SK720BE vibe log help please.

[SpeedTape]

Originally Posted by fretman

can't make up my if I like this sk700be now... The vibe logging is great! Then again without it I would have been flying happily in ignorance.

Well at least your 720's polite enough to tell you that your heli is shaking like a washing machine! As a lot of nitro guys know, the flybarless control works great even under high vibes. The self leveling needs a smoother platform, but most mechanically healthy electrics run smoothly enough. Better to know in advance that you've got a bad bearing or bent tail rotor shaft before things get expensive.

[fretman]

This is kicking my behind like nothing else has since I've picked up this hobby.

I'm still thinking the peak is a tail vibe.. got my motor back from KDE, actually a brand new one tested to run smooth as glass. And I saw that when I tested with only the motor.

there is still the peak that shows up with the tail blade on, but on one flight the peak goes up to almost twenty. sometimes higher and then on the next it may be less than a third of what it was without changing anything.

Since my last post in this thread, I've switched to a belt. Switched the mounting tape from the thick omicron gel to the thin 3m clear tape(4010).

every time I make a change it seems to lessen the vibe, sometimes significantly. But the next flight usually worsens again. Just can't seem to get a consistent reading. Thought this would be a simple dynamic tail balancing but with the inconsistent vibe reading don't know what to think.

Any ideas what this could be?

Attaching two logs no changes were made between the two, couple hours apart.

[rs2k]

Your motor vibes appear to be gone now. That already looks like a better log. The tail vibes look like an out of balance tail rotor to me. Is this a hover flight? Same battery packs on the flight? Maybe your tail blades are out of track due to a bent tail shaft?

How well does the heli fly?


http://www.skookumrobotics.com/wiki/...lance_the_Tail

[georgi UK]

=] be sure the belt isn't too tight, boom expands in hot temps...

[fretman]

Thanks for the replies guys, still not making much progress unfortunately..

Originally Posted by rs2k

Your motor vibes appear to be gone now. That already looks like a better log. The tail vibes look like an out of balance tail rotor to me. Is this a hover flight? Same battery packs on the flight? Maybe your tail blades are out of track due to a bent tail shaft?

How well does the heli fly?


http://www.skookumrobotics.com/wiki/...lance_the_Tail

Thanks both logs are from hover flights, using 2 different packs. One is a 1350mah 35c, the other is a 1200mah 30c, 6cell.

And it does seem that with 1350mah pack I do consistently get higher vibe readings.

All shafts are new and look straight when I spin them up.

Balanced the tail blades again with the tail hub but didn't seem to make a noticeable difference.

Heli flies ok, but it does have a slight slow wag. Which I had in the beginning when I had the Gov Gain too high. I have gov gain down to 20, and have even turned off completely but it is still there. Nothing binding in the tail, the tail control rod is a bit tight because the tail server horn, control rod support and the tail doesn't quite line up straight. It doesn't feel like its binding at all though.

Originally Posted by georgi UK

=] be sure the belt isn't too tight, boom expands in hot temps...

Belt is actually on the loose side, I have tried a bit tight and loose without making much diff on the vibe reading.

Could this be coming from something else other than the tail?

1750kv, 6cell, 3200 sk governed headspeed, 10.9 gear ratio, 4.6 tail ratio. tail should be a bit more than 15k rpm. In the log the peak show at a bit over 16k rpm, I figured its close enough to tail rpm. And when I lower headspeed the vibe peak move to lower rpm along with it.

This still wouldn't be the motor right? i think motor rpm is at about 34k rpm.

And this peak show only with the tail blades on.

[sctholson]

I'd try a few things, 1. I'd see if the tail balances if you take off the belt. Remove the belt and reassemble tail onto the heli exactly as if you have the belt installed. This should allow the tail to free wheel. In this configuration I'd see if the entire tail is balanced.

