Travel Adjust/Dual Rates and Exponential.

[Ross Clarkson]

Hi,

 

I'm pretty happy i understand what Expo is. In my head, i believe it basically effects how sensitive the control sticks are nearer to their center positions. A + value decreases the sensitivity for Spektrum.

 

I am also aware how to set up low and high rates.

 

Problem is, i am getting a little confused about travel adjust and Dual Rates and when to use them!

 

When setting up an aircraft for the first time and you want to get the control surfaces moving the right amount of distances, should you use travel adjust or the D/R function?

If D/R, what is travel adjust for?

[John North]

you should first set up the mechanical linkages to give you as close as possible to the suggested control surface movement at 100 percent of the travel adjustment then do the final adjustment with the travel adjust - this will give your high rates. You then set this as high rate on your dual rates then you can set low rates on your d/r switch. The high rate is then 100 percent of the travel adjust and the low rate is the dual rates switch is set to recommend value or say 70 or 50 percent of the high rate ( actual low rate is dependant on model type and personal preference )

[Biggles' Elder Brother - Moderator]

A nice concise explaination John

 

BEB

[Ross Clarkson]

I feel really stupid, but I'm just not getting this at all!

I have set the mechanical linkages up so they are at right angles to each surface or servo arm and so that they put the control surfaces exactly on the neutral point when the servo is at the neutral position.

Travel adjust is pre-set at 100% on all surfaces.

 

For example, i now want to set the high rate of 19mm of up travel on the left aileron, but it is going 25mm!

Do i reduce this to 19mm using travel adjust or the D/R function??

[Biggles' Elder Brother - Moderator]

Ross,

 

you are probably using a hole on the servo which is too far "out" and/or a hole on the control horn too far "in". Fiddle with these until the control surface moves just a fraction more than your desired HR's. Let's say your getting 20mm then, That give full servo sensitivity to the control surface movement.

 

Then use the limit travel option to fine adjust it to 19mm. Now HR will be 100% of the allowed travel. LR can then be set at, say 60%.

 

BEB

[Tim Mackey]

Either. Why not use travel throw to increase the throw so that the surface moves 19mm.

Then, in dual rate settings, set "HIGH" to 100% - which will be 19mm, and "LOW" to say..... 75% which should then move the surface to about 12 mm. Then using dual rate switch, you can select high (19mm) or low ( 12mm.)

[Tim Mackey]

Posted same time as BEB

 

Incidentally, these days I never use Dual rates, preferring instead to use exponential.

I leave the dual rates set at 100% for each position, and use travel throw to set the maximum deflection that I would ever want. Being "gentle" on the sticks around the centre, I can have small, slow movements, but when I want silly high movements, I just bang 'em into the corners IYSWIM.

Now I know of course that expo and DR are two different things,but with practice I can have the best of both, and dont have to remember to check my DR switch position....and one less switch to fumble for whilst flying.

Edited By Tim Mackey - Administrator on 09/12/2010 23:57:02

[Ross Clarkson]

I think i am getting you.

My servo arms and control horns are set-up as per the manual, quite meticulously as i am a perfectionist, but i will double check this BEB.

But, the control surfaces will still move more than the suggested HR's easily, due to the amount of movement the Yak allows on the surfaces!

 

Now, if i am right in what you are saying BEB, adjust them down using travel throw to the suggested distances. (High rates)

Then this will be 100% D/R high rate which means on high rates the surface will move 100% of the inputted travel throw figure.

Then decrease D/R low rate (rather than travel adjust) to obtain the low rate distances.

 

Is that right??

Edited By Ross Clarkson on 10/12/2010 00:02:08

[Ross Clarkson]

Likewise Timbo.

 

OMG, i think i am there, and it was me just being silly!!!!

I was setting them up using the Dual rates option on each surface, rather than travel throw!!!

It makes sense now that High rate set at 100% will move the surface 100% of the specified travel throw!! Thats the bit that was confusing me!!!

 

I will use travel throw to get the desired high rates, set D/R high rate at 100% then use D/R low rate to obtain Low rates.

 

Wow, cheers guys. Sorry for the stupid questions but my brain would just not click in to it!!

 

Timbo, i think i like the idea of having no rates and using expo but i will leave that until i am a bit more confident at flying! That sounds the way forward though.

 

Once again, cheers, it has

[Biggles' Elder Brother - Moderator]

Yes, all the limit travel stuff from "Now, if I'm right..." onward is fine.

 

But the reason you have too much throw to start with is mechanical - not programming. By adjusting exactly which hole you use in the servo arm and control horn you can alter what total control throw you get from full servo travel.

