Drift Mode

What would Drift Mode do if used on a trad heli?

Hopefully it would fly great. No need for two sticks. Just fly on one - but in mode 2 only.

I hope to have my Logo 400 back in the air soon and it’s one of the first things I’m going to try.

If you get there soon, please let us all know how it went.

I’ll give it try then!
But it will be a little while yet, must test and tweak other modes first and I haven’t even got a first flight completed. And it looks like rain for the next few days…

Apparently if you get “loiter” dialled in properly then “drift” should work fine. But we will be some of the few testing on trad helis so be careful. And good luck…

Complicated topic.

I have tested drift on my 450 heli, and it does work. One important thing to know, is that in 3.1, when you switch to Drift mode, you will get the FULL collective range, not the reduced Stab range if you use that feature. So, when you switch to Drift from Stab, the copter will fall, you have to be ready for it and raise the collective, just as you would when changing Idle-Ups.

I figure most people using Drift will be switching out of Stab, and they will also want the reduced collective range of Stab, not the full range of Acro. So, for 3.1.1 which should be out soon, I have changed it such that it will use the Stab collective, not the full Acro collective range.

Other than that, it works fine… as long as you aren’t pushing it too hard. But there’s an issue at higher speeds. The algorithm was designed to control yaw rates to reasonable levels up to 8 m/s. However, after 8 m/s, the yaw-rate-to-stick-angle flatlines. At high speeds, full yaw stick will cause the heli to turn too quickly, IMO. It can result in a 3+G turn, actually. Meanwhile, the algorithm to control the roll in this mode is pretty much only designed to handle a 1G turn, and without taking into account translational lift, etc.

Net result is that up about 15m/s+, if you push the turn stick full over, you can get a turn rate that will cause the heli to wobble. So be aware of that, and just don’t do it. I haven’t had a crash yet, but… I am not really planning on pushing it to failure.

I do worry about what would happen to a 600 flying at 30 m/s…

Last year, I was working on code that would do something similar to what Drift mode does. The intent being something that works well for people flying helis FPV. The idea is that the yaw follows the direction of travel automatically. So I was going to leave the roll control directly connected to the roll stick, just as it is in Stab. But the yaw would behave more like a rudder gyro in rate mode. It will follow the direction of flight naturally.

You can see this already in Auto mode with helis. The tail already does that. That’s my “Yaw Look Ahead” mode.

I was going to make a mode that is like Alt Hold, but uses the YLA yaw controller. But I found that the yaw heading wasn’t great. It uses the GPS reported ground heading. But that lags behind reality at least a quarter second if not more, and is really unstable in a hover. What really needs to be done is to use the inertial navigational controller reported velocity to determine the heading, as it’s much more accurate and faster than GPS. But I couldn’t do that on APM.

Now that PX4/Pixhawk is available, that’s probably what I’ll do.

Call it “Heli FPV Mode” or something. It would use Alt Hold for throttle, Stab for pitch and roll (so it’s full manual), and a better performing YLA for yaw control. I was also going to leave the yaw stick in the loop. It would add up to 45° to the yaw angle from the YLA heading estimate, that way you could “skid” around a corner if you wanted to.

I’m open to any other suggestions though.

Your heli fpv mode sounds awesome. I use loiter alot with 3.01 for fpv flying. I am always reluctant to upgrade to new firmware until I read how it is working for other people. It sounds like 3.1 is working out O.K. as long as people are using channel 8 out on the APM. I do. I guess its time to update to 3.1 and try out this new drift mode. I really dont fly much faster than about 10 m/s very often. If you keep coming out with all these new modes its going to be easy to forget how to fly without using an APM. Its really come a long way. Good Job.

David R. Boulanger

Well, don’t forget that with 3.1, you get a great new Acro mode, it actually flies well. Just like a FBL controller. So you can keep your reflexes sharp! :slight_smile: