This should be interesting

Bill,
Thanks for the video, it is informative! So that is the kind of oscillation I should see with a P gain that is too high? I’ve run into oscillation on an FBL before, but it was more of a here and there thing where it didn’t happen unless it was in a hover at just the right RPM or on hard stops I would get a quick wobble, but that was using a combined “cyclic” gain term which likely affected more than just P gain. FBL’s tend to block a few different parameters under one single function, probably to make it easier for people to tune?
The only traditional PID’s ive tuned are on multi copters with Cleanflight. Honestly though, those tended to fly pretty good at extremes of P, I or D and seemed to have a pretty wide berth for misguided changes, of which I made many. :confused:

I’m starting to build a picture that points to Pixhawk with Trad Heli being much more finicky and less forgiving than say tuning a multirotor? I’ll find out for sure tomorrow I guess. Weather permitting.

So quickly, I plug in my copter, wait for it to get GPS and do initial calibrations and give the happy tone. Then I can ARM, flip the switch enabling the rotor to spool up and just take off and fly as I would any other heli, then land, shut off the rotor and disarm.
Reason I’m going through this is I was on the bench last night and had spooled it up and was tilting the swash plate back and forth looking for vibrations with the heli up to speed when all of a sudden it said “crash detected” and disarmed and I had to re-arm it and spool back up. No other errors, no EKF or vibe problems. Did I do something to cause this? Is this just normal behavior as it thinks it’s flying when its really not?
I’m just trying to make sure that I am not missing any part of the procedure here and don’t inadvertently do something that will cause the rotor to stop, or control to be lost in the air because of something stupid.
Thanks,
Tim

Tim,
To keep the crash check from accidentally disarming, set FS_CRASH_CHECK = 0. That should disable the crash check. I would disable the GCS failsafe also. Set FS_GCS_ENABLE = 0. I’m not sure what the EKF failsafe is supposed to do. But that failsafe is still enabled in your parameter file. Not sure what to do about that.

No, it’s not more finicky. Just a different type of machine that is way more responsive than the typical multi. Helicopters are capable of extreme manuveurs that multi’s aren’t. A docile helicopter with slowed mechanical rates is just as easy to tune as a multi.

Is the head on your heli the stock Align piece? It’s interesting that using the 10mm throw on the cyclic servos yields that kind of response indicated by your H_COL params. The bellcrank ratio on my flybars is 1:2.38, but flybars use a lot more radical swash movement than FBL does. I don’t know what it is on the FBL ones but you’d probably have to custom-make some lower ratio bellcranks to reduce the mechanical rate on that heli. The scale people build a lot of that stuff. I got an Augusta A109 kit for a 600 with retract gear and the whole shebang that I’m going to build at some point. The low ratio bellcranks came with the kit to slow it down.

Chris,
Yeah, the head is stock V2 Align. It is the standard follower arm swash with the push pull setup all around. I honestly dug hard to find a v2 as all the Aligns went with DFC until recently and I was never sold on that setup.
Now align has gone back to having follower arms with their new FL stlye head, although the servos are oriented around the mainshaft vertically as are most helicopters these days it seems.
Tim

Bill,
Thanks, i will disable the parameter!
Tim

Correct (according to LEDs Meaning — Copter documentation )
Flashing green: Disarmed (ready to arm), GPS lock acquired. Quick double tone when disarming from the armed state.

Fast Flashing green: Same as above but GPS is using SBAS (so should have better position estimate).

Chris,
Just a few snapshots of the mechanics. They are all stock V2 mechanics save for better quality bearings. I swapped every bearing on the helicopter with higher quality Boca ceramic. That immediatly resulted in a helicopter with greatly reduced vibes. I had bought this frame used and had to tear it down anyways so it made sence.
I have some carbon plate i am going to use here and there as well to attenuate vibes if need be, but id like to keep this as simple and repeatable as possible.

As i said before, i went V2 Trex because i never got sold on DFC and saw alot of issues with dampeners on those, ironically later Align has gone back to swash follower arms and away from DFC with the 700L V2 and the 700X. Unfortunatly both those frames are stripped down and built for 3D so not of much use for me. Id like to get my hands on a few Trex 800 Trekker frames with a follower arm head but those are like hens teeth these days.

Well,
If it is getting the corrected signal from the network, then i am impressed. Its no-where near RTK but better than a standard fix.
Has this been a feature of the M8N all along? I guess i missed something somewhere?
I would think two Here modules with a blended fix would be good enough for most?
Tim

Mission Planner detects Here as M8N so yeah.[quote=“timbaconheli, post:249, topic:16800”]
I would think two Here modules with a blended fix would be good enough for most?
[/quote]

I don’t think blending will increase accuracy much (from around 2 meters **it won’t always drift 2meters). I could be wrong but it never hurts to have more.
And from what I read from developers, Here is one of the most sensitive GPS available thanks to its massive ground plate (the reason why the puck is so wide). It locks on 20 sats in no time!
I saw a video of someone’s copter landing within 10cm using 1 normal Here GPS.

