Hitec arm-winch servos?

awallin · Post by **awallin** » 15 Sep 2007, 20:34

Hi all, I've been using drum-winches on all my boats so far, but I'd like to learn about arm-winches and maybe use them on my next boat.

I'm looking at the list of hitec servos.

the big 1/4th scale servo hs-5745mg is rated at 250 ounce-inch and 0,15 s speed. price $70
the spec says 90 degree rotation, but I guess it does more degrees when programmed with the programmer?

then there is the 'robot-servo' HSR-5995TG which has 333 ounce-inches and 0,13 s speed. on sale ca $86
180 deg rotation.

there's also a weaker and slower big HS-755mg for $40

* what are people using ?
* I thought I heard a rumour that the 1/4th-scale servo is more robust than the normal-sized 5995 ?
* Also, there was some info here about the need for extra thick wires with these servos since they draw a lot of power. How much of an issue is this? * Are LiPo's required or do NiMHs work OK too?

thanks,

Anders

Steve Landeau · Post by **Steve Landeau** » 15 Sep 2007, 21:08

Hi, Anders.
Since I've been sailing my Isis (2 1/2 years) I've been using the Hitec 5745 arm. There are smaller ones, but I'm still sailing at minimum weight, so I don't see the need to use the lighter, more expensive servo. I did find it necessary to go to 7.2 volts though with the 5745. Since the smaller servos are stronger, they may work with 6 volts. The 5745 (1/4 scale size), the 5995 (no external heat sink), and the 5955 (does have heat sink) have all been used successfully on IOM's and smaller boats. Here is a link to an ODOM forum regarding the choice of digital arm winches:
http://www.rcsailtalk.com/viewtopic.php ... sc&start=0

Ralph Knowles · Post by **Ralph Knowles** » 16 Sep 2007, 00:53

Hi Anders,

I have also been using a Hitec arm winch in my ISIS for as long as Steve, (I have ISIS hull #041), but it is the previous model, the 5735. I have had absolutely no problems with it and am using 6v to drive it. I have three 6v Ni-Cd packs, with the 3/4 size AA cells, that I bought from Ken Binks who developed the system for IOM's using the quarter scale servos. It must be good as his brother Trevor won the IOM Worlds in Vancouver with the same set up. Graham Bantock uses a quarter scale with a 100mm diameter drum, set ex-centrically on it. I have since installed a 5745 in another design, a 'Sloth', and have built the installation to the same spec. Again, no problems. If other club members have digital servos, then take shares in a programmer, it reduces the individual cost.
I find that a single battery pack gives me about two hours continuous sailing, as long as I don't let the winch servo 'sing' too much.
I know that K Bits are now also supplying the RMG drum servos and possibly Ken and Trevor have changed over to them but if so, it may only be be a commercial move.

RoyL · Post by **RoyL** » 16 Sep 2007, 05:16

Just to complicate things a bit, there is a new generation of high power servos coming out from other manufactuers including JR and Futaba. There is also a HiTec "super servo" that is coming that has lots of power, speed and is standard size. Expected price is over $300 US. A problem with many of these servos, as others have suggested, is heat build up that causes a melt down. Safe bet is to stick with the 5745 and in high winds switch to the 7.2 volt battery back for that last bit of grunt.

Ralph Knowles · Post by **Ralph Knowles** » 16 Sep 2007, 23:30

A small, but important, point when installing such a powerfull servo is to fit a fuse module with a suitably rated fuse. I have this fitted in both my IOM's with lever arms and have saved myself quite a bit of damage . When in a situation where my boat has becomed entangled with another, and the main boom gets jammed, with overload on the winch, then the fuse blows, and saves a lot of strain being put on both the hull internals and the rig. I have been using a fuse rated at only 1.8A which is perfectly OK for normal operation. Ok, so the boat may have to be rescued from the pond, but it is still in one piece and if the fuse is installed on the lever servo power cable only, then steering is still possible.

Marko Majic · Post by **Marko Majic** » 17 Sep 2007, 18:11

Hi Ralph,

I think you may be under a wrong impression of the power that the digital servos (as exerted through a 10cm long arm) can wield.

In particular an RMG 280 is far (FAR!) more capable of destructive behaviour (when things snag) than any digital servo configuration I've ever seen.

I tested a few different arrangements last year (on mine and other people's boats) with 5745s and 5955s with LiPos and NiMhs and in each case I could hold the control line with a thumb and a forefinger (a something that is not very easy to do with an RMG unless you're an exceptionally strong individual).

Having said that, having a fuse is not a bad idea - but not to save anything on your boat but rather to save the servo itself (last year I went through 3 of them in 2 months before going back to an old RMG).

Having said that, though, I must add that I don't necessarily mean the above as a knock on digital servos - they are obviously fine for IOMs because many of the people I know have been using them successfully for a long time (at the very highest of competitive levels)...

Marko

Barry Fox CAN262 · Post by **Barry Fox CAN262** » 17 Sep 2007, 19:00

Good points Marko and you are completely right that an RMG is really hard to beat.

I had a 5955 in a boat and it worked great until teh person sailing it got tangled with another boat and left the sheet control pulled all the way in. The way in which teh boats were tangled didn't allow for the servo to reach its end point so that by the time the rescue boat got to them the servo had burned out. No apparent fire but a definite burned electronics smell below deck and the servo didn't work. The fuse idea would have maybe saved it.

The apparent torque difference between a 5955 and a 5995 is huge. You are right in that it is possible to pull a 5955 although that might be more force than the sails actually produce as I have to say it never wasn't able to pull the sails in during fairly decent winds. With a 5995, particularly on 7.2 volts, it is nearly impossible to move the arm at any point in its travel.

But none of them lock up and shut off like an RMG does so that fuse idea is one I am going to implement right away.

Lester · Post by **Lester** » 17 Sep 2007, 23:52

As ever, I guess the choice of Hitec vs RMG is a compromise, a balance of pros and cons. With a suitable arm or large-radius drum, the Hitec is blindingly fast to sheet in or out. I've won a fist-full of races by being able to flick-gybe while the opposition was laboriously first sheeting in ... and then sheeting out. The downside is I have not found it powerful enough to reliably sheet in on a run when overpowered, even after I installed a thicker wiring harness (which did make a difference). It only became good enough with the cam tensioner, but that added weight, complication, and messy runs of line... And, it does burn out rather easily if it stalls from a sheeting snag-up but you don't realise it for a while. I burned two out in circumstances where the RMG would have simply got a little hotter but not fried. The RMG is powerful enough to rip out a mainsheet post (26 mm drum), particularly if you use a wiring harness which can take the 12 amps of stall current it draws (!). I have fried an RMG (and ripped out the sheeting post in the process), but that was early in my relationship when I had not developed the necessary understanding that if the boom doesn't seem to be going to centreline it isn't a good idea to just carry on for the next five minutes with the stick and trim trying to make it happen. Until recently, the RMG has lost out in the speed stakes, but Rob Guyatt is now supplying a 42 mm dia drum. So I've taken out my 5745 and put in a 280 with the large dia drum to see how it works. The winch spreadsheet at http://www.onemetre.net/Build/Servo/Servo.htm suggests this should be just as fast...

awallin · Post by **awallin** » 25 Aug 2008, 12:26

Hi all,

I've just noticed that HiTec has a new servo out, the HS-7955TG.

With the new HFP-20 programmer it should have an overload protection feature.

Has anyone used this? With the overload protection I imagine no fuse is necessary.

Anders