Re-Programming the AR636a in the E-Flite Timber (Part II)

Part I of this post is here.

When I reconfigured my Spektrum AR636A and reloaded code to make it into (essentially) a standard AR636 receiver and used it as a non-AS3X model by setting all the gains to zero… all was well.  But when I then decided to add back in some AS3X functionality in certain flight modes I overlooked one important plot point.  Luckily while reading some forum posts on the subject of the Timber in general one comment about reversing the servo direction got me thinking.  So I ran up to the shop and checked and guess what?  My elevator and aileron were responding exactly the opposite of what I would want when I tested the AS3X reaction to uncommanded roll and pitch movements!!  This could have been disastrous had I flown in this mode.

Here’s the problem.  When I went back to what I’m calling “standard” receiver mode with no gains so no AS3X functionality at all, I decided to treat this just like every other receiver.  I relied on my transmitter to make all servo adjustments including centering, movement direction and speed, expo etc…. That’s great in standard mode.  The problem comes when I decided to re-institute a switchable AS3X mode.  With the servos all set to standard (not reversed) and the servos reversed as needed (Aileron and Elevator) in the transmitter the stick command work fine.  But, when the AS3X is on and sees an un-commanded pitch change it command the elevator in the opposite direction.  Unfortunately since it does not know the transmitter is acting in reverse it command what it thinks is the opposite direction from the pitch but (the way these servos are connected and linkage attached) is simply more of the same!!  This would result in a sudden increase in whatever uncommanded pitch occurred.  I’m guessing the plane would try to loop… continuously.  For the ailerons a constant roll would likely have occurred and in my case both would have happened and things might have gotten ugly from there.  Of course I could have overridden those command but as soon as I neutralized the sticks it would have just reoccurred and we would have been off to the races again.

Honestly my only shot to control the plane might have been if I could have reached the switch to shut off the AS3X function in time.  Since this likely would have occurred quickly after launch… I imagine there would have been some unscheduled contact with the earth and a lot of cursing and gnashing of teeth!

Lucky for me I have been reading a lot of posts and so this came to mind before an ugly incident forced me to learn the hard way!  So lessons… 

  1.  When working with the AS3X receivers, servo reversing is best done “on board”
  2. Make sure you have a known good working flight mode to use when changing these things.  Take off in that mode and test up high in the air so you have time to switch back to the known good mode if anything seems amiss.
  3. Don’t trust anything you read or are told if the person telling you has not flight tested his tweek/update or whatever!

OK, so quit wasting your time reading on line and go fly!!  🙂


4 Replies to “Re-Programming the AR636a in the E-Flite Timber (Part II)”

  1. Hi,
    I have a Timber and it’s just as you mentioned in this article but it’s only with my AILERONS. Just fine WITH OUT safe mode on, but then they become reversed when safe it applied. I do have the “Computer programming cable”. Still can’t seem to get it right. Any ideas?
    Sincerely a frustrated flyer.

    1. It is difficult to troubleshoot these things remotely but here are the key things I would look for. 1. Maker sure the receiver is installed in the orientation that the computer application is set up for… You can tell the program which way the receiver is mounted and it will adjust… check that section. 2. Make sure your radio has all the servos set to normal and not reversed. If they move the wrong way when you test it, do the reversing in the application, not your radio. 3. If your ailerons are on a Y, skip this… if they are on two channels (usually 2 and 6 I think) check your manual and make sure you put the left aileron on the correct channel. Typically the easiest way is to tell is to set up your wing type for two ailerons and then check the monitor screen to see which channel is assigned to LAIL and which to RAIL. Using the suggested channels makes all the dependent functions like flaperons, the flap system etc… react correctly without having to do a bunch of reversals etc… Good luck.

  2. Hi,
    I have the similar problem with my receivers (or with radio Spektrum iX12 )
    I reprogrammed the AR 636A for normal AS3X receiver without Safe and noticed, the ailreon and rudder started move in oposite direction. Ok, but then I took another plane where all settings worked properly with RX AR 9350 and bound it to my tx, the ailreon and rudder CHANGED THE DIRECTION also oposite!
    Ok, I bound then the normal ar9029 without AS3X, earlier working properly and AGAIN ailreon and rudder went to oposite direction!?
    I tried all possibilities but no results. Something happened and ailreon and rudder work Now in wrong direction. My friend bound his own dx9 to my receiver and the same problem, ailreon and rudder went wrong. Of course I can reverse those ports but before everything was fine without reversing.

  3. Jack,
    Good of you to take the time posting this. Being new to receiver programming myself, I watched the entire group of Horizon Hobby videos on AS3X receivers. ( Everything you’ve been knocking up against is covered in those tutorials. For instance, they make a special point about NOT using the transmitter to adjust DR and EXPO. You did a great job about explaining what happens when you break this rule.

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