Could someone please explain EXPO to me.

[Hrob2Ate]

I've never used the expo or mix settings because I have no idea what it is. I've been flying for 10 years without it. another note, I only fly 600 and 700 nitro heli's and I dont fly 3D, just aero. How would expo improove my flying? should I be using it?

[bstanley72]

http://video.helifreak.com/?subpath=...me=expo101.wmv


However, if you've been flying for 10 years without it I don't think expo will do anything for you other than cause frustration.

[jimmyhorns]

Ok, I wonder how many different answers you are going to get

Expo is short for exponential, meaning the curve you get isnt linear (straight line)

Expo has two purposes:

1) to make the response of the servo more linear;

The servo drives a disc or servo arm that exerts more of an effect (movement) at the centre of travel than the ends, so if a millimeter of stick movement created 2mm of servo movement at the centre of travel, at the extremes it may only create 1mm or maybe only 0.5mm.

In real life, this means that the servos (and therefore cyclic) are much more sensitive around mid sticks. Expo on the transmitter allows you to correct this, giving a more linear response, i.e. 1mm = 1mm all the way across the travel.

2) To reduce the sensitivity around mid sticks:

Either to the extent of 1) above, or further, so that 1mm of stick = 0.5mm of travel for example.

This allows people more control over finer cyclic control.

Expo is neither a must have or must not

[SQRT(-2)]

It won't make you a better flier. It can help calm down a twitchy bird though. I don't use any on my 450, but on my Genius CP (MCPX wanta-be, 8 1/2 inches long) I use quite a bit. So just keep it in mind in you get a MCPX or the like for the backyard and you find it is a bit too responsive without expo. Like anything, it is just a tool.

[gtrsteele]

I always get this confused; does more expo make it more sensitive or less?

[Dave H.]

I suppose that depends on your definition of "more" and whether you mean Futaba or JR/Spektrum.

On JR/Spektrum, more positive expo makes it less sensitive around center. On Futaba - negative. Fortunately most modern transmitters display a graph as you adjust expo so you don't have to memorize.

[gtrsteele]

Originally Posted by Dave H.

I suppose that depends on your definition of "more" and whether you mean Futaba or JR/Spektrum.

On JR/Spektrum, more positive expo makes it less sensitive around center. On Futaba - negative. Fortunately most modern transmitters display a graph as you adjust expo so you don't have to memorize.

I have a Spektrum DX8, which if memory serves me corrrectly does have an expo graph, but I don't really know who to read it properly.

[SQRT(-2)]

Originally Posted by gtrsteele

I have a Spektrum DX8, which if memory serves me corrrectly does have an expo graph, but I don't really know who to read it properly.

Here is a picture. I take no credit, I found it at the address below.


I found this here: http://www.daddyhobby.com/forum/show...eli-Tx-setting

[Hrob2Ate]

OK, I get it. Piece of cake. Thankyou verry much gang.

Now what about mix? is there ever a time where this would bennifit?

[koppterx]

there are numerous discussions about expo on the internet...

first, the benefit, and second, how it works.

I'll use an airplane's ailerons because it is easier to conceptualize than a heli, but the effect is the same. we have an airplane in level flight and we need to make small corrections to compensate for forces acting on the wing. this can be done one of two ways. first, I can use very little throw, so stick movements translate into small movements of the ailerons, or i can use expo. since minimal throw may not give me the roll rate i want, I'll use expo. if i don't use expo and my throws are normal, the ailerons are going to be very sensitive around neutral and I may have a hard time putting in small corrections. the plane will feel twitchy. watch an airplane in flight and it's generally pretty easy to figure out whether the pilot has a good set up. the idea that real men don't use expo is just stupid.

as i add in expo value, the ratio of servo movement to stick travel is reduced, while preserviing the total throw. it's not a great example of an exponential relationship, (like y = x squared) but it's close enough. so what i have done is to soften the center stick while not giving up total throw. the airplane is more docile around center and reaction to inputs is smoother.

the reverse can also be created - by reversing the expo value the center stick can become very sensitive and control authority would decay as the stick moved away from center. one common problem during set up is that guys get their expo values reversed and instead of dampeing the stick around center, it makes it worse.

To dampen center expo values for JR/Sp are positive, for Futaba, negative. anything else I have no idea - but it is easy to visualize by running the values up to100% and watching the control surface movement. on a heli, put the blades perpendicular to the fuse and watch the swash movement. at 100% the swash should be damped around center and have a lot of movements towards the end.

actual in flight values (IMO) for helis seem to be no more than aboot 30%, and fbl has affected somewhat because expo is written into the software as part of the "feel" of each system. it is analagous to amplifiers mfrs "coloring" their preamps to produce a certain sound, other than the pure input. it is allso similar to the cars that change their steering ratios as speed increases to make the car less responsive at faster speeds.

the graphs simply show the change in x/y relationship of the stick and servo movement, the more pronounced the S, the greater the expo value. the problem with high exp values, especially in airplanes, is that the servo movement sneaks up on you and you go from little to a lot of throw in a short stick movement.

the difference with expo will be subtle, but if you have a heli that doesn't want to settle down in a hover, an expo setting of 25% on cyclic will probably help. it is easier to use on fbs than fbl. for example, I've found on my 3GX unit that the software is already damped so I have to turn the expo way down otherwise it's very dead in the middle.

last...if you have read this far....our servos try to convert rotational movement to linear movement and that doesn't work too well. we get away with it because the actual servo movement is a fairly small arc and we rarely use the extremes. it's different with airplanes where the mechanics have greater movement and the conversion decay is more obvious.

hope this helps....

