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Sail servos

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Misterbee:
No such thing as a dumb question, correct?


Here goes;


Is the number of turns on a multi turn sail winch achieved by electronics or gearing?
I.e. if I use only 20% movement on a 5 turn sail winch, am I getting more usable torque due to increased gearing, or just the same, assuming it's linear?


I have a number of 4 and 5 turn winches that I can programme down to 2 or 3 turns, save buying a specific 2 turn winch.
Regards,
Brian.

JimG:
Reducing the number of turns will be done electronically. Changing the gearing would probably need a strip down or a complicated gearbox, much easier (and cheaper) to adjust the electronics.
Jim

malcolmfrary:
Is a normal servo, there is an electronics board that looks at both the signal coming in from the receiver, which is your means of telling it where to point, and the position sensing pot, which tells it where it is pointing.  If they disagree, it tells the motor to drive.  The motor drives its gearbox which in turn drives the pot until they agree.  Co-incidentally, there is an arm attached to the gear driving the pot, which is what we are usually interested in.
In a winch, there is all the stuff mentioned above, but between the output gear that used to drive the pot directly and the winches pot, there is another gearbox.  This slows down the drive to the pot so that for the same swept distance, the output shaft has to turn several times.  In all of the early proportional winches, rather than a gearbox, a 10 turn pot was used.  A normal pot generally uses the middle 1/3 f its sweep, 1/3 of 10 turns gives 3 and a bit, hence many winches were "three turn".  The different turn winches available use different gearing between output gear and pot.
Programmable winches, OTOH, do it electronically, but do have the effect that if you reduce the travel, you also reduce the work done end to end.  The motor doesn't magically produce more power to make up for the shortened run.
Using 20% of its available travel means that you have bought 5 times as much winch as you needed, assuming that it both works and survives.  Reducing travel by programming is OK for small adjustments, but large adjustments keeping the same winch are better done by rearranging the string, paying close attention to the travel distance needed between the boom point and bridle ring, and their positions on the boom and over the deck.  And whether or not to run the line through a doubling block to lose boom travel while gaining lots of torque.

malcolmfrary:
I've just had cause to go winch shopping.  As ever, looking for a lot of bang for my buck.
While shopping, I have noticed one or two "programmable" winches that have no corresponding program card.  What this means to me is that if an actual 6 turns is wanted, I will need to have a transmitter that supports an increase in travel by a sizeable percentage.
The sellers of such items are usually just parroting what is in the manufacturers literature without understanding what is being said.  It is, of course, important to know what a winch is capable of before buying, so clarity helps here.
So, is a "6 turn programmable" winch really a 3 and a half turn winch that can be caused to travel further by tweaking the end stop points on the transmitter?

tigertiger:
In addition to what has already been said, and from distant memory. The servos I bought in the past also had a torque figure. The radius of the sail winch drum is also important. The bigger the drum , the more torque is needed, but also the more of the cord is wound in/out for every given turn.
Adjusting the winch to a higher number of turns would allow you to use a smaller drum thus giving you more pulling power, but the sheets would be hauled in at a lower speed.
If you wanted a very fast response to sheets in/out (e.g. if you are racing) then a bigger drum would give you this, but need a torquier servo, a smaller number of turns would allow you to stop before over pulling the sheets. Which would be wasted time, energy, and more potential for damage.
This was my understanding, but what do I know.

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