How to install the Hitec 5745 servo

[Steven Oosterheert]

For my first and new IOM I bought a 5745 DG servo for the sheets. I still haven't found out what's the best way to install the thing. I am also afraid that if I don't pay enough attention to it the servo is vurnable to melting down: is there a way to protect the servo from overheating?

I know about another topic related to this subject, http://www.iomclass.org/phpBB2/viewtopic.php?t=795 but I need more information.

Bantock uses a large diameter wheel, others an arm, some programm it to 180°, others to 120°, mine does only 90° now. Is it wise to use one sheeting line for both sheets and keep that under tension with a shock cord, or is it better to have the sheets loose and independent from each other. http://www.velarc.es/bitacora/?p=10.

[Graham_Snook]

Personally I didn't like the idea of siting mine in front of the fin, goes back to racing big boats and keeping the weight off the foredeck, whether this is right or worng I don't know, but it works for me.

I have the Kbits CF arm on mine, and it sits just behind the fin (on the centreline) with the spindle aft so it gives me the correct amount of movement from not quite touching the mainsail sheet post to not quite touching the fin box...here's a pic:

<img src="http://static.flickr.com/93/266114942_d3793656d6_o.jpg" width="600" height="379" alt="5475">
Excuse the sikaflex they were permanent patches

I've fitted the winch as low down as possible, I have a plastic tray around it (after one of my patches came loose during a nosedive when the mast head touched the water in a viciousy squall) so if I get any water in the boat it has to be at least 2" deep before my servo gets wet. Not that it will get that much water in the hull, but it's only 5mm off the hull at it's lowest point so the tray affords it more protection for a couple of grams of weight while still allowing air clearance around the heat sink.

Hope that helps

G

[Steven Oosterheert]

Thank's Graham, this is the way I think I will do it as well. Can you tell me about the max. angle of the servo?

Did you think about a shock cord on the other side of the arm to power up teh servo a bit or give ballance to the shock cord on the other side?

[Graham_Snook]

Hi Steven,

The max angle I get is around 110º, but to be honest I set mine up so it goes from full in to full out so the angle wasn't a big issue for me. As long as there was enough movement in the arm to sheet tight in and ease right out so the sails are on the shrouds, I was happy to begin with, now I've learnt more I've got to tweak my system slightly so I can fine tune the sheeted in position as I've found at the top end of A rig conditions sheeting in isn't as swift as it could be, but a slight luff up and in she goes

I've read about shock cord on the otherside or with a cam which will probably eliminate the above problem, but I'd rather have no tension on the arm other than what the sails are providing. My thinking behind this is saving on battery power (maybe) but also in light conditions if the servo is having to work harder than it needs to it seems counter productive to me.

One other thing I must get round to doing, is smoothing off the notches in my transmitter throttle. Not that it adds friction to the throttles, but again from my big boat background I was always taught to ease the sheets softly. Where as, with the notches on the throttle, it jerks out one notch at a time...not a problem in heavy weather, but in light conditions the sails shake as the digital servo perfectly matches the throttle movement of the transmitter. This I believe disturbs the laminar flow on the sails, I don't have any evidence to back up my reason, but it's worth considering if you find the sailtrim to be jerky through no fault of your own

[Steven Oosterheert]

I have encountered a problem: the servo only makes 90° in combination with my Futaba FM set

It has been programmed to 120°. What will solve this?

Ofcourse I can put on a longer arm, but the the sheeting force will be less and the servo will suffer more too, or is it the same for the servo? Does it mean when it is programmed from 90° to 120° that the torque is also 9/12 less?

[Olivier Cohen]

If you push your trim in both ways to the max, you will get 120°...

I had the same problem...

So you have to program more course to get the course you need without the trim...

[Steven Oosterheert]

If you push your trim in both ways to the max, you will get 120°...

that is what I did and still the max was 90°... I asked the programmer and he confirmed me it has been programmed at 120°

I might go and look for someone with a programmer to see if we can work it out.

Still I have the question: will the servo become less powerfull (and more vurnable) when programmed to a bigger angle?

[Olivier Cohen]

Still I have the question: will the servo become less powerfull (and more vurnable) when programmed to a bigger angle?

In fact, it's the oposite, as if you program a bigger angle for the same sheet travel, it means that you use a shorter arm, so with more power on the sheet.

[John Ball]

I would expect that if the angle of travel is increased, the power should stay the same.

I would expect the change to be the travel time "stop to stop". That should increase proportionately to the increase in the angle.

More travel should allow you either to use a shorter servo arm (reducing stress) or a longer sheet and sheet attachment point (improving the leverage and therefor reducing the stress on the servo)

[Graham_Snook]

The geometry of the sail arm to the sheet is the important thing. So that when it's almost in line (or 10º off) with the sheet, it's full in.

This is one of the great benefits of the sail arm system as I understand it. When it's fully sheeted in (say 10º from the centrline) it can be moved say 5º out and because it's at the top of the travel, it lets it out a small amount of sheet....when the arm is at 90º to the sheet and it's let out 5º again the amount of sheet let out will be more.