Need some help please- THE FINAL RESULTS
 

This is an SOS to the jet fliers who have had this problem and solved it. First let me lay out the gear that I have:

Plane: BVM Bobcat std.
Radio: Futaba 9Z
Servos: BVM Recommended JR Servos
Gyro: JR 460T
Battery: JR 6v 1800 mAh
Vtg Reg: Jaicco 5 volt
Receiver: Futaba R309DPS


Ok here is the problem, I was out flying my bobcat today putting it through it's paces. The first flight of the day went without a problem. The second flight I slow down and drop my gear and all of a sudden the plane violently starts rolling to the right. After a couple of minutes I noticed the rudders were deflecting full right and finally I had to put in 32 clicks of left rudder to get the plane to fly straight again. After I got it down I tried to recreate the problem and I could not get it to happen again. This was the first time the plane has done this. I know that this has happened to others and I want to know if any of you who have been struck by this incident have figured out the problem. I am very upset about this because I almost lost my airplane today due to a stupid 100.00 gyro. Thanks to any help in advance about this.

Patrick.

Need some help please- THE FINAL RESULTS
 

Patrick,

Did the servos act fine on the ground before and after the incident? Also exactly which servos did you have and tell us about the setup of the rudders.

For example do you have the servos Y harnessed to the rudders and to the nosewheel or just the two rudder servos on a Y harness? I spoke with another individual yesterday that will likely chime in on this subject and he had the same scenario. His wnet to violently rolling and it straightened itself out after 4-5 seconds.

He was unable to get it to reproduce itself.

Also how many flights have you had with no problems?

David Reid

Need some help please- THE FINAL RESULTS
 

David,
Yes the servos acted perfectly fine on the ground before and after the incident. I have the JR 3421's on the rudders (what bob recommends). The rudders are Y harnessed together then they are connected to the gyro and the gyro is connected to the receiver.

I think today was flights 13 and 14. Unfortunately my problem did not straighten itself out until I put in 32 click of left.



Patrick.

Need some help please- THE FINAL RESULTS
 

OK.. try this. Unplug the gyro and plug the Y harness directly into the receiver. Do you still need the left trim? Need to determine where the problem is..

-Doug Cronkhite
-Team JR

Problem with GYRO
 

Doug,
The problem is with the gyro and not the servos. The problem happened when I dropped the gear which also switches the gyro from low gain to high gain. When it happened I immediately put the gear up and the problem went away.

The gyro is set with about 75% gain with the gear down which stops the bobcat from rocking back and forth due to the gear doors/air brakes.

Patrick.

Need some help please- THE FINAL RESULTS
 

The problems that we have been seeing have been a failure of the servos and not the gyro, the serovs failed hard over and never worked again after that. On Vernon's plane this last time the servos were changed out to some Non Digital Mini's and he flew 17 flights last weekend with them with no problems. The same problem as you described occurred to another friend of mine either Friday afternoon or Yesterday morning. His happened in flight and after approximately 4-5 seconds it went away. He told me yesterday afternoon he was going to do a considerable amount of testing on the ground. He also told me he had a Y harness from the Gyro to the nosewheel, and another Y harness after that to the rudders. I am also using a JR 450 Gyro.

Gyro
 

David,
I think that it is the new 460T gyro. With the new gyro when you change from low to high gain or vice-versa the trim shifts on the rudder. That made me very nervous to begin with but horizon said it is normal and would not affect flight. Well I think they are wrong so tomorrow I am going to start the hunt for a JR 450 Gyro. There are 2 other guys at my field flying bobcats and bandits and they both use the 450s with over 400 combined flights without one single problem.

I also would like to know what kind of servos vernon replaced his with? I might just replace that entire setup from the servos to the gyro.

Patrick.

Need some help please- THE FINAL RESULTS
 

Hmm.. Changing the gain shouldn't have such a drastic effect on the neutral position. I hate to ask a dumb question but you ARE running the gyro in rate mode aren't you and not tail lock?

Can you give me the full details and values on the mixes you're using for both the gear and gyro modes?

Regardless.. please keep all the info coming. I want to talk to Horizon about this as well.

-Doug Cronkhite
-Team JR

460T
 

Doug,
I am absolutely sure beyond a shadow of a doubt that I am running in Rate Mode and not tail lock mode. Plus I have prior flights besides todays that were without one problem.

I took this following quote directly from the Horizon 460T Manual that is online. If you have one or download one it is on page 2 under the section titled "Remote gain control setup: Airplane" at the bottom as a NOTE.

Patrick.

Need some help please- THE FINAL RESULTS
 

I went and test flew my BobCat yesterday. The first flight went off
without a hitch. Perfect.

