Control linkages

[Ashley Warnes 1]

I am building a balsa wood rc plane with a 762mm wing span.

I was wondering how you connect the servos to the control surfaces. I have heard you can use "snakes" but am not aware of what they are or how you would use them. I am looking at using servos like the Turnigy TG9e micro servos if that makes any difference.

All help gratefully recieved as are any diagrams, due to the fact i am new to the hobby and dont really have a clue.

Thanks

Ashley

[GrahamC]

What are you building? Because there are a number of ways of doing it, it depends on you actually want to do.

Why not show us some photos? I'm sure you will get some great advice, but there's not quite enough information there to give you a sensible answer.

[Steve Hargreaves - Moderator]

More info is certainly helpful as Graham sez but basically you need a connection point on your servo horn.....a horn attached to the control surface c/w a connection point & then a rod or similar to transfer the movement between the sero & the control surface.....

Lots of ways of doing it & the rudder/elevator are often different to the ailerons.....

[Ashley Warnes 1]

am going to be building a high wing trainer with rectangular wings. havnt got any pictures as i havnt started building it yet

what other information do you want, being new to the hobby i dont know what information would help

[Steve Hargreaves - Moderator]

OK High wing trainer.....does it have ailerons, rudder & elevator or just rudder & elevator? If it has ailerons is there one servo per side or a centrally mounted one? Where are the rudder/elevator servos located? Under the wing or at the back near the tailplane?

Whats the model called? Someone may have built one.....

[Ashley Warnes 1]

it is a howard hughes engineering lightwing, it has ailerons, elevator and rudder, the plan doesnt show where the servos are located or if there are 2 servos for the ailerons or just the one. I will prob. have one each side if i can find out how to connect them and the servos for the elevator and rudder will prob be located inside the back of the fuselage

thanks

[cymaz]

One of these?

If so use Closed loop connections on the rudder and elevator as per full size. Then a servo in each wing for the ailerons. If it is glow powered you will need a servo for the throttle. Thats 5 in total. So a 6 channel Rx will be needed. FrSky Rx's I will heartly recommend. I you are unsure what a closed loop system is then I've put a link in that will help-a picture tells a thousand words..etc..etc. Closed loop is not hard to install.

With a short looking nose it might be wise not too put the servos in the tail. You might need a ton of lead up front to balance the model properly.

Edited By cymaz on 04/07/2013 10:27:23

[Ashley Warnes 1]

it is that plane, i am going to use an electric motor rather than glow.

I was recommended to use **LINK** as it is a budget rx/tx with 6 channels

i do believe that the link you included didn't have a diagram on it for the 'closed loop' connctions though

thanks

will consider placement of servos, but if i put the battery forward and the motor is at the front, wouldn't tey balance the plane out?

[Steve Hargreaves - Moderator]

I'm a big fan of closed loop....especially on the rudder but this is a very small model at 762mm span so thinks might get a bit tight....worth doing if you can though.....I have some lightweight kevlar thread which would be ideal....PM me if you'd like some....

Now...attaching the control rods to the control surfaces......I like these pin horns.....drill a small hole...push them into the control surface drop of cyano & you're done....connection to the horns or servo arm......these are good & allow some adjustment...the actual link betwen the two can be made using piano wire...1 to 1.5mm thick. put a Z bend in one end to link to the pin horn or servo arm & the jobs a good 'un......

Beware long unsupported lengths of pushrod though....they bend.....if your elevator servo is under the wing then for small models I use some plastic tube from Plastruct (try your local Hobbycraft) it has a 2mm bore & is ideal for this sort of thing....secure it at each end & a couple of times in the fuselage & run the 1mm wire though it & you're done.....

For the ailerons I would think a central servo linked to each aileron using the pin horns & wire would work well....another possibility is to use torque rods from a central servo.....

[cymaz]

Also called Pull - Pull

 

Edited By cymaz on 04/07/2013 10:47:31

[GrahamC]

A few pictures....

The rudder end of a closed loop.

