Lancair-RCU wrote:
With the power of todays servos, losses to friction will be minimal. We're losing more power by using larger than normal control horns on our servo's. Im not sure where I read it, but you loose a LOT of potential torque the further from the servo centre you get. I endeavouring to use standard servo horn spacing but will probably need to go a size up.
The friction losses are independent of the servo "power", its a property of the control linkage setup. It's correct that the hight torque of modern digital servos cause friction losses to be of less importance. There are other problems associated with friction in the control system. With high friction systems servo current draw will increase and also it will be more difficult to achieve proper centering of the control surfaces.
You do NOT loose torque or power by using a longer servo arm. The torque of the servo is independent of the length of the servo arm. Torque is force times lever arm. Using a longer servo arm will cause the available force to decrease. This is compensated for by using a longer control horn that will decrease the force necessary to deflect the control surface.
The good thing about long servo arms and control horns is that any slop in the linkage between the servo arm and control horn will be of less consequence. IMHO, in order to achieve a control system that works with as little slop as possible one should use maximum servo throw, the longest servo arm available and then choose a control horn that is short (or rather long enough) to achieve the desired control surface throw.
/Red B.