Bergen tail going hard over

[TVaillancourt]

Just wondering If anyone has had an EB using GY401/9254 and Nimh batteries go hard over then piro and crash as a result.
I'm having trouble pin pointing the cause.I can find no fault in anything on the bench.:arggg:http://www.helifreak.com/img/smilies/confused.gif
800mm blades/115mm tail
constant drive tail system
Battery is a JR 4500 NiMh LARGE AA type not sub C
GY401/9254FUT combo
Battery was 5.2 volts before flight
tail shaft was greased before flight

Torque tube is solid no slipping anywhere.
I'm really hoping someone has had this happen and has an answer because I can't find the"ah ha" I've been looking forhttp://www.helifreak.com/img/smilies/mad.gif

Really expensive crash and I want to avoid this problem completly next time out.
Thanks for reading

[WayneBrown]

If your charger can discharge the battery and give you a reading of Mah and time, I think you may find your answer.

[cbergen]

I am also NOT a big fan of Nimh batteries, they don't seem to hold their voltage well...

If you have said battery checker as Wayne suggested, give the battery a good load. I'm afraid you may see a drop in voltage, which results in the 401 doing a "reset" in flight....

Of course, once you relieve the load, the voltage pops back up.

This may not happen with ALL Nimh batteries, but it is something seen before....

May not be what caused yours, but is certainly suspect.

[TVaillancourt]

So what discharge rate should I try it at?What Am I looking for.I did a normal check and the battery took 4300 Mah from full discharge.My last flights were calculated at about 800Mah a flight @ 20 minutes per flight.

If the gyro goes into reset what happens?Other than what I already experienced...crash..:thumbdown:.How long does it take to reset and can I reproduce this on the bench??
I'm running
Futaba 9451's on the swash and Hitec 645 on throttle Futaba 9254 on tail.


My last trip out before the crash I flew 2 tanks back to back(40 mins) without problems.I flew fast figures of eight low and a bunch of 360 and 720 stall turns.On my third tank I decided to check backward flight and when I rotated the heli into backward flight the thing piro'd out of control but I recovered and put it into a hover and checked the holding power of the tail and it was rock solid.

My First and last flight(day of crash) was on a fresh off the charger pack and it lasted about 3 minutes.Coming out of a stall turn I made a low sharp turn to the right and it just kept spinning to the right and I lost it from there.No tail control from TX inputs at all.

What type of batteries would be considered OK to use??Would a generator system or battery backer system prevent this from happening??
Thanks for the replies.

[MarkWebber]

If the gyro resets in flight, you probably won't be able to recover. This is because the gyro wants to be motionless when calibrating in HH. Of course, it was in the air in the middle of a piro at the time. Not good calibration conditions.
While I never had the gyro reset in the air on me, I did have a NiMH 2700mah AA pack give me similar low voltage fits. Of course, everything looked good on the ground. I do have an onboard voltage monitor so I was able to see the occasional low voltages during flight. I put a lipo pack on and never had troubles again.

[WayneBrown]

I'd use NiCds or Duralite setup. Not too sure obout the MiMh's discharge curve, but if you assume 4-5 amps as a peak and set your discharger to that, you may find the voltage drops enough to reset. a couple milliseconds below 4.0v and you are done.

[SeaHawk]

I'll second the Durilite recommendations. I've got 500 trouble free flights on a Bergen EB, loaded with camera gear using 401 gyro with no battery issues.

[cbergen]

Additionally, send the gyro and servo in to Futaba to let them check it out. Cover all the bases for peace of mind......

[TVaillancourt]

Well I think I found the "ah ha" I was looking for.
I hooked my pack up to a discharger.
First I tried a 2.A discharge and it was quite happy.
Next I tried 3.5A and it took about 23 seconds to bring the pack down to 4.09 Volts.
Next I tried 5.A and it took 2 secs to brink the pack down to below 4.0V

So As far as I'm concerned this $80 pack just cost me $800 bones:roll:

I guess I can chaulk this one up under learning the hardway:thumbdown:

I'm going li-ion and regs next time out.
Thanks for all the suggestions.

[WayneBrown]

sorry to hear I was right.
It sucks man, The duralite setup will cost a few pennies, but you can get the full setup, charger, voltage tester and battery regulator.

[lperagallo]

TVaillancourt,

Or you can get Raja's generator and never worry about power again.:clappp

Also, I don't think you should be using two grub screws in the tail rotor when they are 90 degrees apart. You will not get the proper set and it will come loose. I know you said it was tight when you took it off, but it will eventually cause a problem.

