jcg1541

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Helicopter flipping like a quadcopter
« on: April 22, 2018, 03:40:57 am »
I have been testing 1080p camera and have been changing the max rate and rate deg/s. It looks like heli's flips max out at about half of a full flip per second.

A 360 degree flip takes at least 2 seconds. Attitude drop will be 20m free fall with zero collective pitch. The 20m drop is almost a landing approach.

600 deg/s for rate mode and max for all modes, but heli physically does less than 180 deg/s, videos



Default 220 deg/s for rate mode and default 300 max for all modes, similar performance,

(in the next flip I waited for the tail punch with the sudden collective pitch zeroing to settle, and that extra altitude drop is fatal) 

(the heli is back in the air without any trim changes 1 minute after the crash thanks to servo saver mod)

My next built for production will have 1080p , sample videos,
(the cyclic vibration is caused by bad twitching servos as someone did a analysis in the second video below)



(the bad twiching servos can be heard like clock ticks in the first 3 seconds before the motor spool-up, the bad servos also overheat CC3D resulting in burning hot board)
(video removed due to private info)

(good receiver setup has no vibration in a straight line flight path)

« Last Edit: May 08, 2018, 07:21:47 pm by jcg1541 »

Re: Helicopter flipping like a quadcopter
« Reply #1 on: April 22, 2018, 04:24:08 am »
Some do, but not all.  :)

If your heli has a flybar (not FBL), then it is a main issue in roll rate.  The heavier the flybar, the slower it rolls.  The flybar is designed to make the heli smooth and easy to fly and it makes it roll slowly.

I am going to make a guess that it is not the best setup to have a heli that will only roll 180 deg/sec, but have the FC set to roll faster than that.

As always, good luck.  :)

jcg1541

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Re: Helicopter flipping like a quadcopter
« Reply #2 on: April 23, 2018, 07:43:05 pm »
Interesting. I remember seeing a few people doing 1-second flips with Blade 200 SRX heli. But they start the flips with quite some forward speed, not from rest.

I am leaving my cyclic rate at 600 deg/s and also 600 deg/s max, so, that when I do start the flips with enough initial velocity, the CC3D PID loop won't  try to slow me down.

My setup is indeed flybarless FBL. But all my video stunts so far all start from rest and free fall. 
« Last Edit: April 23, 2018, 07:48:08 pm by jcg1541 »

jcg1541

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Re: Helicopter flipping like a quadcopter
« Reply #3 on: April 28, 2018, 02:26:51 am »
OK, Got a close-to-one-second flip from rest free-fall without initial velocity. 1080p video below.
 Please notice the audio microphone picks up only the tail motor sound, and the audio track sounds confusing.
The main rotor rpm is at near constant level. But you can't hear the main rotor except wind blowing.
You hear the tail motor spinning up to counter collective pitch increase or whenever the craft turns to the right.

. The fix is to widen up swash travel range in Librepilot PWM output tab, and stipulate collective pitch range on the transmitter side's pitch curve.
Picture of the 1080P camera setup attached.

Also, all the PID gains need to be reduced to tame the large swash traveling.

« Last Edit: April 28, 2018, 05:01:35 am by jcg1541 »

jcg1541

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Re: Helicopter flipping like a quadcopter
« Reply #4 on: May 06, 2018, 05:09:52 pm »
OK. Got flat 1-second flips now. The cyclic stick needs to have full plus and minus 12 degrees on the blade angles when aileron or elevator is at extreme ends.
The Output PWM needs to have very wide range. Mine is 500 to 2500 .

The P gain is small, close to Librepilot's defaults; I gain is large, for diving (discussion in another thread).
And transmitter pitch curve is small. Cyclic stick needs high exponent.

