SK360 on my T-Rex 450

[Skookum]

Easy one first...

Hamslice>"in fff when i give higher collective the heli will nose up..."

That's almost certainly the gyro running out of cyclic pitch to apply. The fixes would be to increase your headspeed, or increase cyclic pitch range to +-10 degrees. You should also increase servo travel and get the swash mix #'s 60% or below to prevent interaction at full collective pitch. The manual's going to be changed to advise +-10 for cyclic pitch :-P

>i have spent more time concentrating on getting all the vibs to disappear than ever before.

Re vibs, I'm not sure it's that vibration sensitive. It does make a difference in how well it holds like for any gyro, but to get random kicks it usually takes quite bad high frequency vibration. Like out of track blades etc won't do it. Static build up from the tail boom can happen though, the cure is just to ground the boom to the frame or motor case.

I'm thinking now that for many the problems are mechanical/aerodynamic. I spent 12 hours (!!!) failing to convert a blade 400 yesterday, which tried to flip at take off, wandered and kicked, and couldn't stand the hiller dial being above 35%, with well-proven SK360 on it. I also had access to directly logged data to graph here. So I could confirm the gyro wasn't sensing or doing anything weird, but the rotor disk and swash was doing weird stuff. My theory now is that the blades for the 400 have a bad chordwise CG and/or the grips are too sloppy, the combo is aerodynamically unstable, and cannot be properly controlled by the servos. So the servos just "lose it".

That's not to say it's everybody's problem though. Int2str's issue started when he rotated the mounting 90 degrees, so it's possible there is a resonance effect happening there. Hard to explain otherwise.

The problem coming out at a certain rpm is another good clue. *All* of the sensors in the gyros on the market work using a tiny part is vibrating at above 10 khz, so it's easy to see how just the right high frequency could mess with them. Rotor vibration though tends to be at most a few hundred Hz; the khz range is more like nitros or gear mesh territory. Maybe one day they'll get a laser ring gyro etched into a chip...

>as soon as it reaches a certain percentage [during spool up], the heli just forces itself over hard right...

FYI the timing is probably due to the "spool up mode" timing out, which applies very high hiller decay to calm spool up. So the gyro either thinks its tilting left, or thinks you are applying right cyclic.

Re the "cold bug", the problem *can* occur at room temperature. The "cold test" was to force it out into the open. What happens with the flawed gyros is the sensor fails to start; if you wanted to pre-flight check to be totally sure its ok, just pick up the heli and tilt it left/right nose up/down, and see if the swash responds. If it responds then, it'll be fine later.

[SpeedVision]

Originally Posted by Finless

Yes when testing my unit on Kevins heli this last weekend it would go full forward elevator at a certain RPM. He had it stuck down with the thin gray double sticky tape. We remounted it with 2 pieces of the 3M white foam stick tape and moved it back a bit away from the tail belt drive bearing and that solved it. I really don;t know if ti was vibration or noise from the bearing that was causing it but it was for sure one of the 2.

Bob

The fact that this is happening on such a wide variety of Heli's is what has me puzzled...

Mine tips towards the adjustment pots.

When I first tested the SK my heli was setup like CRAPOLA and it didn't tip. Bad main shaft bearing, tracking was out by an inch, main blades were not properly balanced, tail blades weren't properly balanced, case of the SK was rubbing on the Titan frame (SK provided tape), blades were so loose that they would fold during spool up, it would do this for a few seconds, then smooth out when they found their centers...

When I get my replacement (failed cold test), I'm going to stick it right where the other unit was, reload the same program and let her rip...

Good part about all this "beta testing", I won't have to buy mulch for the flowerbeds this year...I have a nice pile of red/white painted balsa to use...

[int2str]

So what should I do?

Turn it back 90 degrees?
Move it further back on the heli?
Different mounting tape?

I tried holding the heli with one arm last night (I know, bad idea ). I figured, maybe it's the aileron axis being reversed.

If I spool it up holding it in hand, beginning at a certain RPM, the swash plate visibly tilts to the right and then settles in. The gyro still reacts every motion from there and compensates correctly. But it always goes back to this slightly titled position (that pulls the heli over, if it was on the ground). It seems like the "resting position" is skewed.

I tried re-initializing the gyro a few times and it always consistently settles in about the same spot.

[int2str]

Originally Posted by lbcynya

Mine tips towards the adjustment pots.

