Falling out of the sky problem...

[GGoodrum]

For the second straight time, my WK-M - based X8 has dropped straight down, from about 10 feet, after only about 2 minutes in the air. In both cases, the main LED started flashing yellow at a fast rate, for 5 seconds, and then power was cut, and it fell like a rock. You can see it in the video below. I noticed also that when I unplugged the power, the Deans Y-adapter that parallels my two 4s-3300 packs was quite hot, right at the plug. I then checked the ESCs and the motors. The ESCs were slightly warm, but not hot at all. The motors, however, were pretty hot. The packs took back in about 565mAh each. That's a "burn" rate of about 750mAh per minute, so for a total pack capacity of 6600mAh, that means the packs would be drained in about 8.8 minutes. This ends up being about 6.8C, if I've done the math right, which would be an average current of about 45A. That doesn't sound like a lot, but nonetheless, something is definitely not right here. My guess is that the props are too much for the motors (APC 12x3.8 top; 11x4.7 bottom...) and this is simply too much weight for this setup. The AUW right now is right at 3kg, or about 6-1/2 lbs.

What I'm having problems understanding is why power is being cutoff like this, instead of going into the autoland/failsafe mode. There's still power to the MC because the LED reverts back to purple on the way down. I definitely think it is the MC that is cutting off the motors, and not the ESCs. If it were the latter, they would not all shutoff at exactly the same time.

Here's the video:

Has anybody else seen a problem like this? I guess the first thing I'll try next is to remove themkTR Pro mount, and see if I can get it to run cooler without the extra weight. Any other ideas?

-- Gary

 

[RTRyder]

Can't say I've had that happen to either of mine and I've tested the low voltage monitoring until it autolanded. Do you have the throttle failsafe set to 1/2 throttle? If not you should it may prevent it from falling out of the sky, or maybe not, but worth making sure.

Ken

 

[Tahoe Ed]

I had that happen to me as well. I was flying with 2x3S lipos and was under powered. I just lost power. I checked the lipos afterward and they had only used about 20% of capacity. I did not bind my transmitter to the receiver at mid stick. I will try that as well. I am also going to not use the battery monitor any more. I have a timer on my transmitter that has never failed me. Unfortunately I did not save the video of the incident.

I found the video:

[url]http://vimeo.com/30999290

L[/URL]ook at 1:54 where I lost power.

 

[RTRyder]

I've heard of people having the WKM simply fall out of the sky when it hit failsafe mode due to not having set any, or properly setup, failsafe during the build. I do it on everything although I try for a bit less than hover throttle so that in the case of lost signal the multi will tend to slowly drift downward which is preferable to watching it fly off into the sunset. Appears to be rather important to the WKM but I haven't tested that theory myself...

I only have the power monitoring setup on my WKM quad, it's the one that I test things out on before they go into the bigger (and more expensive) Y6. While it appears to work as advertised I won't be using it on the bigger WKM as that one is working just fine as-is and I also use TX timers for everything I fly so that's my power management tool of preference.

Ken

P.S. I would not use Deans connectors even if that was all I could get my hands on, I use Traxxas high current connectors and have had ZERO problems in hundreds of hours of flight time, including series and parallel Y harnesses.

 

[Choppercam]

Its not the programming of the esc's? Auto cut off like programming for 5 cell and putting 4 cell in it? But i can't see how they would all shut off at the same time????

 

[redridinghood]

A few steps I would try.

Set the esc on Nimh bat setting.
Redo throttle calibration.
Find a better power connector than deans.
Check for a cold solder joint. The harness should never heat up.
Check and set the failsafe's on tx and on DJI.

Also one of those cheap telemetry systems from HK if you tx has no telemetry. I hate flying blind.

 

[GGoodrum]

Yes, mine is cutting out when only 20% of the pack is being used as well. I did not set the throttle to 50% on failsafe. I guess I'm not sure how this is suppose to work. The receiver I don't think lost power, or maybe it did? In any case, regardless of how the failsafe function is supposed to work, I'm still confused about why it comes on with 80% of the capacity left. I have the trip point set pretty low, like 3.4V per cell.

I found some of the yellow connectors, like the ones used on the cable going to the PMU. First thing I'm going to do in the morning is cut off those damn Deans. :dread:

-- Gary

 

[hexa]

did you calibrate both lipos in parallel with the wk-m software?
also disable battery failsafe from auto land to flashing only, and see if it still falls from sky.
is your motors soldered direct to esc?

 

[hexa]

also it could be your lipo C ratings is too low. meaning the craft is pulling a lot of amps faster than what the lipo can send, whats the c ratings for the lipo?

 

[Bartman]

also, what wire gauge are your power leads from the batteries and then from the y to the WKM?

 

[GGoodrum]

I think I've found the problem. There is a slight mismatch in the blades of the Deans plug that goes between the short WK-M power module cable, and my Y-adapter that goes connects to the two packs. I believe the reason it got hot is because of the high amount of resistance that is the result of the poor connection and the high current demands of the motors having to work a bit too hard, due to the excessive weight. As the connection gets hotter, things expand and the connection is eventually broken momentarily. This is really the only explanation for why all eight ESCs reset in unison. You can hear the tones on the video. The high resistance caused a large voltage sag, which caused the 1st stage yellow flashing of the LED. It never got to the autoland/2nd stage phase. Eventually, the connection breaks and the ESCs reset. If it was just the MC cutting the throttle, the ESCs would not reset. Power had to have been cut.

I just checked again, and I found something interesting. The plugs that DJI uses on their PWM cable are the Deans look-alikes that are what you get from HobbyKing, etc., and the ones used on my Y-adapter are the "real" Deans connectors. If you try twisting the two connectors, while they are plugged in together, you can make the connection break. Crap. :livid: I guess the lesson here is that if you must use Deans, don't mix and match the real and "faux' versions.

