Looking for Proper way to eliminate left drift from APM Helicopter

Me again with more questions, Thanks in advance for any help.
Thanks to Chris, Bill, and many others for all their help. I have my second 450 heli flying pretty well without too many snags, EXI 450, Tarot FBL head, APM 3.1 Ver 3.2.1, Flysky Th9X. I have learned a lot of setup tips from different people on this forum.
Question I have my 3 swashplate servos set pretty well, all within a 1400 or less range of adjustment, 90 degrees at mid stick, swashplate is level, 4 to 5 degrees of positive pitch at mid stick. Trouble is I have a good deal of left drift ( not tail drift) as soon as I am lift off, this continues even when 5 or 6 feet up, I know I can keep correcting with the Ail stick or dial in a large amount of right Ail subtrim.
I know I made a mistake on my first 450 heli because to correct this I went into Heli Setup and adjusted the servos to compensate for the drift, I lowered the Ail servo and raised the Pitch servo untill I got the heli to hover without constant correcting to the right or having a ton of Ail subtrim dialed into my radio, trouble is I had servo adjustment numbers from 1230 to 1500, I now know this is wrong.
What is the correct way to correct the constant left drift, use subtrim and then save trim and return subtrim to zero again, isn’t too much trim not good ?
What if a person lengthened the connecting rod length (not move the servo adjustment) from the servo to the swash plate, on the pitch side and shortened the connecting rod length on the Ail side, would this mess other things up, the servos would be where they should be but the swashplate would not be level but heli would not be drifting left all the time?
I know there is proper process to correct this left drift?
Thanks again

William, without looking to make sure, I don’t think there was a hover roll trim setting in AC3.2.1. What is causing your left drift is likely the thrust from the tail rotor pushing the helicopter sideways, and this is completely normal with the swashplate properly leveled.

There is a couple ways to deal with it.

  1. if you do not have a GPS on the helicopter and therefore are not using Loiter flight mode you can simply use the trims in the radio to compensate for it.

If you have a GPS on it and are using Loiter:
2) you can adjust the AHRS trim for roll. This will result in the attitude indicator indicating zero roll when the heli is actually rolled right by several degrees to counter tail thrust

  1. adjust the trim on the two front servos to compensate, raising the left one and lowering the right one by the same amount. This can result in an out of trim condition in forward flight in AC3.2.1

  2. simply use the cyclic stick to compensate for it, which is what most pilots did in the AC3.2.1 firmware.

Thanks again, you are a great help
No GPS yet, so I will just use the trims on radio.