Harley Condra

My Feedback: (4)

David,
You are definately on the right track. I'm glad to hear your philisophy regarding high servo power. I, too am a student from the high torque school, and admit that I did have some concern, although only very slight, when I installed the 3421's. Wish your article had been in print a few months earlier. More of us might have switched to a stronger servo for this application. As usual, hindsight is 20-20. 20-15 in this case!

I understand that BV (according to Tony F. today) that he (BV) took a 3421 and hung a fairly heavy weight on the servo arm and exercised the servo for an extended period of time, and had no failures of any kind. Now I don't know if it was a bloody great weight, or for how long he hoisted it, but he is concerned about this problem. I'll speak with him, and find out the particulars.

Thanks for your comments, and I hope that others will act upon your good advise.

Harley Condra
BVM REP
RAM REP
servo slayer

mglavin

My Feedback: (31)

Harley

I suspect the problem is the update rate that the gyro is driving the servo to maintain...

You fly at Camp Pendleton, right? I was down a few months ago and saw you fly your Bobcat. I was hanging out with that other JR guy from San Diego..,.

Doug Cronkhite

My Feedback: (34)

The only problem I can see with BV's test is that there wasn't a gyro mounted on a 'shaker table' to try and simulate the workload given to the servo.

As far as replacements and such.. I can't speak for Horizon on that one, but I will suggest it for sure.

I want to avoid conjecture on this one if at all possible until Horizon has a chance to look at the servo itself and see exactly what failed (if they can) and give me feedback. IMO, anything else could lead to people being overly concerned about an otherwise perfectly good product.

-Doug

David Gladwin

I too was concerned that such a mechanically small servo would be working so fast, with high frequency reversals as is the case with a piezo gyro AND the possibility that it may also be exposed to potential flutter loads. There is no substitute for real grunt in a critical servo, and that is where the 8411 excells, apart . of course, from its extreme accuracy and reliability history !

I also felt that the anchorage of the aileron horns in the BobCat could be substantially strengthened at little or no weight penalty (it is only captured by balsa ribs in kit form). I replaced these balsa ribs with ply. Took minutes to do, cost nothing, weighs a few grammes, and it is another POTENTIAL weakness fixed BEFORE any problems arise.

I am sure BV tested the BobCat thoroughly before release but no testing is as good as service in the field with large numbers of real customers. This is typified in the car industry. My BMW 530 was recently recalled to have a new cooling system motor installed as, in service, they had been found to overheat with a potential to cause a fire, although that had not happened. No cost to me of course, but BMW did the right thing.
BRG,
David

PR38

Seems to me like you could put some kind of relay inline from the receiver to the servos (maybe with a capacitor for sudden heavy loads in aerobatics) so that if you get a stalled servo, you don't drain the battery. I like to use the Jomar battery backup system, but if I fry the main pack and kill it, the only thing the battery backer will do is switch to the reserve pack and kill it too, only delaying the death of the airplane.
Many people have split elevators, independent ailerons, etc...most planes can loose a rudder or flap sevos and limp it back in... So it seems to me like in most cases you could cut out a servo if it was about to die anyway.
If someone made a gadget like that, I know I would buy one.

Harley Condra

My Feedback: (4)

Doug stopped by tonight and picked up the failed servo plus it's working counterpart to send to Horizon Service tomorrow. He was pretty amazed at the amount of heat damage to the case. We didn't open the servo up to find out what fried, but the case has a large "wart" on each side (mirror images). Lots of heat there. He even brought me a couple of new JR heavy duty extension harnesses to replace the heat treated ones. I really appreciate that Doug. You have gone the extra mile, and I will make mention of your greatly appreciated help to Mike McConville as soon as possible. He should be advised every time one of his reps goes above and beyond the call of duty. I appreciate the interest you have shown in solving this problem.

Harley Condra
BVM REP
RAM REP

DavidR

My Feedback: (1)

Harley,

Have you started shoehorning the 9411's in yet. I plane to do it this afternoon and think my approach is going to be to grind out one of the mounts and just install one new mount and use one of the existing mounts. I have not opened it back up to look at it yet though.

BTW I would also be interested in knowing how everyone did their linkage, in particular where on the servo arm you connected the pushrod, and which servo arm you used. I talked to another guy last night and he was thinking the servo linkage setup has a lot to do with the failures we have been seeing.

David Reid

rcjetflyr

My Feedback: (10)

Harley

I wouldn't mine knowing how you went about installing them also,since I decided to also put 9411's on the rudders.

Thanks Jack

Harley Condra

My Feedback: (4)

David, Jack,
I will install them tomorrow afternoon. I measured, plotted, planned and schemed, and have determined that I will need to remove the aft block and move it aft very slightly. I'll probably install a new block. Should have no problems. The linkage is just as BV designed it, and has always worked free and smooth. No hinges binding, squeeking or doing anything a hinge should not do.
Will fly it on Saturday and report the results.
As I mentioned to Jack offline, I may need to make new poly ply covers, as the slot may need relocating.
The fin is pleny deep enough to contain the 9411's.

