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Largest engine with standard size servos?

Old 01-29-2006, 02:54 AM
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meowy84
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Default Largest engine with standard size servos?

I think I've asked this question before but I can't find the post now so here it goes again. In general, what is the max engine size before you start needing heavy duty servos for the rudder? If I recall anything over a .21 or so needs something beyond the standard servos. Am I in the ballpark?
Old 01-29-2006, 07:52 AM
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Default RE: Largest engine with standard size servos?

I tend to use a larger servo for .21 outboards even though I did run one for years with a standard. For inboards a standard can be ok. My .45s and up do have higher torqe servos. Note, you can save some weight by using smaller servos for throttle and remote needle, if so equipped.

Edit: reminder to self, don't forget to switch from planes to boats when responding to questions
Old 01-29-2006, 08:22 AM
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Default RE: Largest engine with standard size servos?

It's not so much the size of the engine as it is the speed of the boat. Speed = load on the rudder and servo load. That said, I have never used a "high torque" servo in a boat before building my Whiplash. From my .21 powered Wild Thing to my Scale hydro, I have used the standard 40 oz in. servos with no hint of steering weakness. You may read into this that I have slow boats. To the contrary, my Wild thing runs at 47 mph and the scale runs in the low to mid 40"s. Some may say that's slow. The fact is I haven't seen a need for high torque servos yet. The Whiplash I expect to run in the high 60's. 70's would be nice! It has a Hi Tec 945 for the rudder. Have I seen the light? Maybe it's a mind set. When I started model boat racing, a servo was a servo. There were no "high Torque" servos.
Old 01-29-2006, 03:27 PM
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meowy84
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Default RE: Largest engine with standard size servos?

Good reminder to self Piper Chuck as I was rather surprised to see you here...i'm more used to seeing you as a regular staple on the plane forums. Perhaps I should have been more specific. I'm running inboards. So what you guys are saying is that for up to .45 standard servos should do the job fine? I don't expect my boats to be ultra fast, just ultra fun.....they'll probably run average speed as I'm using an old hull design (one in fact happens to be a Chris Craft style enlarged and scratchbuilt for nitro r/c).
Old 01-29-2006, 03:54 PM
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Default RE: Largest engine with standard size servos?

I switch hit, boats and planes. I actually started with boats and then learned to fly. My note to self was because I typed up and posted this long response about using standard servos in up to .60 or larger planes. It happened partly because I hadn't had my morning coffeee and partly because I had just been in a plane forum where several people were asking about servo sizes. I do remember thinking it was a bit odd for someone to mention a .21 engine in a plane, that's a bit uncommon (although I fly one). As soon as I realized my mistake I quickly erased it and wrote a more on-topic response.

For the use you've described, I don't see why a standard servo would not be fine. I would probably go with a higher torque, standard size servo in a .45 racing mono, but that's partly because it will increase the servo's survivability if the boat is in a collision with another boat, or perhaps a bouy.
Old 01-29-2006, 03:58 PM
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meowy84
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Default RE: Largest engine with standard size servos?

Thanks Chuck. I could have been using an HP VT .21 in my plane...so there!....haha
Old 01-29-2006, 04:07 PM
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Default RE: Largest engine with standard size servos?

I used to have one of those, it was a cool engine. If you were going to use that, I'd say mini servos would be fine. The .21 I fly is a K&B.
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Old 01-29-2006, 04:25 PM
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Ron Olson
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Default RE: Largest engine with standard size servos?

I've used standard servos to steer an K&B 3.5 OB and that's a lot of weight to swing. I don't recommend it but with a .21 and under boat the standard servos do work fine. I've decided for safety's sake to use heavier duty ones.
Old 01-30-2006, 11:33 AM
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Default RE: Largest engine with standard size servos?

Thanks guys.

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