t/r - tail rotor

trim is using the trim pot near the actual tx stick (electronic or analog) usually for temporary corrections during flight.

subtrim is using the menus (electronic) in your Tx, to accomplish the same thing.

during take off it SHOULD and will yaw PREDICTABLY - if the subtrim point is set correctly in hover, then during take off you will have a deficient amount of power (assuming a typical normal mode curve) therefore you will have to manually push the rudder right a little bit due to the t/r rpm being lower than in hover.

now once you are in a stable hover, that's where it shouldnt yaw faster than you cant control. (rate gyro might still yaw slowly = drift, but nothing crazier than what can be corrected manually). this is called 'flying the tail'. it needs constant input and correction.

now as the battery dies, the rpm will decrease in the whole heli. that means the heli will progressively start to yaw left. to correct this you might use trim while flying until it stops or youll just have to hold the rudder stick right while flying. your battery will probably be dead by the time you max out trim, either way you should stop by then.

dont even worry about revo mix yet. you wont need that until you start getting more aggressive with the throtle.

basically to find this subtrim point - disconnect the gyro and spool it up without one (dont do this if you suck - youre not supposed to take off lol). add some right rudder manually while spooling it up really really carefully. add subtrim for right rudder until you can get it light on the skids and it is only drifting. do not ever blip the controls while doing this because it will disturb the balance of the heli and without a gyro to compensate it's going to go crazy.

the alternate method, the one i actually use is to spool it up in my hand (versus on the floor) and add subtrim until i can feel the neutrality point in the heli where the tail cancels the motor torq.