Z sensitivity + No collective control in GPS stabilized modes

I’ve just had my first flight on an electric 700 in stabilized mode. It flies, which is nice, but was way too responsive to the throttle/collective input, jerking up and down even for small inputs, so I wasn’t able to hover.

What is the best way to make it less touchy? Bring H_COL_MIN/H_COL_MAX in further to reduce the collective range (currently measured at +12/-2°), or is there another parameter such as PILOT_ACCEL_Z that might make it less twitchy without reducing the maximum possible pitches? Or use both approaches?

A second question, when I try POSHOLD or LOITER on the ground, the collective doesn’t do anything at all. It goes straight to the H_COL_MIN position and stays there. Is that a bug, or is there a clever reason I just don’t understand? I’m running 4.2.3.

Assuming I get get POSHOLD to work, can one take-off and land in that mode as with multi-copters?

Many thanks!

@Brodo

Nice! Congrats. I had recently transitioned a Trex 700 electric to ardupilot and I had the same experience. I only did one flight and haven’t got back to tuning it. So I would say that you should try changing the midpoints on the stabilize collective curve (IM_STB_COL_2 and IM_STB_COL_3). You just have to be sure it is hovering about mid stick. Here is the wiki that describes this set up.

As for the collective response in loiter, it is designed not to respond when the aircraft is disarmed and landed.

Yes you can takeoff and land in loiter, poshold, althold etc

Many thanks Bill!

You beat me to answering my own question about the collective over-responsiveness by a few minutes. For others who find themselves here asking this question, Chris also describes setting the stabilize throttle curve around the 20:00 mark of this video:

I had seen that Wiki page describing it, but at the time I was busy setting up the swashplate and forgot it also described the throttle curve, thanks again Bill.

Regarding POSHOLD/LOITER I did try using the collective with the heli armed, but with the interlock still engaged and it didn’t move the collective. From what you’re saying Bill, if I actually let it spool up in POSHOLD, then the throttle stick will have an effect and I’ll be able to take off? And until then does it park itself at H_COL_LAND_MIN?

The collective stick in poshold commands vertical rate and when centered commands altitude hold. If you are landed, it requires you to move the stick above mid stick to command a climb rate before the code will start its takeoff logic. Any reason that you are focused on poshold? Loiter will offer similar flight characteristics.

One last thing, be sure you get the vehicle tuned in stabilize. Then move on to check the altitude controller in althold. After that then you can move on to loiter or poshold.

Thank you Bill.

I’m open to advice on Loiter vs PosHold. In fact I was Googling the distinction the other day, the best I could find was that Leonard had updated the Loiter logic ‘new loiter’ at some point and the two were pretty much interchangable these days? I originally started using PosHold with my multi-copters because the wiki mode description said it was like Loiter but the controls feel more natural so I just went with that and have never really used Loiter.

I was able to ‘hover’ very briefly on my maiden, so I’ve set the stabilize throttle curve with the sticks centred around that throttle level as read from RATE.AOut. I was also able to get some initial values for the harmonic notch filter from that flight.

Tomorrow will have less wind so I’ll set ATC_HOVR_ROL_TRM and try to get a feel for how well it responds with the default PID params and then aim to give AltHold, Loiter/PosHold a try. I normally tune my multicopters manually but might give the autotune a try in this case - in stabilize.

My final objective is then progress to an Auto mission with some turns etc so I can run MagFit. I wasn’t able to get the second compass to calibrate very well waving the heli around by hand so I currently have it disabled.

Well loiter is designed for the aileron and elevator stick to command velocity over the ground and then hold position when the stick is centered. Poshold just commands pitch/roll attitude. I have not spent much time using poshold.

Well, the default PIDs are very generic and may not work well for your heli to move to loiter or auto without tuning. I would suggest you perform tuning in stabilize. Tuning a heli is much different from tuning a multicopter, so i suggest you follow the heli tuning wiki. The heli autotune is much different from the multicopter autotune. Please be sure to follow the heli autotune wiki.

In most cases, only the external compass is used. The compass in the flight controller is typically not used. Most of time the internal compass has too much interference.

Thank Bill. Yep, both compasses are external and mounted on the tail boom away from sources of noise.