Harley Condra
BVM REP
RAM REP

Harley Condra

My Feedback: (4)

Well, guys, I have finished the 9411 installation in the BobCat. It went very smoothly. All I had to do was to move the aft block a small amount aft as I previously indicated. The poly ply covers fit the same as before the swap, and are held on with scotch double stick tape from the office supply store, same as before.

The linkage required readjusting but no changes were necessary.
Tomorrow I'll flight test the setup, complete with a new battery pack and switch setup. I have instralled two 1400 Ma JR EXTRA battery packs, and two JR Charge Switches. Each battery pack and switch plugs into the receiver, with one requiring a "Y" harness into one of the channels (brakes) because I'm using all 10 available channels. I think that a redundant battery pack is a good idea, without using any type of switcher (battery backer) that adds an extra level of complexity, and another failure point.
I'll report back tomorrow with the test flight results.

Harley Condra
BVM REP
RAM REP
Servo swapper

arw9fmw

My Feedback: (4)

When someone (anyone) comes up with a definitive answer concerning the rudder servos, gyros, etc on the Bobcat I hope they will post it someplace where it can readily be found. Maybe start a new thread as this one is pretty far down the list.

Appears two solutions seem most prevelant. Change to the 9411 servos on the rudder and the JR 450 gyro. I tried to find a JR 450 gyro but I could not find any still on the market. If this is the case what is the alternative to the G450? I do have a JR G400 and a JR 460t. Which would be preferable to substitute to for the G450?

Jack Mathias W9FMW
AMA 7654 since 1937

Harley Condra

My Feedback: (4)

Today I flight tested the BobCat with the new 9411's, and the redundant batteries and switches. All was well, as expected, and I got in three flights before packing it up, in order to get
home in time to take the better half out for lunch as promised. I don't know why she wanted to go.....I wasn't hungry!
So far, so good. Now, lets see how JR deals with the dead servo that we sent them.

Harley Condra
BVM REP
RAM REP

David Gladwin

My guess is that JR will find nothing wrong with the servo, we are simply asking too much of it, I look forward to seeing their findings.

To use this small servo and expect it to drive a ruddder controlled by a piezo gyro resulting in relatively high frequency reversals of the rudder mass is very different from using the servo to drive a control surface which is never moved particularly quickly and hardly ever to full travel, and certainly not at at high speed, (with resultant maximum aerodynamic loads).

For that reason the 3301 is probably fine for the elevator (unless flying with a big engine) but 9411s or even 8411s are needed on this rudder application to cope with the, gear down, yaw instability of the BobCat and ensure long servo life.


The loads imposed on a gyro controlled rudder servo on a fixed wing aeroplane are totally different, and vastly greater than those experienced on a helicopter gyro applications.
BRG,
David Gladwin

wojtek

My Feedback: (73)

I personally use Futabe gear exclusively ... both on planes and helis. JR is good, as long as it does not have to do with gyros. All the heli guys I know that fly JR, still use a Futaba gyro with a futaba servo on the tail or rudder. Speaking of gyros, Futaba is the way to go, from the GY602 to the GY35x series, they are all great... The GY35x series are specifically made for airplanes also !! I have a dual axis GY352 on my 30% cap 232s rudders/elevator, and a GY351 (dual servo mixable) on my ailevators/flaperons. I can hover it , and let go of all but throttle to hold it up. I also have a gy351 on the flaperons on my BVMf16, and A gy350 on the rudder (also got one on my roo)

The only non Futaba gyro I have is a 4 point CCPM rotor head gyro from Vario for my PHT3 powered bell230.

I have never heard of anyone EVER complain about Futaba gyros !! I have never had any issues myself either. Only problem I have ever had was on an old FP-G154 mechanical gyro, which had its bearings fail after 4 years of heavy use.

I do not want to be knocking JR, just think a lot of you guys are too stuck on them. And I do not want to only praise Futaba, I think voltz makes great servos as well ..., and I have heard only good things about multiplex ....


thats my $.02 (+tax)



Wojtek

David Gladwin

There is absolutely nothing wrong with JR gyros, they are excellent ! The problem is some reported failures using JR 3421 SERVOS when used in the BobCat which has considerable yaw oscillation with gear down due to flat plate speedbrake/gear doors.

Perhaps the problem is that the JR gyros are SO precise, as are the servos, so that this little servo is seriously overloaded in this application.

I have been using JR piezo gyros since they were first introduced nearly ten years ago and have enjoyed total reliability and superb accuracy, thats why my top model, my BVM F4, which has state of the art avionics, employs JR digital servos on all flight controls and a JR gyro.

I am sure Futaba is an excellent radio but my JR equipment has been virtually faultless in the 20 years I have been using the brand.

I guess that JR quality and reliability is why BVM uses the brand, after all, the success of the business and the livelihood of the owner and staff of the company is largely dependant on the the radio euipment they use.in their models.
BRG,
David Gladwin

BRG,
David Gladwin