Servo size questions?
 

<div></div><div>What is the rule of thumb for servo sizing? 40 and 60 sized planes use standard servos, do you need to start stepping up servo torque for dual aileron planes and higher performance planes in this size range?. In the instruction manuals of the planes I am building, they really do not say much about the requirements for servos short of standard size.</div><div></div><div>TB</div>

RE: Servo size questions?
 

IMHO No.
Standard servos, maybe ballraced, will serve perfectly well for sport flying. Using 2 aileron servos will reduce the individual servo load (although increase the battery power slightly).
Unless you are using very abrupt control movements, at high aircraft speed, on a larger model, you won't see much benefit in going to digital/high-torque servos.

RE: Servo size questions?
 

For my sport 40 - 60 sized planes I generally fly the Futaba 3004 or JR ST-47BB, which are ball bearing supported. They work great on every thing I have them in, be it a Tower Kaos, World Models Rambler, Hangar 9 Twist 60, etc. Today's sport servo's are much faster and more powerful than the servo's we flew in pattern planes back in the '70's and early '80's.

Hogflyer

RE: Servo size questions?
 

It depends on the model and application. I start to go beefier on the rudder servo even on .40/.46 sized aircraft when flying tail draggers that use a single-servo, especially with lots of control surface.

You never need to go above a standard S3004 on a throttle, regardless of model size.

A plane like the 95" wingspan/12 pound Senior Telemaster can still get by with standard servos. But at some point you ask yourself: "I have $1,200 worth of plane depending on $14 servos. Hmmmmm?" It also depends a GREAT deal on how good a job you did running actuator rods and making clear hinge lines. If the movements are free and light a lighter servo will have an easier time of it.

As you drop more $ on servos you not only get strength but speed and definition. A three-poled servo like the S3004 has fewer increments of motion than a coreless or brushless servo; so it is "jerkier" in movement and may not repeat to the same zero at rest.

RE: Servo size questions?
 

How about a Hog Bipe with hinge gap sealed, do i need hight torque servo?

Tanks

RE: Servo size questions?
 

How about a Hog Bipe with hinge gap sealed, do i need hight torque servo?

Tanks

RE: Servo size questions?
 

Standar servos should work fine. Heck, I got 72 oz in at 4.8v in my t-6 which flew fine. I've seen guys with little extras doing extreme stunts with small standard servos. There really is not much force in the control surface, because the air moves with it, and is not pushing against it.

overall: standar servos should work perfect.

RE: Servo size questions?
 

Tanks

RE: Servo size questions?
 

The Sig Pig (Hog Bipe) will fly just fine with standard size servos. I've had 3 of them so far and all of them have had standard Airtronics 94102's in them.

Ken</p>

RE: Servo size questions?
 

high torque servos are underrated. they make a huge difference in how an airplane flies and behaves.
40oz servos will work just fine but for the same price (or cheaper) the servos below (very high torque) make a huge difference (like straping a .75 engine into a .40 plane, except in a control surface sorta way)

http://hobbycity.com/hobbyking/store/uh_viewItem.asp?idProduct=2&Product_Name=HXT_10kg_ Servo_(metal_gear)_55g_/_10kg_/_.16sec
http://hobbycity.com/hobbyking/store..._bearing_servo

at 6.9 kg of torque (that well over 225oz) your control surfaces will stay where you want them too. this makes a huge difference when knife edgeing, 3d in general or just doing simple things like quick rolls.

best thing is they are cheaper than the others yet are just as reliable (ive fried quite a few 40oz servos from tower by just wearing them out....havnt fried one of these yet and i have well over of these 20 servos in active flying models)
they center jsut as well if not better than the 10 dollar tower servos.

dont think high torque servos make a difference? try for yourself and see. its very noticible and wont break the bank

RE: Servo size questions?
 

Eh, your conversions are wrong.

You are converting WEIGHT, while servos are measured in TORQUE.

6.9kg/cm of torque is about 94oz/in of torque.... not quite the same!

I just about jumped out of my chair, remembering that I had to buy 19kg/cm+ servos for one of my Composite-Arf planes to hit the recommended torques which were in the 230oz/in range....

-

I wouldn't say that high torque servos are "underrated"....

There is not that much difference using low or high torque servos under normal circumstances on smaller planes.. The differnce arises when the control surface is large enough to overcome the holding power of the lower torque servos at speed. Then added torque is not only a good thing but very noticible.

This tends to occur with planes that have larger, non-strip type ailerons and large elevators ( rudders are another matter though... ).

If your flying something like an Escapade, the thin strip surfaces have little chance of blow back, and you are just wasting money using high torque servos on that plane.

There is no problem using standard servos on most .30-.50 size planes ( except extreme speedsters ), 50-80oz/in on .60-1.00 size planes, 90-130oz/in on 1.20-1.60+ size planes ( heck I fly 50cc'ers with some of these... ), 140-180oz/in in 1.60-36cc, 180-240oz/in in 40-60cc gassers, etc.... but that's a very rough rule.

Someone here posted a better measure, equating control surface size in sq/in to oz/in required.... I believe the thread is around somewhere and includes a downloadable Excel worksheet. It is worth a look!

Unless you are pushing a plane to extremes the manufacturer's recommended torque amounts should be fine.

RE: Servo size questions?
 

Most decent manuals will state 'high torque,' or have a minimum recommendation, if anything other than ordinary standard servos are needed.