Hexacopter != Redundancy

Hi, I’ve been persisting with some time on a hexacopter project. My main motivation for using the hex frame was for redundancy in the case of a single motor/ESC/prop failure. I’ve had various failures and made various mistakes and one thing that has become increasingly clear is that ArduCopter can never recover control of a hexacopter that loses a single motor in flight. The copter invariably spirals and wobbles to it’s demise at the surface.

I’ve had a bit of a search here on the forum and I see some discussions about nobody really knowing what the expected behaviour really is when a motor fails.

I’d be very interested to hear anybody’s experiences with getting redundancy to work with a hexacopter, or is the only real benefit of a hexacopter the increased lift? Thanks!

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Ahh, I found some the relevant discussion here:

And more here:


In my case I got the…
2021-06-14 14:35:08.036 Error: Subsys THRUST_LOSS_CHECK ECode 1
2021-06-14 14:35:08.036 Potential Thrust Loss (6)
…messages.

And Leonard’s suggestion of an alternate motor configuration which should improve controllability.

I haven’t found a clearly written summary of what the requirements are to be able to land safely, but from a skim read a Y6 has better chances, you probably need at least a 3:1 thrust:weight and you’ll likely lose yaw control even in the best case. I expect this copter had enough thrust but it still crashed. I’ll need to read more closely through the threads, but I think the short answer is that maintaining control of a hexacopter with a failed motor is very difficult.

You can increase the chance of controlling the craft after a motor loss by using the alternative Hex motor ordering.

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Hi David,
I lost one engine due to a mechanical failure from my hexacopter a few weeks ago and even though it wasn’t fully tuned, l managed to land safely.

If you like, I can try to find the bin log of this flight.

Best regards,

Maarten

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Great to hear Maarten. Do you have it set up in any special way, e.g. the PPNNPN motor pattern discussed in one of the Github issues I linked to above?

No David, just the standard settings. But I am quite sure that I landed in alt- hold mode.
Regards,
Maarten

Just so your aware. Flying a hexa is no guarantee of a safe landing in the event of a single motor out. Well tuned or not. Sometimes the machine just isn’t happy with one motor out and things conspire against you.
Just putting it out there.

Last month my hexa had a ESC failure (motor 5) over the sea - a few minutes after released the fishing line, fortunately, I could do a landing safely.

Log: https://www.dropbox.com/s/vf00f1dkj495oar/log_27_2021-5-1-15-46-46.bin?dl=0 (at 7m41s)

You do need surplus power but I don’t think it needs to be that extreme.

This YouTube video does a great job describing how a hex can safely fly with one motor out.

(The noise while he shows the code is temporary. I have no idea why he ruined a fantastic video with those annoying sounds.)

It looks like if the hex is properly setup, it can safely fly with one motor out.

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