Hi:
I started the constrution of my sail boat. the mast and boons are finished, also the sails, just need to put the eyelets in them.
i am about to start the foam carving for the hull mold and started to think about radio and rigging settings.

i am about to use a 10 cms. long servo arm ( made by myself in aluminum 2,5mm thick). As the servo travels 120 degrees from fully closed to fully opened position it gives me 17.5 cms. in staright line travel.
It means that if I want to get 90 degrees movement in main and jib booms i need to place catch them at 13,5 cms. from their pivot ponit ¿ where joins the mast, for the main boom, and from it is catched to the deck in the jib boom?

the question is: for rigging to the servo, what is more usefull???.....use a direct sheet line from boom to servo or place in between a pulley or ring as described in the drawing.
please any recomendation will be appreciated.

Tato Lazo

As drawn, the travel exerted from the servo will be doubled using the ring, but the force available at the sail boom will be halved.
As the arrangement has to work in a range of conditions you have to figure that all runs must be free enough so that the slightest breeze will allow the line to pull out, but the line and the servo mountins must be strong enough to remain intact through a sudden gust.
Whatever is simplest is usually best - less to go wrong.

Hi mfr02, i undestand that if i use a pulley or ring the lenght of the sheet pulled by the servo arm will be doubled, but using only one pulley or ring does not double the force, as i remember from my science classes ( many years ago, so probably i am very wrong!!!)

if i use the pulley or ring and the force to the servo will be doubled, then using it is meaningless.

will be Ok if i use one sheet of line rig directly from the booms to the servo arm???

Thanks in advance.

Tatolazo

You only want one line going to the boom, keep it simple.

Tatolazo,
More than likely, a single line to the sail will work fine. It will make the sail travel the same distance as the line is pulled by the arm on the servo. By using the single attachment point at the end of the sail line, then using the servo arm to pull the ring over that line, the same amount of travel of the servo arm will cause the line to the sail to be pulled twice as far since the ring pulls in the 'center' of that line (not really the center, but that doesn't really matter). The servo will have to exert more force by pulling that ring, but the sail will travel much further than without doing it that way. [Not a very clear what of explaining it, is it? Sorry. It's been much too long since my last physics class to try explaining this kind of thing - lol.]
- 'Doc

Hi dons boat work and ltdoc:
bothheories seems to be right. sngle line directly from boom to servo arm will require some amount of pulling power.

if i use a ring or a pulley beteween the boom and servo arm the servo will pull double distance ...it means that i can attach the sheet line to the boom double distance far from the pivot point next to the mast ...so pulling power is reduced to the half......finally same pulling power requiered and achieving the same angle movement in the main boom and jib boom.

the only difference is that i could use a shirter servo arm if using a pulley or ring.....

that is my primary conclusion starting from your posts. i will try to check i n real life if i am right...


thanks for the i nfo and the sketch.

may be tomorrow i will start to post my boat construction from plans.

Tato Lazo

All true. Work done is distance X force, and the servo has only so much power available, so spreading it over a greater distance reduces the force available.
If possible, I am all in favour of keeping it simple. If you dont ave room for a long enough arm, the doubling trick helps. Try to keep the anchor point at the end of the line as close as possible to, or at least in line with, the point where the line passes through the deck.

I just started a new post with the construction...search for it in the forums and stay tuned!!!!

Thanks.

Tato Lazo