ORIGINAL: Sherman
I realize that there are other forums for radios and servos, but think maybe this belongs here as it relates to servos as recommended for ARF’s. I have always used the so-called standard Futaba servos, the S148, S3003 and S3004. I just fly the 40-46 and 60 two cycle powered aircraft, and have never even questioned whether the servos were o.k. Have used them in 60 powered planes such as the Goldberg Tiger, and 46 powered planes such as the GP Revolution and the TH Kaos. I noticed recently that more powerful servos were mentioned in the forum in discussing the Revolution, and then saw an advertisement for the Revolution that I think said a minimum of 54 oz-in was required. Also am interested in the Skylark 70, and a review indicated a minimum of 54 oz-in. Wow! This is why I avoided bigger planes, so I could use the standard servos, and knock on wood, have not had any failures (that I know of) from inadequate servos. Some of my friends assure me that the standard servos are fine (I don’t do any 3D) but am nervous going against either a manufacturer’s or reviewer’s recommendation. Any thoughts or information or ideas greatly appreciated.
Sherman,
As you already have alluded too, the type of flying is important among other things to consider. The manufacturer has a minimum requirement that will all but make sure that no flutter from too weak of a servo, the "normal" weight of the plane when equipped as recommended will not over work the servo and a small host of other things.
What you need to remember is even though you may be sport flying you are still putting an air load on the surface, hence loading the servo. Let's use an example using the rudder as the primary control and usually the rudder needs more servo than all the other surfaces. OK, so you now have rolled into a Knfie Edge, the plane is at full power and you have all the throw in that the surface can give and your control rod/horns geometery is good, but the plane will bring the nose up momentarily then drop the nose a bit, what you are seeing is blowback, caused by either not a powerful enough servo, bad geometery, not enough engine power or a combination of all three.
Basically if you are flying along in a certain maneuver and you notice it just will not hold it for very long, it's possible the servo is blowing back because it's not strong enough taking all the other factors into account. Now most, but not all servos, can handle 6 Volts so that is one way to increase servo power without buying new servos.
the other thing is you always want to buy the best servos your budget can afford that match the requirements that are recommended. You can easily see the difference between a plane that has just the bare minimums to one that has a bit too much servo power. More servo power equals a better handling plane.
For me, I tend to use servos with at least 15% more power then needed, I like a safety margin but then I fly 33% or larger planes. I've seen too many planes get torn apart by flutter because of too weak of a servo or bad geometery or a combination of both
for best mechanical geometery, do not set your end points/ATV on the radio below 100% and it will not hurt to set them to 125%