establishing proper linkage ratios and servo requirements

[Oilsands]

So I did have it backwards. So long control horn and short servo arms. Thanks

[Oilsands]

So would this be the same for a 3D setup?

[Mithrandir]

OK.... if I may.... this is how I setup a large gas or electric plane with an emphasis on 3D.....

(Hopefully Don doesn't get P!$$3D Off!!! lol)

I program a model and call it "TEMPLATE".....

I max out all ATV's to 140% (155% total servo throw.. FUTABA users know what I mean).... I leave the throttle at +/- 100% though.

I setup D/R so that the Elev, Rudder and Ailerons are all switched in and out of D/R with one switch. I arrange the control horns and servo arms lengths so that I get "stop-to-stop" travel on each flipper... 45 degrees'ish. SOmetimes on ailerons, I am happy with +/-35 degrees.. (As fast ailerons get me in trouble )

I setup the Expo to about 55 to 65% on all three primary flippers... in the high rate mode.....
I match the expo in low rate to coincide with the high rate expo around neutral... what I mean is that with sticks within say 15%'ish of neutral or center, the hi-rate and lo-rate expo curves are nearly identical. As a result, the plane feels the same around mid-stick in both hi & lo rates.
Initially, I set Lo-Rate to 50% on the elev and ails and 65% on the rudder...

I usually set up the throttle curve so that the bottom 50%'ish of the stick travel maps out to something like 30% percent of the carb travel.. (gas only as the gas motors seem to have more sensitive response on the bottom end)....

I initially setup about 3 to 5% UP elevator with L&R rudder... and 3% percent opposite aileron to rudder in the pre-mixes... (with well designed modern planes... this is very close.. and even if it isn't.. it poses not flight risk)... I have only found the opposite aileron mix to not be the case with Midwing Extras.. (260) and Katanas....

I setup low rates in the air so that I can do a slow rolling circle at 50% power and have enuff rudder to not loose altitude thru the KE parts of the roller.... I setup lo-rate elevator to be enuff to clearly initiate a snap roll without bury'ing the plane too deep.....

This template can then be copied and renamed for all future planes.... and has been a fairly good starting point for me....

I also setup the timer to be switched on and off by the throttle stick.... (Electrics) If the throttle is above 10%, the timer counts down..... below 10%... the timer stops.

Hopefully the above stuff makes sense and isn't too frought with errors!!! lol

[Bad Dog!]

Very helpful stuff. I am Subscribed

[don szczur]

Mithrand, what you show looks very reasonable. I've been giving this thought and the more I think about it the more I like it. Not from the available torque issue, but from the vantage point of decreased sensitivity around neutral. If I'm understanding this correctly its like stepping up your effective trim resolution from 1 percent to maybe 3/4 percent, making it better to trim out, and center around neutral when coming out of a roll. The main caviat is that each servo (left, right surface) be close to each other in ATV (mechanical setups have a way of getting out when the servos are at extreme movements). I think the tradeoff with less speed is reasonable, and loss of control surface speed the lesser of the tradeoff issues.

Don

[gachezem]

sub

[Mithrandir]

Well Don... I set up like this because I prefer to not use as many servos on each flipper as a lot of people use.. so I attempt to get as much out of the geometry as I can.... Very true to get the physical geometry as identical as possible!!!! I should'a mentioned I Sub-Trim the servo arms to be identical (or mirrors) left and right before I hook up pushrods or anything... I try to setup as close as possible each servo arm to be parallel to the hingeline, and the hole for the ball link (in the control horn) on a perpendicular to the hinge line/cord plane. (90-90-90-90) not always possible...but left-right symetry is a must!
It has been my experiance that as the CG approaches a more neutral flying plane, there is less need for aileron differential... so I don't "Geometrically" start off with aileron diff in the setup... (Like we did in the old days before all the Wizz-Bang 'puter radios!! lol)

I should also mention, when possible, I try to use longer arms and horns, preserving the needed ratio, thus making any linkage slop a smaller angular percentage of the total throw... (Hope that made sense???)
thanks

mds

[don szczur]

