Hi Oscar,
Thanks very much for the info, great resource!
I have the KK2.1.5 FC Flashed to Steveis firmware.
I also have the FrSky X4R-SBUS flashed with new firmware, to allow CPPM and/or SBUS, and have also done the SBUS inversion hack.
Please comment on the following, concerning using KK2.1.5 FC with different TX protocols, as
the order of preference recommended by Steveis in his KK2 manual, is the opposite of what you suggest at your blog.
Do you think the differences cancel each other out?
I read this in the Steveis KK2 manual...
"Appendix E – Receiver selection
To achieve the most accurate flight characteristics, the order of preference for Receiver selection is...
Standard > CPPM > DSM Satellite > SBUS
The reason for the above is, the interrupt processing
that is required to process the receiver channel
output, increases as you go down the list.  
Interrupts that occur during the software PWM loop that
generates the output pulses on M1 to M8 need to be
kept as short as possible to minimize the jitter.  
Standard receivers will cause the least jitter, SBus the most.  
It also causes jitter in the self level calculation,
resulting in the KK2.1.X knowing exactly which way is “up”.
If you only have motors and don’t use Self Level, you probably
won’t notice any issues with SBus.
If you have servos connected to M1-M6 you will notice some
jitter with Satellites and SBus."

I don't know to be honest, I haven't used KK2 for nearly 2 years now
Firmware might be written in a way that is more optimized for certain receiver types, so each firmware/FC could have different preferred RX type, it's possible.
Use what they suggest in the manual if you still have doubt you should check with the author

(17-Jan-2016, 02:41 AM)Oscar Wrote: I don't know to be honest, I haven't used KK2 for nearly 2 years now
Firmware might be written in a way that is more optimized for certain receiver types, so each firmware/FC could have different preferred RX type, it's possible.
Use what they suggest in the manual if you still have doubt you should check with the author

Thanks Oscar,
If/when I get a dual trace oscilloscope I'll see if I can measure the response time (from command at the radio to action at the servo/speed control), using different combinations of RX communication protocol, Flight control Bds., and firmware.
I think that information would be interesting/useful.

I myself have two KK2.1.5, a multi wii, a Naze32 Rev6, Naze32 SP Racing F3, and a few CC3D flight controllers.
Wanted to try different ones to see what I liked best.
One of the things I like about the KK2.1.5 FC, is I can fiddle with the adjustments/features at the field without having to bring my laptop computer, and plug/unplug into the FC, everytime I want to change something.
With Steveis firmware upgrade, they have lots of nice features and good flying characteristics.

Not just the signal timing, but also how the code in firmware is written, how they handle the signal etc... For example some can use the value as they are received, but some might decide to store a few values first and take average this causing delay......

I loved kk2 when I started.. But once you try a 32bit board like the Naze you will never look back so much better!

Thanks again for the helpful feedback.
As a retired electronics engineer, computer geek and 20+ years RC flyer, I am really enjoying my new interest in quadcopters.
The information and friendly attitude you share is most helpful :-)
I have set up a few quads with different FCs, and I agree that the Naze and CC3D are more feature rich and powerful processing for better flight characteristics.
Still I find that the KK2.1.5 mini flashed with Stevies firmware is most user friendly for a beginner, has good flight characteristics with default settings, and has the added advantage of field adjustments without computer connection.
For a beginner, less options and better operation with default settings, mean less stress.

In the future I would like to be able to tweek my 32bit FCs with an iPad app and Bluetooth :-)
That would make them much easier to dial in at the field.
Soon I will also be learning how to use my Taranis plus transmitter to adjust 32 bit FCs PID's in flight, that should help too.
The KK gives me something fun to play with, until I get new skills learned.

Yes I agree the Stevies firmware was the best for KK2 board i really liked it
It is possible to change settings including PID and rates with your transmitter now using OSD menu (not sure if you are flying FPV already?)
This makes it even easier than the KK2 IMO