Pitt,
The pixhawk is positioned with setting 20, 270°. The arrow points twords the nose of the helicopter of course, ill have to look at the compass settings in a cpl min.
Tim
Pitt,
Oh and now that im thinking about it, i think only comapss 1 is enabled, 2 and 3 are disabled.
Tim
Alright, this is starting to drive me nuts!.
I am inside on the bench, the GPS had a great dGPS lock, the EKF was low, no error messages at boot or at all really.
Sitting on the bench without input the swash takes a HARD dive to the left and locks up, I have to unplug the servos before it breaks a link, now the safety switch is flashing. Absolutely NO error messages, EKF ststus looks great. I also have the safety switch to start in the “armed and ready” position so I can eliminate having to press the button. No dice. 
I also booted it up without the radio on to eliminate anything there and the same thing happens. It boots, arms the switch after awhile and at some point it will disarm the safety switch on it own without an error message.
It should be noted the swash moves “WAY PAST” the range I have it set to use in the parameters It seriously has popped off a link doing this…
Tim
This is what happens when I manually depress safety-switch.
I believe this happens because the flashing switch cuts the PWM midway, if 1500us PWM got cut in half to 750us, servo will go to extreme position.
If this is true, reverse, trim, limits will have no effect to lock up position and if you re-power servos (without rebooting Pixhawk) they will stop locking up.
I think you should be looking at how safety-switch disarm itself.
Pitt,
Thats exactly what im trying to figure out. It just sits there armed with solid red led for varying amounts of time, then with no error message or useful cluew it starts flashing and i cant press the button to get it solid again. It just goes solid red and ready all on its own. Perplexing… uggh
Tim
I checked all the wires and none of them cross on the Here from the factory, but honestly if a wire was crossed would it even work at any time?
Tim
Well, i “think” i have found the issue. The 6th wire in, the “Button” wire @pin 6 seems to have a weak connection to the pixhawk carrier board. If i wiggle the pin the led will start flashing and its in the “safe position”.
Im going to see if i can “tighten up” the contact of the pin.
It strikes me as odd as the switch functions “when shorting to ground”, so when set to arm it is lit then somehow shorts and resets the switch just sitting there, but if i wiggle that specific pin with the tweezers it disarms and arms the switch.
Tim
Update: so far, so good. I have re-booted the Pixhawk 2.1 many times, indoors, outside etc. and it is working as I think it should! All these issues from a pin in the connector that just didn’t contact well. I had removed and re-inserted that very connector many times but just didn’t get it right I guess.
The Here GPS acquires a 3D lock very quickly indoors and shortly thereafter it gets DGPS. My arming on the radio works perfectly as does the safety switch now. I even went so far as to arm the heli and hook up a 6s pack and confirm the channel 8 throttle is working correctly with the Castle gov. Another check plus!
As to the EKF errors and such, I turned off all but one compass and it seems to work perfectly, I have monitored the EKF status and even violently shaking the heli along with spinning it around and holding it upside down does not produce an EKF error or a lane switch anymore.
Is it bad to only have one compass active I wonder? If not would another calibration help the issue? I have the Here GPS and that contains a compass as well, should I be using that one and if so do I have to adjust the orientation? I read a thread where someone had it mounted with both arrows on the Pixhawk and the GPS pointing in the same direction, but it sounded as though they had to change the compass orientation In the Here as well?
I’m off to start getting permanent wiring made for the Pixhawk on the heli and hopefully be able to move forward to a controlled spool up next week? That’s a big maybe though. I still have a lot of material to sift through before I am confident with this system.
Tim
Tim, good to hear you’re making progress with finding the problem.
I have only used internal compass on one helicopter and gotten it to work. The Pixhawk is mounted near too much magnetic interference (usually) for the internal compass to be reliable or accurate. There’s usually servo battery, BEC for that for the servos, the servos themselves, on an electric a big ESC, battery and motor nearby, and on combustion engine an electric fuel pump, RevLok governor or ECM nearby. And it all causes problems with the internal compass (normally).
Chris,
So im selecting compass one, and as advised its set to “external”. The other compass’s are not selected. Does that mean its using the gps compass only? Or does external in this case mean something all together different?
Im hoping the pixhawk being down on the side of the frame seperated by the carbon frame from all the emi is a good thing? I have a secondary carbon plate i can mount to the frame, and then mount the pixhawk as well.
And standing by, if this Pixhawk 2.1 doesent like the heli vibes, is the standard rubber/silicone ball dampening mount.
