Setting hover collective after reducing head speed

[Fowler (Iain)]

Hi,

I have modified a TREX450 running ArduCopter. I’ve been going through the setup, but before starting with AutoTune I want to get my head speed correct.

I wrote a blade element momentum theory code from Leishman’s Helicopter Aerodynamics book, and have verified the output against past flights/data from my helicopter. From this, along with the blade aerodynamic data, I have concluded that a head speed of 2500 RPM and pitch of around 6.1 deg will give me the thrust to hover nicely with my setup, while still giving enough margin to blade stall.

I currently run a 2800 RPM head speed governed by the Castle Creations Talon 35 ESC (ext RPM sensor on the main gear). I want to drop this to 2500 RPM, so I will therefore need more pitch to hover. The heli currently hovers at around 4.8 deg with the higher head speed.

With:

H_COL_ANG_MIN = -2.7
H_COL_ANG_MAX = 11.4

I calculated that CTUN.ThO needs to be around 0.62 to achieve the ~6.1 deg.

I have been flying in Stabilize and AltHold mode for now, so am I correct in saying I need to change the curve of IM_STB_COL_X to achieve hover at mid stick in Stabilize?

And for AltHold, do I also need to do something with H_HOVER_LEARN, or will ArduCopter learn the required hover collective itself?

Thanks in advance.

[bnsgeyer (Bill Geyer)]

@Fowler

I wrote a blade element momentum theory code from Leishman’s Helicopter Aerodynamics book, and have verified the output against past flights/data from my helicopter. From this, along with the blade aerodynamic data, I have concluded that a head speed of 2500 RPM and pitch of around 6.1 deg will give me the thrust to hover nicely with my setup, while still giving enough margin to blade stall.

Nicely done! It’s always good to see that theory matches the real world

@Fowler

I have been flying in Stabilize and AltHold mode for now, so am I correct in saying I need to change the curve of IM_STB_COL_X to achieve hover at mid stick in Stabilize?

Yes that is always a good idea to set the stabilize collective so that it hovers around mid stick.

@Fowler

And for AltHold, do I also need to do something with H_HOVER_LEARN, or will ArduCopter learn the required hover collective itself?

No, the code will learn the hover collective for althold.

As for autotune, you can use that if you choose. If you have the engineering background then you may want to look into the analytic tune. Here is a link the post that talks about how to use analytic tune.

Using Analytic Tune Web Tool to tune your helicopter

Here is a video that describes how to use the analytic tuning tool to tune your helicopter. This only covers tuning the pitch and roll axes. The yaw axis is tuned similar to the multirotor pitch and roll axes which is described in Leonard’s video. This describes the basic tune. There are other techniques that involve using the PID notches that will provide a better tune. But just want to get folks started using the tool and asking questions. [Analytic tuning of helicopter]

[Fowler (Iain)]

Thanks for the clarification Bill, this helps a lot, I’ve made the changes, now I just need to wait for some good weather!

I’ll take a look at analytic tune, sounds right up my alley to be honest!

[bnsgeyer (Bill Geyer)]

Yes, I think it gets you to a good tune with less flight time. Let me know if you have any problems with it.