Hey Dick, Mark,

We are talking about two different issues. There is the resolution issue, and then there is the torque issue. Let's look at each one:

1) Torque. You are correct. If you halve the motion with a linkage, you are doubling the torque. Of course, no machine is 100% efficient, so you actually lose a little torque in the conversion. BUT, torque is not an issue with the servos we have today. If you need more torque, get a stronger servo. If you want to use a weak servo, then you MUST use a linkage to increase the torque. My view (as a trained engineer) is why add an unecessary linkage just to increase mechanical advantage when your servo gears already do that for you? All you have do is choose the right one for the job! As for working the servos harder...I have servos with over 1,000 flights on them. They can't be too overworked with that longevity.

2) Resolution. As I stated earlier in posts, you are correct in saying that reducing the throw will reduce the servo "gear" slop seen at the control. Servo slop is only a fraction of the total play in a set-up, though. The rubber grommets alone that you are using to mount your servos are giving you more deflection than normal gear slop. Then you still have to add servo arm twist and bend, connection play, rod deformation, and hinge play from your linkage loads. Your linkage can only increase all these other factors. Direct drive eliminates them! Flutter suppression is greatly increased when you have nothing to deflect. And, with two servos on a control surface, you can completely eliminate gear slop too. Adding a linkage to slightly reduce gear slop, at the expense of adding at least triple the other slop, just does not make sense to me. Does it to anyone?

The only linkage we have that is even close to linear is a well engineered pull-pull system - because it is the "pulley" you mentioned. It has limits in control travel, though, is VERY hard on the servo bearings, and is rarely installed properly without binding. Then you have cable stretch to deal with. ALL rod style linkages are not even close to a pulley, and very far from linear. They are only linear if you look at them over a very short range of motion. To add insult to injury, they have a different divergence curve for each direction of travel - not good for an aileron or rudder. It is not possible to have more linearity than a direct drive.

There is really little need to build a servo with reduced throw. If you need less, then just software it where you need it. Personally, I haven't built a plane in 5 years that uses less than 50 degrees of control throw. That's the whole beautyof this system...60 degrees of throw with pattern precision.

But, hey guys, flying one of my planes speaks for itself. If you ever make it to Fort Worth, give me a call and we'll go flying!

John