You cna bench test self-level to a certain point, basically making sure it is correcting in the right direction, that is doesn't tilt the swash in a crazy way when engaged, etc. But ultimately you will have to fly it, turn it on, and see what it does an then tweak the ail and ele settings as needed to get closer to level flight.
How I bench tested:
Blades off for all this!
Motor off:
1) Heli level, turn it to the SL bank setting on the Tx, does the swash move? If it does, how much. A little slight movement may simply mean you're from your set level just a hair. No big deal. Move a lot, then reset SL level setting. And repeat.
2) Heli canted in a direction (tilted back, forward or off to a side) by a lot (over 10 degrees), turn on SL bank setting and see if the swash moves in a direction to correct the bad bank angle of the heli.
3) Heli level, turn it on, still level? If yes, tilt the heli and the swash should fight the movement. But unlike normal where the swash would normally start to recenter, it will stay tilted against the tilt of the heli.
The I did all of it over again with the motor on at various governed head speeds to make sure vibes were not a factor.
Then you can take it up in the air.
Again, set the level setting close on the bench (I used a bubble level on the motor or the ikon itself and shimmed the skids as needed to get bubble level on X and Y axes). But don't go nuts trying to get it perfect, it is not that important to be perfect on it. A slightly off will just result in a slight movement in SL mode in the air. As long as it is upright and saved from going in, you'll be able to regain control and fly it (even fly it in SL mode). Once in the air, you can test it and note the direction of drift and attempt to correct it with the advanced ail/ele settings for SL to get it even closer if you wish.
