mario tavarez14

My Feedback: (37)

Hi guys my 2 elevator servos shaken like crazy make me think that I have a bad servos but I change for 2 jr 8911 and still with the same problem , a friend of mine tell me to put a rubber band on each side of servos arm , I did that and the servos stop shaken , this is safe to use because this is the first time that problem happen to me . Ok I need some help from the expert .

Best regard

Dave Wilshere

Mario

On an all flying tail? Its usually where they have a long arm and the leverage from the tail makes the servo over travel fractionally and the servo trys to re centre and over shots again so on.

It rearly does it in the air, and the rubber band trick will work, but can you post a pix of your set up? Normally only happends on big armed 3-D models

regards

Dave

Greg Wright

My Feedback: (6)

Mario

It also sounds as if possibly one servo is fighting the other a little bit which could be causing them to go over center and bouncing back and fourth. Like Dave said on an all flying stab it could be a leverage issue. I have two 8911's on the tail of my BVM F-100 no issues at all.

dribbe

On flying stabs, I use some servo slow to reduce the chance of the pilot 'exciting' the servos.. Reduces the oscillation.
Does not seem to be a problem in the air. (Lower voltage can help... shorter servo arm/longer stab arm if possible helps)

David

schroedm

My Feedback: (1)

That's 3 guys now over the last couple of weeks I've heard mention using servo slow on their primary controls??

How much do you use and is it just for cases like this? Seems odd to buy top of the range servos that you pay for for speed and power and then run servo slow and lower voltage?

Intrigued.....

FenderBean

this happens on one of my elevators when I pop the control, but it only happens on the ground and I was told its normal sometimes.

Vincent

My Feedback: (61)

I have used servo slow on elev on a couple of my jets. Sometimes there is no way to calm down a snappy 86 or 8711 plus you add an over excited pilot on final and you have a recipe for a crappy landing. I set mine up so the travel works about the speed of a analog servo. Just enough to get the twitchy out and still move exactly with the stick movement. Also in the air on a high speed pass the elev will be less sensitive and it will make for smoother flying.
Vin...

dribbe

I don't buy the servos for speed (in this application).... They don't make the servos I would like to buy....
I buy them for the torque, precision, and reliability (flying stab).

If I recall, I slow them to something like .35 sec. (But I will check)
I don't really want my F-16 stabs moving any faster. (it is hard on the horns and linkages... it is not needed.... I wonder how fast the full scale can move? It is not unlimited.

Keep in mind in this situation the two servos/stabs should have any variences removed and should track each other 'perfectly' for precision flying and sync.

(I don't run a lower voltage here... but I do on my MIG flaps. The should last longer and be more durable at a lower voltage. Torque likely down a bit)

Flying stabs and flaps are an application where the MFG would do well to make a state of the art lower geared high torque and slower servo... steady... locked...

David

schroedm

My Feedback: (1)

Hmmm, thanks. Food for thought.

Where do you cross the line between slowing them down and using expo? Personal preference I guess..........

Doug Cronkhite

My Feedback: (34)

The biggest contributor to this is the often awful mechanical advantage setup used on jets, especially those with flying stabs. ANY slop in the linkage at all makes it worse due to the incredibly tight deadband on today's servos. Dave's suggestion to use servo slow will help, but the rubber band to slightly pre-load the servo is the best solution IMO.

PaulD

My Feedback: (39)

Sounds like a recipie for PIO's???

Of course, the mechanical linkage should be set up to give the required travel without using end points to adjust the throw to a lower percentage. I recently looked at a similar problem for a guy and he was using end points set down to 40% to correct for the wrong linkage set-up.

Analog servos had a reduced centering deadband at higher supply voltages but does this apply to digital as well? It shouldn't but who knows?

PaulD

PaulD

My Feedback: (39)

mario tavarez14

My Feedback: (37)

Greg Wright i have those servos independent from each other and i am using a powerbox royal spectrum , and today i put a rubber band and the servos now stop shaken ok guys here is the pics of my twin turbine fej