Its easier to do on larger aircraft in my opinion, and I probably would not try it at the size you are building [big fingers and thumbs!]

Rudder again, and elevator push rod. These are metal clevises, and fairly beefy horns.

The servo connections. Servo on the left is the closed loop rudder, and servo on the right is the elevator. The small metal servo arm connector, is really useful. A great way to do it.

This is a larger aileron servo than you will use, but the principle is the same. This is the easy way to do it. The metal push rod connects to the servo arm by means of a Z bend. You can buy special pliers to do this. I'm a fan, not everyone is!

A neater way to do a servo. You can make up ply plates for your aileron servos just like this, or buy plastic ones ready made.

At the scale you are building, I would use nylon clevises, carbon fibre push rods, and those little metal connectors for adjustment. They need to be tight, but don't over tighten them or you will crush the carbon fibre.

A push rod exit for a build in process. Basically, its a nylon tube, into which you insert another nylon tube, and various connectors can be screwed into either end of the inner nylon tube. It does need supporting at some points along its length, and small ones would be suitable for your build.

And finally

A carbon fibre push rod, inside a snake outer with a push rod adapter on the servo arm. This is the elevator control for a 47 inch balsa build.

Hope that helps and gets you thinking!

[cymaz]

This may help

[John Olsen 1]

Nobody really explained about snakes. They are really a form of Bowden * cable, as used on motorcycles. There is an outer tube and an inner rod that slides easily inside the outer, even if the outer is not completely straight. If the outer is fastened near each end, then the inner cannot cause any problems by flexing under compression loads. However the length between the end support and the servo arm can, so should be kept fairly short. There does have to be some length here that can flex, to allow for the angular movement of the servo arm, and the control horn at the other end.

Snakes can be very handy since they will thread through places where a solid pushrod might not be very easy to fit. You need to choose a size that is suitable for the model.

* Colonel Bowden, who invented the Bowden cable, was an early motocyclist and also an early builder of model aircraft. I'm not sure if he used his cable in his aircraft since radio control was pretty rare in those days.

John

[cymaz]

I've even done closed loop ailerons on a big build !!!!!!!!!

[PatMc]

Posted by John Olsen 1 on 04/07/2013 11:03:08:

* Colonel Bowden, who invented the Bowden cable, was an early motocyclist and also an early builder of model aircraft. I'm not sure if he used his cable in his aircraft since radio control was pretty rare in those days.

John

Wrong Bowden, John.

**LINK**

[PatMc]

Ashley, as you will have gathered there are numerous methods of linking the controls in RC models. Your model is very small so may be quite restricted in what is practical. The placement of components is especialy important in a small model to enable it to be balanced at the correct point without having to resort to excessive nose weight.
IMO it would be best if you posted the name of the plan or kit that you are making so that some definitive advice could be offered.

[Ashley Warnes 1]

Thanks for all the help so far

the plans are on **LINK** , if you scroll down the page, it is the Howard Hughes Engineering Lightwing. (30" model)

"

This is a larger aileron servo than you will use, but the principle is the same. This is the easy way to do it. The metal push rod connects to the servo arm by means of a Z bend. You can buy special pliers to do this. I'm a fan, not everyone is! "

would this system wrk for my sized plane. and if so what are all the parts called and how many of each would i need.

Thanks again

Ashley

[kc]

I dont think anybody mentioned that snakes ( as used in small RC models anyway ) are plastic not actual Bowden cable which is wire inner. Snake inners are plastic with a hole in centre to allow a threaded end to screw in ( often M2 ) See the SLEC website for info and prices.

I reckon that a 30 inch scale model is not a suitable RC trainer --it will be too small, too fast and too delicate to stand up to a beginners landings. More work to build scale than a larger proper trainer. Choose a more suitable RC trainer in the 50 to 60 inch span range is my advice --this will save you money in the long run and avoid disappointment. Consult your local club for advice and see what their instructors suggests to train on.

