quote:

Gosh generally speaking in my opinion, I dont think you can get the servo TOO Close to the control horn as long as you have the structure to support it in the wing, and you have the mechanical room in the linkage. You will just need to make sure that you set the control horn in the right relationship to the servo to get the geometry you are looking for.. I would think that dual axis rod ends would give you a little extra freedom of motion so that the pushrod doesnt bind up at the servo arm or control horn.. On my Genesis,, the servo is so close to the control horn that I had to clip the threaded titanium rod ends for the CF pushrods off because they were too long end to end.

Assuming that the servo arm is pointing to the fuselage, I like to setup my geometry so that at full throw on my highest rate setting, the pushrod is parallel to the long side of the servo and paralled to the control horn, this equals max leverage at full throw.
When it comes back to neutral, the pushrod is angled slightly from the servo arm to the control horn and is no longer parallel to the servo. This should give you increased mechanical advantage as throw is increased and less at center, which is what you want... If you start out at neutral with the pushrod parallel to the servo and at 90degrees to the servo arm,, it looks pretty, but as as throw is increased the pushrod angles in or out and you are losing leverage,,, at least thats the way I understand it.. If Im wrong thats fine but thats the way it was taught to me and looking at it it really seems to make mechanical sense.

quote:

Mike,

Good way to put that mechanical advantage thing.

Let me add a different view for you.

Where do we need the most mechanical advantage on say ailerons....It’s in the pull or push of a loop right. Where are the aileron servos sitting when you pull a tight corner? In a tight corner the servo needs to hold those ailerons as perfectly aligned at zero as possible at the neutral position so that the model loops properly right? If one aileron gives more than the other side then it will cause the loop segment to spiral off to one side. If both ailerons get moved by the forces then it will change the pitch rate of the model. This can look like a segmented loop in the extreme case and in a not so extreme case it can cause you to miss the exit line or the vertical (over or under pull-push). You end up pulling past the point where you need to stop so you adjust your flying through practice to stop a little earlier so that you stop going perfectly level after the vertical downline. Point is the surface will blow back some no matter what servo you have on it, and no matter how good the linkage. This is affected by the servo's dead band and power. Digital servos are much better at this holding power than analog servos of the past. But the better chance you give you ailerons of staying absolutely centered the better your loop segments will be.

If you want to prove this is the worst place for the servos power go put some standard 40oz servos on your ailerons. You won’t be able to pull straight corners consistently. However your roll rate will likely not change too much. This test will show that the servos at their end deflection values are not needing as much power as holding the neutral in the loop element. Now if you roll rate was cut in half going to weak servo then I would say you need to more powerful servo or maximize you linkage for this deflection angle.

The reason the roll rate will not change much going to the wimpy servo is because the aileron is acting with the wing to create lift in different directions for the roll. The load on the aileron itself during a roll is not as much as during a hard pull or push. In a roll you are changing the shape of the airfoil on the wing to create the lift and the wing is doing the work. In a corner (pull or push) you are using the servo to maintain the shape of the airfoil that is already there. So combine this with inertia and gravity and sometimes you can have some pretty high loads on the ailerons trying to move them off of neutral. How often do you fly across the sky holding aileron? If you are like me you level your wings and then you let the model fly with its wings level right? I flew today and I don’t think I ever held Aileron input for a sustained period of time. I held some rudder as we had a pretty good cross wind. But I don’t think I have ever had to hold a sustained aileron input to make the model fly a straight line.

This is where I feel the mechanical advantage is best in a pattern model.

For control throws we are only talking 10-15degs of travel on the ailerons anyway for precision flying. Now I will agree with you that if you are flying 3D and large control deflections are needed then you need the power out where the surface is deflected...but we aren't flying there with our pattern models.

Pattern sequences are flown with rates very low like I said 10-15degs and we are not using this for rolls. This rate with the stick pegged is a super fast roll rate so we are actually using way down in the 5-6degs for normal rolls. So I optimize my linkages to give mechanical advantages at this near neutral position. This is where I fly all the time and this is where I want the model have the most locked in feel. I want to level my wings and let the model track straight. I want to then get to the end of a horizontal line and just pull straight back on the stick and have the model loop to vertical aileron input free.

Again if we stick more servos on the surface then we can get more power out of the servos so less mechanical advantage is not a big deal. But we are not sticking 2-3-4 servos on an aileron like the big 40% models.


Now take my Showtime. I wanted it to be able to hold those large deflections 50degs and so on. So I setup the mechanical advantage to hold these deflections. I also stuck huge power servos on all the surfaces. This way I can do rolling Harriers like the big boys with the aileron stick pegged over at 40+degs and just hanging there on the prop. This is an extreme case. Now the guys that are doing 3D and Precision with their 40% stuff they are sticking 3-4 servos on a aileron to get enough power to overcome this geometry issue. Also the guys doing this on the big models are trying to get a compromise between precision and 3D rates. SO the use of the linkage that you describe is helpful in maintaining the control input and holding it there....but when you go to a precision setup you need more servos and more servo power to keep the surfaces in the right spot near neutral.

Think of this way:
In Pattern flying how often are you holding a sustained control input?

A vertical roll is about it…or maybe the entry into a spin where you are holding up elevator. However in the spin you have very little load on the elevator in this case as you are going slow. If you had too much speed the model would climb…All the other stuff the control input is changing over time and mostly it is at or near neutral position with only very small angles of deflection. So maximize your setup to work where you fly the most.

Just some food for thought. This is the not really the thread for this discussion as its the Insight thread but think about where you do most of your rolls in terms of stick inputs and rates...Then look at your model and see just how much your surfaces are moving you will be very surprised. The end points are not the important values but rather the position you stick them when actually flying a sequence.


I feel you will find a difference in the models performance by maximizing your ATV values and setting up maximum mechanical advantage at the servo neutral not its end points. Again different strokes for different folks.

There is also a discussion we can get into about maximizing speed of the servos output versus the power of the servos output....There are many ways to do it. There is more to a linkage and control setup than the parts wiggle in the right direction let’s go fly it!

Good discussion. I don’t many modelers think about this stuff when setting up their linkages.

Troy Newman

quote:

The part I have trouble with is the idea that max leverage is obtained with aileron servo arm perpendicular at neutral (perpendicular servo arm to pushrod, and straight into aileron control horn). If you set up this way (the usual way most models are set up), then the blowback, it seems to me, would have maximum effect in deflecting the servo arm.

quote:

Next problem I see is guys run their ATV values up really high to 140% to get maximum resolution then run their D/R values back to 30% because they have way to much travel at 140% ATV. The answer I get is well I have max resolution because my ATV is at 140%.


Wrong! You are still giving it away running your D/R down low. A little trick Tony Frakowiack taught me. Go into your servo monitor screen. The Futaba 9C, 9Z both have it. The JR 10X and 9303 both have it. Look at the bars travel as you move your controls. If the bar graph doesn't get up to the 100% mark on the graph then you are not using you radio to it maximum resolution. When I started looking closely at it I was using 60-70%...now even though my D/R value is 80% I'm passing above the 100% servo throw mark on the bar graph. Reason is I'm 80% of 130-140%....

We pay $500-1200 for a radio that has all this performance and resolution why would you give it up by having a poor mechanical setup?

quote:

quote:

ORIGINAL: bwick

Pretty sure there's not a lot you can do about that Mike.

I've got another question: does subtrim affect the movement of the servo at all? Also, how are you dialing down your throws mechanically. Are you just adjusting the arm on the surface so it's higher? Finally, what do you guys use as a throw meter?

Thanks

quote:

Pretty sure there's not a lot you can do about that Mike.