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[John W E]

hi there all

A quick and easy method which I have used in the past to equal out the length of the steering push rods is to use the ever useful terminal block insert.  Basically, one of the pushrods has been made up from 2 lengths which are joined in the middle with the adapting block, to allow adjustment of length of that pushrod.

When we are happy that the pushrods are of equal length, I either, put a drop of solder over the pushrods and brass insert or, some epoxy.

I have attached a sketch/scribble to explain me meaning:

With hindsight, and going back to the original question and also looking at the model - this model may be built with scale rudders - these in past experience do not give the best turning circles on models for some unknown reason.   So, by increasing the rudder size slightly; rather than trying to tamper with the throw of the rudder may be of a more successful approach.

Aye
John E
BLUEBIRD

[tigertiger]

Scale rudders are never really effective. You cannot scale the density of water.

And while some things are affected by a power of 2 (area = squared/sqrt)
Others are effected by power of 3 (vol = cubed/cbrt)

There is a rule/law to explain this.

[Robert Davies]

I am with Bluebird on this one.
With a single operating arm it is possible when going astern that the force of the water forces the rudder too far one way and it ends up jammed as the pivot has gone over centre.

Not only possible, but I've seen it done on several occasions. The servos we use may have approximately 90 degrees of travel, but they do not have stops to prevent overtravel from external forces - going astern, collision with underwater obstacles, operator in blind panic mode etc. The closed loop system is an excellent failsafe highly recommended for a vessel which may be sailed on waters from which recovery maybe somewhat tricky.

-Rob

[malcolmfrary]

With a servo going 45° each side, this is more than enough given a rudder that is big enough and in the right place. 
Trying for a larger throw by having a longer servo arm / shorter tiller arm usually results in the tiller arm going over centre and locking up sideways, to the embarrassment of the owner.
A single pushrod, assuming it is rigid enough, does the job, unbalance strain being taken by the bearing on the servo output shaft.  This is unlikely to wear out in any of our lifetimes, so should not be a problem. 
Two pushrods works when both the servo and tiller arms are the same length - otherwise, either the rods bend, or the servo or rudder post are pulled out by the roots.  If the pushrod to arm connection has any play, then the longer the arm, the smaller percentage the play.

[sunnybob]

Blimey!!! That woke you lot up!!

Ok, I cant possibly answer all that individually, so heres a brief run down and (hopefully) a pic that will explain most things.

Boat is 40inches long, 12 inches across.
twin motors, single esc. ACT distribution board. twin screws. twin rudders. single servo for rudders.

I realised after posting that just extending the arms wouldnt work.
I only want a small improvement in steering. i cant fit bow thrusters, and do realise the limitations of a long ship steered from the rear. I dont want the extra expense of fitting another esc to allow one forwards and one backwards.

I have also found the hard way, that the servo arm to wheel system in the mock up pic is flawed.

The large / small gearing combo would seem to offer what I want, but suerely that would not work, as the distances between the connection points of the arms will change as the arms turn, causing either excessive drag, or sloppiness.

My main reason for starting this was I had heard of a kit that turned a 90 degree servo movement into something closer to 120.

As said before, my budget for this boat is totally expended. Any solution costing more than a fiver will NOT be taken up ::) ::)

I'm going to stick to the push me pull you, for the reasons already listed, and the angle of the boat stern stops me from locating the servo any closer, so I physically cannot shorten the linkage.

Thanks for the interest, keep it coming.

[Shipmate60]

A fiver, can beat that!!
Try adding plasticard each side of each rudder to extend the rudder length.
If possible both fore and aft.
If it is successful extend the rudder by soldering a brass plate to it and fairing in or just make a longer blade.


Bob

[portside II]

That might work on the model shown Bob ,i tried it on a RTR southampton and it did "xxxxx" all .
The other cheap optoion for sunnybob might be to fit a couple of micro switches on the servo to kill power to either motors ,ie steering port then the port motor is off so the st/board motor has the thrust.50p for a pair of switches .
daz

[Shipmate60]

Daz,
The rudders look a bit small and half the propwash is passing under the rudders.

