Model Boat Mayhem
Technical, Techniques, Hints, and Tips => Other Technical Questions... => Topic started by: peter61_uk on January 26, 2014, 12:31:35 pm
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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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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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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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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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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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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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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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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.
(http://i455.photobucket.com/albums/qq277/rbm109/DSCF3407-1.jpg) (http://s455.photobucket.com/user/rbm109/media/DSCF3407-1.jpg.html)
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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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.......... A hung jury ????? :-)
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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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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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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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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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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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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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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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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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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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No it isn't...................... <*<
DM
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No it isn't...................... <*<
DM
Is this the five minute argument.................? :embarrassed:
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who has got the wooden spoon out I think I KNOW who !!!!!!!!!!!!!!!!!!!
Dave
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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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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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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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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?
Thanks Gazou ........... I think the single cable is now the way forward ......... It is well supported at each former, hardly anything in the way of a curve, and no movement in the outer.
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Dave,
My main concern isn't the use of a bowden cable but the length from the last bulkhead to the tiller arm as in the pic of the installation.
This looks long enough to allow the inner cable to flex when under tension.
Thanks Circlip under compression, Doh!!
Bob
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What you have to remember Peter is that the "Norm" before snakes was a Balsa or spruce stick, with bits of bent wire spliced on each ends, a throwback from bang-bang escapements. and yes Bob +1
This looks long enough to allow the inner cable to flex when under tension.
Compression.
Regards Ian.
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From the alternate thread.....
Peter....just a thought........why not keep the Q&A to this build all in the one thread?...it will be simpler for you & will make more sense for others reading it in the future.........Derek
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Hullo Peter.........many kits are understandably made to a price O0
However many builders see certain attributes that could be installed or modified to provide a more reliable or better design build
Bowden cables is such rudder applications may be an improvement.......however even running in a nylon cased tube.....if it is a true cable construction is subjected to PUSH-PULL forces which by consideration is not really conducive to long term life <*< [stranded wire is designed to be used in tension..........not in compression]
However two Bowden cables....one on either side of the balanced rudder attachment>>>>>>to the servo arm balanced attachment ...when adjusted is a balanced mechanical element :-)) .....Derek
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From the alternate thread.....
Peter....just a thought........why not keep the Q&A to this build all in the one thread?...it will be simpler for you & will make more sense for others reading it in the future.........Derek
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Hullo Peter.........many kits are understandably made to a price O0
However many builders see certain attributes that could be installed or modified to provide a more reliable or better design build
Bowden cables is such rudder applications may be an improvement.......however even running in a nylon cased tube.....if it is a true cable construction is subjected to PUSH-PULL forces which by consideration is not really conducive to long term life <*< [stranded wire is designed to be used in tension..........not in compression]
However two Bowden cables....one on either side of the balanced rudder attachment>>>>>>to the servo arm balanced attachment ...when adjusted is a balanced mechanical element :-)) .....Derek
Thanks Derek......... I'll make sure I keep it all in one place in future. {:-{
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What you have to remember Peter is that the "Norm" before snakes was a Balsa or spruce stick, with bits of bent wire spliced on each ends, a throwback from bang-bang escapements. and yes Bob +1 Compression.
Regards Ian.
I've taken a couple of measurements on that .......... It's difficult to be precise as it's a "dry fit" ..... But I reckon, with the tiller arm at the mid point the inner cable is out of the outer about 30mm and at full extension about 50mm. I guess that'll be the same at the servo end as well. as both arms are the same length.
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Peter,
On your measurements that only leaves about 10mm free.
That is not enough to fit the connector to the cable and tiller arm.
Assuming the connector is 20mm long that will leave at least 30mm, at present dimensions, exposed.
This should be fine initially but will be subject to bending on compression so might need changing in the future.
It is of course your choice just pointing out any possible problems.
