Hover Point at 75 % collective with symmetrical head setup

I’m currently doing my head setup with a symmetrical pitch range of ±12 deg. I know it’s not really necessary to have -12 deg with a helicopter used with Pixhawk in a UAV operation. Nevertheless I’d really like to keep the symmetrical setup, because I fly all my other helicopters like that and it’s a way to feel where I actually am in the pitch range. So in any flight condition I can feel where the collective stick is and I instantly know what the helicopter is doing.

Now my problem is that the helicopter hovers at approx. 75 % of the collective pitch range. (Of course not at mid stick, because that’s 0 deg.) Switching to an automated flight mode (or back) would probably lead to a very rough transition. So my question is, if there is a way to move the deadzone of the stick from mid stick up to 75 %.

I looked at the THR_MID parameter, but as far as I understand that’s the exact opposite thing which helps me to move the hover point to mid stick. Am I right?

A workaround would be to program a pitch curve in my transmitter that puts out 50 % when my stick is actually at 75 %. But that doesn’t seem to be a very elegant way to me. Do you have any ideas?

Felix, what do you have IM_STAB values at? Do you have them set for the whole collective range (-12 to 12)? The software was not designed for that. It was designed so that you could make full use of the collective range in Acro and then you have it set for a UAV collective range using the IM_STAB parameters. Typically these are set so that you get -2 to 10 or 12 deg collective in stabilize mode. The transition between the acro and stabilize or althold is done with a ramp over 0.3 seconds or so to allow the pilot to adjust the collective as it switches to the new collective curve.
I would recommend using the software as it was designed.

Ah ok. Thanks a lot for your detailed explanation. Yes, right now my IM_STAB values are set for the full range. But is it actually necessary to reduce the pitch range for the automated flight modes to achieve a safe flight? If I wouldn’t do that, I wouldn’t have the ramp you mentioned and the pilot wouldn’t have to do any corrections on the collective while switching the flight modes. Besides I also like the 3D setup at takeoff. It helps me to know exactly the 0 deg position. Or do I have to expect problems or risks with the controller operating with the full pitch range?

Would it be possible, to just move the deadzone up a little bit? I guess that would completely solve the problem. When I switch from Stabilize to AltHold on the bench, I can’t see a jump in collective. Of course when I’m out of the deadzone, the swashplate starts to move up or down, but slowly. So I guess transition should be smooth. I just would like to have the deadzone around 75 % of the stick range, where my normal hover point is with a symmetrical head setup. Does anyone have an idea how to do that?

Hi Felix
I suppose you could set your stabilize collective to have it cover the entire range of collective. So the collective behavior would be the same for both acro and stabilize. The issue then becomes going from a mode that uses the altitude hold controller where it defines zero climb rate at 50% stick. The dead zone for the stick with altitude controller engaged is +/- 100pwm and is user settable. I think it’s THR_DZ. there is not much else we can do. You are not the normal use case.

Hi Bill!
Thanks for your help. Again!
I set THR_DZ and PILOT_TKOFF_DZ to 220 which covers my hover point. Then I did a flight test. The transition between the modes is perfectly smooth and the autopilot works great. Do you think there is a mode or a situation where the controller uses the definition of zero climb rate at 50% stick? When I switch to AltHold or Loiter it just holds the swashplate where it is and then corrects if the helicopter is actually rising or falling. If it always acts like that I’m perfectly happy.

So let me clarify. the modes that use the altitude controller in the vertical axis will set zero climb rate when the throttle stick is at 50% +/- THR_DZ (in %) So in your case, 50% +/- 22%. then outside of the deadzone, the climbrate/descent rate is proportional to the remaining throw. Also in the deadzone, it is not only zeroing climbrate but also holding a specific altitude when you moved the stick into the deadzone. Hopefully this makes sense.

That totally makes sense. Thank you for the explanation! So I’ll use it like that. The only little drawback is, that in altitude controlled modes I have to move the stick all the way down to descent, but only a tiny little bit up to climb. But that’s okay for now. Maybe in future versions there could be created a new parameter which can move the deadzone up or down. That would be really helpful.