Dual Rates and Servo Resolution

[falconpilot]

Hey everyone,

Looking for a little thought on this. I've set my Dalton 260 up for IMAC only. I'm running Hitec 5955's all around. I had it set upfor both 3-D and IMAC with the SWB 1.25" arms, hinge points 1.25" from hinge line. I was getting around 40 degrees up and down on Ailrs, 50 degree's plus on Elevs. Upon flying the airplane I discovered that ALL these throws were WAY to much, even for 3-D. Upon deciding for sure to go only IMAC, I reset everything. Went in on all my arms to.75 inchs, and all control horns(pivot)points out to the max. (2" from hinge line in most cases). Now, this gives me 2:1 + ratio and thus twice the resolution and twice the power. Now with ailrs at 28 degree max(100% dual rates - I have all ATV's at 150%) guess what? The airplanes snap and rolls almost twice as fast as before with 40 degree throws.

My problems is now with my control setup on the tail(control horn conection all the way out - 2" plus from hingeline - and arms at 3/4" inch in, I'm getting 25 degrees throw on the tail, still way more than needed. The airplane does everything at 10 degrees up and 13 degrees of throw down. BUT, the only way to 10/13 is to use the dual rate/flight mode. When doing this, I have to bring my dual rates all the way down to 34%, thus losing all the resolution that I gained with the mechanical setup.

My ideal setup would be 100% dual rate at 10/13 degrees of throw, but this is impossible to setup, or I'm missing it some how. I know that I need around 20-25 degree for spin mode, but if I set it up this way, it results in my low dual rates %'s in normal flight modes.

I only want enough throw to fly the sequences, and to max out the resolutions. Anyone esle that has gone to this extreme(to get the VERY MOST of airplane setup), please let me know how you did so...

Thanks Jim

[Edge 540]

At a 2:1 ratio, you are getting some serious power out of your setup. 865oz/in going from advertised torque! It sound like the only other thing you could do is ho to .5 or even .25" horns at the servos. That would give you...er.....1332oz/in at .5 and 2664 at .25! 1/4" horns sounds ridiculous, but if you truly are all the way down at 35% rates, it might be an option.

Definitely better to have this problem than the opposite.

[Shawn Berkheimer]

99% of the IMAC pilots out there are using at least a 1" to 1.25" servo arm. The longer servo arm gives you control surface speed that helps with snap exits and being able to stop rolls at the right point. Most guys would just turn down the throw in the TX and be done with that. Yes there is a resolution loss but most pilots are not going to feel the difference. That and as servo gears and ball links wear it won't make any difference anyway. But because you are running 5955s you can have your cake and eat it too. Set your servo arms back to 1" and your control horn pivot to 1.25". Set all your ATV settings to 120. Now to get to your IMAC throws reduce the servo throw with the programmer. This will allow you to keep more resolution than if you reduced the rates with your TX. A higher rate for spins is not needed but some do feel it is easier to get a clean stall with more throw. The downside is that the spin will tend to go deeper and the exit suffers. Try to use as little elevator and rudder throw as you can get away with for the spins.



Shawn

[falconpilot]

Shawn,

The programmer!!! I knew that I was over thinking this, and missing the solution. I can reset all my end points toget the max throws that I want with the programmer, and still keep my ATV and Dual rates at 140%/100%. This way I can still retain my resolution and mechincal setup....Thanks Jim

[Michael Glavin]

I'm a little confused, how does a longer control arm make for better resoultion? And I thought shorter arms moved throught the travel arc faster than long ones too...

[Shawn Berkheimer]

	Quote: Originally Posted by Michael Glavin
	I'm a little confused, how does a longer control arm make for better resoultion? And I thought shorter arms moved throught the travel arc faster than long ones too...

A longer control arm means less surface throw which means the ATV can be higher thus better resolution.

Shorter control arms do in fact move through the travel arc faster but we were talking about SERVO arms here. Everything is a compromise. As I had stated running 1" servo arma and 1.25" control horn will give you a good ballance of speed/power and then reducing the rate with the programmer to retain resolution is about as good as it gets for an IMAC setup.


