Expo... why?

[Andy from Sandy]

A bit of geometry is in order.

With the ball placed at 20mm from the centre.

At 22.5 degrees the ball will be 7.65mm straight across from the centre line
At 45 degrees it will be 14.1mm
At 67.5 it will be 18.5mm
And finally at 90 degrees it will of course be 20mm.

[ghost2212]

Just thinking through this though, with most FBL systems you are commanding a rotational shift rather than directly moving a servo, so by default the rate of reaction you get should be linear if you have zero expo. It is the control loop in the FBL unit that has to correct for the non-linear servo movement.

Adding expo to the FBL system really is just changing the sensitivity around the center rather than dealing with servo geometry correction I'd have thought?

+1, As I understand it FBL maps stick input to x number of degrees/second.

I personally use 20% expo to soften the response on my heli's, I don't want to be faffing about with the switches and dual rates so use expo to give me the full travel but also allowing me to be precise around mid stick for those fine adjustments in flight. If I used DR instead of expo then the heli would have two or more different "feels" which would not be nice IMO.

[Heli_Chris]

Well I was living with a misconception of the whole Expo thing, and really appreciate knowing that it is intended to compensate for the rotational movement of the servos.

This being the case, would I be correct in saying that there is no need to use Expo for the Blade MSRX, Nano, 130X (or any helicopter that has liner servos) as there is no rotational movement in the servo to compensate for?

Thanks, this has been a real eye opener for me and makes a lot of sense.

Best wishes,

Chris

Just realized, the links going to the swash plate create a rotational movement that would presumable mean the travel is not linear, so I was wrong in suggesting that linear servos don't need any expo to compensate.

[coolice]

Hey.

Interesting facts, so in basic terms you are slowing the movement down around centre where the arm moves the linkage and associated control the most.

How does this then translate to linear servos, such as the ones used on the smaller 130X models? These don't move in an arc but in a straight line.

Also a model with an extra set of arms in between servo arm and swashplate will change matters further.

Going to an FBL setup, as most gyro's are rate demand, control of rotation in the various axis's is controlled by the FBL controller and not the servo arm length. Servo arm movement is broken down into steps, more steps sent to the FBL controller command more degree's per second.

Anyone who's flown F3C will attest to the benefits of some exponential, how much you use is personal taste, I know the amount I like does not suit others.
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[Andy from Sandy]

Just thinking through this though, with most FBL systems you are commanding a rotational shift rather than directly moving a servo, so by default the rate of reaction you get should be linear if you have zero expo. It is the control loop in the FBL unit that has to correct for the non-linear servo movement.

Adding expo to the FBL system really is just changing the sensitivity around the center rather than dealing with servo geometry correction I'd have thought?

I will go along with that as we have no real way of knowing what Mikado do with the expo value that can be set in the controller.

[coolice]

Just thinking through this though, with most FBL systems you are commanding a rotational shift rather than directly moving a servo, so by default the rate of reaction you get should be linear if you have zero expo. It is the control loop in the FBL unit that has to correct for the non-linear servo movement.

Adding expo to the FBL system really is just changing the sensitivity around the center rather than dealing with servo geometry correction I'd have thought?

Hey Mark.

Yes, my thoughts exactly. Most gyros are rate demand, the more stick input you send them the faster the model flips/rolls/piro's etc so expo and dual rates are only changing the speed at which these signals reach the flight controls.
I compare expo to progressive suspension springs on a sports car, as the spring loads up it get's tighter. On a control stick, depending on the type of expo used, positive or negative, depends where the control changes in it's movement.

A beginner will benefit from the right amount of dual rate and exponential to avoid over controlling, then as confidence grows they can tailor the feel via the dual rates and expo to their own taste.
.

[Andy from Sandy]

These last couple of posts are a distraction from the main thrust of this thread though as to what expo is all about.

[Mark_T]

These last couple of posts are a distraction from the main thrust of this thread though as to what expo is all about.

I guess my reason for raising the point was that 'what expo is about' depends rather on what it is controlling at the time

I don't dispute that what it was originally intended to do was to correct for non-linear response in a control surface driven by a rotational input.

[coolice]

These last couple of posts are a distraction from the main thrust of this thread though as to what expo is all about.

Andy.

Care to explain why?
We fly models that are flybarless do we not? Do you fly flybarless models?

Well then talk of flybarless and the effect of expo when using a flybarless controller is relevant is it not?

You do make me laugh!
.

[Andy from Sandy]

My final comment on the subject then is, "Unless someone has a direct link to the Mikado programmer none of us has any clue as to what the controller is doing when expo is set in the v-bar software."

See you tomorrow?

[coolice]

My final comment on the subject then is, "Unless someone has a direct link to the Mikado programmer none of us has any clue as to what the controller is doing when expo is set in the v-bar software."

See you tomorrow?

Andy.

I think that logic is not limited to Mikado only, Align, Beastx and all FBL controllers that can take expo.

Tomorrow me? Yes.
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