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Please explain exponential

Old 04-24-2015, 01:23 PM
  #26  
mackeyjones
 
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Originally Posted by drac1
Expo is not used instead of dual rates, they are 2 completely different things. I use triple rates for precision aerobatics and set different expo for each rate. Each needs to be fine tuned to accomplish what you need to do.
Which is why I did make an exception for 3D, but perhaps should have included precision aerobatics as well. It could be a long argument over it. I use expo, and dont feel the need to use dual rates, you may use it differently depending on your flying style and what plane you are flying at the time.
Old 04-24-2015, 02:51 PM
  #27  
JollyPopper
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Gene, you think you're confused? You should be inside my head after that garbage I just wrote.
Old 04-24-2015, 08:07 PM
  #28  
OliverJacob
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Originally Posted by mackeyjones
Which is why I did make an exception for 3D, but perhaps should have included precision aerobatics as well. It could be a long argument over it. I use expo, and dont feel the need to use dual rates, you may use it differently depending on your flying style and what plane you are flying at the time.
+1 expo works great for most rc pilots and most planes without the need to flip a dual or triple rate switch while flying.
3D or precision aerobatic pilots still want to use D/R, but for the casual sport flyer, expo works well.

I use D/R only on helicopters, where I use a flight mode switch. This allows me to change rates, engine rpm and gyro settings all at once.
Old 04-25-2015, 01:25 AM
  #29  
teebox11
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Wow! Now that everyone's brain is scrambled who is not a book bred math genius, me thinks Tony has the right idea. Now I say this because it's the way most things are done with our planes and things. Engines, retracts, radio gear, bombs, parachutes, smoke, ejection seats…………wait…….that's only for my car when my gf is with me! Put it there and try it. You can also shorten your sticks btw, that helps a lot. But, each to his own, and may the rc gods have mercy on your soul!! Don't worry, you will do just fine. just say'n…………..
Old 04-25-2015, 04:19 AM
  #30  
BobbyMcGee
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Originally Posted by Bob Pastorello
Add to this that if you are using approx. 1" standard arms, with maximum deflection of 60* either side of center, the "early" movement off neutral at the servo with ZERO expo is significantly over-sensitive. Please measure one...you'll see immediately what I'm explaining. As the servo arm moves, it becomes less linear because of the arc of movement. On JR, Hitec, Airtronics, Futaba, ANY flavor of radio, this is absolutely true. For Hitec, getting to 28% expo makes the movement of the control surface actually "linear", that is, the percentage of control movement will match the amount of stick movement, proportionally.
This isn't a magic function...it is simple rotational geometry of radial movement against a linear goal.
It is absolutely accurate, also....SOME amount of expo to "de sensitize" neutral WILL be required simply to get the linkage system to be truly linear and proportional.
Doubters, fire away, but please do so AFTER you've actually measured amounts of travel at the servo arm takeoff point both WITH expo and without.
Folks who already know this to be true - please help clarify my explanation, as it's a little bit about explaining Ackerman...
Your explanation is clear and to the point.

If you wanted to dumb it down for anyone who can't understand that, you would have to write it with crayons.
Old 04-25-2015, 04:58 AM
  #31  
Cobra1
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Originally Posted by BobbyMcGee
Your explanation is clear and to the point.

If you wanted to dumb it down for anyone who can't understand that, you would have to write it with crayons.
I agree. Expo makes the non linier circle geometry of a servo feel linier at the stick. Once you use it you will never be without it
Old 04-25-2015, 10:17 AM
  #32  
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If you have a simulator, try playing with the expo value's there. I learn all my new radio's on the sim. That way, when I am at the flying field, I get to fly! I use both dual rate and expo on my radio setup ( if you have a 3 position select switch).
Old 04-25-2015, 11:34 AM
  #33  
A. J. Clark
 
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Another way to think of expo is view it as if you were walking up a ramp to a fixed point. With no expo the ramp would be at a 45 degree angle from beginning to end.
If you add expo to soften the control around center the rate of change of the ramp would be less than 45 degrees at the beginning and become greater than 45 degrees at the end.
If you add expo to make the control more sensitive around center the rate of change of the ramp would be more than 45 degrees at the beginning and become less than 45 degrees at the end.
Old 04-25-2015, 01:10 PM
  #34  
ahicks
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Maybe this will help-
I generally start off with plans/direction suggested throws for for my dual rates. If suggested expo is also given, I use those suggestions as well. As the plane is sorted out, the throws are optimized as I switch back and forth between the high and low rates. Generally taking off and landing accomplished on low rate, and flying is on high (if I feel like it). Once I have the throws so the plane is behaving as expected, then I start playing with the expo, paying special attention to those while on high rates. If the plane seems touchy in pitch, I add expo (reduce sensitivity) to the elevators - and keep adding until it feels comfortable. I do the same for aileron and rudder, getting them equally comfortable as well.

