I believe I have a problem with my Pixhawk and was hoping for some help. Also posted this on rcgroups.
The issue is that when my speed controllers are hooked up to the Pixhawk they exhibit a bad sync issue. However when they are connected to my old APM (3.1) or just a receiver directly they do not exhibit these symptoms. This has resulted in 4 crashes now until I just tonight narrowed down the issue to the Pixhawk.
Can anyone advise what is going on? Here are the specs of my setup:
Afro 30A ESC's with SimonK firmware (have tried all versions, and made my own with various parameters)
Tiger MT2216-9 1100kv motors
4S 3700mah battery
Fact of the matter is, APM 2.XX has 5 volt PWM output and there were no problems related to motor sync issues. It was the decision to use 3.3 volt PWM and not 5 volt PWM when it was readily available, evidently causing the motor sync issue only with PixHawk at 3.3 volts.
Let's hear from the users as to what they would prefer....3.3volt PWM or 5 volt PWM They aren't easily fooled.
While I perfectly agree this is a difference, its not the only one, and we shouldn't conclude this is *the* relevant one (as explained in my last post). Pixhawk's output *changes* at 400 Hz, while APM maxes out at 200 Hz changes (APM has a 490 Hz update rate, but the actual PWM width only changes at the main loop rate - so the ESC sees a step response with 200 Hz max).
Our tests suggested that when lowering the maximum signal update rate some ESCs stopped having sync issues. This however merely means that the ESCs are not doing their input signal conditioning correct (we don't want to make the flight controller slower! that would limit performance.).
One ESC notoriously having issues with signal speed was the AfroESC with its own firmware. Changing to SimonK firmware on the same ESC resolved it. *Interestingly* HobbyKing has since completely halted shipping it with the original firmware and ships with SimonK as default now.
Unlike other ESCs come with an "airplane" firmware - with features like braking, soft-start or voltage cutoff - and can be reprogrammed with open-source code, the Afro series was designed by Mr. Hamasaki (aka TimeCop) and ran SimonK code from birth.
There is now an option to use BLHeli firmware on the Afros, but otherwise they only exist with SimonK. No other "original" firmware.
I can just refer to the user reports we got - it very well might have been an update to the Firmware revision which made the difference.
You still have not explained why, you chose not to have 5 volt PWM when it was readily available. Are you saying 5 volt PWM is bad?
There are two main reasons we opted for 3.3V: The first reason being that in the complete population of receivers we tested (Spektrum, Futaba, FrSky) the output voltage was 3.0 to 3.3V. So essentially the de-facto standard is 3.3V (also in normal TTL logic) and with the drive capacity Pixhawk has its well within the standard range (outperforming e.g. a Spectrum AR10000 in terms of current drive capability, as one of the authors in this thread or the corresponding one on drones-discuss found out and highlighted). Now you could still ask why not 5V like on APM, even though the rest of the market uses 3.3V. The reason to not do this are the other peripherals like camera triggers people hook onto these pins (the APM Firmware when running on Pixhawk supports the use of these pins as GPIOs). We do not know if the peripherals people connect are 5V tolerant and with most RC receivers and other flight controllers outputting 3.3V levels, we wanted to rather be as standard as possible for maximum compatibility.
"The first reason being that in the complete population of receivers we tested (Spektrum, Futaba, FrSky) the output voltage was 3.0 to 3.3V."
"even though the rest of the market uses 3.3V"....
The market of what? Receivers? Is the Pixhawk a receiver?
Sorry but I think the rest of the market use a 5v output! (APM, Naza, Wkm, Crius, Mk, Rabbit, Naze32, Vrbrain, KK, CC3D, Zero UAV, etc etc etc ....)
Very well said Lorenz
I feel like inserting a rant here.... but won't feed the Troll....
My investigations about pixhawk sync issues :
I have just constructed a 3dr DIY Y6 following the instructions. I did all of the calibrations etc. and the motors spin fine with no props on them. After I add propellers some of the motors sound like they are loosing sync or something. I can hear the tale tale ticking and sometimes see a propeller slow down or stop then restart. After the first flight attempt I took the hex back apart and tried to better separate the PWM cables from the motor wires and got the same result. With no propellers on I tried varying the throttle quickly and it seemed fine, but not so with propellers. It seems that the motors that visibly have issues are the bottom right and left motors so that would be numbers 2 and 6. I have uploaded a log file if anyone can help that would be great. I dont really know where to go here and would rather not waste time tearing the thing apart again to replace 2 escs that may or may not be bad. I also enabled IMU logging and see a few spikes of high accels, but as I was testing the motors I tried to give command inputs to cause roll and pitch to see if the working motors behaved properly. Oddly when I gave forward pitch the copter pitched backward. I will check in my radio calibration to see if I have that reversed. Thanks in advance for any help, I am really up against the wall on this project.