Wayne,

Maybe some flying in the afternoon if the winds are relatively quiet. I should be available after noon. I'll give you a call.

Lou

[TVaillancourt]

I will take everyones advise on the single grub when I replace the new hub.I bought this used and it had 2 in there.It was always part of my preflight things to check but I will replace the hub and use just one grub.Thanks

[TVaillancourt]

I think I might get raja's gen system and like you say never have to worry about power again.It's about the same cost as new batts regs and stuff.

[phoneman]

I'm not knocking on Raja's generator but if you have the EB version you could run 2 4800 mah li-on packs with a Duralite Geminii regulator like I have on mine. It has an arming switch that turns on both sides of the regulator separately and a 5.2 volt port for the gyro/tail servo--if the switch fails or becomes disconnected the system stays in the " on " position. You can get rid of some of the dead weight you used to counter the tail weight when you balanced the heli and have peace of mind about having enough voltage or amperage---especially if you are using a 2.4 system to fly your heli. With 9600 mah on board you're not going to run out of juice. Now having said that--if I shorten my EB to the standard length I would most likely use Raja's generator as it seems to work very well, Good luck--Dean

[TVaillancourt]

During my rebuild I will be cutting the boom back to standard intrepid size.No need for EB lenghth and I can get cheaper blades.

Hey Dean why would you not use your system with standard size?I am keeping the twin gear box on the tail.Just too much weight up from?

[lperagallo]

TV,

With Raja's system you don't even have to worry about the switch. It gets wired to the RX so it generates power even if the switch is bad or not turned on. Ask me how I know:P

If you switch out to the smaller boom, you probably want to go to the Magnum tail box. It gives more tail authority and is lighter. Ask Chris about it.

Lou

[TVaillancourt]

I'm quite happy with the speed of the tail right now.I only do sport flying so it's good enough power for me.I'm trying to keep the cost down on this repair and another gear box is not in the budget.I'll put that money towards a new power system ;)

[phoneman]

TV--if I change mine over to the standard length I would most likely also change to the smaller/lighter gearbox on the tail so I wouldn't need the extra weight up front. At that point I would probably use Raja's generator. With the system I'm using now I have redundant power and each side is more than capable of running the heli---if I use only one battery pack I would lose that--with Raja's setup you would have a battery pack and an onboard generator with each being able to provide the juice to the electronics.

[rbort]

But call me crazy as I don't understand why one would want to invest in a fancy battery system? After all its still a battery and no matter how large its still going to run out and need charging/maintenance. With a generator its UNLIMITED power its never going to run out, built in redundancy with a standby cheap 4 cell NiCD battery and you can fly to your hearts content and piss off the nitro guys with their expensive fuel and battery chargers.

I was at MHA this past weekend, I put in sixteen (16) flights on my gassers or 4 hrs in the air and I never had to take the helis up to the hotel room to charge them all weekend long. They stayed locked in the trunk and they only came out to play on the field!

TVaillancourt: On a side note, I would say YES do put in two set screws in the tail rotor drive gear. The setscrews are 90 degrees apart and it will work just fine and give better insurance against slippage in my opinion.

-=>Raja.

[cbergen]

Someone needs a little math update.

The 2 setscrew holes IN THE TAIL ROTOR HUB are 180 degrees apart. One on each side. 360 degrees/2 = 180.......

[rbort]

Thanks for the generator mounts and the muffler studs for the twin AGAIN!!! Much appreciate you replacing the studs for Aurora a second time, I'm going to fly for them tomorrow and will be handing over the studs and will specifically say DONT LOSE THESE!!!

They are insisting they want to fly tomorrow in 100 degree weather and run their mission. I wish they would wait until thursday until the heat breaks, but they are on some sort of schedule and I'll watch the engine temps to make sure all is good with the gv-1 on/off switch periodically in flight.

Sorry I missed you at MHA. It was a good time but I would safely say it was also the hottest time (weather wise!)

-=>Raja.

[lperagallo]

OH yeah! When the screws are opposite it's 180 degrees. I guess I flunk math 101:thumbdown:

Lou

[cbergen]

:) :) So does Raja!!

If we had the setscrews at 90 degrees apart, then it would be correct to install the extra setscrew.

[TVaillancourt]

I'll be putting one screw in as per the manufactures manual...but why did you(BERGEN) drill and tap the second hole??Is this meant for a back up hole incase we strip the first one out??:confused:
Is there a preference as to which hole is supposed to be used or just pick one:thinking

[cbergen]

Is this meant for a back up hole incase we strip the first one out??

Yeaaa, that's it!! :) :)

It really doesn't matter which one.