Im really hoping the way i have it mounted with the included 3m foam blocks to the frame works out as its easily repeatable and requires no modifications. I can dream i guess.
Tim
Then it should use only the external compass.
You really won’t know what you got for interference and vibes until you run it. Here’s an example of what you can do if spend enough time “tweaking” it. The only reason there’s any “jello” in the video is because of the slow flight speed and the tail “hunts” a bit. It is being flown at 15mph in a 8-10 breeze from the north. Speed up to 25-30 mph where the vertical stabilizer starts to work good and even video from this thing is jello-free with a solid mount camera in a less than ideal location.
Just to show you can get 'em to fly super-smooth. And this is just an old “antique” 600 flybar with straight-cut gears in it, with the camera mounted off the landing gear with a piece of aluminum flat stock with no dampers or gimbal whatsoever. Bolted solid.
Chris,
That is definatly some stable footage from a hard mount. Good setup and tuning skills go very far in this hobby ive found. Oddly enough, ive seen plenty of gimbal footage not nearly as clean, once again, its all down to who is setting it up, tuning and using it.
As to emi, your exactly correct, i wont know until its all wired up and powered on with the motor running, im going to bench test it with the emf meter i have for kicks, and see just how happy the Pixhawk is. As i said, i have a carbon plate i can use as well as some other sheet materials for sheilding if i have to go that route.
Tim
I had some high frequency vibration problems in that 600 heli that I think were caused by the straight cut gears and the old 1620kV “L” motor running at 25,000 rpm. That affected the IMU’s in the Pixhawk. I used an aluminum plate instead of fiberglass or carbon fiber, and mounted it on the corners with regular hardware o-rings and it “fixed” it. The vibe monitor showed the vibes were fine. But that vibe monitor doesn’t measure the high frequency vibes that caused problems with the EKF, as I found out.
I’m just experiementing with the electric. It only flies for 19 minutes at 40mph with 3 minutes reserve, as long as I don’t waste too much power hovering with it and get it into ETL right away. It takes 15-20 mph flight speed to get the amps to drop to ~17 on 6S, which is less than 400 watts. It takes 22 amps to hover it. I plan on using this year some to shoot some NVDI imagery on crops.
So the moral to the story is, until you run yours you just won’t know what you got. I thought this one was perfectly acceptable but it took some more tweaking to make it actually work. Flying 3.4.6 in it.
Chris,
After finally delving into all of this after the long wait to get my Pixhawk 2.1, all I can say is I hope this all pans out. Using beta firmware…3.5rc4…using the newer untested on helis Pixhawk 2.1…
Although most of these initial issues ive had are either user error, or something simple like a pin not contacting well, i’m finally coming to the realization of how much is in play here vs what i’m used to working with. I definitely want to be totally confident in my settings and have a reasonable grasp of what is going on before I hover it for the first time. I can fab good cabling, redundant power sources, failsafe for the radio and such, but in the end there are many things that can have a play in crashing my rig that seem like they could be easily missed, or not evident until it gets airborne and makes that first 90 degree turn and loses its orientation and blows the EKF.
I’m meticulously reading through “all” of the parameters available and trying to comprehend them and how it pertains to my specific use of a heli. This is proving to be somewhat of a task as a lot of the parameters i’m finding are not anywhere near the values it seems other people are running with a traditional heli. I’m getting that this is mainly for multirotors. so i’m sure the defaults are tailored to them, but I just want to make sure I don’t miss something stupid and put it in the dirt.
PID gains I understand, cyclic ring, end points, setting a hover point etc etc. All of that makes perfect sense even if it in’t called the same thing elsewhere. It’s the deeper parameters i’m worried about missing… I see many late nights ahead.
Either way i’m hoping for an efficient, stable flying platform that ultimately can serve my needs while having access to guided GPS missions and even just the simple loiter function would be handy as I could eliminate a second operator and control the gimbal from the second module in my Horus on some missions.
Tim
I hope you get it. I’m not a big fan of FBL helicopters because they are inherently unstable. But it’s fun to see somebody try to fly one with a Pixhawk2.1.
I know how that feels.
This is my heli the morning of its first take off.
About external compass orientation, I found that it must me set as “relative to Pixhawk” so if you set your AHRS orientation to roll 270°, you must set compass1 (external) orientation to roll 90°.
Just in case you don’t know.
