Hi all,

I am new to FUTABA and just wondering if anyone can help.
I have a FUTABA 10CAG 2.4 and I am a bit confused with setting the end point adjustment to take advantage of the total resolution of servo.I hope that makes sense.

Anyway I am trying to set the control throw to about 15 mm up and down but when I set this with END POINT ADJUST it reduces to 40 % .Does this mean 40 % of the servo normal travel .... not sure.....

However by reducing the DUAL RATES Percentage to say 40 % I can get the desired throw of 15mm......Is this the correct way of setting it

Thank you in advance

kind regards

Mavros

AUSTRALIA

Hi Marvos,
To maximise the resolution you MUST do it mechanically.
Using either end point or DR at your eg of 40% is just that ; 40% of available (normal) travel.
As you can, with most servos anyway, use up to say 135% 40% is now just equivalent to 30% of actual available travel.
Therefore you only get 30% of available resolution.

So let's say, for the purpose of this conversation, that 15mm is the most you want on a particular surface.
Set end point to 135% (limit at 135% also) and DR at 100%.
Then adjust the links in on the servo horn or ,perhaps preferably, out on the control horn to give the desired 15mm.

Brian

+1 to what serious power said. Move your linkages in at the servo arm and/or out at the control surface to reduce the amount of throw. The end point adjustment should be used for minor adjustments as it will be difficult to get exactly 15mm by adjusting the linkages alone. The larger your endpoint and dual rate settings remain, the smoother and more precise your sticks will be.

Here is my procedure. I set my endpoints to something greater than I will need after setting the subtrims. The sub trims match the servos/linkages at neutral and now you want to match them at the max throw. So I would set something up in the 135 range to give me more than some specific throw I do need, like 25 degrees of control surface up and down for elevators or right and left for ailerons. So use endpoints for matching servo/linkages. Then use AFR/Dual Rates to set the throws you want for each flight condition or mode. Never touch the end points after the servos are matched.

I'm not sure I should start this here, but you cannot change the resolution of the servo itself, unless it is programmable. It's output arm moves so many degrees per microsecond change in the input pulse width. That defines its resolution. Now with the linkage we can get finer resolution in terms of control surface degrees per microsecond change in pulse width by mechanical advantage. If the servo arm is half the length of the control horn on the surface we double the resolution of the servo/linkage system. There is a limit to how far you can go of course because in addition to resolution you need a large throw for spins and snaps etc.

So why is it better to use high values for ATV and AFR/dual rates? Stay tuned.

Jim O

Thank you all for your inputs...please keep them coming I am learning so much from you blokes.

rgds

Mavros

I want to clarify/correct my statement. The change in output for a given change in input does not literally define resolution. Resolution is the ability to distinguish the smallest difference in two values. In the case of our servos, a servo that wouldn't change its output until it saw a 1.0 microsecond change in input pulse width wouldn't have as good resolution as one that would move with a .5 μsec change in input. Yet both could have the same change in output rotation for a large change in input pulse width.

In my discussion in post #4 above I assumed the servo resolution was better than required to detect the smallest change in pulse width coming out of the receiver. So, you can't change the resolution of the servo but you want a servo who's resolution can detect the smallest change in pulse width coming out of the receiver. Programming the servo throw doesn't change the servo resolution either but it does allow you to change output rotation for a given change in input pulse width. So if you were getting the desired throw with end points at 40% you could program the servo to give you the desired throw using end points at 100% and improve the SYSTEM resolution. In other words you would get more steps (finer) with with the 100% setting.

Jim O

On the flip side:
(1) Running low ATV's gives you faster control surface speed ie you get to your 15mm of travel faster (not so important?)
(2) You get better surface deflection vs servo rotation linearity (which would probably get cancelled out with more expo)
(3) Linearity errors resulting from small differences in linkage geometries are minimised.

Using the full range of servo travel ensures you enjoy the full mechanical power and resolution of your hardware no doubt, but giving up a little bit of torque and resolution isn't all negative...

Thanks bjr-93tz,

I have increased the control linkage height and decreased the servo arm ....this enabled me to increase my end point from 40% to 65% .

i have also increased the EXP to 30 % and the transformation is amazing.....a lot smoother.

rgds

Mavros

Like Brian stated, the general idea is to maximize end points and minimize linkage.

Maybe you can't change the resolution of the servo, but you can change the output 'gain' (servo output relative to stick input). If the servo originally moves 100% to get 15mm but then you increase end points and reduce linkage so 120% gives you 15mm, you have lower gain which emulates increased resolution. Maybe this is increasing system resolution, but not necessarily servo resolution.

I guess that was already said too, now that I read through this post again

I think what most people do is maximize the End Point Adjustment, and set the linkage so 100% travel gets you the just enough deflection for a contest flight, and use Dual Rates as necessary for lower rates.