WOT4 ARTF

[Alan]

Just started to build the WOt4 form ripmax and have already ran into a few problems firstly the wing nut was damaged when being fitted,

secondly the there is far to much movement in the rudder when I installed the closed loop most likely i have done sometheing wrong.

But  I read an other theard on the forum with the same problem, and they replaced the closed loop with a snake.

Would you need to fit a snake to either side of the rudder as it is done in the closed loop or  just fit it to one side.

 

Alan

Edited By Alan on 06/11/2009 19:32:19

[Andy Gates]

A snake is a pushrod in a tube and only one will be need to be fitted to one side of the rudder to replace the closed loop system.

 

If you have too much movement in your closed loop, the answer is to adjust it.

Hopefully on one end of each cable there is an adjustemnt preferably with a clevis.

Depending on which end the clevis is at, depends on which way to move the clevis.

At the servo end, move the clevis in towards the center of the horn.

At the surface end, move the clevis out away from the control surface.

[Gary Murphy 1]

Just into a artf build myself and the loop system does look "iffy".

Can i ask if a snake/pushrod is a better option?

Can i ask what the benifit of a closed loop is over pusrod.Is it keeper for the lkit?

[John Privett]

Nothing wrong with closed-loop control linkages - several of my models have it on rudder, one on elevator too.  It's light-weight, usually easy to setup and doesn't suffer from the pushrod/snake flexing under compression.  I can't see any reason, if the kit suggests closed-loop, to change it. 

 

Gary, what do you think looks "iffy" about it?

[Gary Murphy 1]

The rear bit looks good with clevice BUT the photo showing the servo setup as the wire going straight through the holes in the servo arm.The holes in my servo arm are big compared to the wire,is this not going to cause slop and wear?

[Steve Hargreaves - Moderator]

There is another build thread for the Wot4 here which might be of some use to you Gary...

 

With regard to the closed loop you would normally set this up so that both wires are under slight tension to avoid any slop......note the word "slight" there...the wire just needs to be taught...you don't need to be able to get a top C out of it when plucked ...too much tension will trash your servo bearings. Ideally the width of the servo arm will be exactly the same as the width across the rudder horns.....this means that the whole system describes a rectangle/parallelogram & slop is eliminated.

 

An alternative method of attaching the wires to the servo arm would be to thread the wire through the threaded part of an M2 clevis & tighten the wire onto that (note that the threaded portion of a metal clevis is usually formed & has a split down one side...use the other side so the wire can't pull through , then attach the clevis to the servo arm. Note you must have a threaded adjuster in both lines to adjust the neutral position of the rudder.....otherwise you will lose the wil to live trying to get the wires just the right length before crimping them....

[Biggles' Elder Brother - Moderator]

Gary, without wishing to be to dogmatic  closed loop control systems are the absolute bees-knees as far as I am concerned! I use them on everything I can - I've even done closed loop ailerons!

 

What's so good about them? Well lots of things...

 

1. Totally slop free - more so than any other system because they are set up under slight tension.

 

2. Almost infinitely adjustable and extremely precise in operation.

 

3. No problems on "control runs" - just connect the wires to the servo at one end and the control horn at the other and bingo - they sort of find their own route between the two.

 

4. Its lighter than any other system

 

5. Its as cheap as chips.

 

6. Its dead easy to repair - though you'll probably never need to!

 

7. It follows full size practice - if it was good enough for Sopwith, DeHav's, and Fokker it'll do me!

 

The funny thing is everyone looks at them and says exactly what you did "It looks a bit flimsy/sloppy/dodgey etc". But if they try it - they are invariably pleasantly surprised - I know I was.

 

Final thought - Mr Foss knows a thing or two about designing model planes and the WOT4 has always had a closed loop rudder - in both the kit and the ARTF - nuff said?

 

So, go on, do yourself a favour put that snake back on the shelf and install the closed loop system - you wont regret it I promise!

 

BEB 

[John Privett]

Gary, if you're concerned about the closed-loop wires wearing through the servo arm then don't worry.  My Limbo Dancer has 10 years of (hard) use behind it and there is no wear that I can see in either the elevator or rudder servo arms - both have closed-loop wires through them.  I would say that it will stand another 10 years of use - but the airframe will have fallen apart by then!

[Gary Murphy 1]

OK i will give the loop a go.Only thing is the servo horn and rudder connections are different in with so the "parrarellagram" is not  a go on mine.Does this matter.I would say the rudder is double span of servo arm!

[Biggles' Elder Brother - Moderator]

No Gary it doesn't matter. A wild difference isn't good but a departure from parallelogram of the scale we deal with in modelling makes no real difference in my experience.

 

BEB

[Steve Hargreaves - Moderator]

No Gary it doesn't really matter......you will notice that the wire on the "pushing" side goes slack at full throw but thats all. It is worth getting the servo horn size & rudder horn size as close as possible (you can get extra wide arms from the model shop!!) as this is "best practise" but don't beat yourself up over it....

