sail control for sterling emma c berry.i am building the emma c berry and am going to put a sail control unit in before the deck goes on .i havent a clue. how many channel radio/2 or more and pics would help.

Maybe this video will provide some ideas.

RC Sailboat Build Detail - Sail Winch System (3 min 30 sec)

I don't know if you every got the sail control installed but I am doing it a much different way. First, I am using 3 hi-torque but standard size servos for sail control. One will control the main and topsail. The second will control the middle and in/out control on the staysail and jib. The third will control the port/starboard control on the staysail and jib. I am using 60mm arms on the first two and doing a 2 loop pulley system to increase the total line movement to around 10 inches. I am using a 110mm double arm on the foresails, again with a pulley system to increase the movement length. This servo pulls the jib and staysail to either side of the boat just like a real jib and staysail. Furthermore, the input lines for the foresail servo come from the second servo instead of jus being fixed. This allows these sails to billow forward when running downwind, again with port/starboard control.

One of the beauties of this system is that it can all be put in after the deck is on. On starting to set up servo positions, before the deck is one, I saw that if I add a cross member close to the servo I can add that end of the pulley system to the cross member before installing it. Doing this also adds a little length to the total line movement.

I'll add photos as they become available.

I've finally got a drawing done for my sail control. The upper servo shows how the main is controlled. All servos are 12Kg hi-torque servos but are standard size. The servo arm is 60mm or roughly 2.4 inches. It has three holes in the aluminum arm. I have three eyelets on a rib. The sheet starts at one of the eyelets then threads as show in the diagram. The arm is set so that full in on the sheet is at 135 degrees from straight up and full out is at 45 degrees. This gives and average of 3 inches of movement for each hole. Therefore the sheet has a total travel of 18 inches. The effective torque of 4.4 pounds should still be enough to handle the main and topsail since a 5 lb torque handles the main and jib on your typical 24 inch sailboat.
A second identical setup is used for the forward sails. This is where I need to do some experimenting in order to both get more effective torque and reduced travel. One sheet goes to the foresail. A second par of sheets go to the third servo for the staysail and jib.
The lower servo shows how the staysail and jib have sheets on both sides of the boat. As one side is pulled in the other side is let out. The arm is 4.2 inches so it has about the same 18 inch total travel as the main. The leads from the staysail allow these two to be pulled in when the throttle is down and the main and foresail are pulled in and allow them to be let out yet still have the control for which side they are on when the throttle is up and the main and foresail are out.
What I have yet to make a final determination on is how to control the foresail servo. The main is controlled by the throttle and is ratcheted. The jib and staysail are controlled by the aileron which is self-centered. I would prefer to control the foresail by the throttle but I want to use an additional channel for fine tuning. One thought was to set channel 6 to be controlled by the throttle but the receiver setup I want to use only has channels 1-4. A second thought is to mix the throttle and elevator. That way the ratcheted throttle still has some control over the foresail with additional tweaking with the elevator.

rgburrill, are you sure you're calculating that right? 12 kg-cm servo torque, thru a 1:6 purchase, on a 2.4" arm? 10.4 lb-in, / 6 / 2.4 = .7 lbs or 11 oz. And then subtract your friction losses. Not a lot of sheet load.

Multiple purchase gains sheet length for an equal loss of load. Same for arm length. Will that be enough load at the sheet to get the job done?

Some suggestions...
Making a 180 bend thru a brass ferrule/grommet has a lot of losses, even with slippery line. Use large glass beads. Or just bend the line around a section of carbon fiber tube.

Use the fewest reductions possible, to minimize losses. A 3.6" arm with 1:4 is the same as a 2.4" with 1:6, except is has two fewer friction points. Also, if you need that much line, what about the multiple turn drum types?


Dave

Thanks boater_dave, good points and things I am concerned about. My thoughts are that a standard servo has about 3kg torque and can swing both sails on some 24 inch boats. and that is using a 3.6 inch arm With the 1:6 purchase I have 2 kg and a 2.4 inch arm. What I have not said here is that at the boom I have a 2:1 purchase by running the line through an eye-hook on the boom to a cleat on the deck. I've done this for several reasons, not the least of which is to prevent the sheet from tangling with the compass post. I'm estimating that 9 inches of movement from in to out with the eye-hook at about 8 inches on the boom will give me the range of motion I need. And I can always fall back to a 1:4 purchase at the servo with a straight tie onto the boom. That would give me 12 inches of motion. I could also just put in an even higher torque servo.
FWIW I dislike drums. They are expensive and take up way too much room.

Purchase is a strange term for this. I wonder if it leads to the phrase buying leverage.

Purchase is a common term for the mechanical advantage of a pulley system. But in a model boat sheet system, the equation gets flipped because we are powering the other side of the system. And like I said before, if you run a 1:2 feeding a 2:1, why not run a 1:1 and skip all the friction?

And I would check your references. A 'standard' servo, like the Futaba S3003, will not even work in a footy. I am not aware of any boat that uses a standard servo for sheeting. The Fairwind, a 36" boat, uses a Hitec 715 with 200 oz-in. The S3003 has only 57 oz-in of torque.

Dave

My first boat was a Huson 24. This is from the Dumas web site:
"This smaller version of the Huson 36 is fun to assemble and easy to sail. You assemble the cleanly die-cut frames and then strip plank the hull with balsa wood strips. The kit contains sewn dacron sails, carbon fiber mast, and complete rigging. A two channel radio is all you need to radio control the model. You do not need a sail control unit, simply use one of the RC servos from your radio. A simple and fun way to enjoy radio controlled sailing."
And I have seen this on other 24 inch boats. And a standard Hitec HS422 servo has 3.3 kg-cm of torque on 4.8 volts.
I do agree I made an error in my calculation, though. I accounted for the 2.2 lbs per kg multiplier but not the 2.54 cm per in divider. I will just have to see what friction does - I don't expect it to have a lot of effect. My design makes the rigging more realistic and should help keep the boom down on running downwind.
I do have fallback positions if it doesn't work.

BTW, I found a lot of Footy designs that use standard servos. One specifies the S3003 and one even mentions micro servos.