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Old Feb 10, 2012, 09:11 PM
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Crash investigation - Need help!

I need help figuring out why my new FBL copterx 450 crashed. At the end of the first hover flight I had goosed it one last time to get a small taste of the punch it would have. After obtaining 40 ft or so the power and cyclic response started getting mushy. It started to sink and direction control was limited. I gave it more throttle and to my surprise it jumped up again with control back for a brief moment. The happened several times until I had to give up and pull the throttle hold and cut my losses. Damage was descent since the head hit first on the black top. I need ideas so I can try to elimate the cause of this crash.

Copterx FBL super combo with TT
Copterx 430XL motor
Copterx 50 amp ESC
Copterx 9g analog servos
Fusonic 9257 servo
Copterx FBL 3x1000
Spektrum compatible rx with satellite

Ideas I have come across so far:
Loose pinion - seems tight by feel and when loading the rotor up on the bench
Slipping one way bearing - same as pinion
RX failure and loose of all control - no reason to believe this
Overheated ESC - this what I think happened
- I forgot to change me throttle curve from 0-25-50-75-100
- I reshrink wrapped the esc and forgot to cut a hole for the heat sink
- I was probably at 60-70% which I hear runs hotter than 100

I tried to reproduce this on the bench after running three batteries at about 60% throttle with three different pitch settings: 4, 5.5, and 7 degrees. Im thinking maybe the heat shrink tightened up during the failed flight and is making better contact now.

My next test will be without the heat sink on the esc to see if it will show the same issue so I can sleep at night!

Any thought?
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Old Feb 10, 2012, 09:22 PM
just gotta mess with it!
2Doggs's Avatar
North West Louisiana
Joined Nov 2009
4,846 Posts
Logs!

Sorry to hear of your crash!

It's true that an ESC will generally run hotter at low throttle percentages. I have a Turnigy Superbrain that definitely doesn't like less than 65% throttle, and can overheat even at 13A at that kind of percentage. A sure sign of ESC overheating is the inability to run the motor for some time while it cools down - but you were probably in no mind to check that right after you crashed! You can also feel that the ESC is hot.

Another thing that might give the results you describe is the low voltage cutout on the ESC. If, under load, the voltage sags enough, the ESC might reduce power. That can happen if you have an old pack, or maybe a pack with a bad cell. You should check the cell voltages to rule that in or out.

After your rebuild, you could test out the ESC overheating theory by running the heli on a test stand or Lazy Susan - though the lack of relative airflow will cause the ESC to go into thermal shutdown earlier than it might in flight.

Of course, if you treated yourself to a data-logging ESC, such as the aforementioned Superbrain, it would take all the guesswork out of your mystery!
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Old Feb 10, 2012, 09:59 PM
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United States, CT, Trumbull
Joined Dec 2007
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i am almost positive its the links on the head . they need to be sized and loose so the head moves freely but not too loose so they pop off easily . amain has a JR ball link sizer
http://www.amainhobbies.com/product_...izing-Tool-All
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Old Feb 10, 2012, 10:48 PM
Crash and learn
United States, PA
Joined Dec 2011
1,605 Posts
Perhaps a stupid question from a beginner, but what kind of range does the radio get when the helicopter is in free space and the transmitter antenna is pointed at the helicopter and the helicopter turns to point it's antenna at the flier.
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Old Feb 11, 2012, 12:31 AM
just gotta mess with it!
2Doggs's Avatar
North West Louisiana
Joined Nov 2009
4,846 Posts
With 2.4G systems, range is not an issue. My FrSky RX has a claimed range of 1.5 - 2.5 km, way further out than I could see the (450) heli. With 2.4G, you generally have the TX antenna side-on, and two or more antennae on the RX, usually at 90 - 180 degrees to each other.
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Old Feb 11, 2012, 12:50 AM
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Thanks, I was really upset the next day but now I just want to solve the issue and try again. That is what you have to with this sport!

Ok, so I think I ruled out the esc overheating. I just ran two more packs on the bench with the heat sink remove from the esc transistors. That should make it run hot. But, it never shut down or got over 110F as read by a nice ir meter. That with 7 degrees pitch again at about 60% throttle (20 amps) with occasional starts and stops and short burst (up to 35-40 amps for a second).