So, regarding dual rates, eventually, I will find myself taking off and landing on high rates - as they feel no different than the low rates around center. Doesn't sound like I'm doing anything unusual, until you see the plane is set up as a full on 3D, and full stick on high rates will have most controls surface throws at 45 degrees either side of center. Without exponential (or some fancy mechanical differential) there is no way on earth this old man might be able to fly a plane like that. With expo, it fits like an old shoe..... tailored/custom fit to my flying style.

I would also note that I'm often using 80-90% expo. on high rates. It's available, it's not a sin to use it, and I believe it helps make the plane easier to fly. It does this without affecting what's happening at extreme throws/stick movement, or by limiting the plane's capabilities. The only guys talking expo down are those that haven't figured it out yet.

Last, I'd also note I'm using as much expo on a 32" electric foamy as I am a gasser. Properly understood and set up, there's really no difference between them when it comes to expo.
Old 04-25-2015, 02:43 PM
  #35  
Bozarth
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Originally Posted by Bob Pastorello
...getting to 28% expo makes the movement of the control surface actually "linear", that is, the percentage of control movement will match the amount of stick movement, proportionally.
This isn't a magic function...it is simple rotational geometry of radial movement against a linear goal.
...
I disagree. Given a somewhat symmetrical geometry, there is no need for expo...the system is proportional...20% movement of the stick moves the servo 20%, which moves the control surface 20%. 80% movement of the stick moves the servo 80% which moves the control surface 80%. The motion is rotary-translational-rotary, resulting in a linear and proportional output. The SIN function is working on both sides of the pushrod.

Kurt
Old 04-26-2015, 12:19 AM
  #36  
drac1
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Originally Posted by ahicks
Maybe this will help-
I generally start off with plans/direction suggested throws for for my dual rates. If suggested expo is also given, I use those suggestions as well. As the plane is sorted out, the throws are optimized as I switch back and forth between the high and low rates. Generally taking off and landing accomplished on low rate, and flying is on high (if I feel like it). Once I have the throws so the plane is behaving as expected, then I start playing with the expo, paying special attention to those while on high rates. If the plane seems touchy in pitch, I add expo (reduce sensitivity) to the elevators - and keep adding until it feels comfortable. I do the same for aileron and rudder, getting them equally comfortable as well.

So, regarding dual rates, eventually, I will find myself taking off and landing on high rates - as they feel no different than the low rates around center. Doesn't sound like I'm doing anything unusual, until you see the plane is set up as a full on 3D, and full stick on high rates will have most controls surface throws at 45 degrees either side of center. Without exponential (or some fancy mechanical differential) there is no way on earth this old man might be able to fly a plane like that. With expo, it fits like an old shoe..... tailored/custom fit to my flying style.

I would also note that I'm often using 80-90% expo. on high rates. It's available, it's not a sin to use it, and I believe it helps make the plane easier to fly. It does this without affecting what's happening at extreme throws/stick movement, or by limiting the plane's capabilities. The only guys talking expo down are those that haven't figured it out yet.

Last, I'd also note I'm using as much expo on a 32" electric foamy as I am a gasser. Properly understood and set up, there's really no difference between them when it comes to expo.
I'm using 80% on rudder in my pattern ships.
Old 04-26-2015, 12:30 AM
  #37  
drac1
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Originally Posted by Bozarth
I disagree. Given a somewhat symmetrical geometry, there is no need for expo...the system is proportional...20% movement of the stick moves the servo 20%, which moves the control surface 20%. 80% movement of the stick moves the servo 80% which moves the control surface 80%. The motion is rotary-translational-rotary, resulting in a linear and proportional output. The SIN function is working on both sides of the pushrod.

Kurt
No need for expo? Interesting.

