Help me diagnose this problem? - RC Groups
Thread Tools
Dec 19, 2009, 08:48 PM
define("BEASTMODE", "1");
Bonafidepirate's Avatar

Help me diagnose this problem?

We had a stretch of bad weather the past couple of weeks, so I took that time to put a new motor and ESC on my Slowstick, as well as make some other changes to the airframe.

I used a 2409-12T outrunner motor, and a 25A TowerPro ESC that comes in the combo with it. I had another of this same combo on this plane before and loved it, then I moved that one over to my Easy Star, where it's still at. I also moved my servos and receiver farther back on the tail boom to offset the heavier motor than what was on there before, and put a beefier landing gear on it. This was also the second flight with a new PCM receiver. (Futaba 149DP) The previous flight, first one with the receiver, went well enough. I did get a hit on it closer than I would have liked, but it was a small quick glitch, and I hadn't even range tested it on the ground to get my wiring situated properly, so I figured that once I did that it would be ok.

Yesterday I tested range on the ground with everything in place and powered up as usual, and was happy to see that I got the full length of my runway (400 feet) with the video gear off, or on. It seemed to be working great, as I expected it to, since it was flying before with the same layout, but with the servos and receiver closer to the video transmitter than now. With them a few more inches away, I figured it would be better if anything...

Today I took off, trimmed the plane, tested the failsafe, then headed out towards the back of the field where I usually go to test range. I didn't make it very far before I lost total control of the plane! The failsafe did not kick in though, as my pan servo panned left, and the plane dove down. Literally a few feet before impact, I got control back for a moment, long enough to pull out of it and get the motor running again. Then control was lost again, the plane rolled over, and control came back. I got it pointed for home, and caught my breath again... About half way home it lost control again for a moment, then came back. I landed safely.

Now, what I don't understand, is that if it were a loss of signal, shouldn't the failsafe have kicked in? Will electrical/RF noise onboard the plane cause that? I thought PCM either locked on or went to failsafe, with no glitching like that.

Here's the video from the flight:
Near crash, not sure what happened! (4 min 46 sec)

At this point, my plan is to take the PCM receiver off, and put my tried and tested Electron 6 back on it, and fly it again. If it works well, I'll test the receiver and go over it well on the ground before I fly anything else with it. Maybe it's damaged, I bought it used and have two flights on it so far... If that doesn't help, I'll try a different ESC, since that's really the only other thing that has changed.
Sign up now
to remove ads between posts
Dec 19, 2009, 09:20 PM
Registered User
With the failsafe not kickin in, it sounds like a power loss somewhere. It could be within the receiver or ESC as you pointed out. The motor stops running too, so maybe leaning towards the ESC as the culprit.
I'd also check your connections/crimps, wiggling them as you go.
It could be just a loose wire, that motor seems to have a good kick to it.
Dec 19, 2009, 09:22 PM
Lars k Jensen
If failsafe dittent kick ind, i would look for a reason for loss of power to RC, ie faulty bec, lose conektions, broken vire, if RX have pover, failsafe tested to work, and faulty or no signal it wil go to failsafe, if it dont go to failsafe i dont think RCtx got anny power and you get spiral of death.
AAAAR Eves you beat mee.
Dec 19, 2009, 09:30 PM
define("BEASTMODE", "1");
Bonafidepirate's Avatar
I was thinking the same, but then again, the pan servo keep panning even after the motor has stopped running the first time. I think I'll try using a BEC for the next flight and see if it works better. If the ESC is cutting power to the receiver, at least I'll still have control on the servos. I'd rather loose the motor and have to walk a half mile to get it than loose power to everything and walk a half mile to pick up the pieces! lol
Dec 19, 2009, 09:36 PM
Lars k Jensen
You are shure it wasn't the wind who moved the pan servo, its is been heard before.
Dec 19, 2009, 09:40 PM
define("BEASTMODE", "1");
Bonafidepirate's Avatar
Not sure, looking at my pan/tilt, everything is situated behind the pan axis, so in theory the wind would push it back straight, rather than to the side like it did. Looking at the video again with the power loss thing in mind, notice that when the plane rolls upside down, there was a complete loss of control then, and the motor is still running that time.

To be honest I'm finding it tough to trust the ESC OR the receiver right now... lol

I did go over all the connectors and wires, and everything seems fine, nothing is loose, and wiggling things doesn't seem to have any effect on it. I wish I could replicate it on the ground, that would make it a lot easier to solve.
Dec 19, 2009, 09:53 PM
define("BEASTMODE", "1");
Bonafidepirate's Avatar
By the way, here's a picture that shows how things are situated on the plane as of now...
Dec 19, 2009, 09:56 PM
Senior Gravity Checker
Test the voltage of your battery. post what it is.
Dec 19, 2009, 10:12 PM
define("BEASTMODE", "1");
Bonafidepirate's Avatar
11.48v, right now after that flight in the video. It was fresh off the charger when I took off. While I had the meter out I checked power at the receiver, it's 5.18v, drops to about 4.9-4.8 when I wiggle the controls.

