Servo doesn’t recentre to same point

[EGB 953]

I recent bought a second hand air Frame with all the servos and engine.   Having Done a full setup all the servos are ok except the rudder one which doesn’t return to exactly the same place when you pull full stick to the right versus the left. The servo is a 148 Futaba indirect drive.  I have removed the servo and checked the cogs which are all clean and in good repair. There is no wobble in the linkage.  Do I just consign the servo to the scrap heap? Not sure what else to do.  Any suggestions or recommendations welcome. 

[Martin Harris - Moderator]

There were a lot of fake Futaba servos around a few years ago - maybe one of those?

 

Personally, I’d replace it - the model would be nasty to fly at best and a full blown failure in flight could destroy the model. 

[RottenRow]

Plug the servo into one of the other receiver outputs just to check the problem is with the servo and not the transmitter.

Assuming it is the servo at fault, then it most likely has a worn feedback potentiometer. Realistically that means it will end up in the bin. Or kept for spare gears etc. if you have other 148s.

Brian. 

[Mike T]

I'd also try these tests with the linkage disconnected, just to ensure there's nothing 'external' to stop the servo centreing.

[Brian Cooper]

Regrettably, the venerable old Futaba 148 is (was) at best only ever suitable for aircraft of low weight and low performance. . It was a very basic servo and was only ever on the first "step of the ladder" in the "starter" or "intro" range. Mostly they were supplied as part of a package with a new radio outfit. 

 

The servo output shaft is not ballraced, and it soon wears out and becomes vague and floppy. It can be likened to driving a car with the steering and suspension ball joints worn out. Yes, it will still steer but there will be a distinct lack of precision. 

 

There are far superior servos available nowadays and they are not shockingly expensive. 

Do the model a favour and upgrade to higher quality servos. . . You can feel the difference. 

.

[Nigel Heather]

As you say that the gears are in good order it is mostly likely the potentiometer - either a warn or dirty track.  You could try spraying some electrical contact cleaner (you could try WD40 in the absence of a dedicated product) and then operate the servo over full travel  several times - if it is just dirt that may solve the issue.

 

But the 148 is only a basic servo, better modern alternatives are cheap, so personally I’d say replace it - not worth the time and effort to try and fix, and if you don’t have contact cleaner, buying some will be a similar price to a new servo.

[Engine Doctor]

As Martin has said there are a lot of fake Futaba servos out there . Look at the moulding particularly the " made in Tiawan " and the "CE" mark on the botom of the case if not crisply molded then its a fake . Also cases were shiny plastic and internal were totally different to genuine version . They also sound clunky and agricultural ( rough) . Check the other servos as they might be fake. A set of these only cost around  £10 delivered and made a second hand model look more appealing. 

 

The last set of these I encountered were in a model  I was asked to test fly . All appeared fine on the ground and they centered ok . As soon as it took off the model was only just controlable . I landed after low buttock clenching circuit . Stripped it out to finf it had fake servos. Better still the owner couldnt believe that he had bought fake servos off of ebay ! At £9.99 for four alarm bells should have rung loud and clear.

[Cuban8]

I see that the old 148/4001 series of Futaba basic servos aren't listed on the three large websites that I just glanced at - not even Servo Shop, unless I overlooked them - have they finished producing them all together?

Most affordable basic Futaba servo seems to be the 3010 priced at around £22 (out of stock though) - quite an increase on what a beginner would pay for a 4001  a while ago. Cheap fakes still on Ebay which is not helpful.

Hitec offers some reasonable servos so all isn't lost - I tend to use their well priced ballraced offerings in various sizes and powers now.

Edited June 19, 2023 by Cuban8

[EGB 953]

50 minutes ago, Cuban8 said:

I see that the old 148/4001 series of Futaba basic servos aren't listed on the three large websites that I just glanced at - not even Servo Shop, unless I overlooked them - have they finished producing them all together?

Most affordable basic Futaba servo seems to be the 3010 priced at around £22 (out of stock though) - quite an increase on what a beginner would pay for a 4001  a while ago. Cheap fakes still on Ebay which is not helpful.

Hitec offers some reasonable servos so all isn't lost - I tend to use their well priced ballraced offerings in various sizes and powers now.

Thanks, I will get some decent replacements.