This is new to me

How about this, 3 servos, all the same, work fine on the servo tester. When tried on the RX, TX binds, ESC beeps, motor spins when throttle is input, servos do not move on stick input! Change ESC, the same again! Swap servos for a different type, everything works fine!
Any ideas?

Some background....  I wanted to test servo action and centring prior to gluing them in.  The initial layout was 3 9g servos.  I ran them through the servo tester, sanded the slot so they didn't bind and then went to see about setting limits in the Futaba.  When wired in via a 20A ESC and a 650MAhr 2 cell battery (same as used with the servo tester) I didn't get any stick response.

 

Tried a different (15A ESC)  Same lack of servo actions.  Tried another 20A ESC. Ditto.  And considered falling back to old dumb Sport version of Futaba.  Then I remembered that in the past that some 9g servos were problematic - either they seemed to get some cross-talk from other channels or were intermittant or seemed dead.  So I pulled out some 5g servos and they worked.  I suspect the BEC on those ESC were delivering just under 5V or whatever the critical threshold was.  The 5g servos happily run on a slightly lower voltage.

Seems overly fiddly.  5g servos are not up to the Balsa Cub build.  Seems silly to lumber the printed paper airplane with a 30A ESC for an 8" prop and a 22x6 motor seems a silly extra weight. Boosting the V into the reciever to better drive servos is something I have not tried.  Or perhaps I need to look at the fine print when buying an ESC to double check what they are feeding to the reciever...

Klippy - Not enough VOLTS getting to the servos or receiver! Most are intended for 5V operation. You may have heard of 'brown-out' - which is where the volts drop below the level at which the receiver can function - Spektrum radios were prone to it - especially in E-flight, with the corresponding high current draw which can cause the battery voltage to sag whilst on load.
Jon - the speedo AMPS are irrelevent for servo operation, that pertains to the flight motor current draw! A servo only draws a few milliamps unless the linkage has jammed and stalled the motor - in which case the servo amp (inside the servo case) will go phut after a couple of seconds!

Also - check you have plugged the speedo/voltage regulator into the THROTTLE socket on the receiver - some makes refuse to 'boot up' if they don't see the correct pulse-length! (ie throttle closed!)
 

Yes, from ESC to channel 3, which for the receivers I was testing is the throttle. 

The servo brand that didn't work was Tower Pro Micro Servo 9g SG90 - probably got off Amazon. They must have
worked on some combination in the past because I seem to have a half dozen in the box.

One brand that works is a FlightTest ES9051 marked as 3.6-5.3V - I recall being rather expensive...
Another that works is Hextronik HXT500 5GR

Silly thought - did you plug them in the right way around? The rx socket pins are not assymetrical, so the servo can be plugged in backwards!
It doesn't help when some people use black for the neg wire, but others use brown or yellow! Pos is (almost!) always the middle pin.

I sent Tony a close up and he confirms that they were attached correctly.  We are tending to the opinion that the fault is in the RX not passing sufficient V to the servo because when I substituted a servo rated for a 3.8-5.3V it worked fine.

Interesting that there is no place I could find in the Futaba manuals or receiver data sheets that mention orientation for the servo connector (other than to not slot them in 90 degrees rotated).  

Memo to self - take close up photo of known to work electric layouts and combinations of components so that when doing initial rough layouts there is less risk of diving off into rabbit holes....

Ah but - if you use a genuine Futaba receiver, and genuine Futaba servos, there is a tiny 'tab' on the servo plug that slides into an equally tiny slot on the receiver casing, so they cannot be plugged in backwards! 

Yup, and I have carefully filed dozens of the tabs off over the years. So far I have not had any mishaps due to doing this 

I further investigated the no-servo-action by the expedient of ordering some different metal gear 9g servos (see image).  Better quality certainly and the spec sheet quotes allowing V starting at 4.8V.  Both my Futaba Rx are working with these.  Is it because of the V difference or better internal controller is unknowable at this point.

From what I can see the non-working servos were panned in lots of reviews as a marginally useful that has go downhill into basic rubbish. I will root around and toss the rubbish so as not to be bitten in the future.

I checked it out on the servo tester as well as the Rx and the movement certainly is smoother.  So note to self - for some things spending a few more pence is worth it!

And, of course, the supplied arms are slightly different so had to tweak and reprint the extension.  Nice comments about alternatives to arm extensions in other chats that I will keep in mind.

 

 

Korean copies of Chinese copies of Japanese copies of whatevers!
You should know the old saying - buy cheap buy twice! 

From what I understand the minimum voltage a servo will operate at will depend on the circuity used and the specification (or not) of the electronic components used. A cheap servo manufacturer will use the lowest price components they can get. Supplier "quality control" costs!
A cheap servo is likely to basically operate as well as an expensive one but don't expect it to function within the same specification. 

Buying expensive servos will not always work, the servos in my SU27 were Hitech 25Kg at over 120 quid each in 2012 and one burnt out resulting in the total loss of everything in and on the model £7000 worth gone 
Hitech will never be allowed into the house never mind a model again 

Manufacturers cannot give every individual item a long-term 'soak-test'. They make them by the thousands, if not millions, and can only take one, now and then, to give a thorough testing, once the design has been approved. There is always a chance that a duff one can get through 'quality control'.
I've told the tale before about Savox servos. I bought four for a new model, one was duff, so took it back, sme more were brought out, and I plugged them nto a servo tester I'd taken, on purpose. Two of the new ones were duds straight from the packet. One of my working ones later developed a fault, so it was fast in one direction, but dead slow in the other! The shop refused to replace it, as they claimed I'd damaged it!

I see your point Eric and i swear by Savox servos as they are my go to servo, and iv never had a issue with any of them, touch wood