Single servo ailerons

[Martin Harris - Moderator]

No thanks Nigel - I'm happy with my empirical logic and life's too short!

[Jon H]

Posted by Simon Chaddock on 16/08/2019 12:03:15:

I bet the OP is beginning to wish he had never asked.

lol too true.

I hated probability at school so getting into the nitty gritty is of no interest to me at all.

The point i was trying to raise earlier is that to claim dual servos on ailerons is for redundancy is a flawed argument if you dont double up everything else (someone else said this too).

No matter what you do there are still single point failures in the system and the biggest of those is the pilot. With that in mind, and considering the reliability of well maintained equipment vs the reliability of the average pilot the entire redundancy argument is almost a moot point.

[Nigel R]

Indeed it is Martin

Ultimately, servos are pretty reliable beasts, particularly if you avoid the chaff.

I have models with multiple servos in the wing and I'm perfectly happy to fly them!

Making our installs mechanically good is far more important than arguing the toss over the tiny chances of different types of failure of our varying setups - we're just shooting the breeze here

As a thing to note, the only servo failures I have ever experienced involve undersized servos and big surfaces. Mechanical mistakes on my part, in other words, during the install. Or, pilot error leading to a slight donk with subsequent damage that later caused complete failure.

[Keith Berriman]

I am reading all the responces thank you all. Appreciate I did have a control set up slightly higher than should be without my usual expo set up for my flying routines.

And without going off on another tangent is more up than down a better set up with a single or two servo set up ?

I have over 20 plus years building and flying IC models and tamed them all but this one is not to my liking as yet

Thanks again for all your inputs

[Nigel R]

"is more up than down a better set up with a single or two servo set up "

are you referring to the acrowot? if so I'd aim for equal movement in both directions

you can do differentially easily with either a single servo or dual servos

for a single servo, use a disc, and a pair of holes offset forward (low winger) or backward (high winger)

for dual servos, you can offset the servo arm, or program it in the tx

[gangster]

RC Plane Flyer Sorry you are having issues setting up this plane, some are just like that...but I believe you still need to stick to the basics.. The Acrowot dates back to the time when people were flying basic four channel radios and it has always has had a reputation for doing that All computers, bells and whistles and fancy words will not solve the issue if it basically isnt right Nothing wrong with a single servo, we have used them for years, put something half decent like a Futaba 3001 or hitec equivalent in and it will be reliable.. With a good basic set up get it flying perfectly then you can gild the lily if you wish by playing with your tx settings If it wont fly a base set up eg like a good old Futaba M series then it will never fly with the most expensive TX in the world.

[Martin Harris - Moderator]

Posted by Jon - Laser Engines on 16/08/2019 13:36:43:

The point i was trying to raise earlier is that to claim dual servos on ailerons is for redundancy is a flawed argument if you dont double up everything else (someone else said this too).

No matter what you do there are still single point failures in the system and the biggest of those is the pilot. With that in mind, and considering the reliability of well maintained equipment vs the reliability of the average pilot the entire redundancy argument is almost a moot point.

Moot point? Four models I can think of would probably not exist today if the servo that failed was the only one fitted. Despite the convoluted and almost certainly incomplete statistical analysis modifying the conclusion by a few percentage points, the likelihood is that this would have been the case in two of them.

Yes, even a well thought out model aircraft installation with redundancy will have numerous single points of failure but having redundancy on primary flight controls operated by complex electronic/mechanical systems which can't be easily checked internally and can fail instantaneously gives you a fighting chance if one fails. How do you "well maintain" your servos? Functional checks will pick up gradual failures and some intermittent faults but even replacing them on a service life basis introduces the possibility of early life component failure...

I don't use independently controlled surfaces on all my models but where I can do so practically, I would always opt to do so.

[Nigel R]

Posted by Martin Harris on 16/08/2019 14:32:05:

Despite the convoluted

It really wasn't.

[Martin Harris - Moderator]

Maybe not but it was almost certainly incomplete.

[Nigel R]

It was a contrived example.

It is far from complete.

[Bob Cotsford]

RCPF - one servo or two has no effect on how differential acts, dif is dif. Only the modeller cares as two servos makes it easier to implement differential, either by offsetting the horns or by using two channels and implementing it at the transmitter.

Now how about twin servos through a Y lead (minimum 3 connectors) or twin channels (minimum 2 connectors)?

Incidentally, my WotsWot failure was with a Futaba 148, and while I controlled the roll I failed when it dropped into a spin/flick while trying to turn it on rudder. Ultimately pilot error - ambition exceed ability to quote Casey Stoner.

It turned out that the soldered joint between lead and pcb failed (fatigue due to insufficient support?)..

[Nigel R]

Out of interest, what kind of servos were the failures on?

edit: question to Martin H

Edited By Nigel R on 16/08/2019 14:46:39

[Bob Cotsford]

I still say the biggest benefits of two servos for the average club modeller are that the force acts nearer the centre of the control surface, and that this can be accomplished with less slop than using either pushrods and belcranks or curved snakes, as we used to do.