I thought about the battery dying or the low soft voltage cutoff kicking but the heli would shoot up when I gave more throttle and fall helplessly when I reduced throttle. The batt voltage was around 3.7/cell after the crash and my charger put 1500 back in. These are new turnigy nanotech batteries and they all seem ok on the bench. Another thing is that I set my esc to 2s lipo cutoff voltage so that it would be so low it would never kick in. I want to rely on timming my flights and would rather roast a battery than crash due to soft cutoff kicking in.

So now what? Did my BEC overheat (separate but came wired to my cx esc, at least I think that is what is hanging on the wires for the throttle connection to the rx)? I have that buried under my rx inside the frame. I think my cx 9g servos are analog and shouldnt pull much so maybe the BEC malfunctioned. I gues when my new servos get here I will find a way to test that.

I'm not sure how the links would have caused the throttle to surge. My links all move freely and none popped off.

I'm also not sure it was a range/antenna orientation issue because I have a satellite rx installed in addition to the rx. However, I did not do a range check at all so I will do that test also. Dang, adding that to my list.

I will drive myself crazy trying to solve this before my heli is ready to fly again so please share any ideas you have and I can try to make a crazy lab expirement to prove it!
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Old Feb 11, 2012, 01:03 AM
Fly Runaway Fans
United States, TX, Fort Worth
Joined Jan 2009
9,387 Posts
I can't tell you what's going on. But I can tell you that ESCs have no idea how hot their transistors are. And that 110F without a heatsink is a very conservative value and wouldn't shut it off even if it knew the temp.

It IS possible to overcurrent a BEC, which folds back voltage to everything on the 5V rail--RX, servos, gyro, and the ESC logic. Not saying, just saying. In a network, any one component can take it down.
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Old Feb 11, 2012, 10:37 AM
AMA# 548800
jombo's Avatar
United States, CT, Trumbull
Joined Dec 2007
5,178 Posts
Quote:
Originally Posted by Pitchlynn View Post
I need help figuring out why my new FBL copterx 450 crashed. At the end of the first hover flight I had goosed it one last time to get a small taste of the punch it would have. After obtaining 40 ft or so the power and cyclic response started getting mushy. It started to sink and direction control was limited. I gave it more throttle and to my surprise it jumped up again with control back for a brief moment. The happened several times until I had to give up and pull the throttle hold and cut my losses. Damage was descent since the head hit first on the black top. I need ideas so I can try to elimate the cause of this crash.

Copterx FBL super combo with TT
Copterx 430XL motor
Copterx 50 amp ESC
Copterx 9g analog servos
Fusonic 9257 servo
Copterx FBL 3x1000
Spektrum compatible rx with satellite

Ideas I have come across so far:
Loose pinion - seems tight by feel and when loading the rotor up on the bench
Slipping one way bearing - same as pinion
RX failure and loose of all control - no reason to believe this
Overheated ESC - this what I think happened
- I forgot to change me throttle curve from 0-25-50-75-100
- I reshrink wrapped the esc and forgot to cut a hole for the heat sink
- I was probably at 60-70% which I hear runs hotter than 100

I tried to reproduce this on the bench after running three batteries at about 60% throttle with three different pitch settings: 4, 5.5, and 7 degrees. Im thinking maybe the heat shrink tightened up during the failed flight and is making better contact now.

My next test will be without the heat sink on the esc to see if it will show the same issue so I can sleep at night!

Any thought?
cyclic response started getting mushy. It started to sink and direction control was limited. I gave it more throttle and to my surprise it jumped up again with control back for a brief moment.

this tells me that the links on the head were sticking. you giving it more power gave the surge to unbind the head to get more altitiude .
the only way to be sure is to try to move the swash up and down with the links off the servos so you dont damage them . every link should be smooth and not stay in one position when you move it . check out some finless bob videos on link setup and how free moving they should be . i really doubt its anything but binding in the head . you even said hovering it was fine so it didnt surge there. it also could be the throttle and pitch curve , cant really know for sure with only the description you gave .
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Old Feb 11, 2012, 10:51 AM
just gotta mess with it!
2Doggs's Avatar
North West Louisiana
Joined Nov 2009
4,846 Posts
It sounds more like a loss of power to me. Did you solder up any of the connections (battery pack, motor, ESC) and are they good joints?

Your linear throttle curve would also result in an uneven headspeed - I'd use something more like 0 - 70 - 80 - 90 - 100.

If you have another ESC, you might try substituting that.
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Old Feb 11, 2012, 08:01 PM
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I did solder all my batteries and esc connectors. I'm familiar with soldering so I'm not worried about that. I don't have another esc to try unfortunately. When my sevors get here I will try to cause a brown out on the bench and if successful I will buy a better BEC.