« Last Edit: May 06, 2018, 09:29:24 pm by jcg1541 »

Re: Helicopter flipping like a quadcopter
« Reply #5 on: May 06, 2018, 05:52:48 pm »
Increasing head speed will do the same as increasing cyclic range.  Are you running highest head speed?

jcg1541

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Re: Helicopter flipping like a quadcopter
« Reply #6 on: May 07, 2018, 10:36:48 pm »
The head rpm is at the high end when collective is zero'ed. But I don't know if it is the maximum.
See attached pitch and throttle curve. The throttle is elevated during diving and flipping.
I always flip when collective is zero'ed, and I hear the rotor sound at higher frequency than my normal hovering because the zero collective receives very little torque resistance by air.

I am still struggling with high rpm oscillation when collective is between 0 and 8 degrees and trying not to get rpm too high. I plan to zero out all my Derivatives today and then do all my flipping and diving again. The oscillation is not visible during line of sight flying. For example, the video here on-board camera records the vibration , but piloting on line of sight sees a complete frozen in air heli hovering with low collective about 7 degrees and high rpm.

« Last Edit: May 08, 2018, 12:34:19 am by jcg1541 »

jcg1541

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Re: Helicopter flipping like a quadcopter
« Reply #7 on: May 08, 2018, 12:38:58 am »
To add to my problem with rpm, I do have complete smooth on-board video when high collective climbing and low rpm. Here

Re: Helicopter flipping like a quadcopter
« Reply #8 on: May 08, 2018, 01:08:35 am »
Any time you change how fast it flips, you should adjust the PIDs.  This is true with any vehicle with any PID controller.

Simply put, if you make it flip twice as fast (whether it is by increasing head speed or increasing cyclic pitch) you should cut the PID numbers in half to get back to the same tune (avoid oscillation).  Of course it is better to do a full retune, but this ratio sharing should work too if you know accurate numbers for how much you changed the flip rate.

karla

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Re: Helicopter flipping like a quadcopter
« Reply #9 on: May 08, 2018, 08:00:48 am »
Just a thought John.
Most heli flyers that do flips and rolls (the video show rolls I think, not flips), they do that in 3D mode.
A typical 3D heli setup have indeed negative pitch, with a range of collective from -11 to +11 degrees. But your collective do not, it ranges from 0 to +13.
When you do a roll (or a flip) with a 3D setup, the pilot actually use the negative pitch to complete the roll much faster.
Try it in your SIM and you will see?
« Last Edit: May 08, 2018, 08:21:47 am by karla »

karla

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Re: Helicopter flipping like a quadcopter
« Reply #10 on: May 08, 2018, 09:27:51 am »
I think the relevance of this for your issues is that you don't need to have throttle at 70-80% when pitch is low, close to 0, since that will give you very high head speed and induce vibrations.
Instead you can have 80-90% throttle at both ends -11 and +11 pitch but in the middle you only set it to 50-70%.
No vibrations :)

jcg1541

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Re: Helicopter flipping like a quadcopter
« Reply #11 on: May 12, 2018, 05:30:31 pm »
OK, Got subsecond flips now after adding another 3% rpm throttle. Considering a few milliseconds slow start to hit the aileron stick to extreme end in the video,

.
The rate mode vibration is largely fixed with all Derivatives zero'ed. This PID is also OK with diving for less than 7 seconds. But there is still room to improve on this PID for diving.
Some people played softball today, and I moved to the neighbor field, then back. The video montage is from shots from 3 separate flights.

There is always a piro tail punch right after the flip because the stick suddenly released to neutral instantly cancels all torque. The tail direct drive motor/prop retains the momentum for the strong flip that just finishes and does not have active brake to instantly kill the momentum.
« Last Edit: May 17, 2018, 04:12:05 am by jcg1541 »

jcg1541

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Re: Helicopter flipping like a quadcopter
« Reply #12 on: May 13, 2018, 12:05:16 am »
OK, Got the cinematic smooth PIDs . Continuous shot from launch to flip to dive to land video, without any post-shooting processing,
(flip at 0:32 , diving at 1:49)

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