08:33 pm
content: I live in Poland and I might do not do the best job describing my problem I also don’t have a lot of knowledge so It makes it even harder for me, so please be forgiving. What is going to be more painful is schematic that I’ll attach please note its my first project. Obviously I’m open for any criticism.I’m 17 and studying /learning computer science so I decided to designed flight controller for drone (operating on open software Betaflight) without any electronic background what so ever. It wasn’t easy (switching miso with mosi or d+ with d-, or just soldering mcu rotated by 180 degrees) but I got drone to fly. Now I have problem with power supply to my electronics i know for the fact that my input voltage is pretty noisy, because after connecting directly analog camera to it, I saw those typical artifacts/lines. Whole control setup is rather OK but biggest noise creator are brushless motors (5k-21k rpm with 12 magnets I have know idea what frequencies are generated by those) which are powered by the same li-po. which is problematic by it self because in Blackbox is saw on heavy load it can drop from 12,2V to 9V in 1ms(during two cycles at 2kHz). The TPS62133RGTR 5V regulator cant handle it alone and my RCreceiver which is connected to it is shutting down during that dropout.After flying for longer (and some crashes) my gyroscope and accelerometer started to freak out, output of those even during small movement was increased( was showing much to big values) in addition it seemed really noisy/not stable. Reason why I think its caused by the 5V rail is that at the same time I noticed significant decreased in RClink strength. Those are things I need to know:1.do I need oscilloscope to get to the source of those problems(It might be to weak battery, defective motor driver, or most likely my bad design because I didn’t add any additional filtering like “capacitance multiplayer”, lc filter, inductor between bat+ and regulator input. Just some decoupling capacitors and components needed from datasheet of regulator)2. are there any specific methods with such a noise input voltage( I think its pointing out that I’m using max 2A on that 5V rail)3. I noticed that by stopping brushless motor physically while it’s driven by ESC it courses huge power waste/consumption for short amount of time => short voltage sag. i guess that voltage regulator reacts to lover voltage but it doesn’t react fast enough while voltage of battery go backs to normal and kills electronics that was able to destroy my previous flight controller which I bought online I’m assuming that was similar problem occurred that I have now. How can I protect mcu, and other sensitive electronics from such a short voltage drop on battery rail.

author: dany-boy
author_rank: Contributor
timestamp: April 18, 2020, 10:34:34 pm
content: Hi and welcome to the Forum!Unfortunately, I'm just gonna be not very helpful and recommend you to simply buy an off the shelf FC. I know that you are gonna say something along the lines of "But the learning is the valuable part!" I've been there and done that, way back in the multiwii days when I had to take apart a wii knunchuck and cobble together a flight controller with an arduino UNO. I personally really like Holybro and Team Blacksheep flight controllers. They have been very reliable throughtout all my builds. If you really want to fiddle about with power supplies all I can really recommend is you make a LC low pass filter with low ESR capacitors from reputable brands. Follow that with a buck converter to bring the voltage down to some 7 volts, and then use linear regulators to power each individual component. That has gotten me the best results by far. I don't have the schematics at the moment, but in my modified TBS discovery pro I'm running a 6s setup with a TPS54336 (7v output configured) followed by two classic 7805 LDO regulators feeding a kakute F7 and TBS unify pro. For all my other rigs (racing) I just don't bother with any DIY setups. I use components with built in regulators.Cheers!

author: xani
author_rank: Frequent Contributor
timestamp: April 19, 2020, 04:09:53 pm
content: Your options are:Get enough capacitance in the supply (preferably diode in front so current from caps doesn't just flow to the motors when voltage drops)Get separate batteryGet creative with your regulators like getting buck-boost so you it can still regulate when the input drops to very low level.As dany-boy mentioned, adding LC filter will also most likely help.Quote from: BZQ on March 19, 2020, 08:08:33 pmAny scope will most definitely make it easier. But in a pinch a shitty speaker with a pair of antiparallel diodes and serial cap does for a very crude ac probe.QuoteHaving enough capacitance to last thru it, filtering, not having ground loopsQuoteLC filter on input would definitely help as it would basically reduce the rate of change of the voltage, giving regulator chance to react. Regulators generally regulate worse the faster change is. There are also TVS(transient voltage suppression) diodes dedicated to that but that's kinda treating the symptoms, not a problem

author: BZQ
author_rank: Newbie
timestamp: May 06, 2020, 06:29:13 pm
content: HiThanks, you for yours replies after two weeks I lost hope for getting any feedback, especially not from people who are in to FPV as well.I’ve implemented your suggestions to my new design, thanks again for all the advice. But as dany-boy suggested I will probably buy off shelf stuff. The most important thing which for me is being able to repair those FC will apply with my new knowledge.I also have to check how my power supply sounds like, to be honest I would never have thought about that.So thank you again and Cheers!