Hi,
i have a simple question about the trim logic in ardu-plane 3.x. For manual flight i need to trim my elevator to a value of about 1400 pwm. This value is set für RCX (elevator) trim value, therefore switching to FLBW or AUTO modes wont give me a pitch up or down. When i am flying in FLBW/CRUISE now, my elevator is assigned to a climb or sink rate. Which PWM value needs to be set for leveling out? Is it 1500 PWM (typical center of all common transmitters) or is it RCX trim value (1400PWM).
In my last flight i noticed that there are some small issues with holding altitude (leveling out). Maybe this was due to themical conditions but i want to be sure that my setup is right.
Best regards,
Stefan
Replies
The offset is only about ~80 pwm which results in a really small offset for elevator surface because the complete servo travel is used for elevator (950 PWM to 2050 PWM to have best servo travel solution). I may have small changes in CG position between flights because of different payload and batteries. Physically trimming for each flight may be the best solution but not practical at all. Arduplane should handle any small elevator offset at least with I-gain in elevator/pitch loop but whenever it is possible the trim values should be set to best "fit". I cannot find a real definition of trim logic between different flight modes. Maybe after switching to FLBW mode with same trim value as given for manual mode it results in a constant sink rate command.
Why are you not physically trimming the aircraft? Either move the surface or CG. Adding trim into the mix might lead to tail chasing.
There are two steps to doing this as I found out a long time ago with a very sensitive X5 wing. The tuning was good and it flew very well but even when trimmed it would decide to snake in auto sometimes.
Eventually this was found to be the neutral zero point on the RC input Normally it should be 1500 in MP with the sticks released. on this radio set the neutral position was 1540 and the FC saw this +40 value as a pilot input. reseting this figure back to 1500 using the sub trim on the radio completely solved the problem . now its the first action I take for a new model aircraft , program the new model into memory on the Tx and then reset the subtrims to read 1500 on all channels. then the trimming is much easier.
After a flight trimming then I adjust the mechanical linkage to enable the RC trim to remain at or very near zero.