Also incidentally, I've only ever had two cheapy servos fail in flight, one on a flying wing elevon (early Corona) and the other on floaty glider's rudder (DYS). Both proved interesting.

[Martin Harris - Moderator]

Posted by Nigel R on 16/08/2019 14:45:44:

Out of interest, what kind of servos were the failures on?

edit: question to Martin H

Edited By Nigel R on 16/08/2019 14:46:39

1. Futaba S3001

2. Hitec HS225MG

3. Probably a Futaba S148 but I can't be bothered removing the hatch to check and it's irrelevant as it was a connection failure between the receiver and an extension lead.

4. Ask Dickw!

P.S. I've had several cheap servos fail (happily pre-flight) which came pre-installed in foam ARTF models.

Edited By Martin Harris on 16/08/2019 15:04:06

[Nigel R]

Posted by Bob Cotsford on 16/08/2019 14:56:31:

I still say the biggest benefits of two servos for the average club modeller are that the force acts nearer the centre of the control surface, and that this can be accomplished with less slop than using either pushrods and belcranks or curved snakes, as we used to do.

 

A reduction of slop is a definite mechanical benefit.

edit - thanks Martin.

Edited By Nigel R on 16/08/2019 15:14:22

[Geoff S]

I've just bought 4 x Corona CS238MG metal gear/ball bearing servos for my Ryan ST project (which will have a servo/aileron btw). I've soak tested then for a few hours using a simple servo tester and they seem fine. They small (22 grams) and have quoted torque of 4gm.cm (higher than a 148) and I think will be perfectly adequate for an estimated 2.5 kg scale(ish) model.

One feature I like is the supply of a pair of brackets to allow side mounting. That won't affect this model but I used wing servos in that orientation in the past and it's always a bit of a fiddle - these brackets should make it a walk in the park (or a fly at the airfield!).

Single servo aileron operation was always (or very often) using Futaba 148 mounted in the middle of the wing. This meant using torque rods fitted down the trailing edge which don't give very slop free operation in my experience. Also I was always uncomfortable with the reduced glueing area for the t/e stock which sometimes even included the holes for the wing bolts. I admit I never had a failure but it just seemed a bit iffy.

Using small servos, one for each aileron, usually at least doubles the torque available for the control surfaces and provides very positive slop free operation. With a built-up wing it's just as easy (or even easier) to mount and connect the leads. The added advantage of being able to set differential easily and/or flaperons is a bonus.

I use a lot of exponential on the controls (20%+). I like the dead band between elevator and aileron controls (mode 2) because, with limited control over my right hand in particular, it helps a lot. I've never noticed the strange response of the mode; to my inputs; I just watch the model and adjust as required.

Geoff

[Nigel R]

"This meant using torque rods fitted down the trailing edge which don't give very slop free operation in my experience. Also I was always uncomfortable with the reduced glueing area for the t/e stock which sometimes even included the holes for the wing bolts. "

There's always a way... Ditch the dihedral brace and instead glass the centre section; then add a ply speader plate under the bolts, which covers the TE stock and an equal distance forward thereof. Solid.

I've not personally found torque rods to be sloppy. Use med to med-hard solid stock for ailerons; drill very carefully for the rods; final fix with 30 min resin. They are my go to solution for standard sport model type strip ailerons.

If you use mid mounted control horns, my opinion is that they need as much attention to the mount point to avoid a slop, perhaps a pair of 1/32 ply squares on the surface or a dowell embedded into the aileron, etc. etc.

edit: Two micro or mini servos can live in the wing centre if you need flaperons, I think a photo was posted already on this thread of a setup like this.

As ever, YMMV.

 

Edited By Nigel R on 16/08/2019 15:56:33

[PatMc]

When using flaperons, or any other mix involving dual tasking of the servos, the servo torque is reduced & slop increased.

[Richard Wills 2]

Posted by PatMc on 16/08/2019 19:24:35:

When using flaperons, or any other mix involving dual tasking of the servos, the servo torque is reduced & slop increased.

excuse my ignorance, but can you please explain?

[PatMc]

Max angular movement of a typical servo output is 120 deg total. Let’s say we want aileron movement of 30 deg total.
When using the ailerons purely for the roll function, in order obtain best advantage of servo torque the whole 120 deg movement will be used resulting in a gear ratio between servo output & aileron horn will be 1 : 4 – i.e. the ail horn will be 4 x the servo o/p in length.

Let’s say we want to use the ailerons as flaperons by splitting the total servo movement 50 –50 to each function.
If the same size aileron horn is used then the servo output length must be doubled. The gear ratio now becomes 1 : 2. So the servo is being made to do the same work with half it’s movement.

Also the servo’s gear slop is a fixed angular movement. The linear movement at the servo o/p is proportional to the o/p length, By doubling the o/p length for flaperons the linear slop movement is also doubled.