Pitt,
That is good to hear. I am still shocked at how quick it locks on indoors and gets to a dGPS lock. Im glad i went with the Here now vs the Holybro M8n
Tim

Uggh,
So I have made sure the green bar follows my transmitter stick in mission planner. That being said, It was not moving the tail in the right direction so I reversed RC4 in the parameters. Now the heli will yaw correctly when I give a stick command.
BUT, I am noticing that the heli is not compensating properly on YAW.

I push the stick to the right and the leading edge of the blades goes left and if I move the stick left the opposite happens. Now when I physically move the heli the blades compensate in a way that would increase the rotation in that direction. :confused:
I have no reverse in my radio, the unit is mounted with the arrow forward with the correct compensation and the swash moves and corrects as it should.

I came across some material that Randy posted.

Developer
Permalink Reply by Randy on April 16, 2014 at 8:58pm
Evan,
We took those rev switches off the radio calibration screen because they should never be used.
On the mission planner heli set-up page there is a servo reverse button. You know. maybe the REV you need is not on the RC4_REV but the HS4_REV.
:arrow_forward: Reply
Wow! Randy you are right, HS4_REV reversed the gyro only! This is exactly the setting I was looking for.
Whats also interesting is that I don’t have a heli setup section like in that link that you provided, I am running APM Planner 2.0.8…

Thank you very much for the help.

Just took it off for the first time with the Pixhawk, everything was looking good until after about 3 seconds the cyclic started going crazy and the whole copter shook like crazy and had to land. I attached a short clip.

Any ideas off the top of your head what settings I should look into? I am a complete beginner with these autopilots so I am still learning. I will research this issue now in the meantime on the forums.

That’s all well and good, BUT it appears that is outdated info as that parameter does not exist on my Mission Planner Full Parameter List.

Thanks,
Tim

so it looks like the H_SV1_MIN, H_SV1_MAX… parameters were moved to SERVO1_MIN …
So I think you need to change SERVO4_REV to 1 and put RC4_REV back to 0. Hopefully that makes everything work correctly. So right stick causes the tail rotor pitch to move so that the nose would come right. Then check that if you rotate the nose right that the blades change to give a left pedal input indicating that the control laws were working to oppose the nose swing. Hopefully that makes sense.

Bill,
Thanks, i will take a look at that in the morning. Ill reset the RV4 reverse and look for the other parameter.
I was just checking things over and caught this. One thing ill say is the tail compensation is somewhat hard to read. Its not as defined a compensation that im used to with FBL. When you grab the tail with an fbl and swing it one way or the other it clearly pitches the blades to compensate, with Pixhawk it seems very subtle and requires a hard/fast movement to get any reaponse at all with it.
Is that normal behavior? Or is that indicating a problem i wonder? Keep in mind im using the values Chris suggested for YAW.
Tim

That is normal for starting PID gains.
It will act as you expected once yaw tuning is done which is usually after cyclic tuning. Bill seems to be an expert at that :slight_smile:

Pitt,
It should be noted that this happens with numbers Chris gave me for the tail, not low starting numbers. Ive put the P gain up to .5 with no noticeable difference on YAW correcting on the bench, although i put the P gain back to .25.
ATC_RAT_YAW_P .25
ATC_RAT_YAW D .003.
ATC_RAT_YAW_I .17
Those are the numbers im running while experience that behavior. I guess i am just used to a much more defined correction on the bench and along with the tail blades moving with hard cyclic and elevator movements, it just makes me questions things.
As this is my first go with Pixhawk, im decidedly on edge and these questions i have that may seem silly to current users will fade away.
I am only farmiliar with FBL’s on helis, and this acts quite different on the bench, so here I am.
Tim

The old 3DR mounting pads work outstanding. The vibes on my Heli are about the same as my well balanced Multirotors

Let’s wait for others.
I have never used Arducopter with trad-heli myself.
On mine, servos move quite a lot if I rotate it quickly (it’s the angular velocity that matters for yaw) with P ~ 0.08+ but that’s for differential-cyclic-yaw which don’t apply to you :stuck_out_tongue:

I’m also still in the first go with the Pixhawk and all I can tell is it will remain overwhelming for a loooong time :grimacing:

What I went through:

  1. Built a strangest config helicopter
  2. Decided to use Ardupilot >> Couldn’t find reliable Pixhawk
  3. Pre-ordered Pixhawk2 >> Received in December (First batch!)
  4. Messed with the developing tandem heli code without hearing anything from the author
  5. Saved by Bill and my heli now flies like a heli!

It’s been more of a hassle than fun but still loads of fun.

There is a saying: “When idoit asks, he’s no longer an idiot”. <<No offense

Old 3dr mounting pads? Do you mean 3m foam style or the shock mounts?
Thanks,
Tim

The thick foam pads with adhesive on each side. I’m not sure but MRobotics may still sell them. I bought a bunch close to 2 years ago from 3DR. I still use a Pixhawk 1 but they work extremely well.

David