Bob
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Peter....... to your comment..... "I figured we are looking at a low speed tug here and not a high performance race boat"
The following is rather simplistic O0............but clearly confirms an understanding of actual comparative rudder loadings between two differing vessels you mention ok2
NB..... I have used imperial dimensions in the description .....them metricated by approximation %%
Example 1
4 inch square tug boat rudder = 100 x 100 mm, speed 5 km, mass 30 kg
100x100x5
30 = 1666 units of load on the rudder surface
Example 2
1 inch square speed boat rudder = 25mm x 25mm, speed 20 km, mass 7 kg
25x25x20
7 = 1785 units of load on the rudder surface
As you can see...... first thoughts can sometimes be a little :embarrassed:.......Derek
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........and there I was, thinking this cable thing was a really clever idea {:-{
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Don't despair Peter ;)......I still think adequately considered Bowden type cables for rudder control are an excellent choice :-)).......
Digressing a little........over the past months...I have been trying to understand how I can use a 1:20 scale link chain for rudder control & have just taken delivery from the USA....two 1.0 mm diameter wire size Grade 316L stainless steel fusion welded 9 hoops per inch chains O0 for my intended rudder steerage....however it by necessity will be Pull>Pull.........
By the same guestimation method as below....... %) I concluded some 1200 units of loading on my intended rudder
So hence the need for actual fusion welded chain construction.......Derek
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Don't despair Peter ;) ......I still think adequately considered Bowden type cables for rudder control are an excellent choice :-)) .......
Digressing a little........over the past months...I have been trying to understand how I can use a 1:20 scale link chain for rudder control & have just taken delivery from the USA....two 1.0 mm diameter wire size Grade 316L stainless steel fusion welded 9 hoops per inch chains O0 for my intended rudder steerage....however it by necessity will be Pull>Pull.........Derek
Derek....there is a fella in France building the same boat as I am. He is using a chain setup for rudder control. Really quite clever. Tomorrow I will pot the link to his build thread.
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From the Bowden cable article in Wikipedia:
The linear movement of the inner cable is most often used to transmit a pulling force, although push/pull cables have gained popularity in recent years e.g. as gear shift cables. Many light aircraft use a push/pull bowden cable for the throttle control, and here it is normal for the inner element to be solid wire, rather than a multi-strand cable.
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You have been very selective in the text you offer here Plague :o.........
Certain Bowden cables also have a contra wound inner cable core to the outside wound casing O0 which naturally offers greater anti buckle characteristics over conventionally same handed wound inner core & outer casing......
Perhaps another member may offer a more accurate calculation method :-)) for the rudder loading than my simplistic comparison {-)..... Derek
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Peter,
On your measurements that only leaves about 10mm free.
That is not enough to fit the connector to the cable and tiller arm.
Assuming the connector is 20mm long that will leave at least 30mm, at present dimensions, exposed.
This should be fine initially but will be subject to bending on compression so might need changing in the future.
It is of course your choice just pointing out any possible problems.
Bob
Thanks Bob...... It is much appreciated ........... How about I use something like this...... and connect the end of the wire direct to the tiller....???... Bearing in mind that I am now sold on the idea of a second cable for a closed loop.
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And just to add, Goggle "Morse Controls" O0
Existing outer will be in wrong place if you're going for double lines Peter.
Regards Ian.
(bet yer keep yer gob shut next time {-) )
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This is all getting far too in depth for the original question, to which the answer is... yes a single cable will be fine provided the sheath is properly supported, which it is.
I have use single set ups like this in a few boats, fast, slow, little & large all with no problems.
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And just to add, Goggle "Morse Controls" O0
Existing outer will be in wrong place if you're going for double lines Peter.
Regards Ian.
(bet yer keep yer gob shut next time {-) )
Existing outer will be in wrong place ??? How so. I was going to run it from below the exisitng outer onto a double servo horn.........and across and up to the port side stern ???? ......... Now you are going to tell me "both cables have to be the same length ........ {-)
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This is all getting far too in depth for the original question, to which the answer is... yes a single cable will be fine provided the sheath is properly supported, which it is.
