Betalight 3.3 and Kalman filter (BiQuad+FIR2 to be precise) situation

Betaflight 3.3 RC1

Betaflight is at the end of next release cycle. Betaflight 3.3 RC1 has been released only 2 days ago and that brought us a (not) Kalman filter! Long story short:

  • Raceflight was using Kalman (Fast Kalman Filter – FKF)
  • RS2K left RF and brought FKF to Betalight
  • Betaflight did some changes and replaced Fast Kalman with BiQuad + FIR2 (Finite Response Filter) equivalent that gives more less the same results (same response) as Fast Kalman

Unfortunately, someone at Betaflight forgot that users will want to use it and the process of setting up (not) Kalman filter (I will be calling this (not)Kalman because it just sounds better than BiQuad+FIR2 and says all you need to know) is at least stupid. The filter is gyro update frequency dependent and instead of setting up a cutoff frequency, it has to be tuned using gyro_filter_q and gyro_filter_r CLI settings that you have to guess or compute somewhere else. How awesome is that!

Anyhow, to make life a little easier I prepared an online (not) Kalman filter calculator for Betaflight 3.3 RC1 that allows computing filter cutoff frequency based on gyro_filter_q, gyro_filter_r and gyro update frequency.

Also, here is a YouTube video that shows how to use it and configure BF 3.3 RC1 for (not) Kalman:

And another video that shares some more general thoughts on the topic:

Betaflight 3.3 RC2 (upcoming)

Ah yes, there was a small change… Looks like BF guys decided to make life a little easier for us after all, and sped up a small but very important change. Starting from Betaflight 3.3 RC2 (or today's nightly build), (not) Kalman filter cutoff frequency can be specified with a single CLI setting: gyro_stage2_lowpass_hz. More than that, gyro_filter_q and gyro_filter_r are removed and not available at all.

I always knew that developers need some proper motivation, but why could this not be like that from the beginning?

RaceFlight One GPL violation drama, there might be more of that

Previous parts of this cycle are available here and here.

Betaflight community has a grudge against RaceFlight. And they have a reason. Two potential, or maybe I should say confirmed, GPL violations in one year is fully enough. That just does not looks good no matter how you look at it. This whole situation stinks. So it's not a surprise that what leaked as RaceFlight One source code is analyzed like crazy.

Latest news: RF1 code might have at least 2 potential license violations:

STMicroelectronics license violation

* @attention
*
* <h2><center>&copy; COPYRIGHT(c) 2016 STMicroelectronics</center></h2>
*
* Redistribution and use in source and binary forms, with or without modification,
* are permitted provided that the following conditions are met:
*   1. Redistributions of source code must retain the above copyright notice,
*      this list of conditions and the following disclaimer.
*   2. Redistributions in binary form must reproduce the above copyright notice,
*      this list of conditions and the following disclaimer in the documentation
*      and/or other materials provided with the distribution.
*   3. Neither the name of STMicroelectronics nor the names of its contributors
*      may be used to endorse or promote products derived from this software
*      without specific prior written permission.

If RaceFlight do not have an agreement with STMicroelectronics, point 2 is violated since bin is the only way RF1 is distributed

Atollic TrueSTUDIO(R) license violation

**  Environment : Atollic TrueSTUDIO(R)
**
**  Distribution: The file is distributed �as is,� without any warranty
**                of any kind.
**
**  (c)Copyright Atollic AB.
**  You may use this file as-is or modify it according to the needs of your
**  project. Distribution of this file (unmodified or modified) is not
**  permitted. Atollic AB permit registered Atollic TrueSTUDIO(R) users the
**  rights to distribute the assembled, compiled & linked contents of this
**  file as part of an application binary file, provided that it is built
**  using the Atollic TrueSTUDIO(R) toolchain.

One more time, if RF do not have separate agreement with Atollic, they are violating license above. I have not seen information that RF1 was built with Atollic TrueSTUDIO(R) toolchain.

I will leave it without any additional comment.

RaceFlight One Source Code, drama continues

This is the follow up of yesterday entry RaceFlight One source code has been published and what does that mean. Before you continue I suggest reading that post first.

Another day, another drama. Or rather the same drama continues. There are two major updates on the topic of RaceFlight source code and team conflict.

RS2K states that he did not know that RF1 contained GPL code until recently (not directly tho)

rs2k gpl statement

Some people have asked my why I decided to release my project under GPL V3 license instead of more permissive license such as the MIT license. The simple answer is I am required to by law. It came to my attention that there was GPL base code in RF1 that was added without my consent.

rs2k RaceFlight One repository on GitHub is not available anymore

RaceFlight One DCMA takedown

Just like expected, rs2k/RaceFlight-One is not available. It was taken down under DMCA act by request of OrangeCode. OrangeCode is apparently a company owned by Preston Garrison aka proggod. Full details of DCMA notice is available here. If TL;DR, it states that:

  1. OrangeCode owns copyright to RF1 code
  2. Kalyn Doerr aka rs2k is an employee of OrangeCode and had not right to publish the code
  3. OrangeCode (proggod apparently) states that "I swear, under penalty of perjury, that the information in this notification is accurate and that I am the copyright owner, or am authorized to act on behalf of the owner, of an exclusive right that is allegedly infringed."

