I seem to remember talking with Rob some years back about the 3D he was doing with TradHeli. But I digress.
The virtual flybar acro gets rid of the robotic feeling rotate and hold that helicopter pilots don’t like. It is adjustable via the existing roll and pitch bal parameters. Helicopters can be easily flown without any gyro stabilization at all but something must be done to damp the controls so they aren’t so jerky. This is the “feel” that helicopter pilots like because it is what the full-size machines have.
The main problem with ArduPilot and 3D aerobatics is the EKF. It provides the attitude solution, even for the VBar acro. The EKF is quite fragile and can cause a helicopter to roll over by doing something as simple as landing and ground running a hot piston engine at flight idle to cool it down. The VBar acro makes it a lot safer to do this as it doesn’t really care what the EKF thinks the attitude is as long as the pilot is on the controls. The EKF might think the helicopter is rolled 30 degrees, but the VBar won’t force it to that attitude. It was a vast improvement in acro for helicopters, but it is still not as robust as the commercial FBL units because of the EKF.
Again, ArduPilot is designed as an autonomous autopilot system, and for that the EKF is quite useful to correct drift and bias in sensors. But acro does not make ArduPilot a swiss army knife that can go from flying waypoints on one flight to F3C/N competition flying on the next. It does not even have the advanced setup features and options that FBL units have to do so. And, vice versa, FBL units do not have the advanced setup features and options to be an autopilot system. A few have tried it like HeliCommand GPS and Skookum Robotics but they are not as good as ArduPilot at being an autonomous system.
Two totally different applications for two totally different worlds. But that does not mean that pilots who fly the ArduPilot system do not like an acro mode that feels and handles identical to a full-size machine. And that is probably why the VBar acro is one of the more popular features for helicopters in the last 3 years.
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The only way that the virtual flybar changes the way the aircraft flies is if the input shaping (or “feel” parameters in the attitude controller) are not being used because it has not been setup correctly. With Josh’s aircraft he will struggle to tell the difference even with the roll and pitch leak is set extremely high. This is because his heli doesn’t get much more than a degree or two from the target at any time. So there is nothing to leak.
VBar acro is still very dependent on the output of the EKF. The problem isn’t what angle the EKF thinks you are at it is the EKF changing what it thinks level is as this will be translated into acro as another input. This is just as true for VBar as the normal multi ACRO.
I do have two acro attitude controllers that are almost completly independent of the EKF except for the gyro bias.
input_rate_bf_roll_pitch_yaw_2
and
input_rate_bf_roll_pitch_yaw_3
I have been meaning to put an acro type parameter in to let people choose which one they use.
Will people win an acro competition while flying ArduCopter, no. Will we get it to a point where it is capable of full ACRO. There is no reason not to.
There’s a little more to it than that. Helicopter pilots do not want to move the ghost and then have the helicopter achieve that new attitude. The best example is the ground run where the frame can’t move but the rotor’s TPP can move. Say the heli is level on the ground (slope procedure is more complicated) so wind or dynamics makes it necessary for the pilot to make a control input to control the rotor’s TPP. With the conventional acro, make a control input, the ghost moves. Center the cyclic now the helicopter is trying to tip itself over and that’s not what the pilot is commanding it to do. It is a constant game of bump and center, bump and center to twiggle the ghost around. In flight it is the same thing, although now the frame can move. But to make it scale-quality smooth you can’t have the bump and center thing, with snap to attitude and hold. That’s artificial 3D type setup. What we want is scale quality - the flybar feel from a FBL head that a few of the FBL units like the Mikado VBar and AXON have mastered.
Everybody that has flown it loves it. The pilots are the ultimate test of whether or not it works. 
I was simply pointing out that 20 degrees of collective range is not near as smooth in the same stick throw as 12 degrees. Since the system is not set up or suitable to use that much negative pitch you are creating your own issue with not only touchy collective control when switching modes, but also potential for destroying your helicopter. That kind of pitch at only 1,800 rpm can off-track the blades into the tail boom and blow it up. Just so you are aware of the implications of such a setup. The 3D guys run custom expo curves on the bottom side to prevent accidentally overloading the rotor and blowing it up. ArduPilot doesn’t have any of that setup.