I have use single set ups like this in a few boats, fast, slow, little & large all with no problems.
Thanks........ The voice of reason at last O0 O0 O0 ........ I knew I was right all along. :-))
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Naaa, a few of us have already said you'll probably be OK with your existing set up. We just like to offer alternatives for others to think about. Sadly for future use, many seem not to be able to locate or understand the word "Search" O0 >>:-(
Regards Ian.
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Naaa, a few of us have already said you'll probably be OK with your existing set up. We just like to offer alternatives for others to think about. Sadly for future use, many seem not to be able to locate or understand the word "Search" O0 >>:-(
Regards Ian.
Ian ......... Your and everyones input to my question is greatly appreciated......... I'm learning a great deal here as I go along. :-)
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Just had a look at the KG V battleship, even HE's used closed loop on the rudder. {-)
Regards Ian.
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I have bitten the proverbial bullet and run a second cable for the rudder. So we now have the "Holy Grail" of rudder systems in the form of a closed loop ........ Second cable takes a bit of a detour around the formers in a curve. But I've tried the inner cable in it and it runs freely. It's all clamped up at the moment waiting on the expoxy to dry ............ I'll post up some photos tomorrow.
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Probably too late (the epoxy is done) but you need to make sure both sides have exactly equal geometry or it may bind.
That means that the position of the rudder in every position of the servo is the same on each side.
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Probably not too late to cut/grind the epoxied cable out Peter...........I do agree with Plague that the cable geometry should be identical or just mirror reversed O0.....Derek
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{-) {-) {-) {-) You guys have absolutely no idea how much I laughed when I read this "geometry" thing.......... and I so wish I'd never posted this thing about "Rudders and Bowden Cables" in the first place {-) {-) {-) {-) .
Still ......... Given the fact that it all started with me mounting the bl**dy servo on it's side (and there weren't much in the way of choices) ........ and again there aren't much in the way of choices where to have run the second cable (I did measure it before I fitted it and it's 50mm longer than the first one .........
So we are where we are as they say....... I can leave it in place and once the top deck is on then it wont be visible...... Give the twin cable system a try and if it does "bind" then I'll just take the second inner cable out, and run it with "one" which is what I'd planned (right or wrong) in the first place.
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..... and I so wish I'd never posted this thing about "Rudders and Bowden Cables" in the first place .
Worms .... can. O0
.. Give the twin cable system a try and if it does "bind" then I'll just take the second inner cable out, and run it with "one" which is what I'd planned (right or wrong) in the first place.
:-))
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Peter
Other subjects to avoid include the best type of radio to buy, what type of batteries to use, whether or not to fit suppressors to the motor and the best method of finishing the model. Ask ten different Mayhemmers about any of these and you'll get eleven different answers.
Suit yourself.
Dave M
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Peter
Other subjects to avoid include the best type of radio to buy, what type of batteries to use, whether or not to fit suppressors to the motor and the best method of finishing the model. Ask ten different Mayhemmers about any of these and you'll get eleven different answers.
Suit yourself.
Dave M
I already covered the "Battery" question.....and surprisingly it was quite objective and settled fairly easily......... The others, after this ???? Not a chance Dave....I'll keep it to myself. {-)
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Now, about the position of the motor and type of universal joint . . . . . . . . . . {-)
Regards Ian.
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NO NO NO you all have it wrong
the worst question on this Forum is
.............................................
is ...............................................................
hey Mr where do I fit the fuse?
how dare you ask that question :-) {-) {-) {-) {-) {-) {-) {-) {-) {-) {-) {-) {-) {-)
Peter, I have thoroughly enjoyed this thread and laughing - remember when someone said to you - there is no right way and no wrong way.
especially in model boating etc., the way it works is the way that is right for you. :-)) :-)) :-))
aye
John
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How come if a single push/pull Bowden cables is so good they are not used on bike braking systems to save the weight of the return spring on the caliper. ;) Graham
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How come if a single push/pull Bowden cables is so good they are not used on bike braking systems to save the weight of the return spring on the caliper. ;) Graham
.....You would need a push/pull lever on the handlebars........ Which would be pretty cumbersome.