Pitt,
Im just going to say the compass calibration regarding pixhawk 2.1 could be a little clearer. I know i set the Pixhawk’s roll to 270, but compass’s i ticked the boxes for “automatic declination & offsets” and did live calibration at the time of firmware install… i dont believe i added and extra roll to any of them.
Spec wise, there are 3 compass units in the Cube if im not mistaken. Are these all considered “internal”? Or is just the compass sensor that is isolated via the foam considered internal to the pixhawk and the other 2 are external? The one in the Here gps i’m assuming is considered external. Now i only have compass one enabled, and per what ive read elsewhere its being used as external? All i know is that i get no errors at boot, or after spinning the heli and shaking it around a bit. It doesent seem to lose orientation or spike the EKF at all?
Btw, love the overtly large landing gear! Things like that are definatly worth the peice of mind they afford. I can imagine spooling that up the first time was a trip.
Tim
Pitt, with an external compass the COMPASS_ORIENT param is independent of the AHRS_ORIENTATION param. Like on two of my helicopters, the Pixhawk is on the right side of frame on edge, so I use Roll 90. But the GPS/compass units are mounted on the helicopter backwards because it made for nicer cable routing. So the compass is Yaw 180.
If you are using multiple compasses, then it will be different. But I don’t think too many folks have been successful with using the internal compasses on heli’s.
Chris,
I sincerely hope “fun” is the adjective i employ when describing how my first flight goes. As to them being unstable, i think if your setup is “spot on”, your in there. Ive seen a pilot at the field turn off the controller and fly one manually before. He put a ton of expo and narrowed the rates, but made a good go of it and wasent chasing it all around the sky that much. There are a select few going FBL less for the sheer thrill of it these days. I cant imagine how hard it is.
This same person is who walked me through my first few setups when i came back to RC helis after a long break from my old Kyosho Concept.
He kept repeating the “do a good mechanical setup” mantra and basically said the fbl’s job is to correct errors and keep it from being affected by wind and such vs what you are telling it to do or where-ever it is currently, so why would you want to make one work harder all the time correcting an out of track blade or lean in the swash at what you think is good enough.
In the end throughout mant different fbl units, ive found personally most quirks and bad flying characteristics are because of some setup error. Either a geometry issue somewhere throughout the range of collective and cyclic, or just a poor job at maintaining the bearings, feathering spindle assembly or in the case of a tail, a binding control rod or center and travel limits set incorrectly.
In the case of this Trex im building, i have a full set of turnbuckle links for it throughout the head to get the swash and tracking as dialed in as possible. When i set 0° with my helis i block the frame up and level off the top of the motor to withing .01 of true level, i use varying thickness paper squares cut to use as shims, i use a jig or a scorpion driver that goes through the main blade bolt hole and align it paralell to the mainshaft. Then i check the full collective range and if needed i adjust the links or servos to take care of any places the swash is not level throughout the full range. With the tail, i always make sure my control rod will “fall under its own weight” if i unhook the link to the servo and tip the heli up on its nose. Thats my litmus test for a bind free setup. Then, depending on the FBL being used, i either give it dead center tail pitch, or give it a rate mode setup to correct for the main rotor torque. Ive found it totally depends on the unit which method works. Having chased slow ossilations, faster ossicilations and just bad stopping behavior in general those were the two solutions ive came across.
I also check every mainshaft, tail shaft and especially the feathering with a runout gauge. Ive gotten plenty right from the manufacturer with a set in them, which lead to vibrations and or poor tracking.
I get the FBL craze has been about performance, but that aside having used one for something different than its intended purpose to great effect, i know they can be stable… …as long as the gyros are still doing their jobs… The “BIG” downfall i see is what happens in the air if it had issues and stops functioning, then unlike with a flybar, there is no saving it. That is the part that worries me with the Pixhawk. Im very confident the FBL controllers i use now will simply work, but the Pixhawk with its EKF is starting to make me think more than id like to. Like ive said before, there is alot more in play here with the Pixhawk, alot more things to worry about. I dont want to miss something stupid. Its the what happens when the EKF blows up part that has me thinking about a flybar.
Tim
So if my Here GPS unit is facing forward then i do nothing regarding compass orientation?
Also, if i have compass 1 selected and its set to “external”, is it using the compass in the GPS? Ive read through the procedure a few times and its not totally clear about multiple compasses.
Ive been using the logic that if the compass wasent oriented right in the software, i would be getting errors. Hopefully im correct in that assumption? I have manually spun the helicopter a few times on the yaw axis trying to produce and error.
Tim