Yesterday I've received new flight controller for my Reptile X4R 220 quadcopter: Flip32 F4 from ReadyToFlyQuads. This is my first contact with STM32F4 based flight controller and I'm really looking forward to see if it really puts a difference comparing to F3 boards like SPRacingF3 I've been using last few months.
STM32F405 CPU running at 168MHz
MPU6000 gyro connected via SPI interface
Integrated 1.5A voltage regulator
Flip32 F4 (and Airbot F4 which is exactly the same board) is supported by Betaflight, RaceFlight (that due to some GPL violations I'm boycotting) and INAV (at the moment of writing this post INAV support is not complete) and REVO target. Well, basically, this board was designed based on OpenPilot Revolution stripped from radio modem, barometer and those JST connectors (pin headers rules!). There are some differences between Revolution and Flip32 F4 in terms of hardware (voltage regulator for example) or separate LED header (which does not work).
There are two "problems" I've discovered so far:
Whole board is getting very hot. Looks like it's because voltage regulator and battery monitoring are connected. You can not have one without the other even when you have BEC somewhere else
STM32F4 does not have built in inverters. That means, S.Bus has to be connected to UART1, since this is the only UART with external inverter
Although I've been able to install it on Reptile X4R 220 already, I have no idea how it flies yet. Weather outside is very rainy…
Let's be honest: in terms of mini-quad racing there is Betaflight (probably also Raceflight but I've never flew it yet, so will not comment on its flight performance), long long gap, and then it's everything else including Cleanflight, LibrePilot, INAV etc.
Originally INAV concentrated on "big" UAVs with GPS capabilities. After all NAV in name stands for Navigation. Mini-quads and acro performance were left alone, and once again, let's be honest: comparing to Betaflight, it sucked. It was possible, I've even written a short tutorial how to set it up, but it sucked.
Luckily, it is changing. INAV 1.2 had brought some improvements like Iterm limiting and acceleration limiting, and Acro flying in INAV became very nice. Small revolution, or maybe bigger catch up, is planned for INAV 1.3: asynchronous gyroscope, accelerometer and attitude processing. I've been working on it for last few months and results are very promising: INAV can drive a mini-quad with Betaflight comparable performance. Like this (please remember I'm not the best pilot!)
After moving to new, 4S powered, mini-quad based on Reptile X4R 220, EMAX RS2205 2300KV and FVT Littlebee 20A, I’ve discovered that I’m missing some power. DALprop 5040 and DALprop T5040 I’ve been using on 3S did not delivered enough power. So, I’ve gave DALprop TJ5045 a try.
According to specs, they should be most efficient from all DAL 5045 family. Well, efficiency will be determined, one thing is sure: they surely give much more thrust and pitch speed comparing to T5040.
Thrust and speed improved a lot. ATM, hover is at about 32% of throttle and climb rate is impressive. I love it! They also seem to be little quieter that T5040.
They are also durable. Maybe I’m not crashing as often as before, but when I do, it’s much more spectacular. Today I had two of those spectacular crashes and all propellers survived. Nice.
Both MinimOSD and Micro MinimOSD suffers from irritating technical problem. In some setups, they stops overlaying data during hard maneuvers or even right after arming. Problem is very simple: chip MAX7456 is extremely sensitive in terms of supply voltage quality. Working motors and/or servos, can introduce enough power supply noise to occasionally force MAX7456 to reset.
Luckily, solution is simple: separate LC power filter or big enough capacitor connected in parallel to 5V pads of MinimOSD.
Almost any big enough electrolytic capacitor will do (> 100uF, the bigger the better) but best results can be archived with low ESR > 500uF capacitor.
In my case symptoms were not very strong, usually only very fast flips caused MAX7456 to reset, but I’ve decided to go big: 1000uF low ESR capacitor.
Micro MinimOSD has 5V pads on a side and they are the best place to attach capacitor.
As you can see below, capacitor is bigger than MinimOSD itself and I had to think a little how to place it inside my Reptile X4R 220 frame.
Results are great: no more MinimOSD problems. OSD stays on all the time, no matter how hard I use the stics.
Last week I’ve been finally able to put my new mini quad into the air. It’s based on Reptile XR4 220 frame. Looks like I’ve succeeded with my build this time, since there were no major problems. Few minor, yes, but no major.
My Reptile X4R 220 mini quad has following specification:
Motors: EMAX RS2205 2300KV
ESC: FVT LettleBee 20A
Propellers: DAL 5040
Flight controller: SPRacingF3 clone running INAV with asynchronous gyroscope and accelerometer. I’ve already written few words about async gyro updates here
Radio RC link: ***FrSky X4R-SB***
Camera: Runcam Swift
VTX: TS5823S 200mW
Micro MinimOSD with MW-OSD 1.5
Here is short, uncut, video from maiden flight:
The only problem I’ve encountered, was with OSD. It stops overlaying data on aggressive maneuvers for a second and then OSD comes back again. Probably it’s because of voltage drop/noise. MAX7456 is extremely voltage quality sensitive. I will try to fix that with additional capacitor on 5V line this weekend.
After I finished my new Reptile X4R 220 racing mini-quad, I've realized, that there is no way I will be able to mount my RunCam HD on it. Comparing to ZMR250, 220 frame is just small. On a top plate there is enough room to fit battery, RC and FPV antennas and all what is left is around 35mm in the front. Plus, with angled FPV camera, there just no place for RunCam HD/Mobius form factor cameras. So, some time with 123D Design and few hours of printing, and here we are: 25 degrees mount for RunCam HD and Mobius camera specially designed for Reptile X4R 220 frame
This mount has 25 degrees inclination, will fit both RunCam HD and Mobius (not sure about RunCam HD2…) and its base is only 42x32mm. So it can be installed on small frames like 220. But, it will also fit bigger. No problems here.
The best way to install it on a frame is to use either zip ties or double sided velcro straps. There is a slot for 20mm wide velcro straps. To make it better, use 3M Dual Lock between.
To securely install camera also use 3M Dual Lock and use a velcro strap too. That should keep everything in place just fine.
Last week, first parts for my new racing quadcopter started to arrive. One of them, was carbon fiber frame: Reptile X4R 220. Why this one? Like I stated many times: I'm cheap. Plus, I did not wanted to go with another ZMR250 build. This frame was easily available, within budget and good looking. So, few weeks later, here we are…
4mm carbon fiber arms
2mm carbon fiber bottom plate
1.5mm top plate
35mm aluminium standoffs
adjustable camera mount (fits HS1117 and RunCam Swift)
integrated power distribution board (PDB) with 5V BEC
After 2 evenings with this frame, I'm almost finished with a build.
overall quality is good
everything fits, no need to ream holes, sand or cut anything
more nuts and bolts than required
top plate are rather thin. I would prefer 2mm top plate or maybe 2.5mm bottom plate too
power distribution board is an structural element of whole frame. If you want to use different PDB (I wanted to use Matek PDB-XT60) you might have a problem. Some improvisation will be required
In theory, each arm is kept in place by 3 M3 bolts. In theory… In practice, one of those bolts enters nylon standoff. Not metal nut, but nylon. So, instead of 3 bolts per arm, it is only 2.5 bolts or even less… too bad… Still, whole build is rigid enough…
Hey, don't leave yet, there is more!
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