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How do i program DX6I for drag rudder. AKA differential Yaw !!HELP!!

TritonZX

Junior Member
#1
Hello,
I'm just finishing up a flying wing I designed. I just picked up a new Spektrum DX6i and I'm having trouble figuring out mixes. Its a traditional elevon setup however I have drag brakes on each wing (similar to the B-2), each with their own servo. How do I setup so that when left (or right) rudder is applied on the stick only one servo operates? I understand differential for the ailerons but how would I apply this concept to the rudder stick?
Currently if I push Left (or right) on the stick the opposite side (which is fully closed) attempts to move past fully closed and strains the servo. Any help would be greatly appreciated,

Thank you,

Adam

Example of my setup.
http://static.rcgroups.net/forums/a...External Drag Rudder Linkage.jpg?d=1252864606
 

makattack

Winter is coming
Moderator
Mentor
#2
I had also looked into doing this, but abandoned it because I realized the dx6i programming was too limited to implement properly solely via tx mixing. As a result, I added apm to my versa wing so I could use their differential spoiler support:
http://plane.ardupilot.com/wiki/arduplane-setup/first-time-apm-setup/differential-spoilers/

But then found that the apm actually knows how to crab your elevon controlled wing to maintain heading in a cross wind, which was my main reason for trying to setup differential spoilers. This saves me the effort and weight of all that. If I had a larger wing, I might implement differential spoilers, but for I now don't need it.

Here's where I first talked about it:http://forum.flitetest.com/showthre...unt-Nose-Versa&p=100203&viewfull=1#post100203
 
Last edited:

SnowRocker88

Amateur pilot and builder
#3
I had also looked into doing this, but abandoned it because I realized the dx6i programming was too limited to implement properly solely via tx mixing. As a result, I added apm to my versa wing so I could use their differential spoiler support:
http://plane.ardupilot.com/wiki/arduplane-setup/first-time-apm-setup/differential-spoilers/

But then found that the apm actually knows how to crab your elevon controlled wing to maintain heading in a cross wind, which was my main reason for trying to setup differential spoilers. This saves me the effort and weight of all that. If I had a larger wing, I might implement differential spoilers, but for I now don't need it.

Here's where I first talked about it:http://forum.flitetest.com/showthre...unt-Nose-Versa&p=100203&viewfull=1#post100203
Wow, great input! I didn't know the ArduPilot Mega was so well setup for fixed wing too!
 

makattack

Winter is coming
Moderator
Mentor
#4
Yes, I'm still amazed at how well APM performs, even with the older hardware (I'm using a APM 2.5 revision board on my FT Versa) -- I was so impressed with the ability of it to estimate wind direction and speed, that I decided to help it along by adding a wind speed sensor, and it's now even more locked in. Also makes people in the know gawk at the fact I have a pitot tube on a DTFB scratch build!
 

Craftydan

Hostage Taker of Quads
Staff member
Moderator
Mentor
#5
Adam,

I'm not sure the DX6i can do it, but depending on where the mixing and limits are in the output chain there might be a chance. Give this a try:

- plug one servo into rudder, one into the flaps

- on the rudder channel's TRAVEL ADJ, set it such the stick runs the full downward travel, but no (or little) upward travel. effectively, you'll set it to something like (100,0) or (0,100) (depending on which way is down for that servo). Keep in mind, this screen is wierd. It ONLY shows one side of the adjust at a time, and you have to hold the stick left or right to change the left or right travel limit.

- in the mix1 connect RUD>FLP and try mixing it (100,100) -- that should work if the mix happens before it limits the travel, and your servos are setup like ailerons. you'll need to mix (-100,-100) if they're setup like flaps. Set both the switch and trim to ON.

- On the flaps channel servo, set the TRAVEL ADJ in the same way -- they might be the same, might be reversed depending on how you've laid out your servos (like ailerons, opposing, or like flaps, cooperating). you might have to set a value in the flaps and flip the flap switch back and forth to get the limits to respond, but before you fly set both flaps posions to 0 -- no sense letting that switch interfere.
 

makattack

Winter is coming
Moderator
Mentor
#6
Ah ha! I didn't see the link to your diagram until I saw Dan's response. Ah yes, that's what ASSUMEing does... oops. Sorry for the irrelevant tangent!

I now see that you've got a drag/brake based control system, not an elevon based one. Ooops. I believe Dan hit upon it there! You learn something new everyday! I never was able to figure out the DX6i left/right travel limits until I read Dan's note on how to do it!