Weird glitch.
 

This is very strange. Plane, 4*40 with a Magnum .52 4 stroke. Radio gear Futaba 4EXA with standard 3004 servos and reciever. R168DF


A couple of times after starting the engine and picking it up to head out to the runway, the throttle will go wide open. It mainly does this if I hold the nose of the plane up. Radio in my left hand and plane in the right hand. And its the throttle servo opening, not some sort of lean condition. It will only do this while the engine is running and NEVER on the pit table. It happened once in the air when the plane was very close and today it happened just before take off ending the day with a broken spinner where it met a concrete ledge.

There are no other glitches and the range check is fine, in fact, it wont do it when the plane and radio are pretty far apart, but if Im holding the nose up with the engine running and get the radio close, itll rev wide open allmost every time.

My thoughts are that I might be getting some sort of antennea refraction. I had this problem once with a CB antennea mounted too close to a TV antennea. When I keyed up it would open my neighbors garage door. LOL

Since I cant duplicate the glitch on the bench, I figured I would ask yall before I just try re-wiring everything.

Thanks in advance.

RE: Weird glitch.
 

The first thing I would try is replacing the throttle servo. There may be a vibration related problem within the servo. I have had similar problems that I traced down to a bad connection on the servo circuit board.

If the problem persists with a different servo, then you may need to send your receiver and transmitter in for check out and repair.

RE: Weird glitch.
 

Lots of guys have reported issues with a TX too close to the plane.

Can you experiment by having someone watch your plane; taking the TX out to the field box; then moving the plane next?

Or, leave it on the ground securely tied....and move the TX closer and farther to see if the glitch re-surfaces? Rich

RE: Weird glitch.
 

I have an extra servo and reciever and might give that a try. I somehow dont think its a vibration issue.

Thanks

RE: Weird glitch.
 

Thats what it seems like Rich, when the radio is close it is worse. Think Ill try what JPMacG suggested and replace the servo and while Im there, swap out the receiver. A couple of us will be heading to Scobee in the morning if you would like to come out and fly with us.

RE: Weird glitch.
 

Scobee too far. But thanks. I belong to the Houston Sport Flyers and the field is only 15 minutes from my house. Rich

RE: Weird glitch.
 

Cool. I'm 4 miles from Scobee.

RE: Weird glitch.
 

Gary, I think the problem may be that the tx is swamping the rx when they are too close together. This can happen with FM PPM systems. I have one plane where if the tx is too close (2-4 feet) the rudder starts jigging but by moving away it stops and does not occure in flight. The distance is also dependent on whether the antenna is extended. It is worse with the antenna extended.

Bruce

RE: Weird glitch.
 

How close was the transmitter to the receiver when this was happening??? were the batteries on your radio fully charged? things like this can happen when the transmitter is sitting right next receiver, especially with fully charged batteries. The transmitter is simply overpowering the receiver and causing it to go crazy. If it doesn't happen after you a few feet away from the plane then you should be ok. But if you are holding the transmitter in one hand and holding the plane as well you could be overpowering it.

Ken

RE: Weird glitch.
 

I will try leaving the TX antenea down untill I'm ready for take off. Thanks Bruce.

RE: Weird glitch.
 

Thanks Ken, thats most likely what it is. Being an old electric rc car racer, my batteries are not only charged, I peak them! I have had these electronics in another plane and never had this problem though. I'm a little worried that this could be a safety issue and do you think I should change out the RX and servo, and maybe re-route the RX antennea anyway?

Thanks for yalls help. I allmost ran the plane into myself today. I can replace the plane, I don't want anybody getting hurt.

Edit: BTW, it only happens when the engine is running. It will not do it without the engine running. Does this mean something?

RE: Weird glitch.
 

Yes, this is very important!

This often happens when metal is aloud to rub against metal, and I think this is the real cause for the problems rather than saturating the RX with a too strong signal.

My advise is to replace the throttle pushrod (or metalwire in this case) to a plastic one!

RE: Weird glitch.
 

I just tried something else and I have no idea if it means anything. Engine not running. No matter what I do, I cant get a glitch unless I touch the TX antennea to either the engine or the throttle cable from the servo.

RE: Weird glitch.
 

I thought that was only a problem with gas/spark plugs?

RE: Weird glitch.
 

Gary, if you throttle cable is metal, your clevis is metal, and your throttle arm on the engine is metal, then even with a glow engin you can generate static. Is this the situation with your setup? If it is the problem could be a combination of swamping the receiver and generating static when the engine is running.

Bruce

RE: Weird glitch.
 

In the original post he said it happened in the air and while taking of. I'd go back to a vibration problem in either the RX or servo.
Rich

RE: Weird glitch.
 

Yes, but the servo horn is plastic! Shouldn't that be an insulator between the engine and the servo though?

And yes, the throttle arm is metal and I'm using an EZ connector on the throttle arm, which is probably not helping huh?

Hummm. This is finally sinking into my old arse brain and making sense thanks to you guys. And now, I have no idea what to do besides pulling the tank, motor and trying to figure out a new way for throttle control.

RE: Weird glitch.
 

The strange thing about that is, it only happened twice after 40+ flights that seemed to be an intermittent issue and couldn't be duplicated. Holding the plane nose up while the motor is running, with TX and plane in hand is when it happens the most often.

Yea, weird I know!

It could be everything suggested all in one shot. I brought a "Challenge" didn't I? [:@]

RE: Weird glitch.
 