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I must admit to having a little chuckle on this thread.
But I prefer double connections for wire connections too!!!
Just a belt and braces thing for an important pare of the system.
Bob
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And as a warning, the good ole British motorcycle industry used to have a single Bowden cable connecting the twist grip to the carburettor slide on the engine so that when you twisted the handlebar grip back towards you, the bike accelerated and by allowing the grip to twist the other way, assisted by a return spring, the revs and the bike slowed down. As any proper motorcyclist will tell you, in their infinite wisdom, the Japanese really screwed things up by putting the kickstart (?) and the brake pedals on the wrong side of the bike for us imperialists and as a belt and braces, on one machine, besides a return spring on the shaft that coupled twin carbs, they had added another cable to the mix that together with the spring pulled the carb slide shut via a pulley. Velly clever these Orientals, so when out one day, miles from home, the cable that opens the throttle breaks. Oh, woe, no tools, (don't need those cos these bikes don't go wrong). Quick think, return spring still works and with a bit of fiddling, the remaining cable can be fed round opposite side of pulley and wahoo, we have twist operated throttle and spring return.
Only difference is that to accelerate, you need to turn the twist grip away from you and towards you to slow down.
This is not intuitive and created some exciting moments in teatime traffic. O0
Regards Ian
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Hello Faddah! Hello Muddah!
Will you show me
How to fix my ruddah?
Should I use a
Bowden cable
Or just bend a bit of wire upon the table?
It is really, very vexing
To work out the
Degree of flexing
Is it best to make it double?
Or will that really get me into serious trouble?
I have asked the blokes on Mayhem
Should I epoxy
Or just fray ‘em
But they all give different answers
And I really just cannot fancy my chances.
Well here’s my servo, and my tiller
The connection is a killer!
For the one to
Move the other
It really is a total awkward b****r
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Heavens above we got a POET in our midst ..... O0 O0 O0 O0 O0 :} :} :} :}
Dave
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Hello Faddah! Hello Muddah!
Will you show me
How to fix my ruddah?
Should I use a
Bowden cable
Or just bend a bit of wire upon the table?
It is really, very vexing
To work out the
Degree of flexing
Is it best to make it double?
Or will that really get me into serious trouble?
I have asked the blokes on Mayhem
Should I epoxy
Or just fray ‘em
But they all give different answers
And I really just cannot fancy my chances.
Well here’s my servo, and my tiller
The connection is a killer!
For the one to
Move the other
It really is a total awkward b****r
...... A rare talent indeed {-) {-) {-)
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Both cable outers .........
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%)...Peter...a simple question........is the area I have marked up reside under the engine skylight that sits on the deck?........Derek
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Hello Faddah! Hello Muddah!
Will you show me
How to fix my ruddah?
Should I use a
Bowden cable
Or just bend a bit of wire upon the table?
It is really, very vexing
To work out the
Degree of flexing
Is it best to make it double?
Or will that really get me into serious trouble?
I have asked the blokes on Mayhem
Should I epoxy
Or just fray ‘em
But they all give different answers
And I really just cannot fancy my chances.
Well here’s my servo, and my tiller
The connection is a killer!
For the one to
Move the other
It really is a total awkward b****r
Allan Sherman reincarnated {-) Very good, Colin :-))
Peter.
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%) ...Peter...a simple question........is the area I have marked up reside under the engine skylight that sits on the deck?........Derek
It's a bit aft of where you marked (it'll be covered with a small grating)........ It is designed for access to the grub screw on the retaining collar for the propshaft.
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%) ...Peter...a simple question........is the area I have marked up reside under the engine skylight that sits on the deck?........Derek
Derek .......... A rough sketch to show an approximation and location of deck access openings.