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Author Topic: Rudders and Bowden cables????  (Read 11312 times)

peter61_uk

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Rudders and Bowden cables????
« on: January 26, 2014, 12:31:35 PM »

I've hit a question as a result of a (valued) post from a member on my Occre Ulises build..............
The original setup was a servo aft of the motor with a couple of, in my opinion "nasty bent pieces of wire" to the rudder ......... Because the servo position fouled on the gearbox I have had to relocate it and decided on a "Bowden" cable to operate the rudder ........ It has been suggested I need two, to give a push / pull action .......... The sable has a semi rigid outer (low friction) and a plaited inner cable........ It runs freely............... So I would like to hear any thoughts on this as I figured we are looking at a low speed tug here and not a high performance race boat ............ I can, if it's an absolute, run a second cable. But figured, "Is it really a necessity" ????

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Peter

boatmadman

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Re: Rudders and Bowden cables????
« Reply #1 on: January 26, 2014, 12:35:12 PM »

I dont think a twin cable will be necessary. As long as the outer sheath is well supported - which yours is - all should be well.


Ian
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MikeK

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Re: Rudders and Bowden cables????
« Reply #2 on: January 26, 2014, 12:41:35 PM »

I dont think a twin cable will be necessary. As long as the outer sheaf is well supported - which yours is - all should be well.


Ian

Ha ! Just started to write the same thing to find a 'new post had been added'
Agree with Ian, as long as the outer sheath is well anchored it should be ok. Adding the push-pull setup will, if possible, remove any slop there might be but probably not worth the hassle on a scale model.

Mike
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peter61_uk

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Re: Rudders and Bowden cables????
« Reply #3 on: January 26, 2014, 12:45:19 PM »

Ian / Mike .............. Thanks for that......... I read the post this morning about the second cable and thought ""xxxxx"" ...... I can press on with other things now.  :-)
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Peter

Stavros

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Re: Rudders and Bowden cables????
« Reply #4 on: January 26, 2014, 12:54:41 PM »

NOPE you are all wrong with what you are saying....it WILL need a second cable......think about it logically.....on a std build you would use a SOLID wire to move the rudder thus eleviating the need for a second rudder rod..........on a single Bowden cable the inner is FLEXIBLE.......so being flexible by it's nature any resulting force opposite to the way hte rudder need to move can in effect caquse a slight kink in the cable,thus reducing rudder movement......so a second cable is needed to couneract this.
 
 
Dave
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Shipmate60

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Re: Rudders and Bowden cables????
« Reply #5 on: January 26, 2014, 01:01:33 PM »

Unfortunately the "nasty bent pieces of wire" will be far more rigid than the bowden cable which as Stavros says is flexible.
It will be fine in tension (pulling) but will have flex in compression (pushing).
A second cable would counter this.


Bob
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Mark T

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Re: Rudders and Bowden cables????
« Reply #6 on: January 26, 2014, 01:12:05 PM »

Hi Peter - I know that there is some conflicting advice here so I thought that I would put my two pennies worth in  :embarrassed:


I personally would use two cables to ensure that the rudder got a good pull in both directions.  For the little bit of work involved it would give me piece of mind


Your build is really starting to look good keep the photo's coming  :-))
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rmaddock

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Re: Rudders and Bowden cables????
« Reply #7 on: January 26, 2014, 01:18:17 PM »

I've got a single cable in my marblehead and it's fine.
Bear in mind that aircraft use these cables "singly" on control surfaces - only big or high performance setups would "push/pull" and then they'd generally be using wires rather than bowden cables anyway.
The trick is to make the end of the outer cable as close as possible to the end of the inner...if that makes sense.  You can also screw the metal linkage a long way into the inner - so that it goes into the outer (now I'm confused).  That makes it all quite stiff.



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Circlip

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Re: Rudders and Bowden cables????
« Reply #8 on: January 26, 2014, 01:48:04 PM »

Yep referred to as "Snakes" in toy planes. Problem as Stavros and rmaddock  has mentioned, you need to get the distance between the end of the outer and the linkage connector as short as possible to avoid the kink back but the end of the outer needs to be supported.
 
  Another thing to avoid with snakes is that any bends in the system even if fully supported will result in slop (lost motion) on the control, so yes, bent wires are better.
 
  Don't forget, you could have kept the rigid wire by adding a small bellcrank in the back compartment to give a 90deg. connection to the rudder tiller.
 
  You're probably going to be OK with what you've got, just another road to Rome.
 
  Regards  Ian.
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peter61_uk

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Re: Rudders and Bowden cables????
« Reply #9 on: January 26, 2014, 02:07:00 PM »

.......... A hung jury ?????  :-)
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Peter

inertia

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Re: Rudders and Bowden cables????
« Reply #10 on: January 26, 2014, 02:11:13 PM »

I think you '2-cable guys' are overestimating the forces involved in moving a model boat rudder. It's not travelling at any great speed or pushing against anything solid and the surface areas are relatively small c/w say a model aircraft's flying surfaces. Many boat rudders are also 'balanced'.
As Rmaddock says you should take sensible measures to ensure, for example, that you don't have several inches of unsupported "inner" at each end (you could always use a threaded metal rod to connect from the inner to the servo). The purpose of the outer tube is not only to provide a route for the inner but to prevent it from kinking and thus bending. You should make sure that the outer is supported at several places throughout its length and that any curves are gentle and don't cause the inner to bind inside the outer.
Sullivan's Golden Rod always used to be the standard for these 'snakes' and I never even considered fitting two of those to the same surface when I was building and flying models. As far as I know no-one else did either and I don't remember seeing any failures or crashes due to using just one run of snake.
These days models are far bigger than the ones we were used to (max weight 11lbs and max engine size 10cc) so flying loads are much greater, but model boats remain pretty much the same - except for the very specialised types such as offshore racers and fast electrics.
Having said all of that, if fitting a push-me-pull-you setup makes you feel better then go ahead, but in my experience it's mostly a waste of time and effort.
Suit yourselves.
DM

(Circlip's post hit just before mine)
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Circlip

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Re: Rudders and Bowden cables????
« Reply #11 on: January 26, 2014, 02:44:12 PM »

It's handy to know there is another option when the back of the "well" in a cabin cruiser or speedboat etc. is close to the transom and there ain't no room to fit a servo without resorting to a box in the well to hide the servo. Snakes were like Asbestos, an answer looking for a problem but their limitations became apparent and given the precise control of a closed loop, haven't used a snake since.
 
