acerola

I have been flying my NexStar for a couple of months now. I just bought new batteries for it, 2700mAh Rx and 2500mAh for Tx, NiMH, Sanyo, from NoBS. I was using them for the first time.

It was all fine in the beginning. But in the 4th flight, short after the takeoff, the throttle wouldn't respond. I figured that the engine died and started to bring the plane back to the runway. When it got close, I noticed that the engine was still on. I pulled the throttle all the way back and forward again, and it went up a little. The other commands seemed fine.

I was making the final turn before landing when I lost elevator control. The plane crashed in the grass. Since it was slow and low, only some damage to the landing gear and lots of dirt. When I got close to it, I tested all the controls and they were fine.

When I got home, I cycled both batteries, discharging at 0.5A. They yield over 2000mAh each.

I was wondering: could this have been caused by the batteries? Or it was simple interference? I have experienced interference before, but just for some seconds. This one was quite long.

ghendrix01

My Feedback: (1)

Just one question. Are you using the charger that came with the radio system to charge the batteries? If so and the radio equipment came with the usual 600 or 700mAH nicad batteries, your batteries were probably not completely charged.

Some people on this site say that you just need to charge the higher capacity batteries for a longer time, in your case that would be a minimum of 5 days.

If you go to the Sanyo website and read the charging requirements, you will see that the minimum charge rate is battery capacity divided by 10. That would be 250 and 270mA minimum.

I won't argue with anyone about whether charging with the stock charger (60 to 70mA) is ok. I just follow the battery manufacturers recommendation. You can use the stock charger if you like but remember to charge the batteries for at least 5 days before you use them if they have never been completely charged or they have been used until nearly discharged.

Like I said, I follow the manufacturers recommendations. I also feel that buying the correct charger is a small investment considering how much time and money is invested in the planes I build and fly.

Good luck,

George

Time Pilot

5 days sound like a lot unless you are charging at a very low mA. My Futaba charger puts out 100mA at 4.8V. For the Rx battery, I calculate a 38 hour charge would top up an empty 2700 mah Nimh pack. What I was taught, a Nimh battery needs 1.4 times more charge into it than the capacity.

So 2700 x 1.4 = about 3800. Divide this by the mA of the charger (in my case, 100mA at 4.8V), you get the time of charge, in this case, about 38 hours.

The other thing that needs to be considered for Nimh packs is that they need to be cycled a couple of times when new or have been sitting for a while for them to hold maximum capacity. This applies to flight packs for electrics, anyway.

The last concern for using Nimhs is that they self discharge faster than nicads. Don't have the exact specs, but the bottom line is to make sure you charge them before flying if they've been sitting for a bit or check the voltage when you fly.

acerola

I charged them with my Triton at 0.3A for over 10 hours.
When I discharged them after the crash, Triton reported over 2000mAh remaining on each pack.

piper_chuck

My Feedback: (12)

Then it sounds like the battery pack was not the problem. Is it possible the throttle linkage was binding? A stalled servo can sometimes lead to problems on other control surfaces.

acerola

Could be. I am looking for causes other than "battery" or "interference". The battery was fine when I discharged it at home. As for interference, can I have interference only in one channel (throttle)? When the problem started, I lost control over the throttle only. Only after like 20-30 seconds I lost elevator control.

Could the throttle servo got stuck and drained a lot of power, causing the elevator to malfunction later on?

Time Pilot

Sorry for the misunderstanding. I thought you were saying that your nimhs took on that much extra charge after your crash, not that there was that remaining.

Just curious though, it is possible that there is one bad cell in the pack that poops out early leaving you with only 3 good cells? Can you check voltage under load with a half charged pack?

acerola

Well, I can't say anything about the pack "half charged", sice I left the battery overnight cycling after the crash. But when I plugged it in the cycler, after a couple of minutes discharging at 0.5A, the voltage was around 5.2V. I am not sure about the exact value, but it was over 5V under a 0.5A load.

The batteries were fine before and after the crash. Also, I first lost control over throttle only. About 30 seconds later, I lost elevator. That is why this crash is bugging me. If it were interference, I should loose all control, not only one channel, right? If it were batteries, I also should loose all control, and the batteries would not still give 2000mAh.

The servo problem might be the answer. It makes sense. First the servo gets stuck. I lose throttle. The servo drains a lot of power and the voltage drops. I lose the rest of the controls. The new battery pack has a very long wire. Maybe the wire got in the way and the servo stalled.