An interestng item I found relates to servo voltage. I was checking voltage at the ignition side of my YS 170 CDI engine, under load. Recall (or for your info if you are not familar with this engine) the ignition module is nearly identical to that of a gas engine, and the engine fires low oil content glow fuel at high efficiency and improved performance. Any case, I run the flight battery through a switch, through the Rx, and an extension from an unused port of the Rx through another (kill) switch) then to the ignition. This saves several ounces of weight (no ignition battery required, and I've had no interference using the Spektrum 2.4Ghz DSM in this setup). Now, there are four connectors and two switches til it gets to the module. At low current, no issue, but under 1.3 amp load (my normal flight pack check) voltage is about 4 tenths of a volt lower than if measured directly at the battery. So, for servo performance, especially when using minimal servos, extensions, connectors- overall power delivery may have some level of impact on control surface strength.

[Mr. Nobody]

Looks like a dead thread, but here is a well-written article I found elsewhere by Peter Goldsmith. I also attached the instruction manual from one of our kits. Go to page 30 and see the discussion with diagrams about control linkage ratios.

[don szczur]

Tim these threads live on like a book. Folks visit in the future, new to IMAC or 3D. Great references and thanks much.

Don

[The Gardener]

Hi!
Just a thought.
I'm building my first GS airplane utilizing Hitec 7955, I set my JR DSX9 End points to 140% (I leaved 10% for further adjustments like ail diff, etc.) So I'm getting bigger throw, slower speed, but more resolution than 100% travel. Next, I take programmer, set servo travel as it would be when transmitter says them to be at 100% (but really it is in 140%), so I get same speed and travel like if I was at 100% EPA, but bigger resolution than @ 100%. Am I right?
Next what I do is establishing linkage length, I do it with 90 degree angle, so I make 90degrees between turnbuckle and servo arm- this gives me equal travel and travel speed in each direction. Since I will mainly fly F3M, my plane has to be set up for both- Great 3D performance, and good precision performance, so My linkage ratio is 1:1 (distance from ball link center to servo center: Distance from ball link center to hinge center)
So am I on correct path with this one?
Thanks, Andrew

[don szczur]

The servo speed is normally fixed at x degrees per second, so if you have more travel (degrees) the time will increase regardless of servo programmer unless you increase the voltage (correct me if I'm off on the Hitec programmer). Some run higher voltage to the servos, although most servos are rated at 6V. The JR 8711HV is desiged to operate in a higher voltage environment, however. The reference from Mr. Nobody containing Peter Goldsmith's article, suggests 1 inch arms which gives enough for acceptable 3D and precision as well.

[Mithrandir]

The only issue (IMHO) about Peter's article is the arm length for 3D. I think this article is prolly pushing 8 years old, but (IMHO) it takes 45 degrees of elevator and 40+'ish on the rudder to really get the best low speed-post stalled control.
(I don't compete, I am no legend of IMAC/Freestyle... just a dork weekend 3D Pilot lol)

I suspect Peter's remarks were made in the context of what 3D/Freestyle was 8 or so years ago.... (I may be incorrect on this... but I seem to recall reading it a while back)... though he does indicate the deflections he uses are a "Good Compromise".... maybe he still feels the same???

It would be interesting to see what Peter's feelings about this are today???

[The Gardener]

Don, my idea was about increasing resolution in stick movements (140% EPA) but decrease servo travel to 100% @ 140% input, so speed and deflection stays the same, but resolution raises, or not? 1" arms would be ok if you have the same length surface horn. That's why I said 1:1 (in my case it will be 1.25:1.25")

[Flatlandman]

If your going to setup the mechanical and then program the hitecs you should before turning any electric on set up the servo arm; push rod length; and control horn. Set the servo arm to between 60°-50° left and right so that the surface moves for example ele 45° up and down, that ratio will be a little better than 1:1 then turn on the servo programmer and program the servo. if you havent go the mech setup done right programming the servo gives no advantage over just putting in the programming on the radio.