Gary, when I said clevis, I was refering to the connector from the cable to the engine's throttle arm. Looking at your picture with a metal ez-link attached to the metal throttle arm, that could be the cause or a contributing factor. What you might do is solder a DuBro threaded solder stud to the cabel and use a nylon clevis to connect it to the throttle arm. This will eliminate metal on metal. I use an ez-link at the servo end of the cabel to allow the connection to be adjusted for length.

Bruce

RE: Weird glitch.
 

The servo is probably sensitive to vibration. A ny-rod pushrod connection can help isolate the servo better.

RE: Weird glitch.
 

To me that picture shows the real problem.

You have metal rubbing against metal there and the metal wire also acts as an antenna for that. This type of problem will only show up when the engine is running. It caused by vibrations and will happen for any engine (gas, glow or diesel). A plastic clevis and preferably also a plastic pushrod should solve the problem.

RE: Weird glitch.
 

Garry, It looks like your receiver antenna is running right next to and parallel to your battery wires to the receiver for a few inches. That is a very bad layout. That will lead to a lot of coupling you don't want. Get them separated by as much as possible. Dan.

RE: Weird glitch.
 

Check your TX ant. Just may be looseing contact.
Do a running range check

Cean your TX ant. and get any oil or fuel of it. I have seen a ant. intermitent when it is extended by loss of contact at joints. Will be OK when down.

RE: Weird glitch.
 

That was the first thing I thought of and that is something I can do quickly. Replacing the throttle set up wont be easy.

RE: Weird glitch.
 

Well, I did some wire re-routing and will see tomarrow if that helped. If not Ill being into heavy surgery replacing the throttle linkage, RX and servo.

Thanks for the help guys. We learn something new everyday.

RE: Weird glitch.
 

You may watch, your throttle will respond to a signal and the rest will just twich a little . Not anough to notice. I have seen a lot of set ups that are cloberd in a plane and never have a problem. I don't think it is your throttle cable, or set up might be wrong:eek: The first thing you would notice is the throttle;)
Larry K

RE: Weird glitch.
 

wow, it's almost unfair you can fly. I've got 10" of snow to deal with. The charm of living in the Midwest (Chicagoland) I guess.

RE: Weird glitch.
 

I had to wear a jacket today Tom. It was down to 43 degrees. [8D]

RE: Weird glitch.
 

grumble grumble grumble. Wise guy! :D

RE: Weird glitch.
 

Gary, solder a short brass threaded adaptor on the end of your throttle cable. Then put a ball on the trottle arm and a nylon ball socket on the threaded adaptor. That islolates any metal to metal contact on the throttle linkage.

It is susprising how little mettal to metal contact causes problems. I fount that touching a long screwdriver to the idle mix jet would cause glitching of the throtle and some of the surfaces as well. Not on all planes, but some.

Make sure your antenna doesn't have any tight turns in it. That may agervate the problem.

Don

RE: Weird glitch.
 

Bingo! Buy MR. Cox a beer.

...There's your fix. ;)

RE: Weird glitch.
 

That fixed it Dan. I moved the battery lead away from the RX antennea to the other side of the fuse and the evil glitch went away.

Thanks guys.

RE: Weird glitch.
 

Hi!
When looking at your picture I see something that you must fix if you want to keep your plane .
The servos cannot be screwed to balsa longerons!!!!
Instead use 3mm plywood and a router bit in a Dremel to make more sturdy servo trays.These 3mm plywood plates is then glued to triangular balsa stock and then glued to the fuselage sides.
Never ever ever just glue a longeron directly to the fuselage wall. The end grain in the longeron will not provide enough surface area to hold the servos in place when the fuselage sides move under load, and also...balsa is to soft to hold the servo screws in place.

Never ever use metal to metal clevises.

Check your servo potentiometer!

RE: Weird glitch.
 

Some good info here!! I also hit a glitching problem once in the air, turned out to be one loosened engine mount bolt, thankfully got the plane down, but it was one heck of a ride. Doesn't take much metal vibrating against each other to cause havoc.

flynte

RE: Weird glitch.
 

Thanks for the thanks. I'm glad that solved your problem. One of the guys at my field had the same situation and after he had us scatter in the pits a couple of times, he finally landed the plane in one piece, luckily. A quick look inside revealed that he had his antenna tangled up with his servo wires. As soon as I cleaned up his layout, there were no more problems. Dan.

RE: Weird glitch.
 

If youll look close I have added extra bracing fore and aft. Also when I drilled the servo mounting holes I used thin CA to strengthen the holes and the surrounding area. When I cut those servo rails I made sure they were slightly long and actually push the fuselage sides outward just a tad. Even if the glue joints were to fail, those rails will not move due to the square within a square thing which is hard to explain with my limited typing skills. lol

Something to note on your servo mounting. I belive you may have the mounting screws over tightened and squishing those rubber grommets too much and after looking at my pic, I might be too!

RE: Weird glitch.
 

Whats weird is how it only happened when the motor was running. I wonder if this was a combination of isssues like everyone else suggested, vibration, the throttle rod, metal to metal etc?

This was a learning experiance and I hope others have learned something also.

RE: Weird glitch.
 

I was having a lot of "uncommanded input" problems with my Tiger2. It would roll and pitch ubruptly while flying straight and level. Ireplaced the radio, same. Replaced Rx. same. One day the plane was on the starting bench, engine running, and ALL the servos went crazy. A friend looked it over after I shut it down and found my EZ-link on the throttle. He told me to get rid of it. Idid and the problem went away.

Ihad used that system on all of my planes, and all of them would suffer the intermittent "twitches." 3 of them went in the trash because of it. Idon't use it any more. LOL