 

You can do it just the way you say and not bother with this mechanical optimisation - but you will get a small reduction in the available resolution from your servos because you'll be using a smaller proportion of its possible range. Understand?

 

BEB 

 

Edit: PS Posted before Id seen you last post Ross!

Edited By Biggles' Elder Brother - Moderator on 10/12/2010 00:09:11

[Ross Clarkson]

Yep, crystal clear now.

I really do appreciate all the help and couldn't do it without you.

I will re-visit the mechanical linkages and go from there.

 

Phew.

[Pete B]

Ross,

 

Regardless of setting dual rates, I would still advise setting some expo on the flying surfaces. This is obviously a very responsive model and something along the lines of 30-40% expo will make for a much smoother flight and avoid the twitchiness around mid-stick.

 

Pete

[Tim Mackey]

Phew...I can go to bed now - Ross is happy

[Ross Clarkson]

Actually Timbo, whilst i have got you........

 

ha ha, only kidding. Cheers.

[Biggles' Elder Brother - Moderator]

Yep, I'm off too - play nicely boys and girls!

 

BEB

[Andy Harris]

If I got 25mm instead of 19mm travel I'd be quite happy. One always seems to use all the available deflection anyway...

 

Just call 25mm high rates and use d/r to set low rates.

 

Andy

[Roger in Dubai]

Don't get me wrong, I love the new computer radios but, with all due respect, the above seems to be a case of "I've got it on the Tx and I'm going to use it".

 

Get back to basics as per an earlier post and set up as if you did not have the computer available.  I fully concur with setting the arms on the servos and then on the control horn to get the required travel.

 

My first radio, an OS Cougar 4 ch set, had 2 sticks (Mode 2), trims on all 4 surfaces and an On/ Off switch.  That was it, even the placement of servos in the fuselage had to be planned to ensure that the surface was either pulled or pushed to go in the correct direction.

 

I have lost count of the number of times I have been asked to deal with engines that won't idle properly and then establish that travel throws, dual rates and expo are all fighting each other for control IYSWIM.

 

Good luck with the set up as there is nothing like a well trimmed plane that does what you expect. 

[Biggles' Elder Brother - Moderator]

Roger, I've a lot of sympathy with your view. I think a lot of flyers "misuse" the power of the modern computer radio too much - sometimes leading to some rather sub-optium set up.

 

For me, I like to try and get the basic mechanical set up as close to what is desired as possible - then use the wonderful facilities of the radio system to fine tune it. So its servo arms at right angles to the servo, with the servo at its centre point and the control surface at nuetral - at least as accurately as I can get it with the mark one eyeball! I then fiddle with the selection of servo-arm and control-horn holes so that full servo throw is the desired full control surface throw - again as close as I can reasonably get it. Only then do I start to use the tranny's posh features; sub-trim if needed to absolutely nail that neutral, limit adjustment to finalise the control surface travel to be exactly what I want.

 

Sometimes when looking over other folk's models (and sadly not always beginners) I see examples which seem to have used an 'alternative' method. They seem to see the mechanical set up as simply a method of connecting servo to control horn - no thought given to setting it up. The servo centre has the control surface miles out - so that is fixed with "shed loads" of sub-trim. The control throw the servo is generating is often massively too much - so the limits are brought right in to fix this. This results in the servo operating; off centre and over maybe 35% of its range for full control movement.

 

Now the thing is - this works so folks live with it. But its ironic that the same modellers often choose very high spec digital servos - seemingly unware that they are only using a fraction of the resolution these expensive servos are offering. In fact, in terms of the performance they are actually getting and the way they have things set up, a mechanically well set up analogue "cooking" servo would probably deliver at least as good a result at a fraction of the cost!

 

I know I sound like a "grumpy old man" over this. But it really isn't so, Like you Roger I really like all the techno-wizardry of modern radios - and would never want to go back. But, like fire, I think they are excellent "slaves" but very poor "masters"!

 

BEB

Edited By Biggles' Elder Brother - Moderator on 12/12/2010 18:42:20

[Myron Beaumont]

BEB

I for one would like to "go back " but on 2.4 GHz & I wish I had proper trims too ,for first flights especially ,so that things can be adjusted mechanically for a spot on second flight .Call me old fashioned if you like ! I don't like to rely on things I cant alter by hand .

Grumpy Myron

( just watched  X factor for the very first time & the last for 15 minutes -after 35 years of playing & singing for 3 hours a night ,I'd just like to know how they'd get on singing more than one song & playing a multitude of instruments every night)

[Myron Beaumont]

PS

And in English & French !