Development discussion of TauLabs software such as flight controllers, sensors, radios and speed controllers.

Altitude hold refinement

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peabody124

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Re: Altitude hold refinement

by peabody124 » Mon Mar 09, 2015 3:53 pm

Yeah the control loop is fairly fast. I've been thinking about adding in acceleration limiting (optionally) for people that don't want it to be quite as abrupt.
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droney

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Re: Altitude hold refinement

by droney » Mon Dec 07, 2015 1:20 am

Looking for some ideas on setting the Altitude Hold parameters. Tilt compensation is currently set to 220 and all other settings are at their defaults (although I have tried lowering and raising the Kp and Ki values). Problem is tilt compensation does not seem to help hold altitude for roll and pitch movements unless I apply braking to reverse the roll or pitch change. Said differently, if I perform gentle pitch and roll movements during AH, when I release the stick the quad levels back out but drops in altitude gradually as the craft slides in the direction of the requested movement change. Eventually AH catches the error and returns the craft to the proper altitude, but by then the quad has dropped 1-2 meters. If I apply quick braking motion, altitude holds just fine.

Quad is and Alien 680 and heavy (just under 7 pounds with the big battery). Anyone else seen this behavior in AH and know how to correct it?
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cedric

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Re: Altitude hold refinement

by cedric » Tue Dec 08, 2015 12:57 am

I get the same thing on a S500 weighing in at 1300g. I'm using the latest release (safety fix) In AltitudeHoldSettings I use "Attitude comp" at 200, default for the rest.

The other thing I've noticed is in position mode and using the option* which allows xmitter control of altitude(ThottleControl FALSE), a very miniscule change in throttle makes a altitude change and I can't get it to stay at an altitude at all. I like how it goes straight up, but I got a camera and gimbal and want to take video with the thing reasonable still. Don't know if there is something to adjust that?

So I can set the position mode option back to holding altitude (ThottleControl TRUE) and climb using regular altitude hold, then switching to position mode. But recently I read a post saying Return to Home needs the option set to ThottleControl FALSE. If I have to do that, I lose RTH functionality.
I haven't tried RTH with newer releases yet, so no first hand experience to report.

* ThrottleControl in VTOLPathFollowersettings.
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droney

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Re: Altitude hold refinement

by droney » Tue Dec 08, 2015 1:30 am

Hello Cedric - I think I can help with the throttle issue.... try changing the AltitudeHold 'expo' setting. It should be set close to the hover throttle point. If your craft hovers at 50%, set expo to 50. You can also dial down the 'Rate' setting if the throttle movements is too aggressive for your taste. There is a large deadband on throttle position in altitude hold mode (and the deadband setting is not currently working). So you have to move the stick pretty low or pretty high past the expo point in order to get vertical movement. This takes a little getting use to.
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pug398

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Re: Altitude hold refinement

by pug398 » Tue Dec 08, 2015 1:33 am

Generally for the lighter ones 1 - 1.5kg I use position kp=0.8 and velocity kp=0.2. For the heavier ones position kp=1 - 1.1 and velocity kp=0.3 - 0.35. That is pretty much the range I have stayed in. Comp has been 150 - 200 mostly. The baro senses pressure not true altitude so anything that causes a pressure change will cause it to change altitude. Light also causes it to change altitude. At the very least it needs dense open cell foam over the baro to shield it from moving air and light. A dark case is even better. Even then it is not perfect.

When in AH mode the vtolpathfollower settings should have no effect and there will always be throttle control with deadband.
In PH mode if ThrottleControl is set to false then you have direct throttle control and it can be touchy. If set to true it maintains altitude automatically. There is another setting LoiterAllowAltControl that must also be set to true in order to have adjustable throttle control with deadband while doing PH. The settings do not affect throttle in RTH mode. There is a RTH velocity setting that affects speed returning home but that is for horizontal velocity not vertical.
Last edited by pug398 on Tue Dec 08, 2015 2:11 pm, edited 1 time in total.
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droney

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Re: Altitude hold refinement

by droney » Tue Dec 08, 2015 2:40 am

thanks pug398. Which kp are you referring to, velocity or position?
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pug398

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Re: Altitude hold refinement

by pug398 » Tue Dec 08, 2015 2:09 pm

Oops. Thanks for catching that. Meant they are both kp. The first is kp for position and the second is kp for velocity and corrected it.
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alexpaul

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Re: Altitude hold refinement

by alexpaul » Thu Nov 10, 2016 4:10 am

Did a little more testing with the variable altitude hold yesterday with Peabody and today at lunch.

This was last night using stock settings for altitude hold. 4m/s climb rate and 40% throttle exp.
I found these setting to work well LOS, but flying FPV it was hard to visually tell when I was at 50% throttle and neither climbing nor descending.
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