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Does this buffeting look like VRS or something I can tune out?

evranch

Active member
#1
Sorry, the video is pretty bad. I was out familiarizing myself with my quad and playing with the sheep, and I noticed only one really bad tendency - to buffet pretty hard on rapid descent.


Is this the famous "Vortex Ring State" or is it perhaps something that can be tuned out? 8" props, AUW ~1050g. Hovers around 65% throttle with this 7700mAh 3s. Minimal wind.

At the end of the clip I descend while traveling forwards and it still buffets somewhat, I suspect this means it's PID related rather than VRS?
 

PsyBorg

Wake up! Time to fly!
#2
Its a combination of low pids and just falling straight down into your own turbulence. Its gonna be more severe as you are super heavy with that massive battery.

Just be aware and be moving before decending. Maybe come down doing small circles
 

ElectriSean

Eternal Student
Mentor
#3
You can probably tune some of that out, but as Bill says, it's better to just avoid that situation. If anything is going to bend your motor mounts it's that... Forward motion and gradual throttle changes :)
 

evranch

Active member
#4
Thanks guys, I will try to avoid vertical descents. It looks like I will have to do them occasionally in close quarters such as in the corrals, but if I come down gently this issue doesn't occur.

Which PID term would help stabilize this when it does occur? It's obviously easier on the machine if it doesn't go into oscillations.

The 7700 is a massive battery indeed, isn't it. It does feel really heavy, has a lot of inertia, and it's easy to pick up a ton of vertical speed quickly if I drop the throttle just a little too low. Maybe I should keep to HORIZON rather than full ACRO since I could probably put a lot of stress on the mounts and frame by pulling too many Gs by accident.

I'm wondering where the endurance breakpoint is between more capacity and more load on the motors. Is there a recommended percentage that hover throttle should not exceed?

Hover throttle settings with different 3s batteries:
2200 - 45%
6400 - 55%
7700 - 65%

The gain in capacity is obviously worth it from 2200 to 6400, but I wonder if the 7700 is pushing it a little too far. Especially as amps tend to climb rapidly as throttle settings approach 100%. Wish this FC had an ammeter.
 

PsyBorg

Wake up! Time to fly!
#5
I am in the mindset that acro is your best case. Any of the assisted modes will try to correct every little air bubble you bump.

I think if you do like I do on all my quads and set I gains to between 50 and 60 and maybe raise tpa start about 1700 to 1750 then it wont gimp your pids in the lower throttle range. You are heavy so that is already probably in the range tpa kicks in for faster travel and higher rpm just hovering.