However... I tested the failsafe again while it was on (turned off the transmitter) and it didn't engage! I just held the last inputs until the transmitter was turned back on! I did this 3 or 4 times with the same result. I'm thinking the receiver is not working like it should now... Any thoughts?
Dec 19, 2009, 10:54 PM
define("BEASTMODE", "1");
Bonafidepirate's Avatar
Ok, think I found it... I tried another battery that was charged up just to eliminate that, measured them both while running up the motor, etc. and everything seemed ok, tested failsafe again and it's working now. Hmm...

Then, next thing I know, the rudder and elevator roll off to one end, and the pan servo pans full left, just like in the video! Turn the transmitter off, back on, and everything is fine again. Odd! So I keep playing with it, and the servos go nuts again. This time I left it alone, and quickly measured the voltage at the receiver while it was "dead" and not responding. 0.85V! I unplugged each servo one at a time and it never got any better, the ESC was beeping like there was no signal from the receiver, no servos plugged in. I measured the voltage again and it was still 0.84-0.85v, looks like a faulty BEC on the new ESC.

Well that sucks! At least I know where the problem is though. It's probably not worth shipping it back to China to get it replaced, I'll probably just pick up a better one somewhere in the US this time. This was the 4th cheap ESC I've used, and the first one to give me any problems, the other 3 are still going strong! I guess it had to catch up with me sooner or later... haha

The daredevil in me says to disconnect the BEC from the ESC, and use an external one and fly the thing, but I really would hate to make a stupid mistake that will cost me more money and downtime with this plane...

That raises my next question... What's a good 25-30 amp brushless ESC to get in the US? Nothing too expensive, but something I can trust...
Dec 19, 2009, 11:50 PM
my karma ranover my dogma
galaxiex's Avatar
Keith, I have had very good luck with the Turingy Plush line of esc from HK.

Overkill, but the 40amp now has a switching bec.

Nice solid esc, smooth throttle, they just work really well. I trust these esc, no trouble ever from the 6 that I have now.


Dec 20, 2009, 12:17 AM
define("BEASTMODE", "1");
Bonafidepirate's Avatar
Thanks, I may end up ordering one of those to replace this one with.

For what it's worth, I'm only running 4 servos on this one, no GPS, OSD, or anything like that. I did cut the power wire from the ESC and power the receiver with a switching BEC just a few minutes ago, and it seems to work perfect like that. With all 4 servos operating, (servo test mode on my 9C), the BEC is pulling 150mA on the battery side. That's not bad. I would have thought the built in BEC would handle that, but I guess not. Maybe it's just a defective one. Either way I think it'll be ok with another ESC, or maybe even just use the separate BEC instead. Weather is looking good for tomorrow, so I'll probably chance it and fly it with like that and see what happens.
Dec 20, 2009, 12:44 AM
my karma ranover my dogma
galaxiex's Avatar
Hope the flight goes well!

Just another idea... while your servo test is running, try loading the servos (control surfaces) and watch your bec current draw.

My very first FPV SS I had 4 servos, 2 gyros, and the RC Rx all running from the ESC 3 amp bec. (T-Bird 36 amp) (silly of me, I know, to run all that from the ESC Bec)

It worked fine on the bench, but in flight with loads on the control surfaces, and the gyros working overtime when the wind came up....

...BEC overheat/shutdown....

Separate batt for the camera and vid Tx.

I got to watch the ground racing up at me in the goggles from 500 ft. up while I frantically wiggled the sticks, hoping to get control back.

No such luck....

Plane went straight down when the bec shutdown.

If I had loaded the control surfaces on the bench test I might have caught the excess current draw condition under load.

I know your situation seems to be a faulty bec that you will replace, but still a good idea to test current draw with a load on the servos.
Dec 20, 2009, 06:02 AM
Challenging Convention
Andology's Avatar
personally i hate using the built in BEC of ESC, i prefer to always use exteranal (dedicated) one, regardless of the few extra grams it adds...

Gonna use 6v BEC for my Twinstar II build (i like the turnigy ones with the RF sheilding over it), should give me little extra resiliance / power / speed for my servos too @6v!.


Dec 20, 2009, 08:16 AM
my karma ranover my dogma
galaxiex's Avatar
I agree Andy. On a simple non FPV 3ch. park flyer I will use the built in bec, but for FPV, or planes with 4 or more servos, I now use a separate bec.

Thread Tools

Similar Threads
Category Thread Thread Starter Forum Replies Last Post
Discussion Help me diagnose these crashes. atckirk Electric Plane Talk 24 Sep 12, 2009 11:37 AM
Question please help me diagnose this camera issue cmulder FPV Talk 0 Aug 22, 2009 09:12 PM
Help! Please help me diagnose a motor problem. gtfreeflyer Power Systems 6 Jul 09, 2009 04:17 PM
Discussion help me diagnose a problem driftinsequence Mini Helis 9 Jan 19, 2007 01:19 AM
Discussion Please help me diagnose an R/C problem. Tags Dock Talk 26 Nov 28, 2006 04:44 PM