jcg1541

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    • Phones, Networks, And The Red Pill
Re: Cliff Diving PID Setting
« Reply #45 on: April 13, 2018, 04:51:30 pm »
Yes, good idea.

Looking at the picture, the vortex ring seems to be some kind of inverted ground effect that comes out of nowhere.

karla

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Re: Cliff Diving PID Setting
« Reply #46 on: April 14, 2018, 07:31:21 am »
Haha yes that's a way to put it I guess.
Its the number one dangerous flight conditionfor a full size heli and a common cause of crashes. It may happen when descending vertically (90, tops 70 degrees) and rate of descent is relatively high for a normal heli, 2-4 m/s. I don't know how this translates to our smaller helis, the tip of a rotor moves typically at 200 m/s, we have higher rpms but much shorter rotors. I just have a gut feeling our helis will need to have a higher rate of descent to get in to it. Anyway, the heli basically gets trapped in its own main rotor downwash. Descending faster or slower will move it out of the predicament.
I think you could expect to move through this state as you dive.
Other than that it could be useful to your ends.

jcg1541

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Re: Cliff Diving PID Setting
« Reply #47 on: April 14, 2018, 11:52:55 pm »
Karla, My setup is closer to 200 size than 250. The rotor head is from the Blade 180 , and blades are Oxy2 210 blades that are barely over 200mm from bolt screw to the beginning of the sloped cut.
The rotor diameter is close to 490 mm . The weight is less than 250 grams including Raspberry Pi.
I do use the attitude mode to launch/land from/on hand .  The outer loop high gain is very helpful for catching.


I had a look at your PIDs. The only thing that sticks out is your I terms, never seen so high in 250 or 450 size heli. But I would not worry, if its working.
B t w your outer loop PIDs are very high but you only do rate mode so it is not used.
« Last Edit: April 15, 2018, 06:56:41 pm by jcg1541 »

karla

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Re: Cliff Diving PID Setting
« Reply #48 on: April 16, 2018, 07:14:00 am »
Got it John,
Will try later to calculate at what decline rate such heli would expect a vortex ring state.
Meanwhile, I think you can really just experiment and try it out.
Now you know what to look for and how to recover from it.
symptoms
. heli vibration
. random yawing, rolling and pitching
. increasing rate of descend
. less cyclic stick respons
recover by rolling

What do you think?
 
« Last Edit: April 16, 2018, 07:20:16 am by karla »