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Old Jun 12, 2009, 06:14 AM
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Portchester Nr Portsmouth, Hampshire UK
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Still confused with EXPO - DX6i and DX7

With Spectrum DX6i and DX7 radios set up with some 25% expo on Aileron ,elevator - is EXPO thus achievable with pich - is this a different set up or is there NO pitch EXPO.

Thus if the case does one set a heli up with a mechanical pitch curve (say -3 or -4 at the 2nd and 4th points in a 5 point curve).

Clearly how currently set up there is NO expo effect.
This is for 3 Sevo 120 set up.
Cheers
Heritic
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Last edited by Heritic; Jun 17, 2009 at 07:14 AM.
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Old Jun 12, 2009, 08:32 AM
Team Mulikow 3D
Oxfordshire, UK
Joined Jan 2007
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On a DX7 expo does a different thing on the Pitch (collective) - in this instance it simply smooths out your pitch curve rather than having distinct points - from manual

Exponential Throttle Curve Function
With the DX7 system, individual throttle curves are selectable to be either straight (linear) or curved
(exponential). To select an exponential curve, press the select key until EXP OFF appears on the throttle curve
screen. Next press either the increase or decrease key to activate the exponential feature (an “on” will replace
the “off” on the screen). With the exponential function ON, you will notice that any “sharp” angles of the throttle
curve will become more “rounded” or “smooth,” creating a smooth throttle servo movement during the entire
throttle curve range.
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Old Jun 17, 2009, 07:15 AM
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Portchester Nr Portsmouth, Hampshire UK
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Many thanks MikeHRC
Heritic
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Old Jun 17, 2009, 02:48 PM
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Marysville, Ca., US
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Heritic,
You seem to be confusing what expo and pitch curves actually do. Expo refers to modifying the response in cyclic pitch only. Pitch curves set up collective pitch only. There is no way to set a mechanical expo for aileron and elevator. While it is possible to mechanically alter + and - collective pitch by offsetting the ranges in swash movement, the better way is to mechanically set up + and - pitch to be equal, then adjust with pitch curves in the radio.
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Old Jun 18, 2009, 07:02 AM
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No I am not confused, I am trying to explain to a club member the differences.

BUT I miss understood what the DX6i and DX7 can do as they cannot give cyclic expo
BUT other more up market radios can.

I have always set my swash up mechanically.

On bloggs I have seen in the past others hace said to set pitch as a straight line then use the radio curve graph for pitch to dress /drag the line into an S , I realise it is the same only numbers instead of the upmarket graph.
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Heritic
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Old Jun 18, 2009, 02:48 PM
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The DX7 most certainly DOES give cyclic expo. I run 10% expo on ail and ele for my T-rex 450, and 4% to 7% on ail and ele for the Swift 16. The expo on the Swift is just to smooth out the response, whereas the expo on the T-rex is make it less twitchy.
HTH
Bob
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Old Jun 18, 2009, 07:16 PM
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Quote:
Originally Posted by norcalheli
The DX7 most certainly DOES give cyclic expo. I run 10% expo on ail and ele for my T-rex 450, and 4% to 7% on ail and ele for the Swift 16. The expo on the Swift is just to smooth out the response, whereas the expo on the T-rex is make it less twitchy.
HTH
Bob
Yep......cyclic expo for sure on the DX7. Im not sure if they corrected the issue yet, but when the Dx6i first came out it showed that expo was available in the software and programming , but when you tried to use it there was no function. Essentially the DX6i had or has no expo unless they corrected the problem.
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Old Jun 18, 2009, 09:01 PM
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Exponential is just the wrong word to use for pitch curve smoothing. Technically it is not an exponential equation that is used, it is a curve fitting function. For the aileron and elevator and rudder throws, it is an actual exponential curve, or a logarithmic curve (negative exponential).

http://en.wikipedia.org/wiki/Exponential_function
http://en.wikipedia.org/wiki/Curve_fitting

And if you want to get really down and dirty, the DX7 probably uses a polynomial or spline interpolation to find the pitch and throttle curve points in between those that you set, when "EXP" is turned on.

http://en.wikipedia.org/wiki/Interpolation
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Old Jun 19, 2009, 04:22 AM
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Borowed from Model Aviation news.......Q-27: I hear the expressions "dual rate control" and "expo rate control." Are they the same thing? Is one form of control better than another?

A-27: This is an excellent, often-asked question. Dual rate control and expo rate control work differently, yet they do tend to achieve close to the same results. With dual rate control, you have a switch for the function; one switch is usually for rudder or aileron and the other switch is for elevator.

With the switch in the off position, you will obtain full control throw on that particular channel. When you turn the dual rate switch to the on position, you can reduce the amount of servo control throw or travel to at least 50% of the full control.

Let's say you have a fast, heavily loaded airplane. When it flies at slower speeds for takeoffs and landings, it requires a great deal of control travel. But when it gets up to a fast flying speed, it needs far less control throw. At the faster speeds you want less control to maintain a smooth flight. This is where the dual rate functions come into play.

You make your takeoffs and landings with the dual rate turned off. Then during high-speed flying, you turn on the dual rate switch, which reduces the maximum amount of servo travel (control). The key to this is that you must physically throw that switch while in flight to obtain the reduced control. Keep in mind that while that dual rate switch is on, you can not obtain full control throw. So if you needed more control in a hurry, you must first turn off the dual rate switch.

Exponential rate control (which is referred to as "expo") does not have to be operated by a switch. (It can be, but doesn’t have to be!) Nor does it cut back or reduce your maximum servo control throw. Expo rate basically provides for a nonlinear-type control around the neutral transmitter control-stick position. In normal linear control, if you move the transmitter control stick 50% of its normal travel, the servo that it operates moves 50% of its travel. In other words the control response is perfectly linear.

With expo rate, as you begin to move the transmitter control stick, the servo will begin to respond very slowly. By the time you move the control stick 25%, the servo it operates may have only moved 10%. The control response is nonlinear. As you get up to 50%, stick movement, the servo may be up to 40%. When you get to full control-stick movement, you get full servo control.

The degree of nonlinearity can be adjusted. You can set the expo rate for very little nonlinearity, which may be hardly noticeable. Or you can set the expo rate for maximum nonlinearity, which means that when initially moving the control stick, the responding control surface hardly moves at all.

Expo rate control works best on high-speed, highly maneuverable model aircraft. An airplane that appears “jumpy” in high-speed flight will become quite smooth when a good amount of expo rate control is added.

The two best features of expo rate compared to dual rate control are that you get full control throw when you need it and you don’t have to remember to keep throwing a switch in flight.

The relatively inexpensive computer transmitters I wrote about in my "From the Ground Up" series (February 2004 Model Aviation) describe these functions in detail. Even beginners or relatively new RC pilots can benefit from both dual and expo rate control. However, keep in mind you must pay slightly more for an RC system that provides such features.

—Bob Aberle
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Old Jun 19, 2009, 06:24 AM
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Thanks for this Greybeard - appreciated
Heritic
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