Does the throttle servo/channel move more on the top half than the bottom half? I thought I had made a mistake on my radio but then checked another plane and it seems to be the same....just not as noticable. I want to know what you guys think - trying to figure out if im imagining it.

I dont think I understand your question by 1/2. what kinda of radio?

I think I undertand your question, but it is really vague. But let me see if I can figure this out. The servo rotates at a rate that is determined by the setting in the transmitter. For control surfaces, there is exponential which changes the rate at which the control suface will move with linear movement of the control stick. With the throttle, there is no exponential that I know of, so the movement is linear from start to finish, in that it changes with the same rate as you move the stick.

Now, where you place the linkage will have a big difference in the rate that the throttle linkage and thus the throttle moves. What usually happens is that at the beginning of movement and the end of movement will move less if you set the center of throttle opening to the center point of the servo arm with the TX stick in the center of movement. This is where you should set all your throttle points. That way you will have equal movement on the minus side as the plus side of the center of the servo arm and throttle arm. The total movement is set by what hole you use on both of the arms.. the closest to the center of rotation on the servo will provide the least amount of movement, and the furthest away from the throttle body on the throttle arm will result in the least amount of throttle movement. They are opposite of each other. You want to have the MOST movement of the servo arm with the LEAST movement of the throttle arm, but with enough movement to go from minimum throttle to maximum throttle with complete movement of the servo arm. This is basic geometrics. You want linear movement, with good resolution. This is produce by using as much of the servo movement to accomplish complete movement of the throttle arm.

I hope this helps solve your problem.

DS.

The servo movement is uaually linear. On electric planes, it can seem as if all the throttle movement is on the upper end because of the exponential nature of thrust verses rpm. The rpm control is actually linear but 50% rpm at half throttle makes only 25% of the full throttle thrust.

A servo ROTATES. It does the rotation uniformly. It follows the transmitter stick exactly. Move the stick 10% of it's available arc, and the servo moves 10%.

However, if you change that rotary motion into a push/pull, straight back and forth motion with a pushrod, the pushrod won't move linear. There are pictures of this lots of places.

NOW............. The throttle barrel in our R/C engines' carburetors don't open open "their mouths" linearly. And the engines don't increase their power linearly. So this deal is just a barrel of worms. Not a can of worms but a barrel.

I understand exactly, I have a couple of planes that perform that way. Like above, the servo operates in a linear fashion, but throttle response may not be linear. In other words you may get almost full throttle performance with the stick at only half, and the last half of stcick travel doesn't seem to do much, and you don't have as much fine control at lower throttle settings. You can improve this by messing with both ends of your end point adjustment on the throttle servo. I usually set mine up by starting with 100% throw on the servo, I set the stick at half, so the servo is at half of its total throw, and then connect the linkage so that the carb barrel or butterfly is about 1/4 open. Start it up, and then adjust endpoints to get a fully open throttle and a low enough idle.

Some radios have expo for throttle channel. My 9C Futaba has it, and you can make an exponential curve that will give you linear throttle response. My DX-7 does not have expo, one of the few things I don't like about it.

Here's how the servowheel-to-pushrod connection changes the movements from linear to non-linear.

However, the motor response is to the amount of the throttle barrel opening and closing.

Here's what happens inside the carburetor when the throttle stick is moved about 15degrees from fully closed.

And beside that is the carb opening when the stick is moved from full open by about 15degrees.

The same stick movement gives very different openings because of the geometries of the parts in the carb.

Always setup your throttle servo arm and carb arm to use only about 60-80degrees of arc. And make sure that when your throttle stick is centered, the throttle servo is centered and the carb arm is centered. And you want the pushrod to be 90degrees to both.

If you setup the throttle system that way, you'll minimize the rotary-to-push-pull problem. And in fact, the two characteristics shown above will actually sort of cancel each other out.

The DX7 has an adjustable throttle curve if you use it in heli mode, but it would be nice if it had that feature in airplane mode.

I think that some of the top radios are supposed to do that for airplanes. Precision aerobatics pilots have wanted the feature for years.