In general, what direction would PIDs be tuned when moving from 10x4.7" to 12x4.7" props on a mostly-standard ArduCopter? When putting together my current FPV rig I found that I got more stable flight at lower throttle settings using the larger props, with the exception that any descent causes the copter to wobble like crazy. I saw this same effect with the smaller props but it took a much more rapid rate of descent to trigger it.
Note - this is in STABILIZE mode, which is the only mode I'm willing to fly FPV in at this point.
The copter doesn't seem to overbalance but it does wobble through 30 degrees or so whenever it descends, and in addition to making my video look like crap it's rather difficult to control. I assume I need to adjust a PID value to deal with this; any suggestions on what to adjust?
Hey dude, I could be wrong, but from what i understand, the wobbles on descent is the craft falling through its own prop wash/turbulence. I get it too, but not if I'm tracking forward at a decent rate. I've changed to the big props too, seems to not have to work so hard to stay up, quieter too.
If it is quick oscillations you can decrease the Rate P value, if it is slow oscillations you can decrease the Stabilise P value. Remeber to adjust both the Roll and Pitch values :-)
Friends of mine also went to 12" props and found exactly the same as you, and we reduced their Rate P values over 4 flights (small changes) and it now works very well again.
That's great Jaques, thanks for you reply, I'll have a play when I get home. Any idea of what values you guys ended up on?
Owen, I really cant remember the values themselves, but I remember that we reduced the value by 2%, then another 4%, then 6% and finally increased it again by 2%. Its very satisfying to be able to get the craft to fly perfectly.
http://code.google.com/p/arducopter/wiki/AC2_Tweaks - Very very good page, and remember to make small changes and only change one thing at a time! Oh, and another very important thing is to save the setup files so you can go back to previous setups, that leads to the 2nd very important thing: after Writing the values to the APM, Refresh the values in die config screen to see that your changes uploaded correctly. Once I didn't do this verification and I had to install 2 new blades after an uncontrollable takeoff. I now first take the copter and run it while I'm holding it from the bottom and then I can 'feel' the craft's response against my movements - doesn't help much for fine-tuning, but if something doesn't work correctly, you'll know before it costs you money ;-)
Thanks very much for the sound advice Jaques, I'll see how I go :)
When I fly original ArduCopters made by jDrones. I always use or start with these values with bigger 880Kv and 12" props.
Those values are really good starting point to fine tune your frame. (And we fly them a lot :) )
cheers Jani, I've only the 850kv's, but I'll start there and work my way around. Have you an ETA on the upcoming, and much sought after OSD break-out board for the AC? I keep looking, longingly at the Remzibi, telling myself to be patient :)