• This site uses cookies. By continuing to use this site, you are agreeing to our use of cookies. Learn more.

How much expo for beginners?

d8veh

Well-known member
#1
I'm a relatively experienced flyer. I built a Simple Scout for fun. I set it up with about 33% expo. For the maiden flight, I also used the dual rates to reduce the response in case it was going to flip on take-off or something like that.

It took off under perfect control and i was able to fly it round the sky, while i trimmed it out, but I noticed that after each turn, it was rocking from about 45 deg rolled one side to 45 deg rolled the other way and it took a couple of attempts to smooth it back down to level flight.

I figured out that the problem was down to the expo. With the movement reduced by the dual rates and the expo, there was little response until I had pushed the stick about half way. As I had already pushed the stick half-way with nothing happening, the tendency was to push it all the way. That effectively made the stick into a switch - on or off rather than smooth proportional control. With only expo (no dual rates), it wasn't nearly as bad, but I could still see some effect.

it wasn't until I got home and thought about it that I thought the expo might be the problem, so I set it to zero. The next time i took the Scout it flew perfectly and with much better control.

The more I think about it, the less I like the idea of expo. Has anybody else any thoughts on this.
 

Hai-Lee

Old and Bold RC PILOT
#2
Expo comes into its own when you have a plane with a large speed range. Control throws required for low speed are dangerous for high speed flight and of course a nice control feel at high speed can lead to no control at landing speeds. Sure many will say just use dual rate but honestly the dual rate change can be too big a gap in control response if used in isolation.

As for your selection of 33% I try to not set any expo greater than 30% and normally use around 15% on most planes of average performance.

I did actually have one plane that actually required around 70% expo because it was extremely fast and light with large control surfaces and would almost float like a leaf without power being applied. Sadly I eventually buried it in a high speed low level pass!

Set your expo to suit the speed range of your plane and you will find that it is definitely a good and necessary feature of modern RC equipment.

As an example of a newbie struggling with the setting of Expo, at my club we had one gent who, despite much assistance and even the free supply of proven aircraft designs, would crash badly about 50% of the time. In desperation a few of us decided to "Sort him out" as he had been flying, (crashing), for over a year at the time. After we checked and buddy boxed him a few times the result was still the same. As a last thought we asked him what settings he was using on his transmitter and when asked about the Expo settings he simply stated that he did not use it because he did not know what it did. We tried to explain and then insisted he set around 30% expo on the control surface channels. Since that day his crashing has decreased markedly and he is starting to really enjoy flying. He still has a few troubles but he is now actually improving and far less dangerous!

Just my opinion of course!

have fun!
 

Hai-Lee

Old and Bold RC PILOT
#5
I was thinking more about beginners planes than high-speed ones that need expo.
having once been a beginner who had to learn on Equipment that did not have expo I can tell you that learning to have a soft touch on the sticks was a difficult thing to learn.

Overcontrolling sue to a lack of experience is a common cause of newbie crashes. Expo does reduce the initial sensitivity of controls so the inexperienced can move the sticks in panic mode but with the plane responding at a more leisurely pace. This alone can help reduce the chance of an overcontrolled ground impact quite significantly.

Yes Expo should be set for all beginners but NEVER set too high or the whole flying experience can be such that the transmitter sticks can seem to act like switches with little real control between extremes.

Have fun!
 

d8veh

Well-known member
#6
Overcontrolling due to a lack of experience is a common cause of newbie crashes. Expo does reduce the initial sensitivity of controls
I agree with that.

so the inexperienced can move the sticks in panic mode but with the plane responding at a more leisurely pace. This alone can help reduce the chance of an overcontrolled ground impact quite significantly.
I'm not sure about this at all. When in panic mode, a beginner would be wagging the sticks a significant distance to where the where the control response is the steepest and over-control is most likely to happen. Heck, never mind beginners, this was exactly what happened to me with a Simple Scout, and I have a lot of experience flying basically, an unstable control system.

The maths says that a small amount of expo (round 15%) will make the control response more linear, i.e. the perpendicular distance that the control surface moves in relation to the distance the stick moves will be in proportion.

We have the idea to tame down the sensitivity around the centres, but that only happens at the expense of much increased sensitivity when you move the stick any distance from the centre. If you need a more docile plane, is it better to reduce the control surface movement rather than make a non-linear response system? I've got a feeling that what actually happens is counter-intuitive, and by trying to solve one issue, you can create another bigger one. The amount that happens depends on how much expo you use.
 

Hai-Lee

Old and Bold RC PILOT
#7
I agree with that.