Same as what Fireup describes (away from the PC -> label is towards the pots) and same direction mine does.

When I first tested the SK my heli was setup like CRAPOLA and it didn't tip. Bad main shaft bearing,

Same with mine. I rushed to test it and had worn out main bearings in there and didn't spend much time optimizing the head and layout. But it flew fine.

Now I did it "right" and I can't take off anymore.

[HeathH]

skookum,

i am getting a ton of cyclic in this setup (<+-11deg) so i just dont see how i could not have enough. i am making a new mount for the gyro to provide a sturdier base to mount it on. as far as slop in the head there is virtually none. i am running radix blades maybe they are not right for a flybarless setup. like everyone else i am also having the kick go towards the gain dials on the unit. another thing is that when i have the hiller gains down low it will not kick, but when i have them up to right before i get oscillations the heli will kick. one thing that might have something to do with it is the long servo arms that the hfx frame requires. i am using mixer arms in the head to add a better ratio though so i dont know. i am running out of ideas.

[Skookum]

int2str:

Ugh. I'll experiment here, but the issue hasn't shown up locally yet. I'd rotate it back 90 degrees and see if it happens - try not to bust any more blades :-P
But then why didn't it tilt in elevator?

I wonder if the common thing is that most of the issues are in the aileron axis. As I posted on the other list, there are so many possible causes for "tips at takeoff", that might be obscuring any really new issue.

[fireup]

Originally Posted by Skookum

int2str:

Ugh. I'll experiment here, but the issue hasn't shown up locally yet. I'd rotate it back 90 degrees and see if it happens - try not to bust any more blades :-P
But then why didn't it tilt in elevator?

I wonder if the common thing is that most of the issues are in the aileron axis. As I posted on the other list, there are so many possible causes for "tips at takeoff", that might be obscuring any really new issue.

But mine does tilt on elevator also. It goes in a diagonal direction (forward-left). When we remove the blades and spun it up on the bench, you can clearly see it move by itself at certain RPM. After mounting the gyro differently, the problem went away.

[Skookum]

fireup>But mine does tilt on elevator also. It goes in a diagonal direction (forward-left)...

Just trying to figure out int2str's problem, if it was a problem with a single axis consistently with many helis, I would think it might be the gyro itself.

Actually I have an idea. If the problem recurs, try turning the "vibration filter" *off*, like to zero. The feature is not that important, and there is a small chance the equation involved could have an unhappy frequency. [note: I'm going to run some bench experiments on that tonight]

[int2str]

Well, last night I start my testing to get to the bottom of this. I started off well, but I invalidated all my testing efforts with one crucial mistake...

First I took the blades of and tested if it would tilt on the bench - it did.

Then I hooked up my EagleTree to find out at what RPM it tilts. It starts to "wobble" at around 1600RPM (head speed) and really locks sideways at around 1800 RPM. If you come back lower than that, it goes back straight.

After that test, I set vibration filter to "Off". This seemed to "slow down" the wobble and also seemed to make the tilt less severe, but it was still there at the same RPM ranges.

Then I decided to increase my servo travel from 100 to 125 and lower the swash percentages to 50%. I also changed the hiller gain down to 33% (from 40%+). After these changes it still tilted the same.

Finally I cut the zip-tie that I had around the SK360 and *boom*, no more wobble, no more tilting....

HOWEVER......

When I made the hiller gain changes above, I *think* I only switched the micro switch from setup to flight. I did not power the SK360 off and back on. Therefore, I think all the testing above is invalid. I may have carried the setting without updating it.

So I can't tell at this point if the zip tie or my setup changes made the difference.

I added some hiller gain back, but it still seems like it's behaving a bit funny. If I tilt the heli on the banch now fully spun up, the SK360 doesn't seem to correct enough. In fact, I did a quick test-hover in my garage last night and it seemed like it was "swimming" quite a bit.

I'll have to take it to a field and experiment again.

The zip-tie *might* have solved the problem, but I won't know until I can really fly the heli and adjust the gain up again to a point where it holds the heli.

[SpeedVision]

Lookie what I found here!!!!

http://www.helidirect.com/product_in...oducts_id=6360

These would be long enough (might need shortening) to go from my swash to my reduction arms...

Now, finding ball links to fit Align balls and and the 1.8 mm TB diameter will be the trick...

Any ideas???

