There is nothing in Tx setup you can do about this problem (well, almost, see below). On flybar setups you could do what Tony said and modify your elevator channel travel settings to get it level at top and bottom collective. However with FBL, since it does all mixing internally and collective travels are driven entirely by a single channel (pitch). Adjusting elevator channel travel will do nothing but impact your cyclic behavior (adjust the forward/backward roll rate for a given cyclic up/down stick position). If the FBL controller does not offer you a way to adjust elevator servo endpoints at min and max pitch, there is nothing you can do aside from finding a mechanical solution.
It is pulling a little extra at minimum pitch and pushing a little extra at maximum pitch. So adjusting link lengths will not be able to correct it. You are already at the inner hole on that servo arm (ELE servo), so that won't help either. You could try moving the two other servo arm balls (PIT and AIL servos) to the outer servo arm hole. This will make those two links push and pull a little more at the extremes of collective, making the swash a little bit closer to level at those positions. Given the amount of difference, I doubt it will completely close the gap, but it will improve it a bit.
Also, this gap is going to induce a forward/backward roll as you use max or min collective. The FBL controller will sense this and attempt to correct it, keeping it level through the climb as best it can. As a result, it is entirely possible that in flight you will not even notice it. If you do, you can setup a Tx mix (if your Tx supports it) to counter it. This mix can't really be setup on the bench though. I'd do it during a few test flights, little by little. And I'd test forward flight while using collective to climb and drop altitude, making sure the mix wasn't causing it to nose up/down unexpectedly.
Also, I learned it as anti-rotation bracket, not auto-rotation bracket. It keeps the lower swash from rotating out of alignment (it does this along with the mainshaft itself, which is the second point needed to brace it).
It is pulling a little extra at minimum pitch and pushing a little extra at maximum pitch. So adjusting link lengths will not be able to correct it. You are already at the inner hole on that servo arm (ELE servo), so that won't help either. You could try moving the two other servo arm balls (PIT and AIL servos) to the outer servo arm hole. This will make those two links push and pull a little more at the extremes of collective, making the swash a little bit closer to level at those positions. Given the amount of difference, I doubt it will completely close the gap, but it will improve it a bit.
Also, this gap is going to induce a forward/backward roll as you use max or min collective. The FBL controller will sense this and attempt to correct it, keeping it level through the climb as best it can. As a result, it is entirely possible that in flight you will not even notice it. If you do, you can setup a Tx mix (if your Tx supports it) to counter it. This mix can't really be setup on the bench though. I'd do it during a few test flights, little by little. And I'd test forward flight while using collective to climb and drop altitude, making sure the mix wasn't causing it to nose up/down unexpectedly.
Also, I learned it as anti-rotation bracket, not auto-rotation bracket. It keeps the lower swash from rotating out of alignment (it does this along with the mainshaft itself, which is the second point needed to brace it).
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