@ChrisOlson brings up a good point here and probably where the Vbar (attitude error leak) shines. The air/ground transition aspects become much better with having that attitude error leak off when the airframe is being held while the pilot is making inputs. I would be curious for @JoshW to try the Vbar acro with @Leonardthall approved setup to further explore the implications in flight. In theory, I agree with Leonard, now that he pointed it out, that a perfectly tuned helicopter should not see any difference with Vbar versus regular Acro.
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Good call, completely agree with your point on this. Thank you!
Is this in the controller or the RC TX? I’m asking because I never had this on the BeastX set up (rookie FC, I know…) and my friend who has helped me even get started in 3D Heli a while back who runs IKON also had nothing in his radio like what you’re describing… That is what has me wondering if this curve was in the controller and maybe some 3D Heli pilots don’t know (or don’t communicate to me) that it is actually present in the controller?
Can confirm, and agree, Helicopter pilots are used to being able to move TPP and not the ghost in this situation. Regardless of whether or not there is consensus at the control system level on the approach here, that is absolutely what Heli pilots are going to expect.
The difference between theory and practice is that in theory there is no difference. In practice there is.
On a smaller helicopter, maybe not much difference, if at all. On bigger ones night and day difference. The rotor’s TPP moves around more than people suspect. The blades on a 766 have 165mm clearance to the tail boom at static. I can tip the rotor’s plane enough to have the edge of the blade disc come within about 25-30mm of the boom with full aft cyclic input. However, there is a nick mark and small dent in the tail boom where the blades have hit the boom before in flight.
What the controller measures is the frame angle, not the rotor’s TPP. The pilot doesn’t measure either one. He/she measures by response to stick inputs, and this is where VBar acro shines.
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I am happy to try as long as one of you doesn’t say “IF YOU DO THIS YOU WILL EXPLODE YOUR HELICOPTER” (or something to that effect but maybe with less caps). Let me try some “basic Acro” in the system as configured now, and then switch to the Vbar acro (Assuming it is in Stable and not Master, because if it is in Master I know there are changes and will request some assistance in that upgrade) @Leonardthall @ChrisOlson @bnsgeyer sound good? I do want to give the Auto take off and landing a try with the recommendations out of Bill and Chris first before going to the vbar system, but, I go to the field with enough batteries for at least 2 flights if not 3 (and an option for 4) so I am not opposed to getting everyone some data to analyze if it is helpful.
If you can get any 3D or F3C/N competition pilot to actually share their secret combo of setup you’re probably married to her. Because I’ve never been able to eek it out of anybody except for generalizations. It’s always the same - you gotta tune it to your own liking.
The setup is in both the controller and the RC radio. The gains in the idleups are different from Normal to Idle1, Idle2, etc… And the curves, rates and expos in the RC follow suit. Even throttle hold many times has different setup than Condition Normal.
The “trick” in these 3D style setups is how to transition from one to the next without getting big jumps in handling and collective position. ArduPilot has none of this built into it. ArduPilot assumes one “tune” works for all, and there’s only one way to tune it. FBL units are way more advanced than that.
The VBar acro is in master. But not in the 3.6 official releases. But you can get it in 3.6 with the ArduHeli build on 3.6.7.
The 3.6.7 build will have the least impact on your existing 3.6 setup. The 3.6.9 build has a new swashplate library (that is also in master) and requires carefully going over your swash setup and selection as it does not automatically convert existing 3.6 settings to the four-servo support, etc., used in the new library.
Those two builds are the only way, at preset, to fly VBar acro in 3.6. I would suggest checking in on the VBar acro thread as to setup, how to tune it, etc… It went thru an evolution from the first design to what actually went in master. My first design totally screwed up acro for multicopters. Bill fixed that and made it specific to helicopters, and doesn’t affect multicopters, before we put it into master. The version in the 3.6 builds is what is in master.
