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Old Jul 29, 2012, 03:15 AM
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Originally Posted by Maxthrottle View Post
The very nature of expo means you are removing the resolution that exists in a given system. If a servo has 1200 steps linear, expo immediately is skipping some of those. In some cases you may want the in between but expo engaged has removed. So down in the EDF jet section, pilots new to tailerons find them sensitive, dumb them down and then find it doesn't fly level at certain velocities. The stab is either inducing a pitch up and down tendency because the expo has it sitting either just above or below what is needed for a given speed. You can re trim but then go a little faster or slower and you have to do that all over again.
Doesn't fly level at certain velocities because you used expo or d/r? I don't pretend to be an aerodynamics expert, but I think you should be looking at something other than expo or d/r for that. You have finer control of the servo at the center of stick travel. No expo = coarse control. Expo=fine control. Or do you know that already?

This is a funny thread.
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Old Jul 29, 2012, 03:17 AM
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Originally Posted by Maxthrottle View Post
It doesn't change the resolution of the servo it changes the resolution of the surface movement. .....
So sorry if you didn't understand my meaning.....
I didnt miss-understand anything. Resolution in terms of RC systems has a very specific meaning:
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Resolution is the term used to describe how many steps there are when moving the sticks over their full range. The transmitter measures these steps, and 2048 resolution means that there are 1024 steps in one direction and 1024 steps in the opposite direction (e.g. right/left rudder stick)
Exponential does not reduce the resolution of any part of the RC system.. period

I think you just used the wrong word? Possibly what you mean is the precision of the control surface movement? Again though, expo doesn't reduce precision overall, the same total stick movement gives the same total surface movement as a non-expo system. In fact expo gives greater precision when the stick is near centre (which is where you usually want greatest precision). Admittedly this is at the expense of less precision when the stick is near the end of it's travel.
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Old Jul 29, 2012, 08:04 AM
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Originally Posted by xmech2k View Post
Doesn't fly level at certain velocities because you used expo or d/r? I don't pretend to be an aerodynamics expert, but I think you should be looking at something other than expo or d/r for that. You have finer control of the servo at the center of stick travel. No expo = coarse control. Expo=fine control. Or do you know that already?

This is a funny thread.
you are absolutely correct, for a particular velocity. The 3 flight mode become more necessary to a jet pilot because the jet flies in a wider range of velocities has a different aspect ratio, foil, AC higher wing load etc so the net effect is you have to have either a steady alpha approach or land at high enough velocities to ware landing gear.
To hold the alpha you are in a different pitch setting and usually no longer at the finer movement in expo. Since all moving stabs create high changes in lift for every degree change, while in that alpha approach and you're not at the finest point in the expo curve, your input then tends to induce porpoising.

Thus the point about retrimming but trouble is on approach its hard to hit the same velocity that the entire system is trimmed to, the expo can start working against you. Case in point the first F-22 crash was because of an incorrect expo curve that induced the porpoising and had it belly land because the pilot couldn't keep it level for the approach velocity.

You are correct that one may need to look else where which is why I highlighted the linkage resolution, servo resolution and TX resolution and how the radio maker allows you to define the curve. Thus I use either very little or a lot because you don't want to experience the curve in those in between areas of a flight manuever.
But this is where Hances skill developement comes in. Since you can't always have your expo defined for a wide range of conditions, you just have to learn how to fly the in between without it.

Its also why newer radios have even more definable curve controls and now more flight modes. A newbie usually doesn't have such a radio.

So understanding how you get it all to work together for you, not just expo becomes important.
Spektrum has an interesting quote about radio resolution. Paraphrasing them, they have increased the radio resolution but a system is only as good as its weakest link. Pilots often undo these good features because of their setup or even their basic approach velocity. Thus supporting Hances arguement where features can mask other bad habits that a pilot should learn, but sometimes doesn't realize he even missed learining it.
Balanced, not nose heavy
Approach attitude with pitch, altitude control with throttle not glide in with pitch control till you hit stall
Linkage set to the finest mechanical resolution not etc.
Much of the reasons why pilots seek to manage the above with expo is often because they haven't learned the other causes for needing it.
Once those have been exhausted then expo comes along for the ride to smooth thing out for you.
Too many words.
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Old Jul 29, 2012, 08:17 AM
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Oh and we've been talking about resolution long before radios and servos had the ability to increment them so yes the term resolution, movement per step for X number of steps is seen across the system and is definable in specific areas of the system. Because we recently define it in a TX doesn't mean it still doesn't exist in many other areas.

Thus the point of expo definition vs the servos.
As expo moves along its curve it initially used near maximum step available from the servo but at some point in the curve it has to start skipping steps available in the servo. You may have the same number of steps from the expo perspective but the net effect at the servo and surface doesn't.
It is even worse than most realize.
Most radios have trim step adjustments defaulted to 4 steps in 100 for each click of the trim. You can change it to 1 in 100 on both the TX and on digital servos. No matter how little you move the stick in analogue, you can never move it as little as the trim does. Expo in certain positions of the curve starts moving to 10+ in 100 thus blanking or dead banning what is available to the system in the net effect.

