Originally Posted by cravenjw

.....Pumping works a servo alot more than most of the control surfaces.....

Originally Posted by BansheeBoy

Recently I had to park a 50cc mxsr in a near by wheat field due to a throttle servo failure. The plane was damaged more then I will repair. I have been using hitec 5645 on all of my gassers with no issues (throttle servos) . The only thing different was the length of the servo arm. 1.5" where typically I use a 1" arm. The gear set stripped in this particular case. Most servo manufactures rate the servos at a given kg/cm or oz/in. Do most people actually calculate the required torque for a particular length of arm? I have to purchase new servos for a Pilot Yak 50 that requires a min of 180oz/in. In different post I have read, this plane requires 2" servo arms for max surface deflection. I just want to make sure I am ordering enough servo to achieve the required torque. Also, I need to settle my mind on other planes. Is this me over thinking again or a Real concern.

Originally Posted by cravenjw

We had a 30cc pilot yak55 go in bad last weekend. It was ugly. Not a fixer upper either.

I would like to point out the following (and sorry for those who don't like psychics);
Servo torque does not change with arm length.
Force applied by the arm to the surface or to a throttle linkage varies with length.

Torque = force x distance, where distance is measured from the servo shaft to the arm hole you choose to use.

A servo with a 1" arm has same torque as when using a 2" arm, but 1" arm can push (force) twice has hard, while the 2" can travel twice as far.

You choose arms to get the mechanical throw required for the surface, usually to maximize the allowable travel, while staying in the normal rotation range of the servo (which is usually -45 to +45deg).

Personally, i think throttle setup is simplest, when you use an arm with the same length as the arm on the carb. I was all electric, when i went gas, i found the throttle very non linear. A buddy showed me how to setup mechanical expo on the throttle. its simpler with a slightly longer arm.

If your a sport flyer, the servos you listed are fine.

It you are a 3d flyer and are a throttle pumper, consider upping the torque, and using a aluminum cased servo, to keep it cooler. Pumping works a servo alot more than most of the control surfaces.
I have used savox 1251 in most of my planes. no issues. Metal gear, metal case, and light.

Recently, i put a savox 1267 in my 50cc slick. I had is lying around. It moves real fast a 6.6V. Its around 220oz.in at 6.6V. I am a throttle pumper, and when i come down its not hot, but it is lot warmer than any of the surface servos. In terms of torque, seems like overkill, but the temperature suggests that i might have trouble with a lesser servo. The throttle speed is noticeable, and i like it.
thats my 2cents, good luck

Originally Posted by BansheeBoy

Recently I had to park a 50cc mxsr in a near by wheat field due to a throttle servo failure. The plane was damaged more then I will repair. I have been using hitec 5645 on all of my gassers with no issues (throttle servos) . The only thing different was the length of the servo arm. 1.5" where typically I use a 1" arm. The gear set stripped in this particular case. Most servo manufactures rate the servos at a given kg/cm or oz/in. Do most people actually calculate the required torque for a particular length of arm? I have to purchase new servos for a Pilot Yak 50 that requires a min of 180oz/in. In different post I have read, this plane requires 2" servo arms for max surface deflection. I just want to make sure I am ordering enough servo to achieve the required torque. Also, I need to settle my mind on other planes. Is this me over thinking again or a Real concern.