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Author Topic: Rudder to Servo connection points  (Read 4312 times)

BlueWotsit

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Rudder to Servo connection points
« on: July 09, 2010, 02:04:36 PM »

In the attached image is a rough sketch of the scenarios available to me for connecting the tiller arm / rudder connection to the below decks sail servo - using strong cord.

Normal connections are either

A to C ...... B to D

or

A to D...... B to C  (using cord crossover)


However because the run from the tiller arm connector to the servo is about 8 inches I am considering putting two brass pulleys into the sequence.

Being useless at geometry (and drawing) I would appreciate any guidance as to which position for the pulleys might be best. Additionally would infact using the pulleys be beneficial or not.


Using the pulleys the connection sequence would be

A, E, C .....  B, F, D

or

A, G, C........B, H, D


Hope this makes sense - I have to consider one of these options because space for the servo is restricted within the hull of this particular cutter.

The sketch is not to scale, and usually the servo arm has dimensions equivalent to the width of the connector bar on the tiller so a straight cord run is obtained.
- using pulleys would mean the arm can infact be lengthened

thanks
Andrew
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dreadnought72

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Re: Rudder to Servo connection points
« Reply #1 on: July 09, 2010, 02:38:09 PM »

Run the control line C - E - F - D, and between E - F connect to a (fore and aft) tiller on the rudder?

Andy
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BlueWotsit

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Re: Rudder to Servo connection points
« Reply #2 on: July 09, 2010, 03:00:02 PM »

Hi Andy - when I was testing it on the bench, that seemed to be my favoured approach as there seemed to be less strain on any of the connections.


cheers
Andrew
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tigertiger

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Re: Rudder to Servo connection points
« Reply #3 on: July 09, 2010, 03:11:19 PM »

Sails etc do some nice sheet leads that will help things run smoothly, I don't know if they will help in your case.

http://sailsetc.com/fithull.htm#
Items 60a, 60b, 60c etc.

A bit pricey though.
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BlueWotsit

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Re: Rudder to Servo connection points
« Reply #4 on: July 09, 2010, 03:59:12 PM »

Hi TT - blimey they are expensive, must be gold or platinum plated methinks  {:-{

60A is similar to some flexi metal piping I have which I think is used in model helicopters - been told by someone local that its ideal for going through the deck and holding a run straight or otherwise internally - main thing apparently is to get a good angle coming out the top of the deck
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derekwarner

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Re: Rudder to Servo connection points
« Reply #5 on: July 10, 2010, 02:13:43 AM »

Andrew - there are clear advantages & disadvantages selecting between B>F>D to B>H>D sequences

Just go back to your plan view & consider the requirement of rotating the tiller arm C>D clockwise

a. servo arm B rotates clockwise via F, so B>F>D = all in tension  :-))
b. servo arm B rotates clockwise via H so B>H = residual tension only, but H>D = in tension

Not only from a mathmetical point, but also from a mechanical or physical point it is far better to have each element [in the train of forces] experiencing the same direction of force  O0....Derek

Question for a Moderator......is there an issue with the server spell check this morning? ........



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Derek Warner

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tigertiger

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Re: Rudder to Servo connection points
« Reply #6 on: July 10, 2010, 02:18:29 AM »

Spell check page is working for me at time of posting.
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derekwarner

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Re: Rudder to Servo connection points
« Reply #7 on: July 10, 2010, 03:22:52 AM »

Thanks TT...appears I had spell check open in the background...hence could not reopen it - my error  %% - Derek
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Derek Warner

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BlueWotsit

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Re: Rudder to Servo connection points
« Reply #8 on: July 10, 2010, 07:59:56 AM »

Andrew - there are clear advantages & disadvantages selecting between B>F>D to B>H>D sequences

Just go back to your plan view & consider the requirement of rotating the tiller arm C>D clockwise

a. servo arm B rotates clockwise via F, so B>F>D = all in tension  :-))
b. servo arm B rotates clockwise via H so B>H = residual tension only, but H>D = in tension

Not only from a mathmetical point, but also from a mechanical or physical point it is far better to have each element [in the train of forces] experiencing the same direction of force  O0....Derek

Question for a Moderator......is there an issue with the server spell check this morning? ........