[SQRT(-2)]

I have heard plane guys talking about it, having one surface respond a bit when you move another, but I really have not heard heli guys talking about it. Not to say none do it, but not that I have heard of.

I did do 100% mix on rudder and aux 2 once to get two channels doing the same thing because I did not have a y adapter and I wanted one servo to drive the rudder and a separate servo to drive the nose gear on a plane. I imagine if I did 50% on the mix the servo on the nose gear would only move half as much as the one on the rudder. That would probably have been good to do, seeing that too much movement of the nose gear and I could tip the plane quite easy. Well, something to remember for the future.

[koppterx]

mixes...

in general, helis do not use mixes. there are exceptions, and you see them used in precision competition. for example, if there is a swash interaction that produces a small pitch diversion with what would be pure aileron, then the user would set up a mix that would introduce a small correction of elevator (pitch) with aileron. the goal is an axial roll.

another use for mixes is to create kill switiches where one might not exist. my 9503 does not have a dedicated throttle kill so I create one by using a throttle to throttle mix and assigning a switch.

mixes are much more useful on airplanes where "coupling" is common. coupling is the interaction of pitch and roll with the application of rudder. in an aerobatic airplane when rudder is applied, you want pure yaw. what you will likely get is some combination of yaw, pitch, and roll. mixes are used to dial out the coupling. when you see that big old 40% airplane tearing down the runway in knife edge while the pilot is waving to the crowd with his right hand, it's because the mixes are set up properly.

for the foamie crowd, mixes can be used to keep the nose down with flaps, like on the larger t28s and mustangs. as flaps are deployed, they tend to cause a pitch up in the nose. a down elevator mix will keep the nose pointed toward the runway without building up excessive airspeed. makes it much easier to set up for approach when you are not fighting the elevator.

the mix example for the nosewheel is pretty good, and yes, reducing the value would have toned down the nose gear, when you generally don't want more than 15 degrees of throw.

that's it for now....

[Varc]

I still dont get the expo thing either.

[fourbie]

I always use 10+ % expo on some surfaces. Only on the littley helis do I like the rapid response of no expo.

[Heli,Ed]

Originally Posted by bstanley72

http://video.helifreak.com/?subpath=...me=expo101.wmv


However, if you've been flying for 10 years without it I don't think expo will do anything for you other than cause frustration.

I agree +1

[fourbie]

Originally Posted by Varc

I still dont get the expo thing either.

If you add expo the sticks (for whatever surface control) have to be moved a bit more in the early part of the movement to get a reaction and as the stick is moved more the control surface moves more than it did in the early movement. This makes the action exponential. In a graphical description you don't have a straight line effect but a curve which rises more steeply as the graph progresses.
Think of a number sequence 1,2 4 8 16...the farther along the number sequence you go the greater the jump to the next number.
If you have a twitchy finger the twitch isn't passed on to the servo in short movements of the stick. And I still ain't explained it well enough.

[koppterx]

if you ain't figured it out then disconnect your motor, put your tail in rate mode, set up your dual rates so they are both at 100% travel, then set the expo on one to 0 and other to 100%, and switch back and forth as you move your sicks away from center. what you will see is that you have less movement around center with the high expo settings.

[rstekeur]

I find the expo in the DX8 a bit confusing, but I think I figured it out. By the way while were in the same menu, whats DR?

[drfrankencopter]

Expo is intended to add some non linearity to the relationship between the transmitter gimbals (sticks) and the resultant servo deflection.

To throw some numbers out as an example, imagine that full throw of one of your transmitter sticks is +/- 45 degrees, and let's say that on your model this results in +/- 45 degrees of servo deflection. With the usual linear relationship this would mean that every degree of stick deflection results in a degree of servo deflection. By adding positive expo we alter that linear relationship by softening the servo deflection around the 0 degree (center), while still ensuring that we get a full +/- 45 deg servo deflection at full stick throw. We might want to do this for several reasons including compensating for non linear relationships in the mechanical linkages from the servo arms to the swashplate, or to allow for easier fine tuning/trim in the hover or steady flight. We could do the latter with dual rates, but then we wouldn't have full servo throw available, do expo gives us a bit of the best of both worlds.

Of course you don't get something for nothing, and too much expo can lead to control difficulties when the sticks need to be displaced far from center...but there's a pretty big range of 'acceptable' expo as you'll see.

Hope this helps

Cheers

Kris