[Gary Maker]

I purchased a Great Planes J3 Cub on-line complete with OS .46 FX engine and a 6 channel Tower Hobbies Radio system with 3 Futaba 3003 and 2 Tower Hobbies std servos. The complete package although used, is fairily new with only 4 or 5 flights reported on everything.

I checked the whole plane over, installations, links, gear etc etc and made a few adjustments, everything was set to go! Took it to the field yesterday for its maden flight. Did a range check at about 100'...perfect! Fueled her up, three flips and she started right up....excellent! So far so good!

Idle was good but I needed to check and make sure it wasn't too rich or too lean on the high end. When I advanced the throttle it happened. Above half throttle, the servos went crazy! All control surfaces went to full deflection with wild jittering and the throttle jumped to full even though the stick was only half advanced. Nothing responded to stick movements but just continued its wild jittering. I managed to stop the engine and immediately the controls went back to normal with full radio control.

The plane was held firmly in a safety stand thank goodness. I started it up again and left it idleing having full control of the radio again. I did a range check with the plane idleing and it was perfect. As soon as I advanced the throttle it again went crazy!

Never had this problem ever before. I checked that there was no metal to metal contact on the control links....none! Checked antenna routing..fine!

Is this a receiver problem with perhaps something loose that is affected by the vibration of the engine at higher throttle settings???

Any help or suggestions would be greatly appreciated. As it stands there is no way I can trust this radio system.

Thanks in advance for you help!

[JimMcIntyre]

Is your receiver wrapped well in uncompressed latex foam?

My immediate thought is it sounds like a crystal problem, made apparent by vibration ....

Try this, unwrap your receiver, turn on the radio and lightly tap it with your fingernail. If the servos twitch, try another crystal, check out the connector seating as well.

HTH, Jim

[ronm]

Could be metal on metal vibration somewhere Gary.
As you throttled up, something vibrated loose.
Check all metal on the plane.

Ronm

[Guest]

That receiver is the same shift as the Futaba and Hitec product. If you can locate another transmitter of the same frequency do the same test with it. If it still happens it is the receiver or the set up. In that case you can replace that receiver with a different one and if it goes away most likely it is the receiver or crystal as those here has said. If the problem still exists it may well be the set up. Long or bad leads or a servo that may have bad connections or pot. You may even have to start unplugging and replacing one servo at a time till the problem goes away.

If on the other hand the problem goes away when you use a different radio then I would carefully open the back and turn on the radio and move the wires around a very small amount where they connect to the pot and the gimble on the throttle and rudder quadrant. I had one plane that flew fine many many times then one day I was coming in for a landing and when I throttled down the plane went nuts in the air with every control surface jumping all over. Advancing the throttle it went away. I ended up nice and high and reduced the throttle trim and when I shut the engine down the plane went nuts again but when the engine quit I advanced the throttle full and was able to dead stick it in no problem. Once on the ground we opened the back of the radio and by moving those wires we were able to duplicate the problem on the ground. It turned out to be a single wire had broken and the connection was made only by the tension of the insulation.

Good luck and let us know what you find.

Dennis Pratt

[rchrf]

Try changing your throttle servo.

Good luck

[Gary Maker]

Thankyou very much guys! I really appreciate the advise.

I find it amazing that now matter how long you've been in this hobby, from time to time something like this happens that throws you for a loop! Even though this is a serious problem, I find it interesting doing the trouble shooting and tracking down the problem. I will definitely through process of elimination find out what the heck is going on and will let you know what I find.

[Lord Kimbo]

Looks like my equipment gave yours a virus where I was there a week ago.

Adam.

PS. I sent my Tx and both Rx along with 1 of the digital servos and battery pack to Futaba for investigation. I'll let you know what they find.

[airframe]

I'm really grasping here but how about a bad bearing in the engine. I've heard of this before but never believed it. As the engine spools up the bad bearing causes the problem due to " metal to metal interference" .

Let us know what you find, I'm curious as to what the problem might be.

Mike

[JimMcIntyre]

Not too far fetched, this is a far too common problem with bearings in helis... another reason I fly pcm....

[Vulcan1]

Gary,
I had something like this quite a few years ago. The problem was a joint crack on the pc board in the receiver. One of the components would vibrate when bringing the rpm up and created all sorts of hell. Check with another receiver first and see if that eliminates the problem.
Also if you think you have a bad bearing which I kind of doubt I would pack them with grease to try. You won't lose the lube for quite a bit and the balls would have something to skid on. Most of our bearings are rated for around 30k with grease or oil.
John