Very sluggish alt hold on overpowered Octo

Hey guys and girls,

I've followed DIY drones for a while and there's a ton of great info on here. Unfortunately I've run into a problem. I've got a very overpowered octo on Ardu 3.01 that needs dialling in on Alt Hold and Loiter. I have the alt hold working well, it holds altitude nicely but when I want to climb or descend the rates are very slow, to almost nothing at all.

I'm used to the alt hold on DJI WKM which basically felt like having manual control except it locked in the altitude better. With Ardu so far I'm getting a decent alt hold, but no climb/descent performance. I mean it's barely a crawl at 10 cm/s or even nothing at all sometimes.

This is an early foray into Ardu for me and overall I'm loving it. Stablize is working really well so I'm happy with that. I studied flight control and PIDs at Uni for my aero eng degree, which is one of the reasons I went with Ardu because I could get into the nooks and crannies of the flight controller. Something you can't do with DJI. And I feel this has let me tune a big octo better than I could with DJI. Stablize is working better than it did with DJI.

The rig this is for for pro film work, it'll be carrying a Red Epic and anamorphic lenses. So as you can imagine it's very overpowered in it's current state (with no payload or gimbal). Specs:

Ardu 2.5 board with 3.01 firmware
Cinestar 8 centre frame with 550mm custom booms, 1.25 m diameter
Motors: KopterWorx KV10-V2
ESC: KopterWorx 80 amp
Props: Aerobot 15 x 5.5 carbon
Packs: 6s2p 16,600 MaH
Castle BEC for Ardu power

Video of the second test flight:




Everything has been calibrated and as I mentioned, stabilize mode is great. It's just alt-hold that has be scratching my head. Once that's sorted I can get to work on loiter.

Any thoughts guys? I've tried adding I to THR_RATE, increasing the I max, I've ramped the THR_ALT P up to the max of 8 and down as low as 1.5 with no difference in cimb rate, I've maxed out the I_MAX on this as well to 500 cm/s and still no change.

Am I expecting too much for the climb/descent rate to be similar to what's in manual? Right now it's barely 10cm/s.

Cheers!

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Replies

  • THR_ALT_I might also be missing or too low. Warning: too much I will cause bouncing. The desired maximum rate is 1m/s...does this seem about the right speed you're seeing?

    Edit: watched the vid (without sound) - all looks ok?
  • Developer

    Hey Shahid,

    Could you give us a log of one of your flights where you show the slow Alt_Hold?

    Sorry that the dev's missed your post!

    Thanks

  • Well in the end, with work coming in and not much time to sort Ardu I've resorted to using DJI WKM. It works a treat out of the box. Stock gains are fine for AP work, maybe a little tightening up but as usual I'm impressed. GPS etc all fine. Be interesting to know what control architecture DJI uses to achieve this.

  • What values are you using for: PILOT_VELZ_MAX, THR_ALT__MAX, THR_RATE_IMAX, AND WPNAV_SPEED_UP? It sounds like one of these values is capping the max vertical speed at a lower level than you prefer.
  • Hey guys and girls,

    No one has any thoughts? Is alt hold supposed to work that way or should I expect more of a climb/descent rate?

    Thanks in advance!

  • I managed to grab some video so you guys have a better idea what this all looks like. Thanks very much in advance for your help and advice :)

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