Dialing in a Large Helicopter

I have been working on a Trex 550 stretched to a 700 size for fun. Now that I have that flying so well I had to move on to the big bird. Custom frame with 980mm blades weighing in at around 30lbs. I have been working on dialing in the this helicopter in loiter mode to where it’s very consistent meaning where I tell it to stay it stays with no hiccups. I have gotten to the point where it flies pretty well but sometimes fight me in loiter mode.

If someone has time to give me suggestions on dialing in this monster that would be awesome!

Attached is my log files and a few shots of my roll in roll out and pitch in pitch out.

Thank you,

Hi Sean,

Is this electric or gas?

First off, this machine has pretty bad vibrations. It’s enough that it can probably cause the AHRS attitude estimate to go off due to aliasing (remember “leans” back in the day?). You may even find it’s not very stable in Stabilize. At the very least, it’s too high for Loiter. You need to get that fixed. Check your bearings, shafts, blade balance and tracking. Also check the Pixhawk mounting.

Secondly, the roll vs. desroll shows a constant off-set. This indicates either the transverse CG is off (not likely) or the swashplate isn’t quite level, so adjust your servo trims and/or linkages. Basically, it constantly is righting to stop a roll, and due to the Leaky-I-term, it can’t ever quite get it level.

Oh, wait, your pitch and roll I-terms are quite low. You should be able to start at 0.100, and go from there, maybe up to 0.500, some people even go up to 1.0. But 0.038 is certainly too low. Also increase the Imax to 2500. This will all help with the above issue.

Your Rate yaw Imax is 30,000, this is well out of range. Reduce it to 4500 max.

That’s what I see so far.


Large Electric.

Wow I had no idea I was so far off. The helicopter seems to fly pretty well in stab mode but not in loiter so now I know.

I will be working on dialing in the helicopter today hope it goes well.

I think I found my vibration problem I had a bearing issue so I will pull the logs today to review them.

Off helicopter topic is it a good idea to run a high I gain for a quad copter as well?

Yes, typically you would run the I-term at 1 or 2 times the level of P-term on a quad. But on heli, the spread is much more. P tends to be very low, and I-term tends to be very high. This is because of the very different response characteristics of the two systems.

Also, the default Imax is too low. I tend to run it at 4500 on all machine types. It won’t take it if it doesn’t need it. And if it needs it, it needs it. I’ve never seen anything bad happen from an Imax being too high. I guess, maybe with a multicopter if you left it idling on the ground too long it might built up a huge I-term and could flip on takeoff. But a skilled pilot won’t do that, or will hear it in the motors on the ground and abort the takeoff.

Well helicopter now flies amazing! Loiter is now rock solid.

Thanks for your help.