So,Move the GPS puck onto the main frame and get it out in very swirly conditions, but it loiters reasonably well. I know I need to re-tune after the blade change, but itās good enough.
I then send it on a simple auto-mission and itās clearly confused.
I land and now I keep getting Compass Variance Errors. Maybe itās struggling with the new compass/GPS location?
I try to re-calibrate and it wont. I then take a look at the Compass orientation and the external compass did not pick up the right orientation when I updated to 3.5!!. Somehow it allowed me to calibrate both compasses with one of them pointing the wrong way!. I correct the orientation, disable the internal for expediency, re-calibrate and it now flies happily. Argh!!!
It has also change the default speed and yaw rates in auto, but I ignored that and was just happy to see it fly again.
Do you think that was the problem all along? Or did you just change the orientation of the external when you moved it? Regardless, I donāt like putting them out there on that tail boom. Thereās vibration there even on a smooth-running heli when the tail blades ābiteā in a turn or whatever.
Not related, but I found a good use for old APMās with an internal compass yesterday. I put one in a Trex 500L Dominator, no GPS/external compass, no MavLink - just using it for a FBL unit. Just two flight modes - Stabilize and Acro. It works perfect and handled hard 3D no problem at all. Cheapeast $30 FBL unit there is.
Now Iām trying to figure out how to get it to work with a Spektrum DX-6i with a Orange 615 receiver with CCPM output. Just thought Iād throw that out. If you got an old APM2.5 or 2.7/2.8 and a heli you want to use for fun flying. It was easier to get that APM tuned to match any of the modern FBL units than it is to tune a Pixhawk with the newer versions of Copter. Took all of about 30 minutes to tune it in and it ājust worksā. Those are some tough old boards, not near as finicky as a Pixhawk 
No, the original problem was definitely GPS glitches. Add the random radio-link failures, there was something going on, which is why I swapped out the Pixhawk unit. Similar, before the erratic behaviour was always linked to some kind of events, where as this time, There wouldnāt be any.
I also made sure that I mounted the GPS the same direction when I moved it.
As an aside, I saw on one of your videos that you were also using 10.000mAh Multistars on one of your helis; Could I ask you how much voltage sag you get one those? Iām getting almost 1.5v of drop, when pulling ~20A, which means I barely get 50% out of the battery before the voltage becomes too low for comfort.
It drops about dead on one volt with that MultiStar battery under load. The hovering amps is about 18-19. I have a power module on that one (donāt use the power modules on 6S and 12S). I donāt use the battery failsafe. But I have the low voltage warning set for 13.0V. If I fly it all the way to low voltage warning it recovers with the cells at around 3.7V. It has been a pretty good battery for that size heli. The only problem is that itās pretty big and not a lot of options to mount it other than some sort of custom rack like I made in the landing gear.
They make those MultiStars in 5A too. I think the 5A one would fit in the normal battery tray under the canopy, then put another 5A one in a belly rack like that. I think that would be a better setup and allow to put the belly battery more under the heli. I had to set the 10A slightly forward to get the CG right.
Edit:
The battery I was thinking of is actually a 10C 4S 5200mAh MultiStar. The dimensions they give for it should fit in the battery tray on my 500 and allow to still get the canopy on. That is actually the design I wished I had gone with is two of those in parallel.
Iāve mounted my battery on a small sliding tray, so that I can adjust for the CG. It does mean mounting it āsidewaysā, but it works reasonably well. Pixhawk is now on the old battery mount. Wiring still needs tidying up after moving it around, but I wanted to make sure everything worked before making custom wirings.
Also designed a new canopy:
This is just a printed prototype, but Iāve printed a plug for a mold, which I should hopefully get made soon. (Making plugs is time consuming!!).
Also got my new VTX blades today. Should get to try them out tomorrow. If they fly as good as they look, theyāre going to be amazing 
That is an excellent setup to adjust the CG. Really cool looking canopy too 
I LIKE that. The stock canopy on most of these heliās doesnāt allow much room under it for stuff.