However, the second flight almost turned into a disaster. I had been
playing around with the rudder rates testing the knife edge
characteristics of the plane on up wind. Shortly thereafter, on down
wind the airplane went bananas. It was almost uncontrollable. It
seemed to be doing half snaps or SEVERE non-axial half rolls for a
second or two and then I would partially be able to stabilize the plane
when it would repeat this phenomenon. I do not think that my radio was
going into fail safe and it didn't appear that my elevator or ailerons
were involved in the aberrant behavior. It looked and felt like the
rudders were moving to some extreme position and then back again. This
continued for about 10 seconds after which all of the problems
disappeared. I thought that the plane was going into the woods so I
therefore shutdown the engine midway through this episode out of my fear
of causing a forest fire. I was very fortunate to then have it float
back for a dead stick landing in the grass. The plane is unharmed
except for bent main gear wires and a broken NG.

I read your and the other folks posts on RC Universe about the problems
that y'all have had with the 3421 servos. I have 3421 servos on my
rudders and a JR 450 gyro setup for the rudders. Have you come to any
conclusions?

I am configured with the RX rudder channel as follows:


RX -----> JR 450 gyro ----> JR Y-harness ----> NG-Steering servo
|
|
|--------> JR Y-harness ------->
Rudder
|
|------------> Rudder


I posted this directly from my buddies email. His "episode" occured with the JR 450 Gyro so I am not so sure about the 460 being the only culprit.


Here is a solution I just programmed into my 10X. I have 3 rates for my primary control functions so I programmed my "zero" rate on my rudder to zero. Then if I should have the rudder go nuts I can hit the rate to zero and just fly it without rudders that way even if my gyro comes loose in the airplane I can control it to land.

Need some help please- THE FINAL RESULTS
 

I too have the 460T but only hooked to the rudders with y harness between gyro and rudders. I did not use the gyro feature in my JR 10X because the gyro channel was used for nose wheel...I think. Anyway, Steve Elzey programed mine with just a small amount of sensitivity and no on/off switch. Did not use the gyro set up stuff in the radio. Did not program multiple rates on the gyro. No problems with mine so far with 18 flights on it. Using the JR digitals in rudder per plans.

Wonder if mine has the potential for problems as well.

Dave, see you later this week in Austin.

Mike Jensen

Need some help please- THE FINAL RESULTS
 

Mike,

I did not use the Gyro set up page either. Mine and Vernon's are both set up with a mix, (Gyro gain on Aux 4) and using the retract switch to change the gain. I can also adjust MAX gain by rotating the aux 4 knob. This way if it is windy and I need more gyro I can dial it up.


We will be getting there Thursday afternoon sometime. I hope to put close to 40 flights on my BC next weekend. I got close with the Bandit last year. Vernon and I should do some formation flying as well.

Need some help please- THE FINAL RESULTS
 

When Steve set mine up, I decided not to have an adjustable gain. Not really sure the damn gyro is worth it. Don't need it on takeoff, just thought I would try it to smooth out dutch roll.

Will be in Austin Thur evening as well. Not sure if I am going to fly the Phantom on that short runnway. Just started doing split s's with the Bobcat. I could barely sleep after the last few flights 2 weeks ago. Kept dreaming of split s's!!! Boring life I have! Hope to burn a few gallons of kero as well.

See ya soon.

Mike J

Need some help please- THE FINAL RESULTS
 

I have been painting the new Phantom this weekend. It is almost ready but will not be flying until Afterburner. I would not risk it on the short runway. Vernon won't have his with him this year either.

Need some help please- THE FINAL RESULTS
 

Patrick,

Can you give me a rundown of the electronics in your rudder setup from battery, to switch, to Rx, and all the way through to the rudder itself, including all extensions, y-harnesses etc.

I'd also like to know how your radio is setup to change gains. I'd like to know the values in the radio as well as how the mixing is done.

Trying to put a mental picture together to see if I can come up with any red flags.

-Doug

Need some help please- THE FINAL RESULTS
 

Not that this post is any help, but I had a re-occuring problem whe I was running a JR450 gyro in my Phantom. It to just took an abrupt left anytime it wanted to. Fortunatly every time was on the ground and I could not duplicate the problem after I had turned things on and off a few times. Last year @ Hearn it went full left just as I was pulling out to fly. I removed the gyro, called JR the following week. I told them I had 2 450s and they both did the same thing(which they did). They told me to send them in and they replaced them with 460ts. I have since sold the 460 ts. I sold them because When I talked to Jim Wiegle at FJ, we were discussing servos and he said he replaced the 450 gyro in the rafale because it went hard left when Terry was flying and they almost lost the plane. Fortunatly as all f-4 flyers know, you simply dont need a gyro on a f-4 for steering and I cant tell much difference without it on the rudder. ( I think the correct cg is more important than the gyro on the rudder on a f-4). If anyone comes up with a rock solid solution, I will try on a lesser plane than my phantom, untill then I dont trust the JR gyros. Dont get me wrong, I have always and will always fly JR. ...... Looking forward to Austin......... RB

