Multicopter failures - what to look for

[FLAP]

New guy here. Don't own a multi, yet, but have been flying the regular heli's for 25 years.
I fly gas and electrics so I'm very familiar with what can go wrong with those. Not counting the low
Battery issues, which one must also be aware of with conventional helis, what common failures affect multi's?
Are they ESC related or motor failures, or central controller? Can a failure to a single motor be compensated for by unaffected motors in a 6 or 8 motor configuration?
I've seen some of the posted mishaps, just wondering what is most common cause. Are multi's (after experience acquired) anywhere as reliable as conventional helicopters?

 

[Stacky]

I can only go on the failures I have had. Firstly bullet connectors caused a crash for me, also a poor quality solder joint on a motor wire. Second failure I have had was when I had my esc's programmed to Lipo instead of nicam. Third failure was on my X8 when a cheap nasty EPP prop broke in flight however I was able to land safely.

 

[Gunter]

Flap, it's all down to quality of the components! If you buy good stuff, it won't go wrong and you should be okay. My big worry was soldering, just one bad joint could cause a crash, so everything needs to be soldered very well.

If you want to go for ultimate failsafe, Mactadpole lost a motor on an octo and managed to fly/land it perfectly. I think anything less than 8 motors might be difficult to fly with a blade out.

Cheers,

Gunter.

 

[FLAP]

great info Stacky and Gunter. I'm with you on the value of quality components. I try to get the best of everything as I've found in the long run, it saves $$. Couldn't afford that approach 25 years ago, but can do it now. I'm either older and wiser, or have more money than sense I did see an interesting video on photoship one site when they took off 3 props off a decorator and it still flew well. I would guess that 6 motor configuration would be the minimum config to recover from a motor/esc/connector failure. So, I"m leaning toward 6 or 8 multi.
Glad to find this forum. Time to do some reading.

 

[RTRyder]

great info Stacky and Gunter. I'm with you on the value of quality components. I try to get the best of everything as I've found in the long run, it saves $$. Couldn't afford that approach 25 years ago, but can do it now. I'm either older and wiser, or have more money than sense I did see an interesting video on photoship one site when they took off 3 props off a decorator and it still flew well. I would guess that 6 motor configuration would be the minimum config to recover from a motor/esc/connector failure. So, I"m leaning toward 6 or 8 multi.
Glad to find this forum. Time to do some reading.

The only 6 motor configuration that you can rely on to continue to fly after loss of a motor is a Y6, a flat hex can theoretically still fly but the fact is it depends a lot on the weight and size of the hex as well as pilot skill. Losing any one motor on a flat hex is roughly equivalent to losing the tail rotor on an RC heli, problem is you can't just hit throttle hold and auto it down like you can on the heli. Loss of a motor on a flat hex will result in continuous yaw which can be dealt with by a good pilot, the bigger issue is if the hex still has enough lift on just 5 motors to be able to compensate enough to not flip and that depends on a lot of factors. Assuming it can continue to fly you then have to bring it down while in a continuous spin in either direction dependant on the rotation direction of the failed motor, not too big of a problem given plenty of space and nothing underneath that will get damaged in a hard landing. If you have a camera on a gimbal hanging off the bottom the likelyhood of the hex being able to stay in the air and land without damaging anything is about slim to none, more so if you are flying over buildings or in confined spaces with hard objects at ground level.

The only truly redunant configurations that are known and proven to be able to withstand loss of a motor in flight are the coaxial Y6 and X8 plus the flat octo, pretty much anything else goes into brick mode at that point. As others have said, using good components lessens the potential for a failure to happen, if you want to be certain that in event something does you will land safely then its either coaxial motors or a flat 8 at a minimum.

Ken

 

[FLAP]

Ken, thanks. You just saved me many hours of research. You certainly have narrowed my choices. Flat 6 & 8 were on my short list of considerations. That list shorter. I'll read up on the other options you mentioned.

 

[MombasaFlash]

I too come from the single-rotor AP world and bought a MikroKopter octo to 'test the MRC waters'. Did a small photo job with it and a prop blade broke off in the air (cheapo EPP as supplied in the kit). It didn't phase the Octo one little bit. THAT sold me on Octo redundancy and I have just commissioned a Droidworx flat 8 heavy-lift.

Had I known about the Y6's ability to survive a motor loss I might well have gone with that because it is the most camera-friendly configuration with a nice big open space in front of the lens allowing upward tilt without booms and props coming into frame.

 

[Efliernz]

One thing to look out for with the cheaper motors with cir-clips underneath holding them together - Make sure they are intact after a hard landing by trying to lift the motor off the mount.

After a minor 217' drop (after one of my motor solder joints gave way...) and my hex being placed firmly on the ground, several of the lightweight cheap motor mounts had flexed enough to pop the clips. Not obvious until a bench test showed two motor/prop combos trying to climb out of the base housing! I had already done 3 more flights before noticing!
Just give them a quick pull before each flight before connecting the battery

Pete

 

[seattle_helo]

Are multi's (after experience acquired) anywhere as reliable as conventional helicopters?

Flap, I've been flying RC since the early 80's and conventional helis for about half that time. I just got into multi rotors and I'm astounded at how low the parts count is for these machines. It's a flat okto and it's a pretty big bird but it still has less parts overall than any CP heli except maybe a Blade mSR. The only moving parts, aside from a mounted camera gimbal, are the motor bells and the props secured to them. It's very odd not messing with torque tubes, pinion and main gears and all of the main and tail rotor linkages. It's also amazing to me how quiet this thing is. I was truly shocked at the low noise level. I expected it to sound something like the buzz/whine from a Trex250 size machine but it's nothing like that at all. With so few moving parts I suspect that a well maintained multi-rotor could last a very long time without any failures. From my limited experience, like these guys have mentioned above, the most critical aspect to these builds is proper soldering. The whole thing is truly fly-by-wire and every motor pulse and every sensor command needs to jive at all times. Also pay attention to nice, neat, twisted cable routing and layout. Other than that it's a cake walk with your experience. They could not be easier to fly. The only challenge I'm finding is keeping orientation. The symmetrical shape makes things tricky. Even with super high intensity LED's for position lighting things go black quick when your high and far away. I'm going to supplement my lighting with some additional LED's on the tips on the booms and see how that does. It really highlights how nice the visual cues are from a nose and tail rotor on a conventional machine.

 

[FLAP]

looks like Cinestar 8 will be my starting point. Thanks for all the info and advice.