I think youāll notice that when you yaw the heli in Loiter it wonāt tend to move around in a circle like somebody is swinging it by the tail with the GPS mounted in closer to the mainshaft. At least not as much as they tend to do when itās mounted way out on the tail boom.
You donāt get any twitching on your rudder servo with the MavLink radio mounted there? Iāve gotten servos to twitch before just running the MavLink wiring alongside servo wires when the servoās donāt have any ferrites on the servo cables.
Yeah, the telemetry was just supposed to be temporary, while I got things set up, but much to my surprise it hasnāt caused any issues there.
Hrmph. The new VTX477s appear to be a lot less efficient that the Edge blades. Vibrations are up too.
Since the Rails donāt come in 470mm, what would be your second choice?
Do you have enough tail clearance to swing Rail 516ās at a little lower headspeed? Theyāre only 1.5" longer than what you have and they are designed for 550ās. If you look thru the internet forums and such youāll be hard pressed to find anybody that ever flew Rails that had anything bad to say about 'em.
I got three sets of 'em here now on different heliās and have gotten the same results on all three. Just got this one flying yesterday with 626ās on it. Iām making a different mount for the Pixhawk and still have to put a decent landing gear on it. This is a 550 with the E5S stretch kit and it could swing 696ās if I wanted to, but Iād have to put the E7 main gear in it to fly 696ās.
No, 480 is the max, I"m afraid. I did find a stock of Edge blades in Germany and shipping is reasonable, so I may order from there.
As this is my ātest frameā, Iām also keen to try out a 3-bladed rotor and have my eyes on this:
http://www.cnchelicopter.com/flybarless-trex-500-etc-500-size-helicopter-cnc-head-3-blades-system/
Itāll have to wait a bit, though. Iāve decided to do a complete re-tune of the Protos (With the old Edge blades). Itās annoying as it was flying really well before the GPS started freaking out, but on the other hand, itāll be good to do it again.
I donāt like to bash any companies but I have had reports of poor quality from the scale builders on that one. There is also an Align head available for thee blade rotor for both the 700 and 500 that the scale guys have spoken highly of. I donāt know if Align makes it anymore but you might be able to find one on eBay or something. Even though US dealers donāt carry it I think itās still orderable from Alignās Taiwan website. The Align one is more expensive but it uses the same blade holders, thrust bearings, etc as two-blade, just with different feathering shafts and center section.
The scale guys get pretty excited (not in a good way) if they got a head that has slop in it and the helicopter doesnāt handle right.
Jakob, here is the one that is highly praised by the scale guys but it is for a 550/600, not a 500, so it has a 10mm mainshaft. And it is in stock in the US Align store.
http://www.aligntrexstore.com/550E-Three-Blade-Rotor-Head-H55H004XX_p_4475.html
Does this also apply to the Align Blade on a 450 and could this also be part of the reason for the rubber bandy tail 
It could be part of it. On the flybar Trexās, higher headspeed usually fixes that ārubber bandyā tail effect. Take a look in your logs and see what the elevator servo is doing when it pitch bobs. Graph the actual pitch attitude vs RC3 OUT. If the graph show the elevator servo is over-reacting and actually causing it due the inherent instability of the head, speeding up the head to make the head more inherently stable will magically āfixā it.
If the elevator servo is doing nothing, then you got a flybar setup problem, head out of balance, blades not tracking, etc. Setting up a flybar head still remains more of an art than science. Tracking a three, four or five blade FBL head is even more of an art. Iāve spent a whole day before helping one of the scale guys track a four blade head on a Bell scale model until it flew with absolute precision. We used a high frame rate video camera with chrome tape on the blades so we could see which one was causing the issue
Jakob, if try the method I outlined for tuning, please report back on that. That is the method Leonard recommended for tuning. It has worked on every FBL heli Iāve tried it on. No drama like the wiki method because you always have control of the helicopter. And cutting the D and P gains in half from the oscillation point has yielded a superbly stable heli in cruise flight where porpoising due to over-tuned P gain can quickly lead to loss of control.