Expo isn't used to make the control surface directly proportional to stick movement. It's just the opposite. Expo is used to move the control surface less than stick movement around center to make it less sensitive, which makes flying smoother.
I have my elevator throws set for 20% of full throw when flying pattern and I still use 40% expo. The other surfaces also have similar set ups in relation to full throw. Full throws are used for landing and take off and have higher expo percentages.
Old 04-26-2015, 05:24 AM
  #38  
Rob2160
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Originally Posted by Bozarth
I disagree. Given a somewhat symmetrical geometry, there is no need for expo...the system is proportional...20% movement of the stick moves the servo 20%, which moves the control surface 20%. 80% movement of the stick moves the servo 80% which moves the control surface 80%. The motion is rotary-translational-rotary, resulting in a linear and proportional output. The SIN function is working on both sides of the pushrod.

Kurt
With a similar geometry what you say is true. But how many planes have control surfaces that deflect 45 degrees up and down?

With a control surface that only moves 20 degrees (10 up and 10 down) for 90 degrees of servo movement you will have non linearity.

The amount of expo you need to actually get linear movement on your control surface depends on the mechanical set up between servo and control surface. .

A good article here

https://www.physicsforums.com/thread...l-rate.524002/
Old 04-26-2015, 07:49 AM
  #39  
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Expo is not this complicated....if you find that the airplane is too sensitive then soften the center. No matter what rate you're using.
In other words if your aircraft is flying along and you find yourself "chasing a control surface, it was ailerons for me, add expo. A formula there is not. Start with 30 expo and fly if you like it leave it. It will be better, if you think it can be even better add another 10 expo.
Here's where the arguments begin. I don't believe in expo for learning to fly. If you don't have shaky hands learn to fly with your fingers first.
Old 04-26-2015, 09:31 AM
  #40  
Bozarth
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Originally Posted by drac1
No need for expo? Interesting.

Expo isn't used to make the control surface directly proportional to stick movement. It's just the opposite. Expo is used to move the control surface less than stick movement around center to make it less sensitive, which makes flying smoother.
I have my elevator throws set for 20% of full throw when flying pattern and I still use 40% expo. The other surfaces also have similar set ups in relation to full throw. Full throws are used for landing and take off and have higher expo percentages.
You misunderstood what I wrote...I was responding to an earlier post where someone stated that one needs to add a certain amount of expo to try to bring the control surface response to something near linear. His logic was based on the sin function motion of the servo in the x-axis. I was pointing out that this opposite relationship occurs at the control surface also, thus no need for expo to make the response linear...it already is!

Kurt
Old 04-26-2015, 01:49 PM
  #41  
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Originally Posted by flycatch
Exponential replaced dual rates and makes flying a lot easier. The only place I would not recommend it is flying helicopters.
Why not on helis?
Old 04-26-2015, 02:55 PM
  #42  
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Kurt my response was in no way aimed at anyone. I just find it hard to believe that we muddle the waters with over complicated answers.
After reading some of this I wouldn't touch expo.
Old 04-27-2015, 01:46 AM
  #43  
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When the OP asked "is there a formulae for calculating Expo" I just asssumed he was asking if there was a formula the transmitter uses for expo, which it obviously does, part of its programming. If the OP was asking if there is a formulae to work how much to set expo too...its up to your personal preference. The way I set mine I dont need dual rates, even though I have maximum throws on my Pitts (45 Deg deflection), if I need to make small adjustments to a control surface in flight I can do it comfortably using what I have set for expo, and still have huge deflections in manoeuvers. I fly a wide variety of planes with different amounts, and to me I just adjust the settings until it feels natural for the plane I am flying. I also use a different expo setting for up and down elevator.
Old 04-27-2015, 03:25 AM
  #44  
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Originally Posted by jetmech05
Expo is not this complicated....if you find that the airplane is too sensitive then soften the center. No matter what rate you're using.
In other words if your aircraft is flying along and you find yourself "chasing a control surface, it was ailerons for me, add expo. A formula there is not. Start with 30 expo and fly if you like it leave it. It will be better, if you think it can be even better add another 10 expo.
Here's where the arguments begin. I don't believe in expo for learning to fly. If you don't have shaky hands learn to fly with your fingers first.
Exactly, try then fly, the only real formula if you wish to call it that is what you yourself dial in that makes it comfortable for your thumbs and a particular airframe. It's that simple, for the most part the rest of this is just allot of BS you don't need to think about. Just try it, fly it and then you will know.

Bob
Old 04-27-2015, 04:08 AM
  #45  
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As I assume the OP's question to be, yes, and its coded in the transmitter, and it may or may not be consistent from brand to brand or even different transmitters within a brand. Thats why you're getting the answers you are, tinker and try.
Old 04-27-2015, 06:23 AM
  #46  
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IMHO it's more a matter of personal preference than anything a model requires. I have none at all on some of mine.

