I have a 120cc PAU Edge 540. In the manual it says, “One or two servos for rudder equaling 400oz.” Does this mean I cant go to 800oz? Do I have to stay at 400oz? I was going to use two 400oz servos. (I know thats a lot of torque, but still....)

You can always go more torque, the 400oz min is established as the minimum needed for that size plane. I have the same plane and use a single JR s-8911 coreless $149.00 rated at 855 oz at 8.4v

You can. But honestly, anything over 500oz in of torque, is not needed.

I KE Loop 35/7% airplanes on Savox 1270, Savox 2270, JR 8711/HV, Futaba 9157. And they will do it all day long.

Its your bird, outfit it the way you want.

+1 to Bunky.

Servo specs have been doing the telephone game for years.

Builder #1 uses 150oz. Builder #2 hears that and says well I better use 200. Builder #3 wants to show up 2 and installs 300. #4 says well if 3 uses 300 and I think I fly harder I will use 400. Then MKS servo reads the forum and decides to make a 600 because obviously guys will buy it. Futaba sees what MKS did and comes out with the 1000oz A700 monster to stay ahead of everybody else.

And so on. Someday the madness has to stop or else you are going to see somebody try and rig up a DeWalt impact driver to a rudder....


The reality is most of us probably dont need anywhere near these crazy numbers. Years ago there was a spreadsheet floating around that would calculate real servo loads if you plug in the surface geometry, throws and airspeed and I remember the numbers it spit out where surprisingly low. I'm still flying an old 18lb PAU Edge and 300oz on the rudder (at only 6 volts!) will KE loop that all day just like Bunkys 35%ers....

Originally Posted by jharkin

+1 to Bunky.

Servo specs have been doing the telephone game for years.

Builder #1 uses 150oz. Builder #2 hears that and says well I better use 200. Builder #3 wants to show up 2 and installs 300. #4 says well if 3 uses 300 and I think I fly harder I will use 400. Then MKS servo reads the forum and decides to make a 600 because obviously guys will buy it. Futaba sees what MKS did and comes out with the 1000oz A700 monster to stay ahead of everybody else.

And so on. Someday the madness has to stop or else you are going to see somebody try and rig up a DeWalt impact driver to a rudder....


The reality is most of us probably dont need anywhere near these crazy numbers. Years ago there was a spreadsheet floating around that would calculate real servo loads if you plug in the surface geometry, throws and airspeed and I remember the numbers it spit out where surprisingly low. I'm still flying an old 18lb PAU Edge and 300oz on the rudder (at only 6 volts!) will KE loop that all day just like Bunkys 35%ers....

Exactly.. we been thru the exact same thing with engine/plane sizes....50cc then 55...then 60 and so on.

Originally Posted by jharkin

Years ago there was a spreadsheet floating around that would calculate real servo loads if you plug in the surface geometry, throws and airspeed and I remember the numbers it spit out where surprisingly low. .

Is this the spreadsheet you're referring too:
http://www.mnbigbirds.com/Servo%20To...0Caculator.htm

Originally Posted by Hinckley Bill

Is this the spreadsheet you're referring too:
http://www.mnbigbirds.com/Servo%20To...0Caculator.htm

Hey! I have that one, it is pretty good. I find it is usually nearly half of what the mfg recommends. And I also find even at the nearly half I still don't use any mah's, a good sign of no loading.
But my situation is more of normal flight, I would imagine 3D would require the higher torque ratings.

You can use more than 400 oz., just don't fly over 400'

Astro

Originally Posted by Xpira

I have a 120cc PAU Edge 540. In the manual it says, “One or two servos for rudder equaling 400oz.” Does this mean I cant go to 800oz? Do I have to stay at 400oz? I was going to use two 400oz servos. (I know thats a lot of torque, but still....)

You can definitely use more then 400oz. Just the question is, do you really need it. Unless you fly hardcore 3D, you really don’t need a ton of torque especially with today’s servos. I’ve seen guys use one Hitec HS-7955 on there 35%er rudder and fly the heck out of it with no issues.