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Old Aug 03, 2011, 11:41 AM
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Main causes of multicopter failures.

Hello,

I want to implement an in-flight diagnostic systems for the Quad I'm building and I'd like to hear from experienced people which are the main causes of failure in order to try to avoid it.

For example, I've heard that people crashes because of ESC overheating so I'm thinking about installing a temperature sensor in each ESC to report me when it's being overpowered.

Any suggestion or ideas?

edit: Let's just list equipment failure. Something avoidable if monitoring while flying.
Piloting and building mistakes are already implicit.

Thank you!
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Old Aug 03, 2011, 11:43 AM
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the biggest problem is crappy flight control code.
then the pilot. why would esc overheat if you didn't overdrive it?
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Old Aug 03, 2011, 11:54 AM
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Quote:
Originally Posted by timecop View Post
why would esc overheat if you didn't overdrive it?
It wouldn't, or shouldn't. If the ESC is undersized for the motor attached to it that's a manufacturer or builder problem and nothing an in flight diagnostic is going to fix.

Biggest source of inflight failures/crashes I've seen have been either crap components and/or poor build quality, followed a close second by dumb thumb syndrome. Bad controller code would have to take a distant third place in my book.
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Old Aug 03, 2011, 12:05 PM
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Thank you for the answers,
So you guys think that temp. sensors for the ESC and Batt are waste?
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Old Aug 03, 2011, 12:15 PM
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The biggest cause is still the pilot/builder.

I doubt if there is going to be an objective answer from this thread. No one is willing to admit their own mistakes.

To me the biggest cause of multi rotor crash has to be poor soldering.

Improper connections of electrical components. In sufficient wire size.

Lots to go wrong before we can get to the electronic components such as speed controllers and flight controller.
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Old Aug 03, 2011, 12:33 PM
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An inflight monitoring system with telemetry say it all: You decide how many parameters/sensors you wish to follow. This will help you visualize the kopter health to engage the right decision (to avoid/limit crash).

But first of all, it is about monitoring a well conceived and built system (avoiding a "crash by design").
Beyond a good design, is a design provisioning redundancy at a given level (example 2 independant sets of Lipo/ESC/Prop)

Finally, you have the human factor crashes, where manual piloting, bad payload lead to a CFIT (controlled flight into Terrain).
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Old Aug 03, 2011, 12:45 PM
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Quote:
The biggest cause is still the pilot/builder.
PILOT is main cause.
BUILDER second.


esc... firmware whateverproblems number 99
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Old Aug 03, 2011, 01:51 PM
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Quote:
Originally Posted by Rivello View Post
Thank you for the answers,
So you guys think that temp. sensors for the ESC and Batt are waste?
Some years ago I read an article about the MiG-29 design, one of the engineers said something that is worth keeping in mind as designers/builders, it went something like:

"The best system on an aircraft is the one that it doesn't have, because it can never fail"

ESCs and batteries should never overheat to failure if they were properly selected for the requirements of the model, adding extra sensors and code to handle a problem that shouldn't happen only adds extra elements that may fail on you.
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Old Aug 03, 2011, 02:01 PM
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I agree - poor selection of components, poor quality of components, poor assembly (particularly soldering), excessive vibration, laziness (pre-flight inspections), etc.
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Old Aug 03, 2011, 02:06 PM
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The implication from these replies is that once you have overcome the bad soldering, poor software, bad wiring, unbalanced motor/props, etc. then you probably have a reliable system that will not require a diagnostic system.

Some 'copters (eg Arducopter) have a logging facility built in which often helps with diagnosis.

Peter
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Old Aug 03, 2011, 02:26 PM
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Being new to the forum I don't know how to set it up, but some type of voteing system should be here like:

main failures

1.pilot=
2.builder=
3.wireing=
4.esc=
5.vibration=
6.frame=
7.software=
8.other=

like I said I'm not good at this but it seems like somthing most people could understand and contribute to, any good Ideas everyone?

keep smilin
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Old Aug 03, 2011, 02:42 PM
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Actually the last six crashes I had weren't pilot error at all but either build or component failure. Here they are in order of occurance and the solution implemented.

1.Motor wire came loose - Now gently tug on all motor wires after each day of flying to ensure solid connection
2.Front motor came loose in flight - Used thread lock on motor mount screws
3.Left motor ESC failed - Repaced all ESC's with slightly higher current rated one's
4.Front motor failed in flight - Replaced all motors and now closely inspect windings after each day fo flying
5.Prop snapped in flight under virtually no stress - Could have been defective/Switched to stronger props
6.Prop came off in flight - Used thread lock on prop adapter threads
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Old Aug 03, 2011, 02:55 PM
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An add-on comment about ESC failures: Most ESCs fail NOT because of excess motor current, but because their built-in BEC circuit is overloaded. The BEC circuit is responsible for dropping (and regulating) the pack voltage down to what's acceptable for the receiver, FC, gyro, or whatever (normally about 5 V.). The higher the pack voltage, the harder the BEC has to work. Always best to use a separate (switching-type) BEC instead of the one(s) in the ESC(s) (linear type for most ESCs).
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Old Aug 03, 2011, 03:02 PM
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Ok, I'll tell on myself,

1. first setup tri: 1.5 lift to weight ratio, fast desent=crash
2. tri tail seup: wire flexing at motor for tilting motor= broken motor wire=crash
3. no locktite on motor set screw=motor turn=broken motor wire=crash
4. dumb thumbs=crash,repeat,repeat,repeat,etc.


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Old Aug 03, 2011, 03:13 PM
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Quote:
Originally Posted by AleG View Post
Some years ago I read an article about the MiG-29 design, one of the engineers said something that is worth keeping in mind as designers/builders, it went something like:

"The best system on an aircraft is the one that it doesn't have, because it can never fail"

ESCs and batteries should never overheat to failure if they were properly selected for the requirements of the model, adding extra sensors and code to handle a problem that shouldn't happen only adds extra elements that may fail on you.
Yup. Extra sensors add weight, add more failure points.

The best is to keep things dead simple.
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