Read one of David Boddingtons books for beginners ( library or Amazon for cheap s/h copies )

[GrahamC]

On your plane... yes basically you can do that but scale it down a bit. It doesn't need to be that beefy.

What I would do is either...

A. Use nylon clevises cyano'd onto 1.5mm or 2mm carbon rod for the linkages, and then connect them to the servo arm using the linkage stoppers that Steve linked to above. I do this with foamies becasue its very light.

Or...

B. Use a bit of piano wire with a 'Z' bend at the horn end and a linkage stopper on the servo arm. You don't need to invest in special pliers to make the 'Z' but if you plan to continue building, I consider them an excellent investment. This is probably cheaper [once you have the pliers] but a bit heavier. You can make a judgement about the thickness of piano wire yourself - you want it not to flex over the length of the push rod. You won't need wire that thick on your build.

Obviously you will need something secure to fix the servo to in the wing. For your purposes B&Q sell 6mm sqare lengths of pine wood, [for less than £1!] which could be set into the ribs either side of the servo.

Why not start a build log - you will get lots of input!

[PatMc]

Ashley, sorry but I'm afraid the model plan you've chosen is for free flight not radio control. It could be converted but TBH only by someone with experience of building small models & using micro radio gear if it is to have any chance of success. Even then it would probably take some patience to trim, suffer a damage & be repaired a few times before being flyable. At this stage it would only be suitable for flying in the lightest of winds.

My advice is the same as KC's - forget this model & look at something designed as a trainer.

[kc]

I suppose the Bushwhacker plan from RCME or kit from Ben Buckle Plans is the most modern trainer plan available. Maybe somebody has the pullout plan (from RCME a few years ago) they dont need.....that's the advantage of joining a club -somebody is bound to help you with a plan like that or maybe a Super Sixty or Mini Super, Tyro Major or a similar trainer of 48 inch ( minimum )up to about 60 inch span.

[kc]

I checked and found that DB Sport & Scale sell a plan for the Tyro Major 54 inch for 10 pounds and for another 7.50 pounds you can buy a set of ready cut ribs. I would suggest this is the best / cheapest way for a beginner to build a trainer.

Tyro was designed by David Boddington and the techniques used are mentioned in his book " Building & Flying Radio Controlled Model Aircraft" and similar variations of his beginners books. Linkages are nicely explained and illustrated in that book.  There are a couple of secondhand copies of this book for sale at 1 penny (plus 2.80 post ) on Amazon today.  Also his Primer book is for sale but I think that's a shorter version.

Make sure you check to find what radio the instructors at your local club use for training -- you will need a similar make to use a buddy lead with their transmitter. Almost all training is done with a buddy lead now. If they use Spektrum you will need Spektrum, if they use Futaba you need Futaba. If you turn up with any other make than the one they use you will need to buy an extra transmitter!

Edited By kc on 05/07/2013 11:48:10

[Frank Skilbeck]

Also the radio set you put the link to is a mode 1 set, that is aileron and throttle on the right stick, no problem with that, but if you plan to join a club flying on the same mode as them is recommended (all of our power club fly mode 2 and I only know one mode 1 flier), that way you could get an experienced flier to do the test flight.

[Murat Kece 1]

Posted by GrahamC on 04/07/2013 10:49:24:

A carbon fibre push rod, inside a snake outer with a push rod adapter on the servo arm. This is the elevator control for a 47 inch balsa build.

Hope that helps and gets you thinking!

Hi

Doesn't insertion of the carbon rod directly into the servo connector cause issues as the carbon rod may weaken? I am using a similar arrangement but I am trying to add a steel wire to the servo end of the carbon rod snake.

Regards Murat

[Robin Colbourne]

Hi Murat

I agree with you. A screw crushing a piece of unidirectional carbonfibre rod is asking for it to crush and break up, leading to a loss of control authority. Epoxying on a snake end or binding a piece of steel rod (softer than piano wire would be desirable) on to the end of the carbon rod would be a better approach.

Robin