  Regards  Ian.
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malcolmfrary

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Re: Rudders and Bowden cables????
« Reply #12 on: January 26, 2014, 02:50:02 PM »

If it was a true bowden cable, scaled to the model (like the device working the brakes on a bike, but smaller), then two, both pulling.  If, as is likely, it will be something a bit different, then one.  The outer guide sleeve should be free of sharp bends, reasonably rigid and supported.  If the inner is a single moderately heavy wire rather than a bunch of strands and the right distance has been arranged at both ends to allow for a bit of swing (both servo and tiller describe arcs) there should be no problem, especially with a model of modest size and power.
If the original bit of bent wire does the job and is reasonably well hidden, it is quite possible that it could be the best solution.  Just as long as its strong enough to do the job, and that none of the bends flex in use.
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hammer

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Re: Rudders and Bowden cables????
« Reply #13 on: January 26, 2014, 04:00:23 PM »

I am a ex flyer and again used bowden cables for both rudder, elevator & motor controls.  If there is any play with surface controls with aircraft flutter will occur. Like every thing if fitted correctly, then one is enough. No one has mentioned the type using both outer & inner from plastic, better in most ways than cable inner.   
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peter61_uk

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Re: Rudders and Bowden cables????
« Reply #14 on: January 26, 2014, 04:06:14 PM »

Thanks all ......... for your input. It's caused me a bit of a dilemma. But I think I'll stick on the single cable ........ The outer is well supported and taking some measurements for a second cable I' going to be damn close to the motor/gearbox on that .....

...... Plastic inner cable is an interesting idea I didn't know existed and certainly hadn't considered ????
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Bob K

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Re: Rudders and Bowden cables????
« Reply #15 on: January 26, 2014, 04:31:54 PM »

This interesting topic underlines my love of this forum.  Several experienced modellers responding to Peter's question, giving quite a varied set of responses.  Each appears technically correct although for different reasons.  I see no conflict, just a fascinating discussion based on a wide range of expertise.
Thank you everyone  :}
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MikeK

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Re: Rudders and Bowden cables????
« Reply #16 on: January 26, 2014, 05:11:31 PM »

Wow didn't expect that flurry ! I was visualising a sleeve as straight as practible and very well secured in way of any bends, to lessen that flexing that was mentioned. On a racing yacht where precise steering is required, then yes a push\pull system is a must.
All interesting reading though, as usual !

Mike


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inertia

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Re: Rudders and Bowden cables????
« Reply #17 on: January 26, 2014, 05:23:06 PM »

No one has mentioned the type using both outer & inner from plastic, better in most ways than cable inner.
It was this type I was describing, actually. Sorry if it wasn't clear. I only used "real" Bowden cable for throttle and steerable nosegear, where a bit of slop was acceptable and the cable-run had to negotiate round such things as fuel tanks and battery packs.
DM
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rmaddock

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Re: Rudders and Bowden cables????
« Reply #18 on: January 26, 2014, 06:04:54 PM »

I see no conflict, just a fascinating discussion based on a wide range of expertise.

Yes, for such a contradictory thread, it's all been dangerously "nice".  It must be time for a good argument  <*<
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inertia

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Re: Rudders and Bowden cables????
« Reply #19 on: January 26, 2014, 06:29:00 PM »

No it isn't...................... <*<
DM
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rmaddock

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Re: Rudders and Bowden cables????
« Reply #20 on: January 26, 2014, 06:41:25 PM »

No it isn't...................... <*<
DM

Is this the five minute argument.................?  :embarrassed:
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Stavros

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Re: Rudders and Bowden cables????
« Reply #21 on: January 26, 2014, 06:58:31 PM »

who has got the wooden spoon out I think I KNOW who !!!!!!!!!!!!!!!!!!!
 
 
Dave
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Circlip

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Re: Rudders and Bowden cables????
« Reply #22 on: January 26, 2014, 07:05:23 PM »

Quote
No one has mentioned the type using both outer & inner from plastic

 Obviously never heard of Sullivan "Golden rods" that Inertia mentioned. Those were the ones with the spikey inner rods, an attempt to reduce internal friction.
 
  Regards   Ian.
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Re: Rudders and Bowden cables????
« Reply #23 on: January 26, 2014, 07:18:29 PM »

given the length of the boat
seen that Bowden is blocked at each pair

this is just fine

Bowden would one meter and would not be blocked it would be different!
but who would do that?
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peter61_uk

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Re: Rudders and Bowden cables????
« Reply #24 on: January 26, 2014, 07:40:49 PM »


 Obviously never heard of Sullivan "Golden rods" that Inertia mentioned. Those were the ones with the spikey inner rods, an attempt to reduce internal friction.

  Regards   Ian.

I googled that Ian ............. and as far as I could see, from a few forum posts I looked at the flyers don't seem to rate them much .......... But the plastic inner still looks good.
 
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