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Exponential

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Erfolg28/08/2007 18:05:00
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I am seeking advice on the amount of exponential that people would use on a :a) 120 inch powered gliderb) On the elevatorc) on the rudderI am asking this question as I have recently flown my old open class glider on electric power. The brief flight of approx. 100 foot altitude, 1-3 minute flight. Was notable due to the sensitivity to elevator in particular. The flight should not have happened as I broke the end point attachment from the fuselage. This allowed considerable movement of the end of the outer cable with la loss of repeatability etc. The flight had originally been intended to be a 100 -200 foot powered glide. I got things wrong ended up doing a circuit. I do know it should not have happened.However the elevator was extremely sensitive. I wonder what amount of exponential others typically use and why.I am using a Futaba 6EXAP. SShould be set to a negative value?RegardsErfolg  
Tim Mackey28/08/2007 18:17:00
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The amount I use depends completely on the model in question. Some of mine have NONE, and my EDF Sabre has 75% POSITIVE ( on a JR / Spektrum anyway ) on elevator.

On my ailerons, the Sabre has 90% which helps avoid any "twitch of the wings" as I do a low run down the strip and whack the throttle up high  ( mode 1 flyer here ! )

David Ashby - Moderator29/08/2007 07:58:00
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It's often a case of putting in say 40% and flying to see how that feels, then adjust accordingly.

David.  

airman29/08/2007 15:52:00
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Exponential should be set to NEGATIVE when using Futaba radio.

Had  a very interesting first flight after changing to JR radio, after setting up the exponential as my Futaba radio.

Dave

David Ashby - Moderator29/08/2007 15:54:00
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I bet you did Dave

David.  

Erfolg29/08/2007 17:02:00
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Thanks for the feedback

Erfolg

Peter Miller30/08/2007 08:11:00
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I only use exponential on the throttle with my Futaba radio, I use 30% negative which makes the throttel close fast at the start and slow down, this gives very linear throttle response.

I think I set the same on my Spektrum.It is a long time since I set that up.

Doug Ireland31/08/2007 03:31:00
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I used expo for the first time recently on my 80" CAP 232, very effective on the elevator! I read an article recently regarding the use of expo on the throttle if you are using a petrol engine, it too was very effective, nice smooth acceleration.
winchweight31/08/2007 07:34:00
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I'll be honest. I haven't really got a clue about expo. I don't know what it is and why you use it. As for how much to use........

I have a FF9 by the way.

Myron Beaumont31/08/2007 08:30:00
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Peter

Can't get expo on channel 3 on my Futaba 2.4  ,only on ! , 2  &  4  Is it me (again) ?

Grumpy

Peter Miller31/08/2007 08:33:00
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Exponential works in this way, the first part of stick movemnet produces very small control movements but the furhter you move the stick the greater the control surface movement.

Whe I use negative Exponential on the trtottle the first part ofthe movement is large but reduces as I close the throttle. This is because the average model carb has very little change until the barrel is half closed and then the last half of closing has much more effect.

You would use Exponenial on other controls so that a sensitive aerobatic model would not be twitchy on gentlye control movements but you would have the full range at full stick movement.

Someone once thought that it was a bit like rates without having to switch over. I can't really agree but it is  way of thinking about it.

Peter Miller31/08/2007 08:37:00
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Myron

I haven't got Futaba 2.4, mine is Spektrum. My Field Force 8 has it on all channels. Why Futaba used their cheapest set to convert to 2.4 I don't know, well, yes, I can guess they wanted to compete with the Spektrum.

Myron Beaumont31/08/2007 08:45:00
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So that the likes of me could afford it  !   Giving it a little more thought & getting confusedagain "as is my won't" I think it might be possible by jiggling around the channel configuration but although I would love to have expo on the throttle it can wait for a day when I've got my brain cell working at max EPA ! 
winchweight31/08/2007 09:02:00
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Thanks Peter. I am going to have to think about this.

 So if my model is a bit twitchy at low speed in say elevator, setting -40% on the elevator channel will smooth things out?

But how do you judge the amount to set?

PS Mode 2 flier!

David Ashby - Moderator31/08/2007 09:28:00
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Spot on Shaun,

Expo can make a tricky model a pleasurable model

It's a case of trial and error and after a few models you'll find it second nature. I use expo all the time and never bother with dual rates. Start with say 30% then add or take away until you're happy.

 David.

Peter Miller31/08/2007 13:29:00
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I once had a Sanwa Excellence radio, about 20 years ago, it was the first with exponential. I did play with it a bit but din't really like it but that is a personal opinion.

On the other hand It would have been handy on a new model when there was not enough throw on low rates and one was frantically going to high.

Tim Mackey31/08/2007 17:23:00
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I think it is worth stressing here that there is IMHO a big difference between rates and expo, and for someone who is not yet fully familiar with it, I think expo needs further explanation.

Rates are simply a way of reducing the total amount of throw or movement available at the servo output arm, and of course subsequently the control surface that it is connected to  The "way " the output arm moves is the same at either rate position high or low. It is a fairly linear movement from start to finish. What rates do is reduce the total travel, but have no effect on the linearity of movement.

Exponential on the other hand is sort of the opposite...in that with no exponential set, travel is linear, but when expo is added, the stick movement is no longer linear or equally proportional to the servo output arm. EG: ( JR ) if you add say 50% POSITIVE exponential, moving the stick the first 50% of its travel, produces very little movement of the servo output arm, but the last 50% of the stick movement still moves the output arm to its full extent and end position. IT does NOT alter the amount of travel, only "servo travel" function in your menu will do that, or of course our old friend the rate switch.

So....try to think of it as "softening the response" around the first bit of stick movement, yet retaining full travel, which comes in during the latter bit of stick movement. As a further example......I set 80% expo on my ailerons for my EDF Sabre, ( mode 1 flyer ...the right mode   ) because the throttle is on the same stick, and I like to dive down to the end of the strip from a high position, hold her flat, level and low, and then bang open  the throttle wide and fast for a pass down the strip. Now, wiithout expo, banging the stick forward for throttle will inevitably cause a tiny bit of lateral movement on the stick, which manifests itself as slight rolling on the ailerons, which I  DONT want .  Because the high percentage of expo has effectively deadened the aileron stick for that first few mm of STICK movement, the plane stays level. Futaba I believe requires NEGATIVE expo to have the same effect, otherwise of course.... the "softening" would occur at the other end of the stick movement. HTH

Myron Beaumont31/08/2007 17:56:00
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Timblode

 I don't need "softening " at the other end of my stick Throttle that is ! Channel 3 futaba 2.4 job but as i said to Peter Miller it's the only channel I can't expo on ! Maybe I should have waited 'til modules came out for Hi-Tech stuff On 2.4 ?  

Tim Mackey31/08/2007 18:21:00
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If its any consolation, my Spektrum set only has expo on rudder,elevator, and ailerons.

Myron Beaumont31/08/2007 18:32:00
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Ooooooh     so its not all singing & dancing  !!???.   I've got round it by the  way by altering the angle of the servo arm .Just like I used to! In other words it's an angular thing not quite expo but I hope near enough 

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