Hi Derek - early in the morning - well before 8am  ;D , thanks for this and your explanation certainly makes sense (I think to me)   :o

- I had tried to simulate the scenarios on a board with pins and pulleys - which although wouldnt give a 100 percent accurate comparison because of how the tiller arm falls across from side to side - what I did find was then tension on pulleys G & H in this simplistic trial was sufficient to pop the holding pins from the pulleys.

I definitely think its going to be the AEC + BFD route to pursue.

Thanks to all for input

cheers
Andrew
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roycv

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Re: Rudder to Servo connection points
« Reply #9 on: July 10, 2010, 09:45:41 AM »

Hi all, If the pulleys are not on view I use hard plastic tubing to guide 'string' around corners.

Just bend the tube around, say, a ball  point pen for the diameter and angle required, pour over some boiling water to aid the bending, make sure it does not kink.  Cool in cold water and cut to size.  It will now stay like this.

The plastic bend can be tethered lightly somewhere convenient.

I have several boats and use this for rudders and for sail control.

I tried running chain through tubes in a closed loop but it does not work well as chain does not like being pushed!
regards to all, Roy
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derekwarner

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Re: Rudder to Servo connection points
« Reply #10 on: July 10, 2010, 10:07:38 AM »

Roy notes..... "I tried running chain through tubes in a closed loop but it does not work well as chain does not like being pushed!"...

Roy, this is the basic point that .....

'to have each element [in the train of forces] experiencing the same direction of force'

You cannot push a length of chain links ....you can only move a chain link set when in tension >>>>> or <<<<< ...... :-))

Think of 1/2 half of the steering set as in tension & the other 1/2 half as out of tension.........no more no less ......Derek O0
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Derek Warner

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Circlip

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Re: Rudder to Servo connection points
« Reply #11 on: July 10, 2010, 10:48:49 AM »

Change tiller arm to pulley and pin control cable to the pulley groove. Wind a full turn of cable round the tiller pulley from both directions and complete cable run via idler pulleys so that you end up with idler pullys in the corners of the tiller compartment. The cable then runs round pivots or idler pullys at E & F and the cable ends joined together midway between E & F. Then take a Single connection to the servo lever which is rotated through 90 degrees in your drawing.

  The problem coupling levers together is that it is quite easy to get a jam situation. One lever and a string "Square" is easier to sort.

  Regards  Ian.

 In toy aircraft terms, it's called a closed loop system.
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BlueWotsit

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Re: Rudder to Servo connection points
« Reply #12 on: July 11, 2010, 03:53:37 PM »

Hi Ian

Unfortunately changing the tiller arm is not an option available to me.

However your suggestion reminded me of a boat I saw, where instead of having the arms coming out the side of the tiller to support cord to, theres was a closed hook screwed in under the arm.

Cord was tied and knotted to this central point from both sides and seemed to operate reasonable well.


cheers
Andrew
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roycv

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Re: Rudder to Servo connection points
« Reply #13 on: July 11, 2010, 05:03:54 PM »

Hi Ian, I have an old scale yacht (1975) that has used a small hook under the tiller, I used almost invisible monofilament line via bent tubing to a servo top.  On the servo top I have an extended arm (1/2 inch) with an adjustable screw that can pull a modified washer into a captive nut.  The screw can be rotated to put tension into the system and there is some springyness in the mono filament line.  I half expected the tubing to be cut through with the line movement but it works OK.

On a later boat (circa 1980) I used this system with the adjustment lines attached to each chain end, which enables you to push chain through tubes!  Of course keeping the out and back loops in tension is a little tricky, but that has been working well on and off for 30 years.
regards to all, Roy
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