I'm not sure about this at all. When in panic mode, a beginner would be wagging the sticks a significant distance to where the where the control response is the steepest and over-control is most likely to happen. Heck, never mind beginners, this was exactly what happened to me with a Simple Scout, and I have a lot of experience flying basically, an unstable control system.

The maths says that a small amount of expo (round 15%) will make the control response more linear, i.e. the perpendicular distance that the control surface moves in relation to the distance the stick moves will be in proportion.

We have the idea to tame down the sensitivity around the centres, but that only happens at the expense of much increased sensitivity when you move the stick any distance from the centre. If you need a more docile plane, is it better to reduce the control surface movement rather than make a non-linear response system? I've got a feeling that what actually happens is counter-intuitive, and by trying to solve one issue, you can create another bigger one. The amount that happens depends on how much expo you use.
I agree at least partially with what you are saying. The problem is that the whole setup of a plane and radio system is a balancing act! You need to balance the control surface deflections, control efficiency, (a non-linear relationship), at varying airspeeds, the somewhat delayed responses of the pilot and even the plane setup including the effects of "P" factor. Then add a non uniform medium through which we fly and you will soon realise that much of it is compromise!

What I recommend is that the individual use expo and be aware of its function and limitations. I do not speak of expo as the panacea for all control issues as there is still a large number of other factors especially in setup. Dumbing down control deflections can lead to a lack of control at low speed, Things like differential, thrust angle, balance range,, Dual rate settings, and even mix ratios are things that i go through with all newbies not in a dictatorial manner but rather one of enlightenment. I learned ages ago that the settings suitable for one pilot can be inappropriate for others.

There is no BEST setting for expo or else it would be a factory preset. I use expo and love the effect it has but the expo amount does vary from plane to plane to suit the model and my personal flying style/abilities.

As expo is a part of a setup perhaps a discussion on setting up a model for flight which includes transmitter setup would be more helpful.

Again, Just my opinion!

have fun!
 

basslord1124

Well-known member
#9
We've got an older fellow at our RC field who has never fooled with expo and he flies fine. It totally amazes everyone else. It's just whatever you get used to.

Since having it, I love it. I normally set it high on a brand new model/maiden just b/c I get nervous hands. Then I re-adjust later once I am used to a model. Sometimes turn it off completely.
 

d8veh

Well-known member
#10
We've got an older fellow at our RC field who has never fooled with expo and he flies fine. It totally amazes everyone else. It's just whatever you get used to.

Since having it, I love it. I normally set it high on a brand new model/maiden just b/c I get nervous hands. Then I re-adjust later once I am used to a model. Sometimes turn it off completely.
But did you try it the other way round? It could be that your planes are easier to fly with the expo off. My thinking now is that expo can do more harm than good when you're nervous with a new plane or when you're a beginner. Up to 15% should be no problem, but I see on the Flitetest vids Josh Bixler often says 30%. I'm not convinced that that's a good idea. it sounds simple and logical, but I think that there's more to it than meets the eye. Also, it wouldn't surprise me if newbs hear that dialing in a bit of expo smooths things out (which I'm not sure it does), so they think that maybe 50% might be better, or even 60%, etc., then they wonder why they can't steer their planes.
 
Last edited:
#11
When I started I was using a basic "non computer" 4ch 36MHz Tx and no expo, no dural rates and did just fine because I was lucky enough to have a excellent instructor and the model sets up perfectly, and by that I mean very mild movement on the control surfaces by having the servo push-rod in the right servo arm and control horn holes.
Now many many years later I've moved on to 2.4GHz computer radios and have found 30% expo to be a good amount for all my models.
So some expo is good, too much expo is bad, very very bad.
 

basslord1124

Well-known member
#12
But did you try it the other way round? It could be that your planes are easier to fly with the expo off. My thinking now is that expo can do more harm than good when you're nervous with a new plane or when you're a beginner. Up to 15% should be no problem, but I see on the Flitetest vids Josh Bixler often says 30%. I'm not convinced that that's a good idea. it sounds simple and logical, but I think that there's more to it than meets the eye. Also, it wouldn't surprise me if newbs hear that dialing in a bit of expo smooths things out (which I'm not sure it does), so they think that maybe 50% might be better, or even 60%, etc., then they wonder why they can't steer their planes.
Nope...honestly I think it would do more harm for me having it off first time flying a model b/c I do have nervous hands when I have to maiden something. I can build a little junker plane and test that theory though. I do think that Josh B. should not include recommended expo settings with these planes though...throws are ok, but not expo.The reason I think that is 1) it really does sort of depend on the person and what they are comfortable with, and 2) not all radios are created equal...30% for one might actually be -30% for another.
 