-- Gary

 

[Tahoe Ed]

Gary, thanks for finding that. I use deans as well and my "Y" connector is made with "real" deans. I am going to check all the connections and probably replace the faux deans with a real ones. I have used this "Y" on my MK with no problems, so I know that it is ok.

I am also going to rebind my receiver to the transmitter with the throttle set at 50% and calibrate the WKM battery monitor with both batteries connected. Then I am only going to fly at low altitude until I am confident that everything is working properly.

 

[GGoodrum]

Gary, thanks for finding that. I use deans as well and my "Y" connector is made with "real" deans. I am going to check all the connections and probably replace the faux deans with a real ones. I have used this "Y" on my MK with no problems, so I know that it is ok.

I am also going to rebind my receiver to the transmitter with the throttle set at 50% and calibrate the WKM battery monitor with both batteries connected. Then I am only going to fly at low altitude until I am confident that everything is working properly.

I'm in the middle of doing a replacement for the DJI "faux" cable, and I'm also going to reset my throttle failsafe to 50%. I think this will do the trick, in terms of at least keeping in the air a bit longer. I need to put this one on a diet, though, so that the motors don't have to work as hard as they are now. I'm going to take off the mkTR Pro mount and landing gear, and eventually move that to my next platform, which will be a larger Y6 or hexa. for this one, I'm going to use one of the old AskmanAP TRex landing gear sets that Andrey did for me several years ago, along with a new GoPro mount I'm working on.

-- Gary

 

[Bartman]

i still don't understand the Deans bashing that goes on from time to time. they've been around for a long time and have been used in everything imaginable. i've got them on every battery connection I've got in both heli's and planes but I haven't had any of the problems that people talk about. I've found the springs on the male chinese deans (I call them cheans connectors) to flatten out making for a loose connection but this shortcoming is typical for many things from China so it's really no surprise. haven't really had problems with the female cheans.
glad you may have your problems sorted out.
bart

 

[Tahoe Ed]

also, what wire gauge are your power leads from the batteries and then from the y to the WKM?

I don't know about GGoodrum but my power leads from the batteries to the "Y" and the "Y" itself are twice the size of the leads from the PM. They are pretty wimpy in my opinion and better suited to a 3S machine that a 4S.

 

[Efliernz]

i still don't understand the Deans bashing that goes on from time to time. they've been around for a long time and have been used in everything imaginable. i've got them on every battery connection I've got in both heli's and planes but I haven't had any of the problems that people talk about. I've found the springs on the male chinese deans (I call them cheans connectors) to flatten out making for a loose connection but this shortcoming is typical for many things from China so it's really no surprise. haven't really had problems with the female cheans.
glad you may have your problems sorted out.
bart

+1

I prefer to solder them (big iron, held in a small vice with a wet sponge handy) than try and force the EC3 tubes into the plastic housing...

Most of us buy "cheans" - I can't get the "proper" ones in my country.

Pete

 

[GGoodrum]

Cheans... That's rich. :highly_amused:

Below is the new replacement harness I just finished. It has the Y-adapter, for the packs, on one end, with "real" Deans and 12-gauge wires terminating in a set of 5.5mm gold Hyperion bullet plugs. The PWM portion has the XT-60 connector, that goes to the PWM, a female "real" Deans to connect to my ESC harness, and the wires going to the 10A CC BEC.

View attachment 1434


Hopefully, my power problems will be behind me now.

-- Gary

 

[GGoodrum]

I finally got in a decent test flight today, and got some video, etc. I'll post that in my other ServoBlocks mount thread, when the video is ready. Anyway, I'm happy to report that my power problems are gone. :tennis: The new harness definitely solved the problem, and I was able to go for "normal" amount of time before the flashing yellow started coming on. The second surprise I got was that unlike my previous two minute troubled flights, the motors were not hot at all. Just lukewarm. Oh happy days. :highly_amused: I thought it was a bit weird that even at a hefty 7 pounds, there was plenty of power, with the ability to do launches like my old purposely over-powered Raptor electric conversions. The motors were getting hot due to trying to make up for lower voltage by increasing the current. Without the voltage sag, the current demand is much lower, so the motors stayed nice and cool.

I'm still having an issue about the GPS finding satellites in a timely fashion. It actually got down to the single red LED flash fairly quick, in about 1-1/2 minutes, but it took another full six minutes to find that last satellite. I tried Tony's trick, and didn't plug the ESCs in until the red LED stopped flashing. That made me worry a bit about how much capacity I had left in the "tank", so I initially went until I saw the first flashing of the of the yellow LED, which happened when I quickly raised the altitude a bit, and then landed. That ended up being about 4 minutes. I decided to just stop there, and see where the packs were at. According to the charger, they were both at 15.7V and were at 63%. They both took about 1160 mAh back in.

I'm still trying to get the power monitoring function dialed in. The yellow LED only came on, while it was under load, and then went off. It still seemed to have plenty of power, but I don't know how much longer it could have gone before the LED flashed yellow continuously.

I think for the next flight, I'll disconnect both flight packs, and plug in a third one, just until the GPS is set. then I can plug in one of the flight packs, unplug the third one, and then plug in the second flight pack.

-- Gary

 

[jhardway]

I had a similar experience, no idea why but, since then my voltage draw seems to be off. Still trying to figure it out especially in the voltage draw.

 

[Gunter]

Gary, where is your GPS mounted? I have mine mounted on my boom as far from the FC as possible, and when I change batteries, it picks up GPS again in a matter of 10 or 20 seconds.

Gunter.