RaceFlight One source code has been published and what does that mean

In the beginning of time, there was MultiWii and it was good. But then times moved on and 8bit ATmegas were end-of-line for flight control. So, Baseflight was created. In the beginning, it was supposed to be only a MultiWii port to support STM32f1 flight controllers in a for of Afroflight Naze. And it was good for a while. But the guy that was running this show turned out to be a prick and one of Baseflight developers forked everything and called it Cleanflight. One might want to say "Hail Hydra" but let's try to be serious here.

Anyhow, everything was great again. No pricks anywhere and Cleanflight was growing. People started to fork Cleanflight. Betaflight, INAV and Raceflight were created. No problems anywhere, one big happy family.

It did not take long for things to change. Someone decided that he can make money by making code closed-source and run only selected, sold by them hardware. It was RaceFlight by the way and this is a reason I'm not writing much about them. There real problem is that you just can not make an Open Source code under GPL license Closed Source just like that. It is virtually impossible since all commiters would have to agree to that. All of a few hundred. Good luck with that. INAV tried to change license once (and still be Open Source) and it failed. Few devs just said no. End of story.

Back to Raceflight. When in late 2016/early 2017 Raceflight went Closed Source. Some devs decided to check this and that, decompiled RF firmware and compared that with CF/BF. Surprise, surprise, decompiled code for gyro initialization looked exactly like in CF/BF. Raceflight was violating GPL license! They had no rights to close the code of Raceflight. Period. RF team defended themselves as they could but IIRC finally published source code for Raceflight (not RF One) like GPL required. Joshua Bardwell did a video on that topic you might want to watch BTW.

You might think this is the end of a story, but not. Raceflight announced RaceFlight One and claimed that RaceFlight One is 100% their doing, rewritten and does not contain absolutely no code from Baseflight/Cleanflight/Betaflight. So it does not fall into GPL at all. They were more less believed and most of pilots forgot about the whole thing.

Until yesterday. Because yesterday, Kalyn Doerr aka rs2k (one of creators on RF) published the full source code of Raceflight One on GitHub and posted something interesting on Facebook too:

(…) I don't want to say much publicly right now. I have kept quiet as I have been in fear for my safety for some time now. Over the last several months I have documented Preston Garrison's business dealings as he has tried to keep me away from the business. I have had no success in reasoning with him. I created it originally to share with the community and I have poured my lifeblood into it. It will not die here. I am RaceFlight.

Pretty scary, isn't it? Drama and stuff. But what happened is that RF One source code is on GitHub. Take it while it's fresh since it might be removed due to DMCA soon.

Let's leave the drama and see what mentioned Prestion aka proggod posted:

Well apparently Kalyn decided to release our code to the public without consent from me. I have no idea what his intentions are, or why he would decided to do this, last time I communicated him he was working on his home life. I can say he doesn't own the code, and it certainly can't be licensed as GPL, especially since he was not the only contributor to the code base. (…)

In other worlds "_I have no idea what happened but this code is private and GPL does not apply". Well… Betaflight community decided to check again an they found out something very interesting:

//TODO REwrite this better
char *ftoa(float x, char *floatString)
{
    int32_t value;
    char intString1[12];
    char intString2[12] = { 0, };
    char *decimalPoint = ".";
    uint8_t dpLocation;

//TODO REwrite this better is nothing strange. But, exactly the same ftoa implementation can be found in Cleanflight, Betaflight and INAV source code. And by exact, I mean exact. not similar. Exactly the same. It was committed by hydra in April 2014 under GPL license. And that means one thing: whole RaceFlight One is GPL. This is how GPL works. They did not rewrite it from the scratch, they took some elements of GPL code and continued from there. GPL is very intrusive license: if you use anything licensed under GPL, your whole project is automatically GPL too. Period.

I have no idea who is lying. But someone on the RaceFlight side is lying. Why? If you do not know why it's because of money. An old universal truth. And I suspect this whole thing might have legal repercussions and someone will meet someone in a court. Is that good? No idea. Bottom line is: RaceFlight One is violating GPL license of a code it was based on.

Ah, there is one more small thing. According to some RF/BF devs and users, Preston Garrison always stated that RF One is not using Kalman filtering. More, users were apparently banned from Slack for suggesting RF One was using Kalman filtering. Guess what… The published code suggests RaceFlight One is using Kalman filtering… Funny….

I will try to keep my eye on it and if I will keep you posted in case of any major developments (if any)…

Update #1

No, there is no Kalman filtering in RaceFlight One after all. All occurrences of Kalman filtering are commented out

Update #2

After all, there is a Kalman filter in RaceFlight One. The commented out code refers to multi-state Kalman filter. Method PafUpdate that is used for gyro filtering is 1-state Kalman filter. Thanks DigitalEntity for discovery

Follow up for 2017.12.07