RG65 sail servo

How much torque is required for these little guys? I am building my first design and need to know what to order. Is 60 in/oz about right?

Thanks for any help,

That translates to roughly 4.5 kg/cm, which is more than usually found on the “standard” servos recommended for the class. In Europe, at least, the GWS micro 2BB MG is a popular lightweight servo for the sail servo.


After using two Hitec HS-645MG servos for two of my RG-65 boats (Torque is 107 in/oz. 7.7 kg/cm) and having grave concerns about the limited arm travel to assure sufficient sheet travel, I was CONVINCED by a few US sailors and a LOT of foreign sailors (many from South America - thanks, guys) and I have recently moved to a GWS S-125-1T which is a drum winch conversion of the old S-125 style servo. You can buy in 1/2 or 1 turn and drum is roughly 2" in diameter. Claimed torque is 92 in/oz or 6.6kg/cm so I’ve not lost much in the strength area - but with 1.875" diameter inner groove making one (360 degree) turn I’m calculating nearly 6 inches of sheet travel ! (the old highschool math comes in handy: Circumference = diameter X Pi … or … 3.14 x 1.875 = 5.89 in.)

The added benefit is that it costs half of what normal retail price is for the HS-645MG ($38 vs. $18) so with shipping included, I paid ServoHut $24 and it arrived in 3 days.

Thus my final two boats will sport this sail winch instead.

Just an FYI

the Hitec 645 is really oversized for the RG65. I used it in my first experiments with a Fortune612, where the sheets have a lot of friction. A standard servo was only able to pull the sheets tight when sailing upwind in very light winds.

Here in Germany the standard sail servo is the 28g GWS IQ-200 MG with a torque of 54 Ncm at 4.8 V. Using a servo arm of around 60mm and a block to double the sheet travel it fits all wind conditions. Costs are around 16-20 €.

Only a few sailors are using winches, because those winches usually are to big, relatively slow (>1 sec.) and too heavy (>50g) for an RG-65. ALso the GWS winch, Dick mentioned, is for my opinion oversized.

The GWS IQ-200 MG Haegar/Joachim mentioned is sold in the US as the Micro 2 MG BB, just FYI. So he and Martin are talking about the same servo. Which I use, BTW, and am happy with.



Hi All!!!
IMHO… just get the gws winch and you will be fine…



I went with the GWS, thanks for all your help! I am attaching some pics of the build…can’t wait to get her finished.


looks good!!! keep up the good work!!!

I use also the GWS Micro BB MG and have not problems.
I did modifying the servo, tha he is working 180 degrees.
So my arm is smaller (here without a block) then only 90 degrees, smaller torque on the servo, but not so quickly. I not use 0,5 sec for all sheets way.
BUT I also know, that any servos are destroyed. Why??? I do not know. I think it are any problems with the sheet managements in the boats.

Now I did see discussions about a digitally servo from Graupner for RG. But the price is higher DES 678 BB,MG


I maked (no sucsessfull) modifying GWS IQ 200MG.

Picture 1
First I must know, what servo can going about 360 degree or more. This gearwheel is good. I must only take off the iron pin (arrow).
I searched other servos too, but Dymond BX 250 MG and HS 81MG both no well.
The iron pin destroyed teeth from gearwheel
81 MG:
The h eight of gearweel is in 180 degrees only 1/2 heigh. But GWS is good.

My idea, another potentiometer with 15 turns

Spindle trimmer from Conrad electronics

Steps with GWS IQ 200 MG

Picture 2
Here is the original case

Picture 3
Here I reviewed partitional the tube of potentiometer

Picture 4
I disassembled original potentiometer >502HT<

Picture 5
I sawed the shaft of the potentiometer

Picture 6
In the shaft of the spindle trimmer I maked a bore 1,0 mm. The movement of spindle trimmer can go as the originally movement.

Picture 7
Here I mounted the shaft from originally potentiometer with spindle trimmer.

Picture 8
I think all is good.

Picture 9
So it si looking well. But here the 2. variant (spindle trimmer turned 90 degrees) Pc board also inkluded the case.

Why not sucsessfull?
I wished a winch with 2 up to 2.5 turns. But he makes 5.5 turn. And what was bad? 5 Turns the winch was driving quickly. The last 180 degrees only slowly and only smal torque.
GWS China and GWS Taiwan did´t say (would´t???) where I must modifying pc board.
I know, that I must change parts for

  • pulse stretcher (very importand, that everytime 99 % totque)
  • Deadband (is not so importand)
  • electronical damping ( not so importand, if deadband bigger)

Picture 10
So I drawed the pc plane. (Well I know, tat this plan is one variant. I did see other parts and dimensions in other pc boards.) But my old books no gived Help for my problem.
And now I hope that you help me by my electronical problem.

(Hmmmm…? why I can not insert the photos into the text?)


Why did you consider this mod unsuccesfull? if it makes 5 turns instead of 2.5, doesn’t that mean you can use a smaller drum and have more torque? Or install a pot with fewer turns on it. You probably do not need GWS’s assistance as the only thing you are changing is a potmeter used as a voltage divider
You could also try to run your servo at a higher voltage, but that might overheat it.

Just a question about the current ‘best’ winch for a RG65 ? Is the GWS still a favorite ? I think I’d like to build a boat, but most of the info in this thread is from '09. Thanks in advance for any info.


I am still happy with the GWS servos. For when I need a winch (narrow boat) I use the S125 1T sailwinch. When I can fit an arm, then the GWS Mighty Micro works great. Both are available at Servo Hut.


Thanks for the reply Eric. I’ve downloaded the 'Cobra 5" plans/patterns and will start soon.


I used the GWS servos in my Ranger…no problem at all. I used a Stollery PowerLever wire to bring the sheet in close to the servo center when close hauled…seems to reduce stress on the servo a bit.


I look sliek I’m going the route of the GWS for the ranger. tight beam and all… but man the servo is heavy. 1.7oz… my fut 3102 is smaller lighter and same torque…but just not 360* bugger…

oh well

Yes - the 360 degree turn is the problem. I suppose you could add resistors to a smaller servo to increase the throw, but the small ones do not have much room in the case. The extra resistors would probably have to be outside the case, then the whole area covered in epoxy to make it waterproof.

eric, or for 18 bucks plus shipping…its done…

Hopefully I’ll get servo in the next few days…


Which servo did you buy? The 1T GWS or something modified by Servo City or Servo Hut?

1 turn gws from servo hut… not in yet…