Exponential

[Tim Mackey]

Keep us posted as to how you get on....sure we will get you sorted eventually - it does work honest

[Doug Ireland]

Hi Timbo, going back to the expo theme, have you heard of a guy called Len Alessi? He wrote an article back in May '02 that covered the set-up of multiple servos on large models and included a detailed explanation of expo. If you would like a copy of the article I could email it to you.

Your comment on "throttle cut" and the description of the set-up matches the method used on the JR 2720. I also have a JR XP662 that had a dedicated throttle-cut button, a shame the 2720 doesn't.

[Tim Mackey]

Many thanks Doug, no I have not heard of Len Alessi.

I think I pretty much have the xpo thing sorted thanks, but would like to see the article yes. TY.

[Peter Miller]

Timbo

 Got the cut system working. My fualt. I was convinced that the trim return was done by one click on the THROTTLE stick.

Well, I can't help it if I am thick!

I still prefer the kill switch on my FF8

[Tim Mackey]

Oh good. Yes I agree, kill switch is better, as IMHO is analogue trim on throttle - full stop.

[Doug Ireland]

Hi Timbo, I tried to use the email link to send you the PDF file but have no idea how to make an attachment to the message.

[Kelly]

If you reverse the servos on the futaba 2.4, will the expotential setting be reversed?

[Martin McIntosh]

You are all talking rubbish! If you want (why?) expo on throttle just experiment with moving the servo or throttle arm off centre. Martin Mc.

[Peter Miller]

Martin, If one has exponential on throttle why not use it, it is far easier and more precise than trying to set up the arm, furthermore, if you use the old arm setup system you lose travel so you need a longer arm.

You ask why we need expo onthrottle. Well in cas re you hadn't noto=iced the rpm drop on model engines is hardly noticeable for the first thrid of throttle closing, it is slightly better from there to half closed andthen really reduces the r.p.m. more and more over the last half of the stick movement. Using expo makes throttle response much more linear.

Finally, if you look back over this thread you will see that moving the output arm was suggested a long way back.

[Doug Ireland]

With petrol engines its the other way round. Lots of engine response in the first third of butterfly movement then it tails off. Much nicer to use expo to danp-out that first bit.

[Martin McIntosh]

OK point taken, must just be stuck in the mud after 45ish years of linear throttles. MM.

[Peter Miller]

45 years of linear throttles! Wow. That takes us back to 1962. I didn't know that we had proportional radios in those days. I seem to remember that ED and Reptone  reed gear was state of the art and then in 66 there was Orbit reed equipment. Pulse a switch to move the servo a small amount, self centering on the flying controls, non selfcentering on throttle and elevator trim if you were a real plutocrat.

[Mark Lubbock]

I have just designed, built & flown a model on holiday (see my blog) & this was also my first real use of my 7CAP in a situation where expo would be useful-small funfy model with 2 aileron servos. Unfortunately, I forgot my instructions for the radio & ended up with expo the wrong way! Although the model flew OK, I thought I had designed a nasty, twitcy lemon of an aircraft!

On getting back home, I correctly programmed the radio & now the model is a real peach to fly, even on high rates, the expo softens the centre beautifully-quite a revalation after the first flights & much easier to set with more scope than my trusty old Fleet MX7 set.

I'd never been that convinced before, preferring to adjust the geometrys etc. but now I am getting used to the computer set, the advantages seem to be many. Not sure I will still think this way if I try to fly a model with the wrong memory though!!

[Tim Mackey]

Fly a model with the wrong memory! - how could that possibly happen then?.......

...............................................asks a Spektrum DX7 owner

[Bravedan]

All this talk of "Linear" servo movement without expo.................

can anyone prove to me that a rotating servo arm gives linear movement to the push rod as it rotates..............

I think NOT..........????????  

[Myron Beaumont]

It's as linear as your movement on your stick ! Think about it ! Look at it from a different angle   Eh ?  

Grumpy

[Martin McIntosh]

Bravedan, the trottle arm is also rotary. Assuming equal lengths, if the servo moves through 30 deg. then so must the throttle. Agreed that with a lot of movement each end of the travel will become exponential, but scarcely measurable for our purposes.MM.

[Peter Miller]

When we talk about a linear throttle response most of us mean that the actual engine rpm response is linear when compared to the throttle stick. i.e, closing the throtle down by a quarter of stick movement reduces the rpm by one quarter, closing it to half on the stick reduces rpm to half.

It can be done by using the servo output so that the first part of thetravel is over the the quadrant which moves the throttle arm the most and then deducing as it moves further round the arc of travel. It is so much easier with exponential.

[Martin McIntosh]

Personal preference probably. I like the motor to respond to small movements at the low end to  allow small blips to control the  rate of descent when landing. MM.

[Heaton Craggs]

On a Graupner Tx  - Mode 2 - [mine is MC19] - should exponential be set to + or - ?

 

If setting, say 30%, on ailerons, should the same be set [+ or -] for elevator as well.

 

What expo setting do you recommend for rudder/throttle?

 

 

[Bob Cotsford]

Getting back to Erfolg's original question - i don't use expo on powered gliders, I prefer to use rates to reduce sensitivity under power.

On power models, the amount of expo depends on the model and your preferences, I typically use between 30 and 40% on both high and low rates, though  something small and fast like my Little Bit wing or Funjet I'll go up to 75%, especially on ailerons - makes it controllable yet twinkle rolls on full aileron have to be seen to be believed.

[Myron Beaumont]

Hard to explain in words my findings on this subject- But  !! - here goes anyway

.If the throttle push/pull end on the servo disc is arranged to be  in the opposite direction/mode from the throttle arm itself (sort of diametrically opposed at a distance, if you see what I mean ), then the movement of this set up will be more or less linear .This can of course be altered to what you are after by altering the leverage effect either end slightly (or both). The rest can then be done ,  with the use of expo dialled in to give your required response from the now nearly mechanically linear response.I hope you understand what I'm trying to explain!

 I like lots of response from idle to about half throttle & I bet most 3-D'ers do as well ,even though I've not had a model capable of their manoevers ( Oh Dear !-That word again that nobody seems to get right) 

Hope this helps -not confuses .

[Doug Ireland]

Expo for the throttle on the DSX9 (actually called "Throttle Curve") is a bit fiddly to set up but is well worth the effort. I don't use Expo on the rudder though, preferring to use aileron / rudder mix instead. 30% expo on all other surfaces.