[d_wheel]

Originally Posted by int2str

So I can't tell at this point if the zip tie or my setup changes made the difference.

.

Put a zip tie back on and try it again.

Later;

D.W.

[SpeedVision]

Originally Posted by d_wheel

Put a zip tie back on and try it again.

Later;

D.W.

On a gyro, zip tie = bad, regardless.

[int2str]

Good news / bad news time...

Good news

Removing the zip-tie was really all that's necessary to get rid of the strange leaning problem. I flew the heli today and got it in the air without any of those problem.

At first the heli didn't hold very well. But then I decided to change "Vibration filter" back to "1", and increase the hiller gain to 66%. I also upped the swash % to these values:
- Elevator 60% (nice, fast flip rate)
- Aileron 75% (before that the roll rate was super slow)
- Pitch 50%

I do think that mounting the SK360 right under the main shaft helped out my piro's. It didn't tumble so much anymore when piroing. It worked quite well.

There were still some minor niggles to sort out, like some pitchy-ness in FFF.

Bad news

I crashed. Hard.

During FFF, I rolled right, but things went bad fast from there. Instead of rolling right cleanly around it's aileron axis, it dropped nose down (now inverted) and pitched "up" somehow (up being down...). End result - lawn dart.

Total damage? I haven't even really looked yet. But even the centerstick.com battery tray ripped in half and twisted itself every which way...

Not quite sure how it happened or what exactly happened there, but bottom line, I won't be flying for a while now.

Silver lining? No bent flybar

[HeathH]

man that sucks. i have moved everything around and got what i think i had wrong fixed, but i am goin to wait and try the firmware updated before i try again. funny thing is i had the heli flying pretty good at one time. just had the random elev kicks.

[Eury]

Silver lining? No bent flybar

A "glass half full" kind of guy, I love it!

[gpach]

I had a Sk360 since shortly after they were released but had gotten sidetracked with other projects. I planted my Trex450 earlier this week (broke or bent almost everything) and was looking at my diablo last night that I had crashed about a month ago. I decided to rework the diablo over to a flybarless setup. Modifications included.
- Replaced the upper rotor core (CX450)
- Replaced the blade grips to V2 version (CX450)
- Replaced the whole tail assembly to eliminate vibrations (CX450)
- Used the original mixer arms as reduction arms
- Heli has HS65 MG servos

Mounted the SK360 inside the frame at the back with the PC connection facing back. Gyro on the top of the boom block and Rx on the bottom of the boom block. Biggest challenge was finding a means to get the washout base to stay up. Currently have it kinda holding by bending one of the indexing pins slightly but this is a short term solution.

Found setting the blade pitch up without a flybar for reference a bit to get use to. Have the heli set for +- 10 degree cyclic and 11 degrees collective. Have some interference with the frames at full negative but the odds of me running there for any reason are slim to nill for a while.

Got the heli in the air for the first hover with training gear on after reading all the posts about helis tipping over. Mine wanted to back and left as it got light. I knew I had some pitch settings incorrect as the display was showing red (neg) pitch when it was positve on the heli. Emailed SK and he got back to me very quickly with direction on what to do as well as some setup tips.

The reversed pitch would account for the back drifting and likely an unlevel swash was drifting it left (it continued to do this in hover as well).

For the second battery I increased the gains by 20% over stock using the software. I am still not clear how the Dials versus the software settings work together. If anyone can clarify this I would greatly appreciate this.

Second battery was a lot better than the first, I added some expo to the right stick (20%) and this helped.

Lots of setup and tuning to go before I try it in FF but so far its going well. The biggest hurdle is the learning curve of the equipment and the tuning parameters.

[SpeedVision]

Originally Posted by gpach

I am still not clear how the Dials versus the software settings work together. If anyone can clarify this I would greatly appreciate this.

https://www.helifreak.com/showthread.php?t=76895

[gpach]

I read your post in the finless tech about putting together the spreadsheet but didnt realize it was done or up on the forum.

Thanks for putting in the time and effort. In your words, at first it seems a lot to wrap your head around.

Regards

[Skookum]

Be careful about training gear, one user found the training gear caused oscillations in flight.

[gpach]

Skookum. The training gear were there to get me past the takeoff jitters. Had heard about other machines going over. I realize you fixed it in the firmware upgrade but I was more comfortable with them on. When the monsoon season ends up here will take it outside for some flights.