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Control Throws - what's right? What if it's too little?

Old 12-05-2011, 12:05 AM
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prof_fate
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Default Control Throws - what's right? What if it's too little?

OK, how much control throw do you need? Do I need?

I ask thing for many reasons - got a UM T-28 and bound it to my DX6i. Attempted to fly it...ok, it didn't go well. Took it to an experienced pilot for help and he immediately said I had WAY too much aileron throw - to get it to the 1/8" he recomended I ended up with d/r set at 60%!

I bought a 3 channel foamie and while ti can be flown slowly it cna also scream - I know that at higher speeds you need less control throw...this came with no instructions.

I bought an airfield 800mm T38 and it has nothing on radio set up or control throws - not word 1.

I set up my galaxy F3P and for sport it recomends about 1" rudder and for 3D 4" - yes, 4 times as much throw. But at least it has recomendations.

I let my son fly my champ on the included TX and it has a 'trainer' mode that appears to reduce throws a great deal. It still flies fine- may even be easier to fly smoothly.

Here are my questions:
I know what too much throw can do....what about too little?
How do you determine the right amount on a new plane?
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Old 12-05-2011, 12:25 AM
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quorneng
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prof fate
The simple answer is practical testing to arrive at what you are comfortable with.
The size of the control surfaces relative to the fixed surface will give an idea as to its 'power'.
A plane with relatively big surfaces can get by with a smaller throw unless you want it to do high rate manoeuvres but it will then be rather 'twitchy' to fly.
A plane with small control surfaces will be more docile and can handle larger throws but then it probably isn't the sort of plane you would throw about the sky.
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Old 12-05-2011, 12:42 AM
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JetPlaneFlyer
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Yep, whatever feels right for you. if your Tx has exponential then it's possible to set much higher control thrown and still avoid 'twitchiness' by making the movement gentler around centre.
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Old 12-05-2011, 12:50 AM
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Originally Posted by JetPlaneFlyer View Post
Yep, whatever feels right for you. if your Tx has exponential then it's possible to set much higher control thrown and still avoid 'twitchiness' by making the movement gentler around centre.
Mathematically speaking, what does that mean?

I know with D/R if it's at 100% and the rudder moves 3" and you set it to 50% the rudder should move 1.5 inches.

AFAIK expo won't affect the total throw. So if you set it at 30% or 60% what does that exactly mean? If the rudder can move 2" total and you set expo at 50%, where is the stick when the rudder has moved 1" I guess is the question.

I was told if you set expo too high (say, over 50%) you can get a plane that can't be flown.

HELP! I feel lost at the moment on understanding this.
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Old 12-05-2011, 12:59 AM
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I'm no expert, but I'll weigh in. My understanding of expo is that it reduces the amount of control surface movement to a point. Basically, the response of the servo is not linear. That is, with no expo, moving the stick, say, 60% of full results in a control movement of 60% of the total possible.

With expo, you can move the stick 60%, but the control surface will move less than 60%. Now this is where it gets fuzzy for me: Say you set 40% expo. The control surface will move at a reduced amount until the stick is beyond 40%. Then the control surface will quickly catch up to the stick movement.

Hope someone can explain this better (and help me understand a little better)!
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Old 12-05-2011, 01:08 AM
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JetPlaneFlyer
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yes, exponential is a non-linear response to stick movement. the usual way to have it set is so that the surfaces move gently as the stick is moved off centre then more quickly as the stick approaches full travel. This makes response less 'twitchy'.

100% exponential would be where the control surface response followed a true exponential curve, like the green line on this graph:


50% exponential would be where the curve was half way between linear and exponential.....
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Old 12-05-2011, 01:11 AM
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Originally Posted by quorneng View Post
prof fate
The simple answer is practical testing to arrive at what you are comfortable with.
OK, and with years of experience I might have the ability to guess and get close. What is the right throw for a new plane? Get it wrong and you need to get another plane...in my case anyway (ok, the T28 was repairable..my ego is another matter

So for my next attempt I'll dial it back....is there some rule of thumb one can use (like 100w/lb for a planes performance kind of thing?)

The airfiled trojan for example - i'm not gonna try it till I can fly the UM version well, but when I do go to fly it I've no idea how fast it flys, none at all. I know the micro can putt along or scream and I'm hoping my skills are such for the maiden I can control it, but without knowing the stall speed faster is gonna be 'safer' (to a point of course). So if the aileron on the wee one moves 5mm and the 800mm one is 60% bigger does than mean 8mm is a good movement figure? Do such things scale (at least on the same plane)?