[Bob Moore]

There are a good few threads on the Wot a good one here another good build thread here and mine is here

 

As have a few others, I also replaced the rudder closed loop with a snake, though opinion is divided.  One benefit of using a snake perhaps is that it makes it easier to organise the elevator snake (well actually a weird dowel and threaded steel rod was supplied) one through a slot either side.  One thread suggested the small bar supplied to go through the rudder was too short?

 

 

 

Other issues have been the crappy plastic clevis for aileron push rods which slid straight off the threaded rod supplied. I used solder on type.

 

Have now flown the Wot 4 a few times and am very happy with it. I fitted an OS40 and I think it's plenty of power.

[Reno Racer]

I have a closed loop system in my WOT4 and its far more responsive that a snake; snakes tend to bend a bit under compression, particularly if not absolutely straight.  There is a very good reason why most aerobatic and top end F3A pilots use closed loop systems. I am about to fit out my YAK with close loop rudder and short steel push rods on Elevator and ailerons. I would not even consider fitting a snake.

The key is the set up of a closed loop system, as many above have described; enough tension equally on both sides not to be slack and not enough to trash your servos. I think about a 1/2 inch of flex in the mid point of the wires is ideal. Also use threaded rods rather than directy through the servo arm. If your look at the SLEC website you will see what I mean - look at their closed loop system kits.

Hope this helps.

[Biggles' Elder Brother - Moderator]

Interesting side point here. Steve raises the point that the non-pulling side can go slack if the servo arms and the control linkage are not the same size. Sorry - but I don't agree with this!

 

All the systems I've set up I've never seen slack on the non-pulling side. And what's more if the system is carefully set up it can't really happen.

 

Think about it, assuming  the servo arm is at right angles to the servo (as of course it should be in the neutral position) and that both wires are equal in length - that means the control horn is parallel to the servo arm (again as it should be provided no massive offset of the control surface is necessary to trim the model), Then whatever distance one side of this loop moves - the other must move exactly the same distance - and so no slack can possibly develop. The fact that the two arms are different lengths is immaterial because they more as a pair. One side "gives" exactly the same amount the otherside "takes". Its true that the angle of rotation of the two arms would be different - but the distance between their ends remains fixed.

 

Some things would disturb this -  the two arms not being parallel in the neutral position being one of them. But this is a sub-optium set up and wih all my practical experience with closed loop - I've seen this happen!

 

The reason I would advise against wildly different arm sizes isn't the potential for them to go slack - its the opposite - the possibility of them "locking out". If the servo arm is wider than the control arm this is a possility when implimenting large control throws. What happens is that as the servo arm rotates towards the end of its travel the smaller control horn could reach a position in which it was "in line" with the wire - if this happens it will rotate no further and the servo will stall. I've never actually seen this happen either - but it is at least theoretically possible. The servo arm would have to be very wide and the control throws huge with a small control horn before it would become a possibility - and that's not a good set up anyway.

 

BEB

[Biggles' Elder Brother - Moderator]

I've given this more thought and been busy drawing diagrams and doing a few sums. Conclusion?

 

Well its more or less as I said. But the true condition for no slack is, I think, that the arrangement be symmetrical. The arms can differ in length and it makes no difference to wire tension - provided the arrangement is symmetrical. So the best set up for a rudder is with the servo output shaft on the centre line of the fuselage. And for elevators its with the servo output shaft in line with the tailplane - not above or below it.

 

I am sure that you can depart from this ideal a little - given that most fuselages are long and thin and that the servos is often near the front whilst the rudder/elevator is commonly at the back - the symmetry condition is going to be nearly always satisfied - at least near enough! Use different size arms with impunity I say!

 

BEB

[Steve Hargreaves - Moderator]

I don't disagree with you BEB & maybe you are better at setting things up than I am but the non pulling side on my Yak definitely goes slack(er!!) at full movement......don't get me wrong its not flapping in the breeze but is definitely under less tension than at the neutral position. A quick measurement of the arms reveals a difference of about 20mm between the servo (55mm accross) & the rudder (75mm accross) horns.

 

However I think the reason (& I didn't notice/think about this when I was setting it up) is because the run of the wire is not straight. The fuselage is only 45mm wide where the wires exit hence the run of the wires "flares out" from 45mm at the fuz to 75mm at the rudder horn...as the servo rotates non-pulling side of the wire becomes straighter & so the wire is slightly too long hence it goes slack. to keep a straight run I would have to have the wires exit the fuz about 2" in front of the tailplane!!!

 

All that said it is a great system & hasn't caused me any problems in over two years of flying.

 

So, in conclusion then.

 

1) Closed loops are great

2) Try & keep the servo & control horns about the same size (but don't worry if you can't)

3) Try & keep the wire runs straight (but don't worry if you can't)

4) Keep the wire tension to a minimum

5) Don't allow Steve to set up your closed loop systems