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Thread: ALT Hold with AutoTrim

  1. #1

    Question ALT Hold with AutoTrim

    I have the AF-Pilot along with the Tru-Traks AutoTrim module. When I engage the autopilot, while in level flight, by pressing the AP button, it will begin applying down trim after a delay of @ 2 secs. If I don't hit the auto-pilot disconnect quickly, it will apply full-down trim as fast a the trim servo can go. What would cause it to think it needs to apply so much trim in level flight?

    There is a pot on the autotrim module to adjust sensitivity. Will adjusting this counter-clockwise slow down the trim? It is currently set a factory default as I have not made any adjustments to it.

  2. #2
    This actually sounds like the pitch servo's trim sensor needs to be readjusted. The pot on the module only controls trim tab speed. Unfortunately your servo will need to be returned to us for the adjustment. Send me the serial number and I can get you an RMA number for the repair. Thanks!
    Lucas
    Trutrak Tech Support

  3. #3
    Lucas,

    Thanks for responding.

    Before I go through the hassle of taking the servo out, let me try and understand what your saying. Your implying that the pitch servo is moving the elevator down too quickly and needs to be slowed, correct? However, in my case the elevator isn't being moved, only the trim tab. I'm guessing that the autotrim module is sensing that the plane is slightly out of trim and is attempting to level it out using the trim tab instead of using the pitch servo to adjust the elevator. It seems that the autotrim module is either 1) incorrectly detecting level flight attitude, 2) applying the trim tab servo for too long/fast or 3) all of the above. Could you provide an explanation on how the pitch servo speed would affect the trim tab servo?

    I will get the s/n in case it needs to be sent back.

    Thanks

  4. #4
    This sounds to me like you have the autotrim wired backwards? Have you double checked the trim direction following the Trutrack directions?

    Try the following:

    1. Level the Elevator and engage the autopilot by pressing the AP button.

    2. Gently lift up on the back of the elevator trailing edge forcing pressure against the AP servo. If it is working correctly the autotrim should start moving the trim tab in the up position, same direction as you are pressing.

    3. Gently push down on the elevator trailing edge, the trim servo should start moving the trim tab down.
    Rob Hickman
    Advanced Flight Systems Inc.

  5. #5
    Rob,

    I'll perform the test and get back with you.

    Thanks.

  6. #6
    Quote Originally Posted by Rob Hickman View Post
    This sounds to me like you have the autotrim wired backwards? Have you double checked the trim direction following the Trutrack directions?

    Try the following:

    1. Level the Elevator and engage the autopilot by pressing the AP button.

    2. Gently lift up on the back of the elevator trailing edge forcing pressure against the AP servo. If it is working correctly the autotrim should start moving the trim tab in the up position, same direction as you are pressing.

    3. Gently push down on the elevator trailing edge, the trim servo should start moving the trim tab down.
    Great call Rob. My trim was working in the opposite direction so I need to get that switched.

    Thanks!

  7. #7
    I think there is a dip switch to select it?
    Rob Hickman
    Advanced Flight Systems Inc.

  8. #8
    That's what I get for replying so late in the day. I already had brain shut down.

    Quote Originally Posted by Rob Hickman View Post
    I think there is a dip switch to select it?
    If you have the older autotrim with two switches, they'll both need to be moved to the same position (assuming you have the link sensor removed). If it's the single switch just flip it to the other position. I'll try to be awake next time I post. :P
    Last edited by TrutrakTech; 12-07-2011 at 08:02 AM.
    Lucas
    Trutrak Tech Support

  9. #9

    Thumbs up Update

    I have the older autotrim box so I have 2 dip switches. Flipped them according to the manual and also turned down the sensitivity to half way. Went flying and it worked very well in the AP mode. I purposely invoked the autopilot with a 100 foot climb and she leveled out nice and gentle. When I turned off the autopilot the plane flew hands free. No movement at all. She was perfectly trimmed! Nice job AFS & TT!!

    Need to do some more reading on the 4500 to figure out how to work it in the EFIS mode. Not sure from the manual if I need to pre-select a altitude or set the VS to zero in order to fly a D-> course and maintain present altitude.

  10. #10
    If your have the AP/FD mode set to VER:HDG and ALT:ARM it should follow the heading and altitude bugs on the EFIS screen.
    Rob Hickman
    Advanced Flight Systems Inc.

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