I had a bad day today. Fueled up, started and went out to the flight line. We were haveing a bit of a cross wind, nothing unusual. I started to roll out and the plane started to pull hard to the left, I straightened it on the runway and when I pulled up to take off, the plane turned right and refused to lift off. Just as I killed the throttle, it left the ground and just cleared the barbed wire fence on it's way to the pond. It landed in the water, but just barelly. It was setting on the landing gear with the wing slightly out of the water. Good news, its a low wing so the radio wasn't soaked. There was some damage to the bottom of the wing. I got it back to the bench and cleaned a lot of the mud off the wheels, took the wing off and took the bottom covering off to drain the couple of pounds of water trapped in the wing. I did a quick check over and couldn't find anything that could have caused the problem. Pilot error I guess. I then fired up the engine to make sure it hadn't inhaled any water. All was OK there. I shut it down and then noticed the VoltWatch had a glowing red light. No yellows at all. Very strange as the battery has only had five or so flights and I charged it all night, pulling it off the charger just before loading it in car. I figured that there was a bad cell. I got it home and hosed off the rest of the mud on the wheels and let it set outside for a couple hours to dry, then to the bench to pull the battery. I turned on the switch again and I now showed a full charge. It's a 6v Futaba 1000mah humpback pack. I just got it out of the plane and there is no sign of damage. I banged it around quite a bit, watching the volt meter and no problems were noted.

This pack goes in the trash. I can't trust it in a plane again, but I'm really wondering just what went on. I'll cycle it a couple times and see if that shows anything, but it was just cycled a couple weeks back. I'm at a loss.

Don

Take the shrink wrap off and check the welds. I've had two new packs which were missing welds to one of the cells, just held together with the shrink. They caused intermittent power and inconsistent charge/cycle readings. It's worth a try. Tex.

Tex, thanks for the tip, but mine checked out OK there. I put in on the cycler and it had 112 minutes left at 500MA load. I'm going to check out the wiring. I could have had a short or a servo hanging up that was putting enough of a load on the battery that the VoltWatch was showing a dead battery. I liked this better when I though it was just the battery. I guess I'll charge this guy up again and then turn on the radio and put the servos on cycle and see what happens.

Don.

Don,
Before you trash that pack, consider that you may have an issue with your battery switch harness
High resistance on the switch contacts could be the culprit.
Good luck,
Pete

Pete, I hadn't though of that.

I cycled the battery and it showed 112 minutes of charge left. After the cycling, the second discharge showed 120 minutes at 500ma, correct reading for a 1000mah pack. After the cycling, and skinning the cover off and checking individual cells, all were exactly the same voltage. I then plugged in a full complement of S3151 digital servos, seven total and set the transmitter on servo test. I let it run the servos for close to 20 minutes, I stalled one or more and even then I couldn't get the full red light. I could get a lot of yellows and a red flicker now and then, but that was it. As soon as I was through testing the servos, I took individual cell voltage checks again and I found two that were 0.13 vots lower that the other three. I don't know just what to think about this. The battery has been on the shelf for a few days now, so I'll check it out one more time. I still don't trust it at this point.

Conclusion is that I don't know what happened. Pete, thinking back over the switch as an issue, I'm not so sure that was the problem. For the failure I saw to be the switch, it would have to have gone bad part way down the runway, and then healed it's self. I've retired from the Computer industry, haveing spent 30 years in service. The switches that fail will always fail on make, or the toggle will break. Once they are made, they are good until they are turned off. That, and the fact that the switch in the harness is a DPDT wired in parallel, providing two sets of contacts, it doesn't seem likely that the switch was the fail point. Not impossible though. As I was writing this though, the thought of a broken wire would fit the bill nicely. Viberation would make the contact break and then a wiggle would make it again. I'll check it out

The plane is the first one I had built in over 30 years and there were a couple things in the linkages that I discovered I hadn't done correctly, IE the horns were to far back from the hinge lines. I'm taking this oppoturnity to fix all of this before it goes in the air again. I need to add the switch harness to my list I guess.

Don

Hi Don,
Just so happens that I'm also a retired field service tech from the computer/business equipment industry (36 yrs), you wouldn't have spent time in Dayton, Oh. perchance?
I've spent many moons there, also spent almost a year in Denver, before they closed the school there (70/71)
I'd be hesitant to fly with that battery again, not worth losing a plane over.
Cheers,
Pete

Hi Pete, I was an IBM FE specialist in Flint Mi. Before leaving the field for a Service Planning job, I was a Region Designated Specilist on the 308x mainframes.

I cut the wires on the batteries yesterday. I may find a use for them in some other capacity, IE a glow driver or such. Nothing to do with the radio though.

Don

The process of elimination based on facts and physical measurements, not "I think..." is the best way to perform troubleshooting. Ockham's Razor would indicate that after verifying battery voltage and capacity the next thing would be wiring connections. After that the wiring itself. Lastly, the devices connected to the wiring.
Considering that the problem arose when the level of vibration was at or near its highest, and the battery was shown to have good voltage, one can pretty safely conclude a connection/wiring problem.
If only the battery is replaced and nothing else touched, I bet it will crash again.
Good Luck.