establishing proper linkage ratios and servo requirements

[Bill Clark]

I am interested in understanding 3 particular areas of setup
1- how to determine minimum servo power required for the control surface
realizinging that the actual calculations would be involved a general "rule of thumb" would sufice. This would ultimatley have to integrate into the second and third areas below
2- determine the proper linkage ratio for a particular surface
do we max out the servo travel and set the ratio to move the surface to the furthest point we would ever want to deflect to, which would give us the greatest mechanical advantage (power) but may reduce the speed at which the surface moves to a "slower than desired" speed or do we compramise somewhere in between speed and power.
lets assume also that we want to optimize the system and not neccesarily use the hardware a particular plane manufacturer believes to be best
3-set the maximum rate in the radio
on the rate page of my radio a maximum of 150% is possible. is it best for setting max throw and expo to set the rate at 150% or 100% and then use the end point adjustment to set the max throw assuming we are not maxing everything out mechanically and electronically as stated in #2 above? if there is no standard or common method here it is basically impossible to compare expo values with someone else unless they set theirs up the same

in my line of work having things mechanically correct is something i am very passionate about and now that i am building a "big" plane a desire to integrate that passion into it exists aswell. Thank you

[don szczur]

Thanks for the question Bill.

1. Use the best, strongest servos you can put in the plane. Unless weight is a major issue, start by using the best on the ailerons. I over-power most control surfaces except elevator. Ailerons and Rudder always need more, it seems (I found by using a stronger/more servos there is better response and control). However, if you go with the manufacturers recommendation and then step up from there if roll rate changes during a down line (thottle off) or knife edge loop loosens up (you can sometimes see the rudder push back while its flying). Don't forget throttle. Mechanical setup is paramount for this (I've seen ATVs of 19 percent on low and 35 percent on high) with a terrible throttle curve trying to get a linear response, and engine dead sticking since the idle would not go back to center (and a non-JR run of the mill servo that would not come back to the same spot twice).

2. Linkage ratio should give you the throw you need, nothing more. Some IMAC planes are set up just for sequences, and cannot do 3D. The pilot chooses this for better mechanical leverage and resolution. You loose the flexiblity of doing 3D with that plane setup though. I use the TOC setup triple rates (sequence/snaps, spins, and 3D).

3. Maximum rate should be close to 100% as practical. I found going upward to 150 percent looses resolution around neutral. Elevator is not as critical to bump up to 120 or so, but I can feel ailerons suffer from the perspective of being able to finish rolls and snaps consistently with wings level. Plus, if you are at 150 percent there is not any margin for mixes to effectively move the surface (e.g., rudder to aileron and elevator mix).

[Bill Clark]

thank you very much Don for taking the time to amswer my questions. I am using 1 425oz/in (futaba) on each surface on my 33% plane which i hope will be somewhere around 22 lbs w/ DA 85 (LW setup). no set up info from the manufacturer (xtreme comp 540t) but i will make everything move as far as it can for 3d (primary interest at this time)
so just to be clear, I will define the maximum throw of the surface, set the rate to 100% ,max out the end point value, and then calculate the linkage ratios?

[don szczur]

Or, just use the long, metal (e.g., 1 1/4) servo control arms, short horns on the control surface, and try to stay as close to 100 percent on your ATV (end point) and rate value, as practical.

Use rate switches to set up less than max throw for some maneuvers (rolling harriers are easier at less than max elevator and rudder, for example)

[Bill Clark]

Thanks Don.

[Mithrandir]

	Quote: Originally Posted by don szczur
	Or, just use the long, metal (e.g., 1 1/4) servo control arms, short horns on the control surface, and try to stay as close to 100 percent on your ATV (end point) and rate value, as practical. Use rate switches to set up less than max throw for some maneuvers (rolling harriers are easier at less than max elevator and rudder, for example)

For control surfaces with large deflections... limiting the ATV to 100% is giving up a lot of available servo torque.

in the case of FUTABA with 150% ATV available, this is a loss of 1/3 of the available servo power.....

[mmcconville]

[quote=don szczur;790215]Thanks for the question Bill.


"I found going upward to 150 percent looses resolution around neutral. Elevator is not as critical to bump up to 120 or so, but I can feel ailerons suffer from the perspective of being able to finish rolls and snaps consistently with wings level."

Hi Don,

I'm not following on this. Can you explain?

[STLAV8R]

[quote=mmcconville;793349]

	Quote: Originally Posted by don szczur
	Thanks for the question Bill. I found going upward to 150 percent looses resolution around neutral. Elevator is not as critical to bump up to 120 or so, but I can feel ailerons suffer from the perspective of being able to finish rolls and snaps consistently with wings level. Hi Don, I'm not following on this. Can you explain?