You won't know how much you need until you fly the model. And you may even change your mind several times as you get used to that particular model and how it is balanced and the throws are set. Guys flew VERY well for many years before it was even an adjustable feature.

What I found was that anything over 40% - even on hot 3D models - just makes it a jerky on-off-on sensation to the stick and becomes counterproductive. Instead of finesse you have to bang the sticks around. I don't believe now I have anything over 35% (that is on my little 15" EDF Sabre that is tres squirrely to elevator) and normally I use 25% to 15%. Just enough to lessen the center for landing or smooth, straight flight. I normally fly high rates throughout the flight.

Had a bad one when switching between transmitters and thought I was switching to low rates for a fast pass and instead hit CROW at speed with my Hot Stik. Did an instant 90° down and I pulled out just in time to shear off the landing gear (which tore off the horizontal stab) and rip up the teeth of all four aileron servos. Thought I had saved it until I walked over and saw it was a fatal pancake. Learned a lesson on being consistent with how I assign switches on my various transmitters.
Old 04-27-2015, 10:14 AM
  #47  
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Originally Posted by jetmech05
Kurt my response was in no way aimed at anyone. I just find it hard to believe that we muddle the waters with over complicated answers.
After reading some of this I wouldn't touch expo.
Jetmech05...totally agree with you! But I love the math.

Kurt
Old 04-27-2015, 02:29 PM
  #48  
drac1
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Originally Posted by Charlie P.
IMHO it's more a matter of personal preference than anything a model requires. I have none at all on some of mine.

You won't know how much you need until you fly the model. And you may even change your mind several times as you get used to that particular model and how it is balanced and the throws are set. Guys flew VERY well for many years before it was even an adjustable feature.

What I found was that anything over 40% - even on hot 3D models - just makes it a jerky on-off-on sensation to the stick and becomes counterproductive. Instead of finesse you have to bang the sticks around. I don't believe now I have anything over 35% (that is on my little 15" EDF Sabre that is tres squirrely to elevator) and normally I use 25% to 15%. Just enough to lessen the center for landing or smooth, straight flight. I normally fly high rates throughout the flight.

Had a bad one when switching between transmitters and thought I was switching to low rates for a fast pass and instead hit CROW at speed with my Hot Stik. Did an instant 90° down and I pulled out just in time to shear off the landing gear (which tore off the horizontal stab) and rip up the teeth of all four aileron servos. Thought I had saved it until I walked over and saw it was a fatal pancake. Learned a lesson on being consistent with how I assign switches on my various transmitters.
Expo will make it smoother around the centre. The more expo, the smoother it will be for more stick travel. If it is jerky, then you either need more expo, you need to be smoother with your inputs or most likely a combination of both. With a low percentage of expo, it will be jerky if you are moving the sticks quickly past the point where the expo is set for. If you are banging the sticks around, then your expo/throw settings may need adjusting to suit your flying style.
Old 04-27-2015, 06:04 PM
  #49  
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It does make it smoother in the center. But the flatter the center the more rapidly the surfaces have to move in the outer reaches to get to full deflection. If you have a surface that can move 40° up and down, but the first 50% of stick travel only moved the surface 10°, then the last 50% of stick travel has to pick up the remaining 30°. For me that gives a jerky response for some maueuvers.

As I said - personal preference.

Last edited by Charlie P.; 04-27-2015 at 06:13 PM.
Old 04-27-2015, 06:38 PM
  #50  
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Originally Posted by Charlie P.
It does make it smoother in the center. But the flatter the center the more rapidly the surfaces have to move in the outer reaches to get to full deflection. If you have a surface that can move 40° up and down, but the first 50% of stick travel only moved the surface 10°, then the last 50% of stick travel has to pick up the remaining 30°. For me that gives a jerky response for some maueuvers.

As I said - personal preference.
Yes, everything is personal preference. What works for some, doesn't work for others.

More expo will give a smoother action for longer, but as you say it does have to pick up the rest sometime and with higher expo it does come on pretty quick. But when you get that much deflection, it is most likely going to be a bit jerky anyway especially with quick direction changes.

That's why dual/tripple rates or flight modes are good. Less travel can be set for maneuvers that don't require full deflection and you won't need a high amount of expo, which will stop the jerky movements when going to full travel on the reduced throw rate.

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