Another way it shows itself was when the A9 was first released. Many complained that the expo curve had a very different feel to it. The radio maker unless you are working with a curve you can define, sets the curve which may not work for each setup. So a again those are increments of control lost or positioned incorrectly because of the defined curve.

In the end it doesn't matter in some cases because we can live with a little play in our steering; if you allow your brain to adapt to it.
Yes interesting thread indeed
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Old Jul 29, 2012, 09:12 AM
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But set the expo way way up and you can make the surfaces move in much smaller increments than you can with no expo. Try it and watch the surfaces move. My thumbs just don't move in really small motions so I am much smoother with expo. I have noticed even with really good rc pilots involved, you can generally watch them fly and tell who is using expo and who is not. Those using expo will be much smoother in any given move and those using less will be more jerky in their moves.
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Old Jul 29, 2012, 11:41 AM
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But set the expo way way up and you can make the surfaces move in much smaller increments than you can with no expo. Try it and watch the surfaces move. My thumbs just don't move in really small motions so I am much smoother with expo. I have noticed even with really good rc pilots involved, you can generally watch them fly and tell who is using expo and who is not. Those using expo will be much smoother in any given move and those using less will be more jerky in their moves.
And you are correct in saying so. I'm all for expo... but from the OPs opening remark it can become a crutch if the pilot doesn't understand when and how to set it and thus can end up masking certain habits.

If they know the difference and use it when needed then as you describe they will fly more smoothly. Thus my earlier on high end electronics on top end cars. As much as Race drivers or GA pilots may complain that the electronics puts them further from actually control of the system, its been demonstrated repeatedly that they perform better with than without. As long as they use it correctly and are not fighting the machine so to speak, they benefit.
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Old Jul 30, 2012, 12:08 PM
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Originally Posted by bobly View Post
But set the expo way way up and you can make the surfaces move in much smaller increments than you can with no expo. Try it and watch the surfaces move. My thumbs just don't move in really small motions so I am much smoother with expo. I have noticed even with really good rc pilots involved, you can generally watch them fly and tell who is using expo and who is not. Those using expo will be much smoother in any given move and those using less will be more jerky in their moves.
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Originally Posted by Maxthrottle View Post
And you are correct in saying so. I'm all for expo... but from the OPs opening remark it can become a crutch if the pilot doesn't understand when and how to set it and thus can end up masking certain habits.

If they know the difference and use it when needed then as you describe they will fly more smoothly. Thus my earlier on high end electronics on top end cars. As much as Race drivers or GA pilots may complain that the electronics puts them further from actually control of the system, its been demonstrated repeatedly that they perform better with than without. As long as they use it correctly and are not fighting the machine so to speak, they benefit.
You and others have brought up some good points. 35+yrs ago when I started, many features did not exist or only on high-end equipment as compared to whats offered today, Soooo, I only have used duel rates. My newest radio has more features stuffed into it than a Christmas Goose, I have alot to learn. That being said, setting-up expo & mixes has the potential of getting a flyer (especially new ones) into alot of trouble. I have searched for basic guidelines to setting-up/introducing feathers in baby steps but, there's not much out there. I think some form of guideline would be very helpful for many. Dialing in too much or wrong combinations could turn ugly.
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Old Jul 30, 2012, 12:27 PM
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I use whatever makes the model get "sweet". Sometimes, I don't use any expo while other times I don't use any dual rate setups. Sometimes, I use both, or neither.

I think it's naive and far from reality to imagine that ALL models require similar setups to fly well throughout their performance envelopes.
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Old Jul 30, 2012, 12:36 PM
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You and others have brought up some good points. 35+yrs ago when I started, many features did not exist or only on high-end equipment as compared to whats offered today, Soooo, I only have used duel rates. My newest radio has more features stuffed into it than a Christmas Goose, I have alot to learn. That being said, setting-up expo & mixes has the potential of getting a flyer (especially new ones) into alot of trouble. I have searched for basic guidelines to setting-up/introducing feathers in baby steps but, there's not much out there. I think some form of guideline would be very helpful for many. Dialing in too much or wrong combinations could turn ugly.
There isn't a straight guide because it depends on the models design or flight envelope and the pilots skill development. Some may have Hances reflexes other may not. Some may be using a trainer while another has a speed prop flying wing that's a blur for most of the flight.

The manufacturer also gives some input but as I said, understand your radios curve, see where it transitions from fine to more course movement at the surface and make sure that that change isn't where you do much of your flying or is very subtle.

Thus my comment about either a little or a lot. Either way I keep at least one linear flight mode available and keep in mind to make subtle adjustments from each flight. No different than mixing out adverse roll, yaw or pitch.
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Old Jul 30, 2012, 12:40 PM
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Maybe my answer based on my own use over 40 years may have some bearing ? There seems to be camps developing ... the I DON'T USE and the I DO USE !

In 70 .. 80's D/R came in and was used a lot by people ... but many stayed with old style single rates ... flying their models and trimming / adjusting based on what they felt / experienced when flown. People had and still have different levels of control they like. From those early years - I have learnt to be careful about stick centre as I didn't have expo then - even though I flew expensive JR Propo gear.