I'll check out those finless bob videos on the links.
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Old Feb 15, 2012, 01:25 AM
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Well, I installed my new servos and did some bench testing to try and prove if the BEC could overheat or over current and cause a brown out. I did nice the BEC gets pretty hot with everything idle. But, when I ran a battery through it on the bench, with a DMM, on the 5v output it never dropped below 4.8v and with the air flow thE BEC didn't even seem hot. Durning the test I kept torque on the cyclic servos by holding about hover pitch and throttle and working the rudder servo back and forth all to cause the servos to pull more current. I brought in more collective occasionally similar to my flight that ended in the crash. Everything seemed to work flawlessly.

When I changed out the servos I took each one apart. Two are stripped and one is not stripped but wasn't working after the crash. When I took that one apart I saw that one of the wires was broken from the tiny motor right at the solder joint. It is hard to say if this is the cause of the crash or damage from the crash. But, the fact that the gears are not stripped could be because the servo was already dead on impact and did not fight to hold position saving the gears. That would explain the mushy cyclic and the lack of direction control I had. I could have sworn the throttle response was off too but maybe it was wacky collective that was giving that feeling. We may never know but one thing is for sure, it is time to just get this thing in the air I guess! Maybe I will do that range test first.
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Old Feb 15, 2012, 02:15 AM
Fly Runaway Fans
United States, TX, Fort Worth
Joined Jan 2009
9,387 Posts
The 'lab' in my nick was failure analysis for Dell, among others. You have good analytical procedure, Pitch.

Bad gears can overcurrent servos one time and simply fail to drive the next. Depending whether they are locking or skipping. Most likely culprit, by about 67%.
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Old Feb 15, 2012, 12:29 PM
just gotta mess with it!
2Doggs's Avatar
North West Louisiana
Joined Nov 2009
4,846 Posts
Servus Digitalis

Maybe do yourself a favour and treat yourself to some digital servos to go with the CX controller. For around $10 a pop, I reckon they're worth it!

Happy flying!
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Old Feb 16, 2012, 10:38 AM
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Overheated BEC CopterX 50 A with BEC

Ok, last night I was able to overheat my BEC on the bench and that caused all kinds of havoc. I did this with no airflow and a constant 2 amp drain on the output of the BEC by pushing down on the swash plate and twisting the rudder servo a bit to make them all draw current. The most current I could get the heli to pull was 2.6 amps before I felt like I was going to strip gears or break arms. In less than 2 minutes the servos all went limp, throttle started changing slowly, and the rx and satillite started blinking. BEC voltage droped to around 4.5V before the overtemp and then went basically to 0. If I let up on the servos a little everything would come right back to life, even the rx would reconnect right away. I could keep it right on this edge by applying a little more force and everything would go limp again. This is what the end of my flight looked like to me! Once reception was lost I think the servos relaxed and the BEC was able to come back for a second before going back into thermal shutdown.

I've ordered a hobbywing platinum pro with switching 3 amp BEC as a solution. I hope this works!

Thank you everyone for all of your ideas!
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Old Feb 16, 2012, 11:34 AM
just gotta mess with it!
2Doggs's Avatar
North West Louisiana
Joined Nov 2009
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Quote:
Originally Posted by Pitchlynn View Post
Ok, last night I was able to overheat my BEC on the bench and that caused all kinds of havoc. I did this with no airflow and a constant 2 amp drain on the output of the BEC by pushing down on the swash plate and twisting the rudder servo a bit to make them all draw current. The most current I could get the heli to pull was 2.6 amps before I felt like I was going to strip gears or break arms. In less than 2 minutes the servos all went limp, throttle started changing slowly, and the rx and satillite started blinking. BEC voltage droped to around 4.5V before the overtemp and then went basically to 0. If I let up on the servos a little everything would come right back to life, even the rx would reconnect right away. I could keep it right on this edge by applying a little more force and everything would go limp again. This is what the end of my flight looked like to me! Once reception was lost I think the servos relaxed and the BEC was able to come back for a second before going back into thermal shutdown.

I've ordered a hobbywing platinum pro with switching 3 amp BEC as a solution. I hope this works!

Thank you everyone for all of your ideas!
Sounds like a good bit of forensic investigation on your part!

I have a Platinum Pro, and it's a great ESC! It's also 6s capable, should you venture into higher voltage setups.... and has a pretty good governor mode.
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