Uncontrolled elevator movement

Hi folks. I’ve noticed a problem with some uncontrolled movement on the elevator on my Rising Star.

I’ve got a Flysky FS-i6x Tx and a FS-ia6b receiver.

I noticed a few times when setting up the controls that the elevator servo continuously fluctuates up and down with no control input from the Tx.

It happened once in my garage when I was running the engine. It then happened again today a couple of times at the flying field when starting or running the engine. It thankfully didn’t happen in flight though.

The battery is a good distance from the Rx, as it’s forwards in the nose. The Rx is stuck with velcro onto some foam.

Any ideas what could be the cause?

With a twitchy servo, I wouldn't have flown the model! :evil:
If the gear is new, take it all back for exchange, or if not, find someone nearby who knows what they are doing to check it over - not some CB fiddler! I don't recall if you said it was new or used gear.
Try a different servo - or just swap servo plugs about on the rx, see if the fault is the servo or the rx itself.
If it's the servo, bin it and get another. (for the price of a servo, is it worth risking the model).You could try switch-cleaner - NOT WD40 - on the pot wiper and track, in case it is muck. (and you can get access!)
If the fault remains on the ele channel, after swapping plugs aound, then it's either a mucky pot in the transmitter (switch cleaner again), or a dodgy solder joint in the electronics, or a component failing.

It’s all new gear. I’ll swap the ele servo for a futaba one that I have and see if it still happens.

The guys at the club thoroughly scrutinised and tested the model before and during the flight. They are very experienced. They noted the elevator movement and tried to recreate it and couldn’t. So put it down to interference. The plane had already been maidened and put through it’s paces before this happened, and there was no sign of the problem in two subsequent flights.

But I would like to know what it was, for peace of mind.

I would go with Eric's suggestion of a poor contact that is effected by the engine vibration.
A poor contact within a servo plug is not unknown.
Not easy to find. All you can do, without the engine running, is seriously wiggle the wiring and plugs between battery, rx and servo to see if you can make the servo jitter.

How is the throttle servo connected to the throttle arm? A common mistake is to connect the push rod direct onto the metal throttle arm, thus putting interference all through the plane! A plastic clevis usually does the trick.

I’m using a servo stopper on the throttle arm.

I tried wiggling the wires today, but could create the oscillation.

I’ve changed the Rx to a different one in case that had any issue.

Could it be any electrical interference? I’m just using a simple setup. Battery connects to a switch, then switch to battery.

What's a servo stopper?
If it is a sprung sliding link, that allows less throttle movement than servo arm movement, that's a waste of fine control. (see below - metal to metal noise)
If it is an end-stop that jams the servo, so it cannot complete it's travel, that will destroy the servo, as it is stalled, and it will 'eat' loads of power, until the amp goes pop - and could 'brown-out- the receiver! (Spektrum radio's are prone to that!)
What Klippy was referring to was a metal servo pushrod or clevis rattling on the metal throttle arm, due to engine vibration. This will generate electrical noise that can (used to) upset the receiver. (metal to metal noise)

This turned out to be a dodgy servo, so I’ve swapped it for a Futaba that I had.

That's different!
It looks like a component in the servo amp is out of spec, so the hysteresis isn't set correctly, hence the hunting back and to, as it tries to find the 'centre'.

Yeah, I suspected it was something with the servo rather than the Rx. I’m also going to swap the aileron servo to a Futaba one that I have, as I’d rather have reliable ones on the control surfaces.

I’m not sure what the ones I got with it are, or how good they are. The guy gave me them when I bought the rising star kit, and said they’d had good reviews and people in his club recommended them. But first impressions aren’t good.

They are metal gear servos, which is good, but I don't recognise the name.

I can see the nice looking label but what is the name please ?

So i can avoid them, made in china ?

Rich
I think if you avoid servos made in China or Taiwan the choice will be very limited indeed!

Rich - as far as I can make out, they are tiancotorx. I've never heard of them!
Googling gives me a HUGE url, but nothing on where they are from -

www.google.com/search?source=univ&tbm=is...259&bih=605&dpr=1.33

Not sure where they’re from.




www.google.com/search?q=tiankongrc+mg996r