If a champ at 16" ws has a rudder throw in docile mode of 2mm, the fenix at 40" (also a high wing 3 channel) being 2.5 times larger (but much heavier, proportionally in weight) work out to 5mm throw?
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Old 12-05-2011, 01:16 AM
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earthsciteach
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Looking at the control surfaces alone, discounting the programming of the tx, it is a good policy to set the control rods on the outermost hole of the control horn. This will limit the amount of surface travel while allowing the plane to be very flyable.

To minimize throw using the control rod: Control rod on innermost hole of servo arm and outermost hole of control horn.

To maximize throw using the control rod: Control rod on outermost hole of servo arm and innermost hole of control horn.
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Old 12-05-2011, 06:44 AM
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solentlife
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It's one of those "if it looks righ, it probably is right" items.

I find that the brain and eye is often not far wrong in deciding throws.

For a new model - I usually set full throw at just a little more than manual or my eye says ... ie ~+10% .... with D/R set at about 60% so I have both worlds ... crazy and docile.

My thought being that if CoG and other factors are OK .. you should be able to glide on low throttle - so D/R should be enough to do a long glide landing. The little bit extra on full is that you have no idea what will happen at that first take-off / launch and I want a good amount of control to bang nose down or whatever.

Once I have model trimmed and finished that first sortie - I then have good idea of what to reduce or increase to.

That's my way anyway ........... each to their own.
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Old 12-05-2011, 07:59 AM
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FlyingBrick50
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Take a look at your control sticks they normally have a adjustment. This can help alot being that the shorter the stick the quicker the response.
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Old 12-05-2011, 09:31 AM
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solentlife
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Originally Posted by FlyingBrick50 View Post
Take a look at your control sticks they normally have a adjustment. This can help alot being that the shorter the stick the quicker the response.
On that subject - I like LONG sticks and max tension ... as a Mode 2 flyer - that then limits interaction between the two primary controls on right stick ... ie when I want ONLY elevator, there is a tendency to wander a little to side and give a touch of aileron. Stiff and long sticks minimise that.
But on Heli's - I want long and low tension sticks as then you are moving ALL sticks continuously to control the 'beast' !!
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Old 12-05-2011, 11:13 AM
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On a new model of a type I don't know I usually set full deflection to whatever the manufacturer recommends (or about 20 degrees each way if I really can't find any recommendation) and then set up dual rates at about 60% of that in case that proves too twitchy.

So far that's generally been good enough to get a first flight which comes down intact and I can then adjust the control throws based on what happened.

BTW too little throw is not going to be a problem given that in initial test flights you just want to see what it will do and get it round and back down to a landing. Long turns and a gentle flare are NOT serious problems in this context .

Steve
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Old 12-05-2011, 02:46 PM
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Azarr
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Personally I like to think of throws in degrees. Otherwise, the size of the control surfaces affects the throw. 1" of throw on a 1" wide elevator does not have the same effect as 1" of throw on a 4" wide elevator. The generally accepted norm is that 15-20 degrees throw will allow smooth acrobatic flight and 45+ degrees for 3D flight.

Expo is strictly a matter of personal preference. The object as the graphs that JetPlaneFlyer explains is to soften the surface throw around neutral so that it's possible to smoothly fly a plane with extreme throws.

Azarr
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Old 12-05-2011, 07:28 PM
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Having a UM T28 I have to say I'm surprised anyone would find the aileron throw to be overly large (this addressed to your friend who looked at it), the roll rate and control authority is not very high (which is what makes it a good first 4ch plane).

For a new 4ch flyer, reducing the throws is indeed a good thing, even for this mild flyer. A little goes a long way when you are new to it, and at max throws it would seem to be moving about quite a bit with full throws.

Dave
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Old 12-05-2011, 07:38 PM
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prof_fate
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Originally Posted by CNY_Dave View Post
Having a UM T28 I have to say I'm surprised anyone would find the aileron throw to be overly large (this addressed to your friend who looked at it), the roll rate and control authority is not very high (which is what makes it a good first 4ch plane).

Dave
I guess it depends on the radio. I have a DX6i and bound it to that - my ailerons would go a good 1/2 inch up and another 1/2 inch down! Is that a lot?