Bob

[portside II]

Your right Bob , they are a bit on the small size  A bit of extra meat on them would help .
daz

[sunnybob]

Right, I made a new rudder bar, and now heres a pic of the total turn on the rudders.
Excuse the poor quality, i had to lay on the floor with the camera and operate the t/x with the spare hand

[John W E]

Sunnybob, Hi there

Last question, looking at your photographs - it is difficult to tell whether your propellers, when viewed from the back of the boat to the front, turn inboard or outboard - meaning your starboard or right propeller turns clockwise and your port/left hand propeller turns anti-clockwise.

In this rotation mode, they would move the boat forward.   Now, if the propellers rotate in the opposite direction e.g. starboard one turning anti-clockwise and the port one turning clockwise to move forward - this may have some bearing on the steerage of the boat.  Some vessels have a poor turning circle when the propellers turn inboard.  But, having said that there are one or two vessels which having the propellers turning inboard improves the steering.

Now that has opened a nest of hornets 

aye
John e
bluebird

[cdsc123]

What I want to see is a picture of the model, the whole model, with the cabin on. It looks a real beauty.

[sunnybob]

well, I had to go start it up to check that. Viewed from the rear, the starboard prop turns clockwise, and the port prop turns anti-clockwise.
 Is that good? or bad?

I am much happier with the steering now i have made two equal length arms. I shall give it another bash around the lake as soon as it stops raining and report back, but I think it will do, for the limited amount of time this boat will actually be in the water.
attached this time is the boat on her maiden voyage, as requested (lol) The water is very muddy due to heavy rain in the stream the day before.

[cdsc123]

VERY pretty model. The accepted wisdom is that with twin rudders it makes very little difference whether your twin props turn outwards (like yours) or inwards (which gives better steering with a single rudder). My preference is for outward turning on high speed models and inward on the slower longer ones which need as much help to steer as they can get, even with over-scale rudders.

[DickyD]

I get better turning on my minesweeper with inward turning props 

[sunnybob]

I cant change that can I? Even if I swap the props and reverse the motors, those props will always push the same way?

(I never could think in 3D)

[DickyD]

You've just said it swap the props and reverse the cables on the motors. Your props are handed.

[Shipmate60]

DickyD,
Rotation of props wont make a great difference if most or rudders are out of the propwash.
There isn't enough water being pushed against the rudders unless you increase the speed through the water considerably.
Inward turning props assist single or triple rudder.

Bob

[DickyD]

Bob I was just following on from cdsc123's posting and explaining to sunnybob how to change from outward to inward turning props.

[sunnybob]

so can someone clarify this for me please.
Is it worth the effort of reversing the props?
or not?

Ta. :)

[DickyD]

Well it is the cheapest option in that it is not going to cost you anything so I would give it a go first.

[malcolmfrary]

But while down there, I would check that the rudders were actually in the area where propwash can be expected, and extend them as suggested before with plasticard.  If this shows an improvement, it becomes worth doing a prettier, permanent job.
As you have two rudders and two props, changing rotation probably wont make any difference, as some have said, this only changes things where there is a single prop.

[DickyD]

Actually I think you will find changing a single prop from clockwise to anti clockwise aint going to make a jot of difference Malcolm. :-\

[sunnybob]

Okay, i think I'm going to leave well alone here.

The boat is not going to get a lot of water time in, so I think what I have will work for the time intended.

If I were going to use it more, and try manouvering trials, I might get more interested.

Thanks to all for yet another learning curve.

[John W E]

hi there 

Forget all about that has been said by these part time modellers  .... listen, think of this....

Swap your propellers over; then, go to your transmitter.   The channel you use for your throttle (speed control) should have a reverse function switch; depending on the transmitter, it should be in a small panel in the back or in a small panel on the front.

Flip the appropriate switch that corresponds with your throttle; this will now reverse your motors through your speed controller, so that you do not have to swap the wiring around on your motors.  When you do a trial with the model, if you do not find any steering improvements - then, look at increasing the size of the rudders in overall depth.

Make sure that, when you look at your propellers with one of the blades facing downmost (downwards at its lowest point in the revolution) that the edge of the rudder is below this.  This is the correct size in length for a rudder.   If it is short, increase the depth temporarily with Plasticard then retry the steering of the model.  This should improve the steering.

If it does improve the steerage; you have several options then of either manufacturing new rudders or cladding the existing rudders with Plasticard and fairing in to shape.

Try that.      KEEP IT SIMPLE

Aye
john e
bluebird