Bricks

Well-known member
#13
Here is a good little test turn your radio on and plug in you plane ( make sure throttle cut is on or prop is off ) Now move your elevator to full down and full up watch your ailerons do they move if so you adding input that you did not want, same for ailerons did the elevator move. Move your throttle up and down did you input rudder? If so this is where expo helps a lot especially on a plane that is fast. My 3D planes when I am in full throws my expo will be pushing 100, so my center stick is soft for when I speed up for the next movement it will smooth out my stick movements. Did you notice I did not say % when talking expo it is not a percentage if radio, receiver resolution is 1026 steps or 2045 then if I add 30 expo it is taking the first 30 steps out of 1026 , 2045 total at central stick point 15 on each side of center.

To help with a mental picture watch your servo arm move thru it`s entire movement once you have added full throw. divide that movement into 1026, 2045 and imagine taking 30 steps 15 on each side of center stick.


Much of the problem comes from not having your servos and control surfaces linear. When I set up a plane I first go into my radio and set my servos to full throws, do this by listening to your servos when they start to chatter back off a couple of clicks until they are quiet. This is the only way to get maximum resolution from your servos and have expo work as it should. I will center my servos and install the servo arms you will notice the servo arms will center only one way, this is the way I want to mount that servo so I do not have to go into my radio and sub trim to get the arm centered. I will mount my control horns and servos, if I want only 20 degree throws, I will keep moving my pushrods in the different holes of my control horns and servo holes until I get as close as I can to 20 degrees using the full throw of the servo. This way you get the highest resolution possible for the set up where stick inputs and servo outputs are linear. It takes full advantage of the new radios and servos expo will function as intended, if not done for every plane set up you are leaving a lot on the table.
 
Last edited:

buzzbomb

I know nothing!
#14
Much of the problem comes from not having your servos and control surfaces linear. When I set up a plane I first go into my radio and set my servos to full throws, do this by listening to your servos when they start to chatter back off a couple of clicks until they are quiet. This is the only way to get maximum resolution from your servos and have expo work as it should. I will center my servos and install the servo arms you will notice the servo arms will center only one way, this is the way I want to mount that servo so I do not have to go into my radio and sub trim to get the arm centered. I will mount my control horns and servos, if I want only 20 degree throws, I will keep moving my pushrods in the different holes of my control horns and servo holes until I get as close as I can to 20 degrees using the full throw of the servo. This way you get the highest resolution possible for the set up where stick inputs and servo outputs are linear. It takes full advantage of the new radios and servos expo will function as intended, if not done for every plane set up you are leaving a lot on the table.
I may be an "Active Member," but I am a noob who hasn't flown yet. This, however makes since to me. I can see where having the input linear to the output could make a huge difference (assuming one does not need an output greater than the throw of the sticks), both in learning and later on down the road.

My question is: How does one know if they want "20 degree throws?" Myself as an example, I built a TT as best I could following a build video. My assumption would be that the throw on the control surface would be correct to that build. How would I know that I want it different and then know to what degree?
 

d8veh

Well-known member
#15
The 20 deg throw is only a starting point. It's not that critical. Normally, the more the deflection, the quicker and the more your plane will respond. The only real problem is when you don't have enough. Say you had a bit of a twist in the wing or tail, you might need up to 5 deg trim to compensate. In fact when I used to train newbs to fly, some built their planes so twisted that with full left on the stick, the plane still flew to right. So, you're a newb with a trainer plane, you want quite small deflections for easy control, but enough to be able to control the plane above any compensation for deficiencies. 20 deg should be enough for that.

Once you have trimmed the plane out to fly straight and level with neutral sticks, you'll know whether the plane is too twitchy or too docile for what you want, then you can adjust the amount of control surface maximum deflection accordingly.

You know whether you need to start with 20 deg because it says that in the instructions. One must assume that it was rested and found to be right for typical pilots. if you design your own plane, you base it on what you ended up with on similar models that you flew or what other people used on similar planes.

If you have a dual-rate transmitter, something like 60% of the normal value is common for the low rates, but you'll have enough to worry about trying to keep the plane in the air to think about changing rates during flight, though as long as you don't have too much twist, you can make all your initial flights on low-rate, then turn up to the high-rate (100%) when you get the hang of it.
 

Bricks

Well-known member
#16
As d8veh said once your plane is flying and trimmed then you go back into your plane and readjust your pushrods so you can take the trim out of the radio or as close as possible this keeps your servo travel, and resolution correct so expo works as it should..