flyslow

I have a new 50cc Yak 54 fitted with BLS 351 servos all round. Before the first flight two of the control surfaces(one rudder, one aileron) would flutter/vibrate around centre quite severely. It forced me to replace the rudder servo before the first flight. After 3 flights I now have both aileron servos doing the same. This problem was posted in another forum

http://www.rcuniverse.com/forum/PGDr...8083198/tm.htm

One reply was that this is a known problem by futaba?
Can you tell me if this is a known problem?
Has this problem been corrected with newer BLS 351 servo's ?

I am now considering replacing all servo's due to this issues, and I am very reluctant to try more BLS 351's as I think this is throwing good money after bad. I have been exclusively using futaba for almost 25 years and am very dissappointed with this problem after supposedly buying high quality servo's.

Flyslow

Krysta

Hi flyslow,

There is no "known problem" with this servo.

Binding or excessive load on control surfaces can harm the gearing in any servo, and that may be what the other modeller was experiencing. But without seeing his servo or his setup, we cannot be sure what was causing his problem.


Sincerely,
Krysta
Product Development & Support Specialist
Futaba Service Center USA
[email protected]

flyslow

I disagree with you saying there is no problem with this servo. I have had to replace 3 out of 5 of these servo's and the aircraft has only had 3 flights! The control surfaces that were affected were the larger control surfaces on the aircraft, that is the two ailerons and the rudder. I have absolutely ruled out that there was any binding or friction on the servo's due to the control rigging and the problem still existed. The fact that this problem existed on the larger control surfaces leads me to think that the cause of this problem is the deadband being too tight. The momentum of the moving control surface would cause the servo to react (due to its tight deadband) and this would set up a harmonic vibration. This was also happening in flight, as the battery consumption was approx 50% greater per flight than what i would have expected. I have now replaced the 3 servo's involved with equivalent JR servo's and the problem immediately dissappeared.

It is misleading that these servos are marketed as suitable for any rc application as this is simply not true.

These servo's are not suitable for larger aircraft control surfaces. It is incredibly disappointing to spend good money on supposedly good servo's only to find this problem exists.

jtsails

My Feedback: (2)

My BLS 351 servos do this too. I have one on a Wildhare 28% Edge and the other on a Lanier 87" Yak. The Edge has a Pull-Pull set up and the Yak has a direct linkage. Both are free of any interference. The flutter will stop if you momentarily hold the rudder but returns if you move the rudder with the stick. They don't seem to do it in the air as I have not noticed any unusual power consumption with either model. Both planes have done this since new and I have flown both all year. At Imac events people always ask me about it, but even the Team Futaba guys don't have an answer.
James

modtron

In the UK we are advised that the BLS351 is for car use and not aircraft, because of the dead band issues and flutter problems.

modtron
Oxford UK

ww2birds

My Feedback: (14)

No experience personally with the BLS servos (have two, have not installed them...).

But, the same problem happened with the JR 8411 especially on rudder setups where there was a lot of mass in motion. I had a Carden 35% Cap that did it, switched to a different servo and it went away. Too tight a deadband for a high-mass surface. Caused the system (servo + rudder) to oscillate. Not totally unexpected if you've studied control systems. The precision and "tightness" is great so long as the mass of the surface is not too large. Perhaps that is why some of the newer servos have adjustable parameters?

FWIW, the IMAC guys who had this problem with the 8411 just stopped it with their hands, and flew anyway. Said it did not happen in flight due to damping from the airflow... yikes!

Dave

les40

My Feedback: (1)

My opinion is that Krysta (Futaba) has provided a very poor answer to the problem being addressed here. I hope Futaba is preparing a better response to these gentlemen's problems else I will fly JR in the future.