OK, here we go again. Well it happened again. The rudders kicked left on my bobcat again today when I turned up the gain on my 450. After getting the plane back on the ground I gave a call to BVM Jets, where david proceeded to tell me that the 3421's are not to be used with a gyro and directed me to the bvm website.


This is my question, has anyone out their flown the 9411's with a gyro for alot of flights and if so have you had any problems with them? I don't want to spend 200.00 on servos just to find out they won't work either. At this point I am ready to ditch the bobcat and buy a hotspot.

Patrick.

Patrick,

I ditched the 3421's and I am installing 8411SA's instead....

Todd

Hi Patrick,

I have the 3421's in my Bobcat and so far so good, knock on wood. The whole gyro deal is really starting to be a pain though. I am seriously considering adding flaps and tossing the gear doors. In the end this seems to be the best solution.

Here is a picture of Larry Kramer's Bobcat. Dang, wish I could build like that.

GeorgeR.

If I am not mistaken BV's XL has the 9411's in it and has since day one. I have around 30 flights on mine with the 9411's. My gyro took a crap but I had mistakenly programmed it for about 75% gear up and 25% gear down. I now have it at around 50% gear down and 10% gear up. Tomorrow I will reduce the gear down, and go to zero gear up. Ditch the 3421's they are just not up to the task. The 9411's are a heavier and larger servo.


David Reid

A few weeks ago, I had a 3421 melt down on my BobCat. I wrote a thread on it, and started to install the 9411's. At the time, I replaced the rudder and elevator servos, and have 40 flights or so on them, without any more troubles. I feel that the 9411's are up to the task, and the 3421's are not. The stronger servo adds a little insurance, and helps relieve some of the worries I had with the small servos. The 3421's just look kinda small for the job

The weight gain is barely noticeable, and they are simple to install in the BobCat.

It is my opinion that the 9411 is the correct servo for this application.

I also installed a redundant battery pack in the airplane, one plugged into a "y" harness on the nosewheel servo, and the other plugs into the receiver battery port. Both batteries are JR EXTRA 1400 Ma. 4.8 Vdc.

Harley Condra
BVM REP
RAM REP

Well guys..

I wish I could give you a definitive answer at this point.. but I can't. JR has been looking at the problem and hasn't found anything yet. Things are still being looked at though so I can't speculate on what might be happening. I DO know that BVM has suggested people go to the 9411 instead.

The 3421 that burned up on Harley's Bobcat was looked at recently by JR and JR Japan asked to see the servo to further analyze the problem.

Personally, I think the 3421 is a fine servo, but might not be up to handling the demands of a gyro on high gain. I'm still hoping JR can find the cause of the burn out.

Doug Cronkhite
Team JR

BV told me that they (BVM) had attached a weight to a 3421 and put it on a servociser and let it operate for several days with no problems. His conclusion was that the 3421 with the gyro and in some cases with an unregulated 6 volt pack were frying. I still have 4 of them and plan to use them in a quickee 500 plane whenever I get around to building it. I think they are good servos as well but I don't think they are up to the task with a gyro set on ANY gain.

DR

Yeah David,

The only problem with BV's test is he didn't put it behind a gyro on a shaker table to simulate the gyro loading. So while BV's test did show it was up to working hard over long periods of time, it didn't simulate the continual rapid movement of a servo behind the gyro, which is the concern.

Why are so many people making such a big deal on the BobCat rudder/gyro set up ?

The answer is dead simple, use 9411s (just like I recommended in my RCJI review of the Bobcat ) and a piezo gyro set at 50 % gear down and 0 % gear up. Problem solved. Fly it, enjoy it.

Using 3421s is asking just too much of a very good but dinky servo. High frequency reversals of travel, as commanded by the gyro, are obviously hammering this little unit and its throwing in the towel.

9411s are just a LITTLE heavier, just a LITTLE bit larger and a lot more powerful than 3421s. There is no downside to using the 9411s they dont even cost much more and balance is not an issue, at least it isnt on my RAM 500 BobCat. which balances right on the mark with no ballast.

Glad to see that although BV disagreed with my recommendation for 9411s he is now endorsing their use.

My next BoBcat will also have bigger servos on the stab. too. The recommended servos are probably OK but a reserve of power is no bad thing on this or any other high speed model. The need for more than just ample flight control power was learned on the early full size jets, sometimes the hard way, over 50 years ago.
BRG,
David gladwin