Ok did a search but found zip.
What are the advantages of the following
double arm sail servo
Granted space in the hull would dectate weither a double arm or winch is going to fit but there is no problem there as the US1M hull is roomy.
What I am looking for is pro’s and con’s for each item. The sail servo will be going into the US1M Mistral that I am building and being the cheap sob that I am I want the best bang for my dollar.
There is a third possibility half-way between the two – Graham Bantock has tested and is now selling an “arm drum”. It is a large drum with the same radius as arm and is designed to rotate 180 degrees like an arm.
IMHO the pros and cons of the different arrangements very much depend upon the availability of the hardware. A few years ago, there wasn’t an arm winch worth installing in a competitive boat like the IOM, and the Whirlwind drum winch was pretty much the universal standard with the RMG second. Now there is a fantastic arm winch using a Hitec digital 1/4 scale servo, and Whirlwind is no more…
But for the record, IMHO it is easier to play tunes using an arm winch. Easier to have different sheeting rates close-hauled versus reaching or running, to have differential rates for main and jib, and to set up very fine control for close-hauled sheeting. Downside is you need the space for the arm, and drum winches are generally more powerful for the same weight, and/or lighter for the same power. The Hitec arm solution has two unique strengths: it is blindingly fast, though speed didn’t used to be associated with arm winches, and it is very agressively priced, almost half that of a first-clas drum winch.
Lester has done a pretty good job of explaing the inner workings of both drums and arms and has sprinkled his technical pages with the advantages and disadvantages of each type of system:
If you read some of the stuff I have contributed to the arm winch page, you will guess that I am partial ro arm winches.
I think the biggest advantage of an arm winch is that you can get a very fine tune control at close hauled where you want to be able to make small sail changes with precision. A secondary advantage that goes along with that geometry is the ability to “lock off” the sheets which means the holding power of the servo is huge and the power required to do that is miniscule. No more slipping of the winch in a puff and no more battery drain.
You can solve the space issue by adding purchase to the system.
Adding a pulley to the end of the arm (or arms) can double the sheet travel for the same amount of servo rotation. Or, to think about it another way, the arm can be half as long for a given needed sheet travel. Adding the pulley also opens up a few other design variables that can allow additional tweaking of the rates. at various points in the system (check out some of the details on Lesters Arm winch page).
Here is a picture of my first arm winch showing the pulley:
Download Attachment: swingarm.jpg
Here it is in the “locked off” close hauled position:
Download Attachment: swingclose.jpg
(Sorry for the poor quality, but my first digital camera was not so great…)
I have made many improvements to this system since those pictures were taken. I have detailed many of the system’s functional aspects on Lester’s swing arm page. There will also be a detailed article in Model Yachting 135 about this system with some additional diagrams.
Thanks for the responce. DO you have a picture or link to Graham Bantock’s “arm drum”. this does sound interesting. Now depending on the cost and if the local shop can get it in.
Hitec makes a sail winch the 725 , looking at the information it has Torque:193 oz-in Speed:1.13 sec/60? is this the one you mentioned? Or is it the 805 torque 224 oz-in speed 0.20 sec/60?
thanks for the info. True the pictures are not hte best but it shows what you mean clearly.
Where did you find the pulleys? Or did you build them? And what is the arm made from? Some one said Lexan or plexy glass will work but yours do not appear to be either of these.
My setup has gotten a bit more complicated and in the more recent pictures it is difficult to see what is going on. That is why I still use those older pictres where it is clear what it happening…
The pulley is a Pekabe. You can buy these several places. I get mine from Great Basin: http://www.gbmy.com
The Arm is the standard arm that comes with the Futaba s3801 arm sail winch: http://www2.towerhobbies.com/cgi-bin/wti0001p?&I=LXH369&P=0
BTW, Graham Bantoks “Arm Drum” can be seen on this page (about 2/3 down): http://www.onemetre.net/Reports/US2004/US2004.htm
<blockquote id=“quote”><font size=“1” face=“Verdana, Arial, Helvetica” id=“quote”>quote:<hr height=“1” noshade id=“quote”>Originally posted by Albertaclipper
… Graham Bantock’s “arm drum”. this does sound interesting. Now depending on the cost and if the local shop can get it in.<hr height=“1” noshade id=“quote”></blockquote id=“quote”></font id=“quote”>
Not sure about your local shop getting it in (smile). E-mail SAILSetc directly and ask about it. Their Web site is www.sailsetc.com, and e-mail “email@example.com”.
<blockquote id=“quote”><font size=“1” face=“Verdana, Arial, Helvetica” id=“quote”>quote:<hr height=“1” noshade id=“quote”>Hitec makes a sail winch the 725 , looking at the information it has Torque:193 oz-in Speed:1.13 sec/60? is this the one you mentioned? Or is it the 805 torque 224 oz-in speed 0.20 sec/60?<hr height=“1” noshade id=“quote”></blockquote id=“quote”></font id=“quote”>
None of these, I’m afraid. The idea of using a Hitec 1/4 scale digital servo as an arm winch is due to Ken Binks, and I talk about it towards the bottom of one of my pages:
The servo is the HS-5735MG, and Hitec’s Web pages give these specs:
Torque 4.8/6.0v : 222 / 264 oz. 16 / 19 kg.
Speed 4.8/6.0v : 0.16 / 0.13 second
Size : 2.3"x 1.1"x 2.0" 59 x 29 x 52mm
Weight : 5.1 oz. 146 g.
Hard to see from your web page, but what servo is Graham’s “monster wheel” mounted on? Is it 1/4 scale, or something smaller?
<blockquote id=“quote”><font size=“1” face=“Verdana, Arial, Helvetica” id=“quote”>quote:<hr height=“1” noshade id=“quote”>Originally posted by Dick Lemke
what servo is Graham’s “monster wheel” mounted on?<hr height=“1” noshade id=“quote”></blockquote id=“quote”></font id=“quote”>
It is the same Hitec as is used for the arm version – Hitec 5735.
In one of your spreadsheets you calculate sheeting geometries above deck to determine the optimal sheeting radii for the two sails and the show how well they run together (parallel) for different sheeting angles. As you know I have added my below deck arrangement for the arm winch to that spreadhseet. In fact the arm winch is a simple “cam” where the effective radius is simply the sine of the servo angle. you could in fact use that spreadsheet to determine the effect of various cam geometries on the sheeting rates through various points of sail. If you led the sheets onto that cam from different quadrants, you could get very different rates for the two sheets in various points in the cam profile.
The question is what do you want to achieve?
Do you want to speed up the sheeting through various points of sail such as reaching that are rarely used and slow down the sheeting to allow fine tune for close-hauled? Do you want to balance the servo torque across the points of sail so that on the run where little force is needed a large arm radius is used such that you use a greater amount of the available torque? If you could quantify what you want the cam profile to achieve, you could in fact use the inverse relationship to design the optimal cam…
I wonder if when you were done, it would look like an arm?