Blade-breaker

My Feedback: (4)

HI,

Any thoughts or experience you have with my mystery problem would be greatly appreciated!

I have been flying a Ultra Stick 1.20 for a year and a half now (100+ flights) with no problems until yesterday. Yesterday while flying I had a sudden loss of control and the elevator servo twitched down for a split second, also the engine would momentarily go to idle. While flying I noticed that this happed only when the plane was pointed toward me. The engine going to idle I figured was from loss of signal and the fail safe setting kicking in??? Later the same day I did fly another plane with the same transimtter with no problems at all.
Last night I changed out the receiver with one that I have used many times with no problems. Today I flew one flight with no problems at all and about 10 minutes into the second flight the elevator servo twitched again and the plane was to low to recover.

Also every time I had the twitch the plane was at full throttle.

After the crash the servos and receiver all worked fine, I do not think the switch is bad.

Plane: Ultra STick 1.20
Engine: Zenoah G26 electronic Ignition
Ignition: CH ignitions
Transmiter: 10CG ( New about 2 months ago ) flown about 25 flights on various planes with no problems
Original receiver: R617FS bought new never crashed or damaged, Never had any problems until yesterday
Replacement receiver: R617FS bought new never crashed, used many times in various planes
RX battery: 2cell A123 fully charged checked out ok after the flight
Ignition battery: 4.8 NIMH no problems
Elevator and rudder servos: Futaba S3050
Aileron servos (4): Futaba 9001
Throttle servo: Futaba 3004


Please let me know what you think could be the problem. I am currently building my first 50cc plane and am very concerned about having the same problem in that.

Thanks
Ryan

Crash Campbell

Hi Blade-breaker,

Sounds like a problem with electrical continuity. I would suggest a step by step approach eliminating potential sources one at a time starting with the switch, then moving on to battery connections, etc. I have had similar problems with a couple of older models, 7 years plus and in each case it has been the switch so start with Occum's razor.

For you 50cc model I have moved to twin batteries with non-mechanical switches that share the load from each battery pack on these models for peace of mind. With spark ignition engines don't forget to have the ignition battery, wiring, switch etc well seperated from the Rx, 6" min.

Good Luck,

Colin

Blade-breaker

My Feedback: (4)

Colin,

Thanks for the response. I would agree with you about the switch if I had not checked it extensively with the engine off and running. I am confident the switch is fine.

Going through the events in my head here and I have come to the conclusion that every time I had this twitch in the air the ignition was between me (transmiter) and the receiver. Plane was always coming at me when it happened. Not once when the plane was going away from me( receiver on my side of the ignition).

Could something have changed in the ignition system to cause problems?

Edwin

My Feedback: (2)

Just cause the switch works with no engine running doesnt mean its good. Vibration can play hell with an old switch harness. Last year a donated club trainer was test flown and did good until it started climbout and started going nuts. Fortunately the pilot was our old time instructor. Idled back and had full control, dead sticked in. On the ground you could see the servos go nuts when throttled up. Switch harness fixed that one. It could have also been a little corosion build up on connectors, or a loose one. Just unplugging and reseating it can clear up a problem. I tie my extension cables together with kite string. I have tested switch harnesses by using an old orbital style sander (without the sand paper) and press the foam pad against the fuse with the system turned on and an led voltage meter pluged into the receiver. If the leds bounce around when the sander is turned on, somethings wrong.
Edwin

Blade-breaker

My Feedback: (4)

I understand what you are saying and it makes perfect sense. But why would a bad switch make the elevator go to full down? If the power went off the servos stay where they are. Just tested that to be sure that is the case.

Afterthought...Could the plane pitch down with lack of power to the servo? Plane was trimed for level flight (with power on it).

Thanks for your thoughts
Ryan

Crash Campbell

Hi,

If you are satisfied that there isn't a problem with the switch, battery or other connections my suggestions are to check the:
Plug leads/Plug boot.
Earth the ignition module to the motor.
Wrap the ignition module in aluminium foil to make a "Faraday Cage".

Good Luck and happy fault finding,

Colin

Edwin

My Feedback: (2)

The power doesnt necessarily go off completely. You can get tons of voltage spikes which can play havoc with the receiver. But generally all the servos go nuts in that scenario. My guess would be a slight amount of corrosion on the pins of a problem servo. If its an old setup that could easily happen since there are many cases of connectors that are gold flash to tin. Dissimilar metals with current flow CAN (not always) start creating resistance in the conection over a long period of time. Just unplugging and reseating the connector can fix it for awhile. I've seen this same problem in old phone line punch blocks used in our computer switch room when serial or enet lines start dropping a lot of packets. Even at home on my cable connection. That one was found by a cable tech that was formerly a nuclear sub tech. What a wealth of info that guy was.
It could be an intermittantly bad servo. I keep old trainers around for debuging unknown equipment. Maybe a setup board that you can vibrate somehow. Just shootin in the dark.
Edwin

dignlivn

JMO,


Vibration issue ?

Bob

jaka

Hi!
How far can you go with the transmitter antenna fully collapsed?
With a 35 mHz transmitter/receiver you should be able to go 100m without any servo problems.
Think the same applies to a 72mHz system.

Gray Beard

My Feedback: (-1)

After the crash it's a bit hard to try to run down a problem. I was just going through this a month or so ago, one of my planes would start doing jerkey things in the air but it was in one area of the flight line? The plane was heading towards me too. Then one day the plane was on the ground with the systems all turned on and the tail feathers started going nuts on me?? The engine wasn't even running. When I got home I started testing the system, at this time the controls, elevator and rudder were kicking around, I unpluged the switch and plugged the battery directly into the RX, problem went away, connected the switch again and things went nuts again. Problem found. This didn't all happen in one day, it took quite a while to develope to the point it was doing it with the engine off and the plane sitting still, it started with just a small glitch while flying. I flushed out that switch with electrical cleaner and it started acting normal again. I will not use the switch again but I know that it had a case of the crud inside and the cleaner cleaned it up.

Blade-breaker

My Feedback: (4)

Well after lots of looking and trouble shooting I have no idea what happened. More than likely it will be the switch that caused the problem but I cannot prove it. I am sending the ignition system back to CH for a new cap and a check up. I am rebuilding the plane now and will give it a try with a new switch when I get it done.

Thanks for all your suggestions.
Ryan

Crash Campbell

Hi Ryan,

If it turns out to be the switch or you are looking for a "belt and braces" approach for that next "precious" model you might like to consider this switch/battery share device. I have used these on two of my larger models and the peace of mind has been worth the bucks for the device.

http://www.precisionaerobatics.com/p...ls.php?pid=273

Cheers,

Colin

microdon2

My Feedback: (47)

I crashed once on an otherwise very dependable plane. A few days later I discovered that the antenna was very loose inside the transmitter - it was actually unseated inside and was intermittantly connecting. I think that was the cause. Might want to check that on your transmitter.

Mike D