For comparison on the factory freebie radio on the champ the 'easy' setting has the rudder moving 1/16 inch. My son thought it wasn't moving at all. And that's on the stock holes on the surfaces.

From what I know and have asked folks you need a LOT less aileron throw than you do rudder and a three channel tail dragger often needs a bit more rudder throw to work well.

I'm gonna bind a factor radio to the T28 and see what it shows for throws in regular and 'easy'. I"ll report back what I find (may be a few days though - I've got a ton of work to do this week)

Originally Posted by CNY_Dave View Post
For a new 4ch flyer, reducing the throws is indeed a good thing, even for this mild flyer. A little goes a long way when you are new to it, and at max throws it would seem to be moving about quite a bit with full throws.

Dave
Had I done this at home instead of fly in(many distraction, over confidence, etc) I would likely have done some research or tried a 'stock' radio on it first to see about control movements. See, I know to dial it back for my newbie son, but for me? Heck no, I can be as stupid as the best of them!
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Old 12-05-2011, 08:59 PM
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Who needs lunch?
OK, here's what I got for control travel on teh UM T28, one direction, from neutral

factory 'free' radio
Surface Easy Std DX6i (at 100%)
Rudder 4mm 5mm 7mm
Elevator 3mm 4mm 4mm
Ailerons 3mm 4mm 6mm

Assuming as a newbie I should be on the easy end of things the ailerons were twice the throw, rudder nearly double and elevator a bit more. 1mm on a 14" ws model is considerably more effective than it would be a 40" ws model, and its more effective at higher speeds too - so 1mm on the T28 will do more than 1mm on a champ. And for anyone thinking this is a mildly powered machine,it's thrust exceeds it's weight so it will climb completely vertical.

I've dialed it back now to the 'soft easy' throws and added 40% ish expo while watching the surfaces move. We'll see how that works to tame the aircraft -and my thumbs.


Anyone use expo on throttle? I can't see reducing it's total output.
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Old 12-05-2011, 10:05 PM
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I have never measured mine, have only flown with a DX5e.

Anything over 100% with a DX6 or better on the ailerons (and maybe on the other controls) can result in jamming, the linear servos don't like to see any overtravel.

Dave
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Old 12-06-2011, 05:30 AM
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Originally Posted by CNY_Dave View Post
I have never measured mine, have only flown with a DX5e.

Anything over 100% with a DX6 or better on the ailerons (and maybe on the other controls) can result in jamming, the linear servos don't like to see any overtravel.

Dave
Not true.
There are 2 adjustments on on a DX6i - travel adjustment - up to 125% each direction and yes, these can cause jamming if you go too far.
But under D/R Expo you have D/R - the dual rate - and here you set a percentage from 0-100 that is a percentage of total travel. So you can set these to say, 50%, and then the servo will only move 50% of it's total available range.
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Old 12-06-2011, 07:58 AM
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Originally Posted by prof_fate View Post
Not true.
There are 2 adjustments on on a DX6i - travel adjustment - up to 125% each direction and yes, these can cause jamming if you go too far.
But under D/R Expo you have D/R - the dual rate - and here you set a percentage from 0-100 that is a percentage of total travel. So you can set these to say, 50%, and then the servo will only move 50% of it's total available range.
The time that most radios will jam after altering settings is when mixing ch's and having travel settings too high ...

It's not uncommon on flaperons for example to reduce each command set to 50% so that when they add together as in when aileron + flap command is issued - the surface does not overtravel the 100% total.
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Old 09-10-2013, 05:39 AM
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Default Stock throws for the UM T28?

I am rebuilding a T28 and am trying to replicate the stock throws on my DX6i. The factory radio that comes with the RTF version (as well as the DX6i) only has two postions for each of the control surfaces, so I am puzzled by why three throws are listed for each of the control surfaces, which one is low, which high and where did the third one come from.

I did call HH and ask them what the stock throws were for the T28 since, unlike the P51, they are not listed in the manual. And HH's answer was . . . "Gee, we don't have that information."

Anyone know what they are supposed to be "stock?"