Shawn

[Michael Glavin]

Falcon,

Something is wrong the numbers above, my calculations based on your arm lengths are quite different than those noted. For instance @ 60 degrees servo angle, .75 servo arm and 2" control arm nets 18.9 degrees @ the surface. The linakge ratio is 2.67:1. Longer control arms pushes the number even farther apart 2.25"/.75"= 3:1 with 16.7 degrees throw...

If you drop the servo angle down to 30 degrees with your .75/2.00 setup you'll net 11 degrees throw.

[Michael Glavin]

Shawn,

You noted "The longer servo arm gives you control surface speed" a longer servo arm moves through its travel arc slower right? Matters not if it's a control or servo arm me thinks..

Obviously if you turn up the ATV you'll realize more system resolution as you’re consuming the entire control signal bandwidth. I thought based on Falcons comments the consideration was aimed at the mechanical side of things only...

[airriley]

Not accounting for different loads on the servo doe to servo arm length doesnt the servo arm move through its arc at the same speed regrdless of if it is a 2 inch arm or a .5 inch arm?
Torque of course is different...

[hillmanr2]

The end of a long servo arm has to travel further than the center but keep up with it. It therefore must travel faster. The other reason for increased speed is a longer arm pushes the surface with greater leverage, so smaller servo angles= greater surface movement. If a servo speed is say .20 for 60degrees and with a 1" arm = 25 degrees then using a 2 inch arm the servo does not have to go to 60 degrees. Lets say for arguments sake with a 2" arm it does it in 30degrees. The transit time would be half or .1 sec

[Shawn Berkheimer]

	Quote: Originally Posted by Michael Glavin
	Shawn, You noted "The longer servo arm gives you control surface speed" a longer servo arm moves through its travel arc slower right? Matters not if it's a control or servo arm me thinks..

Nope, think of a spinning wheel. the outside edge of the wheel is moving faster at a given RPM then further inside. Imagine these 2 different setups


servo arm 1/2" control arm 2" Ratio 4:1

Servo arm 1.5" control arm 1.5" Ratio 1:1

Look at the ratios and tell me which one is going to move the surface faster?

Shawn

[falconpilot]

Hey Guys,

My uderstanding about servo arm length and speed is this: The arm is going to move at what ever speed the servos is rated at -say .15 for Htiec at 6.0volts. This is a fixed factor reguardless of the arm length. Now, if connected at 1.5 inchs on the servo arm with a control horn pivot point 1.5 inches from the hinge line, then all other things given, you'll get 60 degree of surface travel at .15 speed. If you move the servo arm in to .75 inches, you'll still get the same speed, .15, at the servo arm, but your control will get to the 30 degrees of throw quicker since there is less distance to travel. This second setup will result is exactly twice the mechincal resolution as well. My understanding is that the servo's resolution is a fixed thing, it moves just so many steps.

I have my mechincal setup the best possible unless I went in to 1/2"arms. The resolution that I was losing was in my radio, since I had the dual rates on my elevs down to 34% in order to get the 10 degree of surface travel that I needed. Thanks to Shawn reminding me, since I'm running Hitec servos, they can be programmed, and the end points set. Again, since the resolution of the servo is set, instead of having my end points(of the servo) at 60 degree's, which resulted in the 34% dual rates for my 10 degree of throw, I was able to go in with the programmer,and set the end points of my servo to get the surface deflection that I want. Doing this, I'm now able to run 100% dual rates, 150% ATV , along with my mechincal setup, and get the very best resolution possible.

No joke guys, with my first setup(1.25" servo arms, and 1.25" control horns from the hingeline, I was getting around 30 degrees of throw on my ailrs, but my dual rates where down low. By resetting my end point of the servo's, moving the servo arm in and control horn out to the max, I now have around 20 degrees of throw with my dual rates a lot closer to 100% and ATV still at 150%. The airplane is much tighter, and rolls just as fast, if not faster with 10 degrees less deflection. It makes a HUGE difference in the way the airplane starts and stops in rolls, and snaps. No more lose feel at all.

One down side of this setupis that it being so tight, you tend to have to run more expo resulting in guess what, lost resolution around the center of the transmitter stick.

The draw back is that I can't fly 3-D with this kind of setup, but that in the long run will probably save me the airplane by not tempting me to do 3-D with it....