Prolux S-5009 servo

[Who BootParticipant @whoboot]

How to attach a sail arm to servo

[Who BootParticipant @whoboot]

Hi,

I'm building my first model yacht as per a plan in Model Boats magazine from a few years back. The R/C items in the plan are not prescriptive and it can be left to each modeller decide what their own preferences are or go by what they can obtain. I have a Prolux S-5009 servo and sail arm. However, it is clear that the arm will not fit directly onto the servo and therefore needs some item to fit between them. The sail arm has holes to fit the four small screws that comes with it but there are no holes in the servo to fit these into. Can anybody advise me please on what I need to complete this fixture?

Thanks, Haydn.

[Malcolm FraryParticipant @malcolmfrary95515]

Most servos are supplied with a collection of horns to fit the splined shaft. Often there is a circular one among them. If the holes in it do not match the ones on the arm, a small drill bit can provide them ready to accept the small screws Any horn with the right diameter hole and the right number of splines will do the job.

My personal preference is to use one of the servo size winches for easier mounting and rigging.

[Who BootParticipant @whoboot]

Hi Malcolm, thank you for posting with that useful information. Now you mention it I remember seeing horns (not necessarily with the servo I mention) and should still be somewhere in my possession. I will look through my spare boxes. I will let you know when I find anything and see if I have any that fit the said servo and sail arm.

[Malcolm FraryParticipant @malcolmfrary95515]

While I have formed an abiding liking for drum winches as opposed to arms, I did develop a few mental notes for when setting up arms.

1 To get the travel wanted, there is usually a doubler arrangement. The line, having come through a bulkhead, passes through the end of the arm and then goes off to a point very near the bulkhead entry.

2 To get the best force when going close hauled, you take a line from the bulkhead entry over the servo horn screw head. When the arm is set for the sails being fully in, the hole at the far end of the arm should be on this line.  At the same time, when the arm is at the "fully out" position, he arm end should be as near as possible to the bulkhead entry point.

3 The arm puts a considerable force on the servo shaft. Double bearings are good, but mounting the arm under the horn minimises this twisting force.

4 All of the force generated by the sails goes through the arm and the servo to the hull structure. The mount for the servo needs to reflect this. A rough test is to pick the boat up by the line. If it all survives, the mount is strong enough.

The horns that I have run into (apart from mini and micro servos) all seem to be the same size, but some have 24 splines, some 25. Pushing harder does not cause a wrong one to fit. Don't ask.

Edited By Malcolm Frary on 30/01/2021 13:24:24

Edited By Malcolm Frary on 30/01/2021 13:30:03

[Who BootParticipant @whoboot]

Many thanks for the information Malcolm. I do have horns for the servo and sail arm. I don't have a sail to fit to my yacht yet but I will make a copy of your instructions above and keep them for when I come round to attach the sail to the servo arm.

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