ORIGINAL: TomCrump
I run 645s in almost every model that I build and fly. All but one, are larger, and use more powerful engines, than this Spacewalker. I have never encountered any difficulties, or reliability problems.
What do you base your torque requirements on ?
Here are pics of the 2 two Spacewalkers that I have built. One is 84". with a 1.60 twin. The other is 104", with a Sachs 4.2. Both have 645s and all flight control surfaces.
Very nice looking birds. I'm glad the 645s are working for you. They would not have been my choice for the 84" or 104". At approx. 100 oz inches of torque they are too light in my opinion. However, we need to remember that opinions are like elbows, everyone has at least two.
To answer your question ....I base my choice of servos on the size of the plane, size of the control surfaces, speed and weight of the plane, engine size, and experience. Itry to use enough torque to overcome "blow back" (or whatever it's officially called). I don't want the force of the airstream overcoming the servo. I chose the Corona 558s for my bird because they yield 130oz inches (at 4.8 volts), are ALLmetal gear, and the price is right.
Merry Christmas,
RJ