Need some help please- THE FINAL RESULTS
 

I'm trying to find a pattern here.. some commonality.. because I've run the older 950 gyros in airplanes for hundreds of flights without a problem, and Tony F has probably 500 flights on various airplanes without problems. I know he has over 150 on his Bobcat using the 450. I can't remember if he's using a gyro in the Bandit or Mig-15 or not though.

This just doesn't make sense that they'd have this erratic behaviour. Something has to be triggering it in my opinion. There are just way too many 450/460 gyros out there in use to not hear about this until now.

-Doug Cronkhite
-Team JR

rudder setup
 

Doug,
My airplane is setup as follows.

I have a 6.0v 1800 mAh pack which is plugged into a JR Switch, then the switch is plugged into a voltage regulator and the regulator is plugged into my receiver for a steady 5.1 volts. My rudder servos are 3421's which are plugged into 18" JR 22 awg ext. which are plugged into a JR 12" 22awg Y-harness which is plugged into the gyro input. The gyro is then plugged into channel 4 and 5 on my radio. 5 is for gain control. My gain is set at 0% with gear up and 75% with gear down and the way I set my gain is by using the ATV on channel 5 (gain channel). There is no mix to accomplish the gain control I just assigned that channel to the retract switch in the radio. Prior to it being on that switch it was on my left slider so I could dial it in before assigning to my gear switch. If you have anymore questions please feel free to ask

Patrick.

Need some help please- THE FINAL RESULTS
 

Patrick,

I've been talking with JR Service at Horizon and would like to see this gyro if possible. Have you sent it in to them? If not can you do so attn: Adam Corley?

-Doug

Horizon Service
 

Doug,
Will get it sent off first thing tomorrow. thanks.

Patrick.

Need some help please- THE FINAL RESULTS
 

Doug, I talked to Ken @ JR I think he will remember me if you want to talk to him.......... Ray Blair

Gyrations
 

I have been and always will be a JR proponent because I think it the best.
I think I may have have a good idea of what may cause the problems you describe. The new digital servos are amazing pieces of engineering but it is also important to understand that with all that performance comes a current draw downside. If you were to put a current probe on the battery lead on a good (100Mhz+) scope and you knew what you were looking at you would realize that it is truly amazing that with such deep current spikes through what is at best pretty thin copper leads, our systems cope so well. Now put three servos at the far end of a very sensitive piece of gyro circuitry, the main lead of which now has to cope with current spikes from three servos, and you are depriving the gyro circuitry of its safe operating voltage range. Now to really give it a hard time put a voltage regulator between it and the battery. Take it from me, there is no way a non-switching voltage regulator can cope with the transients presented to it as well as a good nicad can without one, no matter what the manufacurer claims or how many guys say
they work OK. You just found out they do not. Should the gyro glitch due to a poor supply to its main circuitry it follows that it will output some erroneous signal to the servos, which in turn causes a worsening of the supply condition. Hey presto! you have a vicious feedback circle. Now also remember the gyro is capable of very fast signal changes in direction (high current needed to stop the servo and change direction) to the servos, much faster than you can move the stick. These problems may not occur on the ground when there are no control servo loads and no gyro feedback activity. What is the solution then. Use thicker guage wire for your Y leads and battery packs and keep them as short as possible. Lose the voltage regulator. As a last resort use lower performance servos on the rudders for less current draw via
the gyro. All those connectors, solder joints and copper wire add up to significant resistance. The thing with servo motors or any electric motor is that when expected to provide a give torque at a decreased voltage will draw even more current to compensate.

Andre Baird

Need some help please- THE FINAL RESULTS
 

I was wondering about momentary current spikes lowering the voltage as well. I already asked the guys at Horizon for voltage requirements for the gyros.

This still wouldn't account for the HUGE neutral point shift that Patrick has seen on his Bobcat since it wasn't a transient effect.

-Doug

It could....
 

Actually, I think BMT's explanation could account for the huge neutral shift (hard-over) whatever you want to call it.

Gyro sees low voltage-> gyro commands servo to offset, drawing more current-> gyro sees lower voltage-> repeat

Now the surface is fully deflected and bound up, drawing huge current and keeping it locked there.

For a solution, you could also power the servos from a different pack than the rcvr and gyro.

Vernon's Bobcat
 

David,

What non digital servos did you use on the rudders?