Hey guys. I've been looking for the right niche community to join for a while. I used to be a forum junkie, in fact I own a car-related one.

Anyways, I've got a Spedix Black Knight 210, an fpv wing, a large fpv plane with an autopilot, and a phantom - all exclusively goggle flown.

I just put betaflight on the quad and am working on getting it dialed in. Running into some midthrottle oscillations and some wonky post-flip attitude changes.

Would also love to fly with someone else sometime. Anyone else in the Roanoke VA area?

Welcome to the forum Trail X! Lots of help here if you can't solve the oscillations (from some more talented than me).
Anyway, good to have you here.

im new here too. just yesterday actually. wanna come up to Canada and fly??? LMAO...... you get that big snow storm in VA today??

Thanks guys, been doing a lot of reading. We pretty much dodged the snow storm. Just a dusting. Would love to fly in Canada someday.

The midthrottle oscillations seem to be high P, but at the same time, they don't seem to manifest exactly the same as high P videos I've seen.

The flip issue I have can be seen in this video: https://youtu.be/CQQBegk-4bw?t=1m4s starting at 1:04 (I even slowed it down so you can see what's going on better). I intended the fast flip, but gave it no roll command. For some reason the front left motor decided to go to a sustained 100% (per black box), and screwed up the flip. I've heard that it could be a desync issue? But I don't know enough about it to really understand it. I never had an issue like that when I was on cleanflight.

If you see a motor going to 100% in a black box log, what it normally means is that the motor has stopped as the motor data in the black box log shows what the flight controller is asking the motor to do and not what the motor is actually doing.

So, when you do your flip, you bring the throttle down to minimum as you flip over. If the idle speed at minimum throttle is too low, your motor may actually stop spinning and may not be able to start again due to the load on the stationary propeller.

The first thing you should try when you see this kind of behaviour is to increase the minimum throttle setting and see if that stops it.

Thanks for the insight.  I apparently had been looking at the 3d model backwards until you said that - I had thought it appeared to be reacting correctly.  However, indeed the motor did not appear to restart after going to zero throttle - based on the motion of the model in blackbox, the motor didn't produce any thrust during that segment.

I included the black box trace of the motor demands in this attachment:


So your suggestion is to adjust the "min_throttle" value up from the "min_command" value?

Thanks again!

min_command is what the flight controller sends when the quad is disarmed. Don't change that. min_throttle is the minimum throttle value when armed, so that's the one you should increase.

Welcome to the forum! The pros here are very helpful! As you have already seen

Thanks, and yes! I reset my bl-heli min max pwms, which were set way too tight. No more flip/roll issues. I still need to work on my PID tuning though. The quad feels kinda loose since I lowered my Ps to try to get rid of some oscillations.

(19-Mar-2017, 02:24 PM)Trail X Wrote: Thanks, and yes!  I reset my bl-heli min max pwms, which were set way too tight.  No more flip/roll issues.  I still need to work on my PID tuning though.  The quad feels kinda loose since I lowered my Ps to try to get rid of some oscillations.

The only way you should set the Min and Max PPM values on your ESCs is by calibrating them. Setting them manually is not the correct way to use them.

Calibrating your ESCs teaches them what the shortest and longest pulse length is that they will see from the flight controller. As the ESCs each have their own clock that they use to time the length of the pulses, how each ESC sees the signal can be slightly different. If you manually set the Min/Max values on the ESCs, you are making the assumption that each ESC sees exactly the same thing, and that's not necessarily true. Setting the values manually can result in the ESCs producing slightly different power to each motor when the flight controller thinks it is asking for the same from each motor. It can also rob you of top end power, or create an unwanted dead band at maximum throttle.

So, what you should do is set min throttle and max throttle to 1000 and 2000 in Betaflight and then calibrate your ESCs. Check the Min/Max values and if any Max value is over 2000, reduce the max throttle in Betaflight by 20 and calibrate again. Repeat until no ESC has over 2000 recorded as the Max value.

Once that is done, you should check to see what minimum throttle value is needed in the Betaflight motors tab to reliably make each motor spin. Take the highest value of the four motors, add 20 to it and set this as the min_throttle value in Betaflight.

If you get desync problems again, increase the min_throttle value in Betaflight and leave your ESCs alone!