Yeah, Leonard asked me for a wishlist recently, as he was curious from my vantage point what I see missing. My answers so far were only really comparing to the bit I know of BeastX, wherein you have a “Normal” mode for Scale, and then Sport1 and Sport2. I wish I could say I have had exposure to other systems but that obviously isn’t the case.
That said,
I’d love AP to have the interlock be able to be on a 3-pos switch, and you go from locked out, to Normal, to “sport” which would bring the head speed up and adjust the gain scheduling, input shaping, etc to the new headspeed. Any “Auto” mode would force “Normal” gains, rates, accels, etc. There is no debate the system is not ready for this today, and making it ready would be a tremendous amount of work. There are probably better approaches to that end (such as, making the mode switch to acro be the deciding factor for which performance profile to fly) but as a user, for me I would love to see something like that one day.
Josh, the auto takeoff and landing thing is not even a big deal. It should work out of the box as long as you get the LAND_COL_MIN set so it doesn’t drive a bunch of negative pitch at setdown. Just be aware that in these GPS modes on the ground it can crash your helicopter if you get GPS drift or some other problem. And you won’t have control over it.
Ah, so another tuning opportunity, lovely 
So, I do have a 550E I want to pull out of the bag and put AP on. The intent for that heli was to make it more Acro-ey, so perhaps I go down the path of getting Master on that and then could even tinker with the L1 - is that the same Master we’re talking about?
The L1 Nav is not in master. That is in the ArduHeli 3.6.9 build.
The L1 Nav is also in another build I run in my commercial machines. But that build is not publicly available as I have some other changes in it that are specific to my needs. You can pull the L1 Nav commits and put it in whatever version you want, and build it yourself too. Those builds are there only for public testing of the features.
You should not have to touch anything you have done thus far with attitude and rate controllers. Basically you are just setting the acro_trainer to zero (vbar is always enabled with trainer disabled) and adjust acro_bal_pitch and acro_bal_roll parameters to get the feel that you like. a value of zero is basic acro with attitude hold and then greater than 0 up to 3 sets the amount of attitude leak. Of course, that is if it works as well for your tune.
That is the impression I have gotten, and I very much appreciate it, thank you!
Ah, ok, that sounds reasonable.
Josh, there is some caveats with taking off with regular acro. Just be aware it’s like the BeastX and it will tip your helicopter over if you start making cyclic inputs on the ground after you start spooling up. VBar acro won’t do that. I like BAL settings from 2.0 - 2.5 for VBar. With it set to 3.0 it’s like a flybar with super heavy weights on it, which most people don’t like.
Ok, good feedback. I also appreciate you’re able to map to my BeastX-like expectations lol. Thanks again
So this is the interesting part of this discussion. TPP is an important feedback mechanism to the pilot. In Multi we don’t have such an obvious feedback mechanism on the ground and have to take a lot more notice of the prop rpm and air wash to ensure a nice vertical takeoff. In stab we will offset our requested attitude to match the aircraft attitude. On a heli this would align the TPP with the body. In acro it starts at the current attitude unless you play with the sticks while spooled up. Heli is a way behind Multi in regards to the PID and mixer limits during take off and landing so that is also poking its nose into the mix here.
So the interesting question here is what can we learn from the leaky attitude approach being helpful on the ground to improve the transition from ground run to flight. Then get rid of it in the air so we have uncompromised attitude control (and teach heli pilots how to use input shaping).
This could be even more valuable to the multicopter aircraft as they don’t have the TPP feedback that heli does and long landing gear can be a real problem during take off and landing! Heli call it dynamic rollover I believe. I will have to think about it more.
Yeh, just use the VBar setup and start from there. The ground handling is the big thing where that may significantly improve your handling. Once you are in the air you shouldn’t see much until you really set the leak high. It will mainly show as wondering of attitude, probably something similar to the early days of multi-acro.
I have no doubt it works. The problem is you are stuck in a local minima. It works because it is hiding the poor setup.
The engineers are the ultimate reason it works well, as every good pilot knows.