Strange crash

[ghostflyer]

Hello all,
This morning I had a very strange crash and I wonder if someone have a suggestion about the cause.

I was doing a half inverted loop with my Titan Raptor and as I was close to pulling out to horizontal, correcting also with some aileron to level properly, it started to spin around like crazy. I have a Futaba 401 gyro with matching digital servo and was in heading hold mode. I must say it is the second time it happens in the exact same situation. However, the first time I was able to get out of it by flipping to non heading hold and let the wind stabilize the tail.
Today I was not that lucky however.

In all other situation, this helicopter is super fun and predictable.

Any Suggestion?

Thanks,
David

[heli-cuzz]

I'd go over the gyro and rudder servo set-up, double check everything, radio programming, and connectors. Maybe it's a glitch, could always reroute your antenna. It's tough to diagnose strange problems like that.

[ghostflyer]

Thanks Heli-Cuzz for the advice.
One thing that I should mention is that the gyro was working properly before and after both event. Even doing similar mild aerobatic. I have made many flight after the 1st event without a problem. I even finished the flight of the 1st event with the gyro working normally. Like if it was a temporary brain fade of the electronic...

Can it have something to do with the gain in heading hold mode being to high or too low?
Can an heading hold gyro be sensitive to momentary voltage drop (my battery was properly charge but I ask just in case).

Thanks

[heli-cuzz]

Thanks Heli-Cuzz for the advice.
One thing that I should mention is that the gyro was working properly before and after both event. Even doing similar mild aerobatic. I have made many flight after the 1st event without a problem. I even finished the flight of the 1st event with the gyro working normally. Like if it was a temporary brain fade of the electronic...

Can it have something to do with the gain in heading hold mode being to high or too low?
Can an heading hold gyro be sensitive to momentary voltage drop (my battery was properly charge but I ask just in case).

Thanks

Sure you're not giving any rudder input while doing a loop? If you're not, the only thing I can think of, is a glitch. Sounds very odd.

The gain on the avcs gyro, to high of a gain will make your tail hunt/quiver <><><><><><>
You should set your gain according to the 401 manual at 75% and work from that point to eliminate any hunting/quivering of the tail.
I think being very low on your radio, will make your tail sloppy, although I don't know about being to low on the gain. I've always set mine to the manual instructions then rid the hunting and have always had a rock solid tail. My radio is around 60-65% for my gain on the gyro and 50-55 on the avcs side.
I fly only Futaba Super9chp radio/recievers/servos/gyros

Hope ya get it straightened out.

[ghostflyer]

I dont think I am applying rudder.But even if I did, it would stop as I release,no?
I my case, the heli start to rotate big time and dont stop even with all hands of the sticks.

[tdswan]

Did you have your gyro and rudder set to true center and/or mechanical center. When I was new to this, I was messing with my tail linkage and adjusted it to the point it would get real sloppy in meneuvers, but would hold in a hover. It could have possibly gotten out of control if I hadn't gotten lucky. Just a thought. I've been thinking on this one since you posted it.

[heli-cuzz]

Very strange, defective gyro? servo?

check and re-check. end points. centers as td mentioned.

[blax1]

Im sitting on the fence with this one, I will be interested to read the outcome.
Good luck :)

[AaronS]

I think you may have hit on something with the battery voltage, if the battery voltage drops, the gyro may let go before you loose control of the rest of the machine. What kind of battery do you have in there? How have you been charging it? I would look into that and if possible, try to find your voltage drop under load. You could use a watt meter and move the sticks around and watch for a voltage sag, you could run a data logger like an eagle tree or another similar unit to see whats going on in flight with the pack. There is a new volt meter that a friend of mine back in Portland makes, its like a regular voltmeter, but it records the low voltage during the flight for you to see after you land. Its available at www.voltmagic.com, somehting along those lines will at least tell you if the pack is performing up to par. My bet is that you are pulling on the cyclic and the collective just enough during that maneuver to load up the servos and make the voltage sag to the point where, bang, the gyro lets go. I had a similar problem to this with an electric model where the BEC on the speed control could not keep the voltage up under load, and the first thing that happened is the tail let go.

[Fasrc]

Aaron is right. your 401 did a hard rest on you. Read this article it is exactly what you described.: http://www.rcheli.com/current_draw_and_what_it_does_to.htm

Also remember the 401 is meant to run with 4.8 volt battery. If you happen to run 6v use a regulator. :)

[ghostflyer]

Wow, this article is exactly the way it happens. Even how the Gyro reacted as I pulled out of heading hold in my first event.
I will have to do some testing but it make lot of sense to me now. The battery I use was fully charge the day before and I made 3 or 4 flight on it. Usually I cycle it and get well over 1000mA (Nicad) left so it all make me feel confortable to put on a few more flight before recharging (I was trying to finish my last gallon of the season, about 2 flight left). I only have one digital servo and it is the tail, all other are HITEC 635.

I must admit that I was not able to save it like I did the first time out by geting out of HH due to a stupid mistake on my part. I recently had to replace the boom (a screwed up autorotation) and was thinking about checking the setup in normal mode at the field. Of course I forgot and flew perfectly fine due to HH mode. However, it just kept rotating in normal mode leaving me no chance during the problem.

Another intersting lesson is the setting of the kill switch. Mine was setted up to work in the lower portion of the stick. Since I was in idle up, my engine never received the kill command. Ouch. I will now have it active over the whole range. Otherwise it make too many switch to flip during a crisis.

I will keep you posted when I get around to do some testing. Have to find a good way first.

Thanks all guys.

[blax1]

I new if I sat on the fence long enough, there would be answers :)
This is a great forum!! Great work people :D

[heli-cuzz]

Hopefully this will not happen to me, but knowing the answer to a problem ahead of time is good.

Thanks guys.

[Helifino]

I learned something new. Thanks for posting the article Fasrc! :)

[tdswan]

Ya know, that one was right there in front of me and I never thought of it. It's a learning experience every day!

[Nitroburner31]

Hi all new member here. I've had the same thing happen to me (stupid me didn't check the batt before my last flight) but you are right the 401 once it droppes below 4.0 or 3.9 the gyro literly shuts itself off and when the voltage comes back up and the gyro re-initlizes or tries to anyway you are still in a problem because it looses its center and still goes nuts the only thing that saved my machine from boreing a hole in the ground was i had enough altitude to hit throttle hold and auto it down so I have been keeping a close eye on the battery ever scence cya and Nice board :)

[Fasrc]

Ghostflyer,

You can't set throttle kill throughout your Idle up range and if you could you would not want to as that will kill your engine. Try setting up your throttle hold instead. That way your engine is not competely shut off in case you need to turn it back on in flight :)

[ghostflyer]

Good point.
Beside, I must practice to do auto at other time than when the engine quits... :)