Leonard actually recommended setting I gain equal to P gain. But that was not enough I gain in my experience for heliās for high speed flight. So I set it equal the FF instead, which then gave excellent results.
I have not heard any reports from anybody else that has tried that tuning method, and not enough heli test pilots on the project. If it works for you like it did for me, I think somebody should consider updating the wiki on tuning of trad heliās.
I even tried it on a APM with 3.2.1 with my 500 that I set up for pylon racing for the Memorial Day Weekend races at the RC club, and it ājust workedā. With a lighter 2200 6S battery in it I later flew this heli at 70+ mph running wide open at 2,900 rpm practicing for the races. Banked over on her rotor tips in the turns at full collective pitch set to 15 degrees it didnāt do anything unexpected using that tuning method.
Hi Chris
Sorry I have not been back, as the ESC packed in, then had problems with the swash set uo again.
Well I got it sorted out and did your setup this afternoon. It was a bit windy but I thorght I would give a go. All seemed good.When the wind drops I will do a log and send it.
One thing I noticed, When I pressed the button on the Pixhawk and the servoās became active, The Swash was going the wrong way. Like left was going right, and forward was ging back. When I armed the Heli they corrected themselves.
Iāve attached the Paramās file for you to look at.
2017-08-23 16-24-03.log.param (13.5 KB)
That was the plan :). Although I must say that halving the values seems drastic? Iāll try it out anyways, hopefully tomorrow.
Thanks for the heads-up on that rotor head. Unfortunately the Protos has an 8mm shaft, so the 550 size wont work and they donāt appear to make a 500 sized any longer. I did find a couple of other 3rd party brands, but it appears that more reading on the scale forums is required.
Thatās the way Leonard said to do it. And it sure worked here
You could do like I did with my 500 stretch. I made my own mainshaft that fits the 500 bearing blocks but steps up to 10mm for the swashplate and head so I could swing the 550 blades on it. If you want to use 500 blades use some spacers in the blade holders. Itās about a one hour project to make a mainshaft on a bench top lathe. I made mine from a piece of chromoly rod that I got from the local steel shop and itās solid shaft, not hollow.
I do have a friend with a lathe :). In that case, I would probably go with this:
https://www.helidirect.com/helicopters/helicopter-part/sab-goblin/goblin-500-sport/sab-hps3-rotor-system-w-blades-goblin-500.html
One more question regarding tuning; Do you start with all values at 0 (PID + VFF)ā¦or do you have a small value in all fields?
That might already have a 8mm shaft being for a 500? And those SAB blades have gotten good reviews too.
I set them all to zero. I started with the VFF at .15 on both, and tuned the tail first. The heli flies fine on VFF .15. Then pull the microSD out and look at the Rate to see how it tracks. You have to make some stick movements get enough info to get a good idea of how the rate is tracking. That will be totally dependent on your mechanical rate too, because rate control is rate control, regardless of whether it is mechanical or electronic. Itās whatever it takes to get the right rate so actual tracks desired.
The heli may get way more responsive than you want. Thatās where you use the Accel values to slow it down but 110000 is usually pretty close for a 500.
Then do D gain first, P gain next, and I gain same as VFF. Leonard did not recommend doing it the way I did where I set pitch to very slightly less than roll. That was my own invention. He recommended doing one axis at a time. I tried it on pitch and got to ridiculous values without ever getting the shakes. Since I like a little less damping on the pitch I set it a notch lower than roll. Normally that would be a notch higher than roll. But thatās personal preference because I like 'em to lean in smooth and flare smooth, and just donāt like too much damping on the pitch.
Leonardās tuning method, tuning the D gain first, seems to allow use of D gain. Most people leave it at zero because the current instructions say to over-tune the P by not turning it down far enough from the oscillation point, so adding D gain puts it into instant shake. The heli actually flies better with some D gain.