Lightnin Racer

Hi,

I recently upgraded my HobbyZone Super Cub by putting all new electronics into it. Anyway, I am having a problem setting up the control throws and expo. I tested the plane out today, and the servo controlling the rudder is moving way too fast (the plane would be too twitchy in the air). So I thought that I could 'tune it down' a bit by messing with the control throws and expo, but the speed of the servo is not changing. So can anybody help me out? I want to go flying today, but I don't want to crash the plane due to a 'twitchy' rudder. Thanks.... LR

bigedmustafa

My Feedback: (2)

The whole idea of expo is to be able to create a softer center on your control throws and remove any twitchiness while maintaining the ability to have full throws if you need them. What transmitter are you specifically trying to program for exponential?

Lightnin Racer

I'm using a Spektrum DX7....

blvdbuzzard

EXPO, Dual rates, End Point Adjustment does not slow down a servo. They change how far it moves compared to the stick movement.

EXPO, is a ratio where the amount you move the stick close to center is reduced yet gives full throw when you move the stick as far as it will go. EXPO will soften the how the plane feels with small movements of the stick around center stick position out to about half stick travel. Give or take depending on how much expo you use.

End Point limits how far the servo moves. If you get say 1/2 inch of surface movement, you can set it so the servo only moves it 1/4 by changing the end point.

Dual rates at full rate the servo will move the surface 1/2 inch, then you flip the switch and the servo only moves the surface 1/4 inch.


I am sure there are better explanations out there, but this should give you a very basic idea of what EXPO, EPA and Dual Rates are.


Dru.

Lightnin Racer

Thanks for explanations Dru. I've been in this hobby for 2 years now, but I still don't fully understand this radio stuff. Anyway, so will I notice a difference when I set the rudder at +100% expo? Or will I only notice it when the plane is flying? I did not notice a difference testing it on the ground though.... is that normal?

smokeyser

Easiest way to understand expo is to try it. Set up a switch to turn on 100% expo on the rudder, then turn the switch off. Move the stick 1/4 of the way left or right, and flip the switch on/off. You'll notice how with expo on, the rudder doesn't move nearly as far at 1/4 stick. Basically, it allows you to make the controlls less sensitive near neutral. Pushing the stick all the way to either side will still give full throws no matter what you do with expo. Make sure while controlling the plane that you use small movements. I've got a super cub so I understand a bit about what you're going through. The original controls were mushy and slow and you probably got used to moving the sticks fully in various directions as you flew. With better electronics, you'll have to get used to smaller stick movements.

Lightnin Racer

Thank you for the reply smokeyser. I think I understand what expo is now. And you're right, I was used to the old, slow stock servos in the Super Cub.

beau0090_99

LR,
One thing to be aware of is that on some radios (Futaba specifically), you want to use negative expo to soften the center (I think Spektrum is opposite), so I tend to go with somewhere between -30% and -70% Expo on my controls with my Futaba 6EXAP. You can choose positive or negative on the controller, however. You should see it in the throws when you play around with it. I wouldn't go all the way to 100% on the controls, because Expo can hide your finger behavior and make for a worse pilot. Some of the old farts really decry the use of expo and tell their students to not bother and to learn without it. I agree that it will make you a better flyer if you learn without it, but it may come at a cost.
Have fun,
Curtis

opjose

RE: Expo

Servos produce a circular motion.

They push rods that move in a linear motion.

This means that as you move the TX away from stick center, there is the GREATEST relative movement of the pushrods, as you get towards the END of stick travel you have the LEAST movement of the pushrod.... ( think Sine waves on their side ... ).

So setting the Expo UP TO 50% helps equalize the pushrod movement throughout the stick movement.

HOWEVER once you go BEYOND 50% you are buying into trouble.

Why?

Beyond 50% you are effectively throwing all of the pushrod movement towards the extremes of stick movement on the TX.

This results in a fairly dead, center stick area, and the a sudden and imprecise movement of the surfaces as you get further out.

That in turn causes the flyer to tend to over correct.

Do this with your rudder and you'll have a hard time getting your plane to track down the runway at take off...

e.g. you compensate for left yaw with a little right rudder... nothing seems to happen, so you give it more, still not too much occurs so you give it more...
NOW the plane veers hard right, so you slam the stick left... and you end up over correcting again.