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Best Servos

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Paul T16/08/2020 19:57:18
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7172 forum posts
1214 photos
2 articles

Dear All

I am looking for advice on the best (most reliable) servos.

Primarily slim 9g, but also heavy duty sail winch units.

Paul

Brian Dickinson 117/08/2020 03:30:28
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245 forum posts
135 photos

Hi Paul

I am using mg995 servos for the sails on my JIF 65 with an arm Screwed to it. The drag on it will be quite large with the sails In strong winds. It seems to cope well enough. I buy them cheap on eBay.

For the rudders I use mg90s again bought off eBay.

Both are cheap and cheerful

I set the transmitter up to 80% throw as someone advised that it would not burn them out. Not sure how that works but that’s how they are.

In 18 months of sailing they are still going ok.

Brian

Malcolm Frary17/08/2020 08:59:42
896 forum posts

Is this for the pond yacht? Knowing the size of the boat and its sail area helps a lot, along with the intended travel from full in to full out.

Eddie Lancaster17/08/2020 09:12:53
695 forum posts
526 photos

Hi. Paul, I am using a Hitec HS-785 HB winch arm servo in my TSB and IOM boats, they will handle 1000 sq. in. of sail, I have also fitted the same servo but with a winch drum in my current build, a 58” long two masted schooner, it’s not finished yet but it is the winch recommended by the designer, it will give up to 20” of sheet travel, and controls all three sails, both will need end travel control from the tx. to make set up easier.

Good luck with whatever you go with and enjoy the sailing without an engine.

Regards.

Eddie.

Paul T17/08/2020 14:42:44
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7172 forum posts
1214 photos
2 articles

Thanks for the replies and advice.

I am asking for two reasons, the first is for a winch / sail servo for my big pond yacht (that I've not looked at yet) the second reason is for dependable slim servos for larger model aircraft.

Paul

Malcolm Frary18/08/2020 10:09:08
896 forum posts

When picking a sail winch, apart from being able to fit it in the space available, you need to know the sail area and how much string is going to be pulled in. Some just throw the string on and fiddle with the electronics to get it right. It is much better to figure out the travel and tweak the layout of the string first.

Winches usually have a 1" diameter drum, so it is possible to work out the travel that a winch of however many turns will give. Arranging the running rigging (position on the boom, position on the deck) can make quite large differences, allowing you to trade speed and torque.

Arm winches do need a really strong mount to withstand the twisting that they generate - a drum just gives a straight pull. An arm is less likely to create a tangle, but is not immune from the problem. I have had one loop a loose line round the radio switch and switch it off. Amnnoying.

If the sails turn out somewhere in the 6-800 square inch range, anything that is good for an IOM will be fine.

Paul T18/08/2020 16:12:39
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7172 forum posts
1214 photos
2 articles

Thanks Malcolm

Still not had chance to look at the yacht but I've taken the plunge and bought a couple of Hitec HS785HB servos (at £15 each it would have been rude not to) reading the blurb they will give me 8 fully controllable rotations at 12 kg/cm torque.

Paul

Malcolm Frary18/08/2020 21:47:00
896 forum posts

8 turns seems a lot. Much more usual is 3.5 turns. Most normal servos turn 1/3 of the travel of the pot on the inside, standard pots have a 270 degree track, so 90 degrees. To do a winch, the easy way was to use a "10 turn pot", 1/3 of that gave 3 and a bit turns, which was handy. With a normal transmitter, 3-and-a-bit might be it.

Measure from the chosen spot on the boom to the chosen rigging point on the deck with the boom full in, and again, full out. Subtract one from the other, if its a 1" drum, (3 and a bit inches per turn) you can work out how many turns. If it isnt too far out, jiggling the chosen points about can get the length the boom wants to fit what the winch will offer. Then try to do the same with the other sail.

At that price, it would have been rude not to get two. Maybe even churlish.

gecon19/08/2020 08:47:15
200 forum posts
191 photos

Hi Paul, I ended up with Graupner and Krick servos, rather expensive here in Norway. I chose them for the 6 turns of rotaion giving a sheet length of just over 40cm -which I needed for the Fisher genoa control.

Considered the785HB but it is listed here as 3.5 turns not 8. Maybe they mean 3.5 each way? =7? (but there is no central stop for a winch so I'm not so sure that they give 8 turns -unless modified maybe?

Regards,

George

Gareth Jones19/08/2020 11:59:15
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791 forum posts
1067 photos

Hi Paul,

I have used the Hitec HS785HB in lots of different yachts, mainly up to Marblehead sized i.e. 800 sq inches of sail. They have always worked faultlessly and provided you don't need ultra fast response for a high performance competitive racing yacht they are fine.

Based on my records of various types of sailwinch the HS785 HB typically gives about 3.6 turns on a 38 mm drum and about 430 mm of sheet travel.

To get the maximum holding force on the sails you need to attach the sheets as far away from their pivot point as possible. If you assume a boom travel of 80 degrees from fully in to fully out, and you use the full travel of the sailwinch the maximum distance from the pivot point to the sheet attachment is about 400 mm. Usually you will find the length of the jib boom becomes the limiting factor and typically on a Marblehead I find I use a lever arm of 250-300 mm and restrict the sail winch travel accordingly in the transmitter servo travel limits.

Gareth

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