Can a large drone be flown without a flight controller?

[William_Walker]

@bnsgeyer

I still don’t understand this. So you are saying when you were using the arducopter firmware that as soon as full thrust was requested from the ESC that the motor would shut off. That sounds like a set up problem but I don’t know enough about multicopter setup to help.

During many of my test flights soon after the motors rail. The motor signals start to oscillate wildly off and on and then stop, which has caused the vehicle to crash many times. I have asked the community several times for a solution, but know one has been able to help. Ref the following link for the discussions on this problem and for pictures
of the motors signals oscilating wildly and then stoping:

Does Arpupilot use Anti-Windup in PID loops - Does PX4?

Hi, does anyone know if ArduPilot uses Anti-Windup algorithms in their PID loops? The Motor signals in my vehicle are switching off and on shortly after the motors hit their limits. Here is a link that discusses the phenomena and typical Anti-Windup solutions: Does anyone know if PX4 works any better? Thanks. For more details on my problem see:

@bnsgeyer

Completely disagree. It will require a highly skilled RC pilot to fly that aircraft for any amount of time. Based on what I am seeing in the response after the input, the phase lag is substantial. You really need to consider using the arducopter firmware to help at some level. It may at least allow you to fly with less phase lag in a degraded version of acro mode.

Until the problem of the flight controller behaving badly when the motors rails is solved, it is too dangerous to use. This is why I am trying to fly
the vehicle without a flight controller. Once the vehicle is working and it’s flight behavior is better understood, I will try again to integrate flight controller.

What you call phase lag to me is just time delay due to the huge rotational inertia of the vehicle. From the log pictures we can see the time delay for Elev to Pitch changes is about 1sec. And the time delay for Aileron to Roll changes is about 4 times faster. As long as one anticipates for this delay, the vehicle can be flown easily in the flight sim, and during my last test I felt I had complete control up until the point that it stoped reacting to right Aileron stick command.

@bnsgeyer

This equation looks to be correct but the aileron in the graphs appears to be inverted (i.e. + left rather than + right). It looks like that is the way you intended looking at the plot legend. Any reason why?

You are right. I just plotted it this way so as to not have so many lines crossing.

@bnsgeyer

I doubt that. You already have pitch control power problems. Removing the front motors from pitch control will effectively cut your control power in half. Bad idea.

Removing pitch control from the front motors will just slow down the effect of Elevator stick control. Because of the tremendous rotational inertia of the vehicle it is very sluggish to changes. The Elev stick controll actually felt overly responsive. There is currently a 1 sec delay between Elevator stick control and vehicle pitch. Removing pitch control from the front motors will just slow it down to about 2 sec. I think as long as one anticipates the delay, it can be flown.

@bnsgeyer

What were the winds that day? I think that the motors did have an effect but it was delayed because of the effectiveness of the motors on roll response. Right now I have concerns about pitch and roll control power.

It was a very calm day with 2m/s (4.5 mph) wind. We have tested the vehicle in windier condition perhaps double that speed and the vehicle did not seem affected.

@bnsgeyer

I’m not so sure about this analysis. I’m skeptical that the “wing” had much to do with this especially saying it was asymmetric. There is such a small moment arm for both the wing and the motors. This concerns me.

There is clear evidence in the log pictures that indicate that aierodynamic forces were affecting the vehicle as it accelerated forward with it’s body skewed 30 to the forward movement.

1. The Pitch curve shows that the pitch mirrored the Elevator stick command when it lifted off and hovered. But as it moved forward, the vehicle did not react very much to up Elevator stick command. This is because as the vehicle moved forward, the resultant airstream pushed the nose of the vehicle down.

2. The Roll curve shows that the vehicle was level until it started moving forward. Then it rolled 10 deg right. This was probably due to the right wing skewed forward catching the airstream and pushing it down more compared the the left wing that was further back. This would induce a right roll.

3. The slope of the Roll curve gets steeper as the vehicle rolled left, even well after the left Aileron command, and even after applying full left Aileron stick command. This is evidence that the on rushing airstream got under the right wing, due to the vehicle being skewed left by 30 deg, and rolled the vehicle.

@bnsgeyer

I find it hard to believe that in normal operations of this vehicle that you wouldn’t encounter a similar situation in hovering and maneuvering in a low airspeed environment. If the control system cannot arrest roll rate that developed in your short flight then I think you would encounter a similar situation in the routine operation of the vehicle in real flight conditions (winds, urban canyons…).

You may be right, we will have to test more to see how it behaves in winds and gusts. But the manned vehicle will be heavier, at least double the weight, which will make it lass sensitive to winds and gusts.

In the simulator you can see that the vehicle starts getting tossed around a little with 10