Thanks,
Jack Cutrone

Originally Posted by prof_fate View Post
Who needs lunch?
OK, here's what I got for control travel on teh UM T28, one direction, from neutral

factory 'free' radio
Surface Easy Std DX6i (at 100%)
Rudder 4mm 5mm 7mm
Elevator 3mm 4mm 4mm
Ailerons 3mm 4mm 6mm

Assuming as a newbie I should be on the easy end of things the ailerons were twice the throw, rudder nearly double and elevator a bit more. 1mm on a 14" ws model is considerably more effective than it would be a 40" ws model, and its more effective at higher speeds too - so 1mm on the T28 will do more than 1mm on a champ. And for anyone thinking this is a mildly powered machine,it's thrust exceeds it's weight so it will climb completely vertical.

I've dialed it back now to the 'soft easy' throws and added 40% ish expo while watching the surfaces move. We'll see how that works to tame the aircraft -and my thumbs.


Anyone use expo on throttle? I can't see reducing it's total output.
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Old 09-10-2013, 06:23 AM
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fhhuber
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The servo will want to rotate appx 40 to 50 deg each way from center.

For beginner planes you want about half that throw (20 to 30) for elevator and aileron, 2/3 to 3/4 (30 to 40) that much for rudder.
You can start there for almost any model that you are ready to fly. It should be adequate to do a test flight.
This is the "TLAR" (That Looks About Right) range.

You can get these throws fairly easily too... 1/2 distance from servo output arm screw to pushrod attachment as from hinge line to pushrod attachment will give the appx 50% reduction in throw angle for ailerons and elevator. 3/4 as much from screw to pushrod as hinge to pushrod will similarly give about the right rudder throw.

I try to go with the maximum distance possible from hinge to pushrod at the control surface as this helps prevent pushrod flexing and reduces the effect of any "slop" in the linkages.

With just 2 holes on the servo output arm and at the control horn that gives the potential for 4 different mechanical throw settings
(assuming no computer radio or having "dual rate" and/or "ATV" and endpoints at 100%, which is the default setting)

**********

If you can additionally program in some expo to soften the center, you can use TLAR for even advanced "3D" capable models. Mild expo usually helps beginners with any aircraft (20% to 30%) High expo can really help with the extreme sensitivity of a 3D capable aircraft (50% to 70% at times)
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Old 09-10-2013, 07:39 AM
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Originally Posted by fhhuber View Post

If you can additionally program in some expo to soften the center, you can use TLAR for even advanced "3D" capable models. Mild expo usually helps beginners with any aircraft (20% to 30%) High expo can really help with the extreme sensitivity of a 3D capable aircraft (50% to 70% at times)
My only comment here, is from personal experience. It might not be wise to use exponential on the models maiden flight.

Why? I nearly lost a giant scale model on its maiden flight because of this several years ago. On the maiden flight, I ran out of elevator trim adjustment to keep the model from diving. So, had to hold up elevator to keep it level.

And, with expo set to 30% on the elevator function, that put the transmitter in the quick response of the expo, where just a minor movement of the elevator stick resulted in major movement of the elevator servo.

So, every maiden flight since, no expo on either the aileron or elevator servos!
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Old 09-10-2013, 07:42 AM
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If your expo made the elecator super sensitive near center that sounds more like inverse expo (- instead of + for JR or + instead of - for Futaba)

Differnt radios respond differently to expo and some trim is applied before expo, some after.
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Old 09-10-2013, 05:12 PM
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pizzano
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Using the stock (out of the box) Parkzone T-28 and Spektrum DX6i as examples, for the maiden flight by an intermediate pilot with little low wing flight experience, we set the planes surface control linkage (after intitial centering) as follows:

All control horns set to the most outer hole.

Aileron servo arms set to the most outer hole.

Rudder servo arm set to the middle hole.

Elevator sero arm set to the middle hole.

The Spektrum DX6i was programmed as follows:

D/R & Expo only:
AILE 1 = 50%
ELEV 1 = 44%
RUDD = 70% - 85%
Travel = 100%
No other TX programing was performed, since we had previously experienced CCP heli flight set-ups, there would be no real need for any Expo or Throttle adjustments given the flight characteristics of this craft and the pilots flying ability.

We have since (after 14 flights on the T-28), increased the AILE 1 and ELEV 1 values to be a little more responsive................AILE 1= 60%, ELEV 1= 50%, due to the pilots (me) increase in confidence and control....of course, every pilot has different needs and comfort levels, so the examples above seem to fit this pilots abilities and comfort level.

Last edited by pizzano; 09-10-2013 at 05:40 PM.
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Old 09-12-2013, 09:52 PM
  #25  
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I know my parkzone T28 manual showed rec throws in mm. I don't have it with me but if anyone wants that info let me know
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