Direct Drive Fixed Pitch Tail Tuning in 3.6.4

Hello, I put together a Blade230s that is stretched to 250mm blades along with a Radiolink Minipix controller, the tail is DDFP on these little helicopters. I have read about Chris putting a DDFP tail on a couple of his birds and that has helped tremendously with getting the bird off the ground. So far I have vibe checks in stabilize and loiter and I think they are acceptable if I’m not mistaken. The position hold and alt hold works fairly well in loiter so far but I’m trying to figure out the tail tuning. She does hold the tail and responds to inputs but the tail constantly wags back and forth. I have followed what little documentation on the traditional helicopter ardupilot docs page regarding yaw tuning but I havent been able to stop the tail wag, does anyone have any input on my setup? Here are the params and a recent log today, thanks guys!

Good timing! I was also playing with the DDFP recently with a new compound heli configuration. I have the code working and the only way I could get a realflight model working for this config was to use DDFP. However I didn’t have much success in trying to tune the Yaw axis with the DDFP motors.
You may try cutting back your ATC_ANG_YAW_P parameter to 2.5. @ChrisOlson May have some other tips.

I would say you are probably running too much I-gain for a DDFP. They are more like multicopter tuning and a lot depends on how fast the motor can accelerate and decelerate the prop to get the desired result. So not every one will be the same.

Typically higher P and D gain, and less I-gain is going to work. Turn off the rate VFF. Turn off the yaw rate ILMI. I would start about 0.3 P-gain, maybe 0.1 I-gain and .008 D-gain, set the ATC_ANG_YAW_P back to 4.5 and see what it does.

If it’s wagging back and forth that sort of tells me it is throttling the tail motor, producing more thrust than it needs, but the P-gain is not high enough to back off the throttling fast enough when the tail swings.

Might want to increase the FILT setting too. I think at least 30 for a DDFP. The default yaw FILT for multicopters is 100, if that gives you an idea. The faster the update rate, the better it is when throttling motors to vary thrust. They do not react near as a fast as a mechanical tail.

I got DDFP to work on a Trex 500. I tried it on a 600 and it did not work. The DDFP tail is simply not fast enough spinning a bigger prop to handle the torque of a 600 class rotor.

Thanks very much for the insight, those settings fixed the tail, she is pretty solid now!

Good deal. To get it even tighter in the wind you can try turning up the Stabilize yaw P (ATC_ANG_YAW_P) to as high as 6. And even turn up the rate P and D some more. You’ll know when you get too much because the tail motor will start surging very rapidly.

I would not increase the I-gain much above 0.1 though. Too much I-gain makes the tail motor start to sound really mad and it will growl and/or screech like the timing is off. I don’t know why it does that. But the I-gain actually does very little for a DDFP anyway. It’s mostly P and D and really fast update rate in the PID loop that will make it solid. Most ESC’s can throttle at 400x/sec or so.

Okay I will give those a try, heading out for the first waypoint missions now

Waypoint missions with a Blade 250? This is cool! I’m sure folks would like to see a short YouTube vid of that! Only one other user I know of has ever flown a micro on waypoints :grinning:

I packed my camera for some external footage and totally forgot to video the missions! The missions were just 7-8 spline waypoints with the first few at 11mph and the last few at 25mph. She did pretty good as far as I can see without checking the logs yet. Super quiet and depending on wether my power module is calibrated, it draws 9-10 amps at 25mph.

Here is the video of the Blade230s on a waypoint mission


I wouldn’t trust the auto takeoff/land stuff with a big heli. But it is pretty cool with a small one. That sideways drift on landing would knock the blades into lead/lag and cause a big heavy one to go into ground resonance. That would be hairy spinning a 6 foot main rotor.

Those little heli’s are a lot of fun.

Looks like the DDFP tail is working pretty good too.

I totally agree with the auto T/O and land, this bird is just a testbed so I did it anyway :slight_smile: Thanks again for the help on the DDFP