Come fwd to now and I feel spoilt as I can soften the centre by expo, set different rates / expo depending on what I want. It is in my mind certainly not cheating. It's about enjoying your flying, getting the best that suits YOU.

I have models that I don't need expo or DR on ... my Cessna comes to mind. But I have models that without Expo and DR you would be very hard pressed to fly and survive ... my Parkjet with over 700w of power up it's jacksie springs to mind.... that little baby is capable of over 250kph. At launch and slow speed she needs reasonable elevon movement with very soft centre .. about 10mm up/down. If you try fly with that at high speed - believe me it is a nightmare ... it needs to cut back to 3mm max up/down ! still with touch of expo thrown in.

So to OP ......... do what suits you .. don't worry about what others think.
When they see you fly well, enjoying yourselfl - THAT matters !

Nigel
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Old Jul 30, 2012, 12:50 PM
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I use expo and dual rates. Calling it "cheating" sounds like a personal problem.
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Old Jul 30, 2012, 12:54 PM
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Originally Posted by solentlife View Post

In 70 .. 80's D/R came in and was used a lot by people ... but many stayed with old style single rates ... flying their models and trimming / adjusting based on what they felt / experienced when flown. People had and still have different levels of control they like. From those early years - I have learnt to be careful about stick centre as I didn't have expo then - even though I flew expensive JR Propo gear.


Nigel
I know I rely on dual rates just on the first flight or two. Last thing I want is to have too sensitive or too little response. Once I know I'm in the ball park for response level, I begin adjusting off the high rate position and fly that 99% of the time. I'll keep the low rate setting for someone new wanting to fly the plane. It gives them a starting point to get a first feel for the plane, and then they can "kick it up a notch" to exploit the upper parameters.

But it's not uncommon for some of my planes to have the same settings for low and high rates once I get the plane adjusted the way I like and the sole flier of the plane.
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Old Jul 30, 2012, 03:09 PM
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Oh ya! Dual rates. That's something I don't recommend using since expo already solves the concerns without creating limiting effects.
Thanks for mentioning that in the early days radios had rates added first. It was simpler for manufacturers. However, rates, setting a lower deflection end point to reduce your moment effectiveness can be problematic because its not on a curve and may not be in the right switch position to be available if you happen to need it. Why?

We fly LOS VFR Line of sight visual flight reference trying to maintain a moment or rotational rate that is managable for our skills. Expo decreases the deflection per increment to give finer control about the moment. Rates limits the defection or lift to a fixed amount and thus won't allow any faster if needed because its fixed to 3 positions.

The three positions came from usually we are either landing/taking off, cruising or as fast as she's got captain... So the original concept called for three rates.

Trouble is for any aircraft the slower you go the less effective the surface moment, the greater the deflection needed. Thus at take off or landing or going into the various kinds of stalled states, or just going from slow to fast, especially with jets that do not have the benefit of prop wash, the deflection should be at times as much as you may need for 3D depending on what approach philosophy you follow (slow controlled approach under power or higher speed to never lose effectiveness). Because we want our landing gear or bellies to survive, slower is usually better and when nearing stall sometimes you may need a significant snap correction. If you reduced the sensitivity with rate but suddenly need more deflection your stuck. These are two conditions working against each other and thus you are forced to guess you are flying at more specific speeds and with varying wind conditions, you see all sorts of stuff happening in videos with various approaches when the system is setup around rates.


The need and use of rates also came from new pilots over-steering with way too much deflection. This approach continued because most instructors learnt to do it with rates and kept in this way of training students, where all that is now really needed is a higher expo setting.

I use the example of a cars steering. The end point or wheel deflection isn't limited because you are going faster, even as a student driver. You quickly learn when going fast the lateral movement is greater than when slow and that doing a 180* on the highway is just really bad. That is something we all generally have the ability to learn quickly, not to put the sticks hard over unless reaching stall. Some still do it though and thus I've had to reluctantly limit travel with rates with some students.
For this reason I often don't agree with manufacturers settings of High Rate/Expo Low Rate/Expo. My rate remains the same but my expo varies to the type of flying, Landing/Takeoff, 3D, Speed. The variance in the settings again depends on design, flight envelope and pilot.Some aircraft designs you don't have a choice and have a limited degree of deflection. These types are often referred to as having to fly ahead of the plane moving the stick more and waiting for it to respond. Such have very specific limited flight envelopes that a pilot can get into a lot of trouble if they find themselves outside of it.
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Old Jul 30, 2012, 03:11 PM
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Like everything else in this hobby everyone has their opinion. I just experiment and find what works for me or for a particular model. I'm still kind of new at this so anything that gives me better control makes flying more enjoyable. I think most people tent to over correct so adding expo can help with that. Its not cheating.. your just changing the speed of the travel around the center of the stick.
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Old Jul 30, 2012, 03:15 PM
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I know I rely on dual rates just on the first flight or two.
pretty much the same here.
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