Mike,

So what are the optimal percentages to set the ATV's to on a JR 12X radio for:

1) ailerons =
2) elevators =
3) rudder =
4) throttle =

Thanks in advance for the info.

[JimC-MD]

.

Great questions by the OP. This will be a good read.

[mmcconville]

I dont want to hijack Don's thread.

IMHO, this is what I do and why:
The max resolution is at max ATV (Travel Adjust in JR speak). I always set up at about 135%. The 15% is there for tweaking to get everything dialed properly. i.e matched left to right, servo to servo etc.

However I have a lot of respect for Don so I'm really curious to understand what he said. I'm not trying to correct his comments, just understand. I'm hoping I learn something.

[Bill Clark]

so i dont get confused lets clarify the terminology for Futaba and JR. on my 14MZ ATV (end point) has a max value of 155% for limit and 140% for travel and AFR (D/R) is 150%
JR is............

[don szczur]

I really appreciate the clarifications on the 12X and the 14MZ resolutions and end point specifications. My input is really around generic precision setups, but applies to all (and is amplified when it comes to 3D). I'l start by relating to variances in control surface end points (to adjust for equal deflection). One way to illustrate this is the use of a large difference of end points adustment (or ATV) for equal throw (at about 45 degrees or more). A gentleman asked me to come over and figure out what was wrong with his 33% Extra plane---it felt like it was about to crash when I tried some waterfalls and 3D rolling harriers. When I landed we found that one elevator servo was not keeping up with the other. After about 2 hours of mechanically centering the control surfaces and mechanically adjusting the linkages and control arms to get nearly equal throw (and minimal end point adjustments), it flew like a new plane. Now this was not a normal setup to most reading this - one of his elevator control horns was a spline off, and he used a bunch of sub-trim to get the servo "centered", which then required a large variation in end point adjustment to get both elevator halves at the same deflection. He was like 150 percent on one elevator half and something like 120 percent or less on the other half for up deflection, then vice-versa for the down deflection. The result was one servo trailing the other. So, when I refer to resolution, I'm also including speed differences between the servos in that definition, which at 3D deflection can be a factor in aerodynamic performance. It just takes the servo longer time to travel 150 percent ATV than 100 percent ATV (which lowers the control surface deflection speed). So to clarify, as long as each side is approximately the same (e.g. 135 right, 135 left, or 135 up and 135 down) on both surfaces, you loose some deflection speed, but are fine.

Now, for what's deeper behind my thought processes. I like to keep around 100 percent ATV on each side and mechanically adjust the deflection (same issues with control surface speed variances) on my pattern planes. I try to make this a general rule. An interesting story, I had two FOCUS pattern planes (primary and backup). I could not figure out why one plane snapped differently, but later realized that one plane had the elevator horns adjusted closer to the control surface (and thus less ATV) than the other plane. Both planes had equal elevator deflections, and the same servos, but one plane had effectively faster elevator response time. Same issue on the ailerons with impact on roll exit feel between the two planes. Think of it this way, it takes the servo longer time to travel 150 percent ATV than at 100 percent ATV, so ATV differences effect the way the plane responds. Again, most people reading this may not be striving to have two airplanes set up as matched as possible, but that's why I try to keep everything close to 100 percent ATV (on my pattern planes).

Hope this perspective helps rather than hinders your setup processes.

Don

[yakpilot]

Wow, I was actually able to follow that. You are very good at explaining complicated processes.Thank you helping out on the FG site.

[STLAV8R]

In regard to the life of the servo, isn't it better to have a higher ATV value?
(Over 100%).

[Bill Clark]

	Quote: Originally Posted by STLAV8R
	In regard to the life of the servo, isn't it better to have a higher ATV value? (Over 100%).

do you mean so you'll get more travel for more mechanical advantage?


one of the things i am seeing on another one of my planes (which is a combo plane ie pattern and 3d) is that if i was to set my end point at 100% and my rates at 100% and then adjust the ratio for max throw in high rates my low rate (for precision) setting will be like 10% which throws the servo (and radio?) resolution out the window. the way i have it set now is the end point is maxed out and 3d throws are 100% in rate (and im at 25%in low rates). it would seem the trick would be to max the radio out in both rates and end point so you would have good servo resolution in the low rates (low throw)but control surface speed would suffer which may be ok for my attempts at pattern flying but not 3d. i like everything to move real fast in 3d as does everyone else.
im still trying to get my head around the resolution in the radio at higher rates. obviously you cant have it all if you are trying for a combo setup with throws from one extreme to the other but maybe giving up as much servo speed (more servo travel) as possible is the way?
i definetly se the point about using minimal subtrim too