Runway takeoff: initial right rudder causing veer off course

#1

what am i doing wrong (if anything)?..
… this seems to be a persistent problem, except when it isn’t. ;>/
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(runway takeoff) the plane seems to get a right-rudder immediately when mission mode is initiated, causing it to veer towards the right side of the runway. the taildragger plane is affected worse than the tricycle gear (nosewheel), since the tail (wheel) immediately lifts off the ground (taxi pitch is 0deg) as the prop goes to full speed relatively quickly.
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the direction of the plane is set for the takeoff waypoint, and the waypoint is lined up straight down the runway centerline.
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the plane will begin by immediately heading right. sometimes it maintains the heading until liftoff, then corrects towards the waypoint when airborne. sometimes it will attempt to correct on the roll (sometimes overshoot), then finalize correction in the air…
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i looked at the servo output for the rudder on the tlog replay and it surely does activate sharply immediately on mission mode activation.
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i set up a static test (nosewheel plane) by setting the max TO throttle to 2%, aim at the Takeoff waypoint, standing above the rudder (viewing down at it) and switching to mission mode…
… sure enough, the rudder moved immediately to the right. subsequent view of the servo output on the replay showed this. So i moved the plane’s tail right and left to look for a ‘heading corrective effect’, but what happened was the rudder would sit in one direction, the flip to the other direction, then back, then… even when the plane was sitting still.
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anyone know what’s happening here? this is happening on a plane with 1.9 and the other with 1.8.2. both with cuavV5

#2

Could you please share a log where this happens? Otherwise it’s hard to figure out what is going on.

#3

I’ve seen this before, lots actually. Has happened multiple times. Since we use a steerable nose gear in some instances we would see the quick gear movement then have it go back straight. It was so bad in some cases on old 1.9 testing (pre-release) and 180 that we just limited the pwm range of the nose servo but thats not always possible if you are only using a rudder.

One thing is true, it definitely just comes and goes. My thought at the time was potentially heading inconsistencies until a little movement but since it always corrects very quickly. Like a light switch on and off, there hasn’t been much done with it. Only when using a different type of test plane that full right made the plane flip over which led to limiting the servo output.

If needed, I may be able to track down these logs.

#4

ack. I hope I didn’t delete these logs when I cleaned the card the other day.
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anyways, ill probably be able to recreate something if I cant find any. give me a day or 2.

#5

here’s the only flight i had sunday. not sure if the wind had an effect…

mission start yaw right
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and here’s one of the taildragger where it actually attempted to correct, but overshot…
Mission start yaw right, correction attempt overshoot
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and here is a static test inside a house… the rudder flip flopped back and forth after a bit, after moving the plane by hand, but resting it again.
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static mission mode rudder test

#6

some developments since the weekend:

  1. Held plane (by hand) when initiating mission mode… rudder turned right, remained for as long as plane was held. Let go of plane - plane veered right to takeoff.

  2. aimed plane left. plane veered right.

  3. aimed plane far right. plane veered far left. (taildragger)

  4. aimed plane slightly right. plane corrected straight. (taildragger)
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    This test was not conclusive as i used 2 different planes for different stimulus. also, the course/mission direction was changed for each plane (clockwise/CCW) and there was a consistent southern crosswind (to takeoff). Also, i changed the motor rate on the taildragger from 0.2 to 0.5. The ‘test’ conditions were an afterthought and results were a surprise. next time i will be more disciplined in the controls. “Waypoint” was setting for takeoff direction.