Also while the belt is removed, I'd secure the heli down, on a towel, but still secure that it won't move. I'd run it up and see what vibes would be present. Still won't be totally accurate since the heli is held down, but if that vibe is gone, it's likely somewhere in the tail.

If your tail is balanced (or now becomes balanced because of this test and a subsequent adjustment) I'd remove the tail blades and see if the tail hubs run true. I don't know of your brand, but hubs have been known to be drilled wrong now and again.

Just a few thoughts.

[fretman]

I went with the soft mount method, thick foam, thick metal and thin 3m clear gel tape. That cut the vibe peak to lower than half consistently. And replaced the thin Fusuno tail fin with the stock CF fin and that lowered the vibe some further.

Got the vibes down to a low enough point where I can finally try the GPS features. Play back log would show about 1.2 out 10 and vibe logs are showing peak that stay below 4-5 mostly on the same 16k rpm peak.


So out playing with the GPS mounted this past weekend, trying the hard deck, position hold, go home etc... was noticing that usually a couple min into flight the play back log showed not enough satellites... And then I had a moment and totally dumb thumbed it and looks like a rekit.

Thanks all for all the help... looks like a fresh start for me as soon as the parts arrive.

[sctholson]

Been there, done that - in fact just this weekend. Self leveling on a switch is only good if the operator switches to that setting.

[georgi UK]

=] sorry to hear that.....

[fretman]

At least I've gotten really good at rebuilding this X3 chasing the vibes, so I'll have it back together in 10sec. flat!

[Luvmyhelis]

Originally Posted by fretman

I went with the soft mount method, thick foam, thick metal and thin 3m clear gel tape. That cut the vibe peak to lower than half consistently. And replaced the thin Fusuno tail fin with the stock CF fin and that lowered the vibe some further.

Got the vibes down to a low enough point where I can finally try the GPS features. Play back log would show about 1.2 out 10 and vibe logs are showing peak that stay below 4-5 mostly on the same 16k rpm peak.

Sorry for the late arrival. Looked at your logs. The base vibe chatter level is way way too high. The mounting itself may be allowing the large vibe chatter across the spectrum at 5 magnitude or so, which needs to be down below one at most I feel. So soft mounting the gyro should cut these down dramatically. If the new setup doesn't do this, I am wondering if the unit itself may be needing to be looked at?

[fretman]

Originally Posted by Luvmyhelis

Sorry for the late arrival. Looked at your logs. The base vibe chatter level is way way too high. The mounting itself may be allowing the large vibe chatter across the spectrum at 5 magnitude or so, which needs to be down below one at most I feel. So soft mounting the gyro should cut these down dramatically. If the new setup doesn't do this, I am wondering if the unit itself may be needing to be looked at?

Going to a soft mount did cut the vibes down a lot, this is the last vibe log before the crash.

Parts should be here today and hopefully back up with clean vibe logs by the weekend.

[georgi UK]

=] when you build the heli do a vibe log for each stage so we can work through it, ie fit motor only and log it, then maingear and front tail-box log it etc until the heli is built ready for a mains on hover log.....

[fretman]

Originally Posted by georgi UK

=] when you build the heli do a vibe log for each stage so we can work through it, ie fit motor only and log it, then maingear and front tail-box log it etc until the heli is built ready for a mains on hover log.....

The X3 rebuilt and is better than new!
I did log vibes in stages of the build, but hover test came out good so won't bother posting them.

I did have one scare on the first hover test. I lifted off before the GPS locked in and did it's little jerk with the cyclic servo. while in hover the heli jumped up a few feet on it's own. And being in my rather small backyard and not wanting the heli to go out of control hit throttle hold and had a rough landing. luckily got away with a broken landing skids.

I think and hope that it was the GPS locking in and doing its servo dance that caused it, and not something else wrong with the 720.

I replaced the landing skids and tried another short hover, and this time waited for the GPS to get its lock and do the servo thing. And happy to say that was uneventful with a vibe log I'm happy with.

[georgi UK]

=] looks like having that shunt did you a big favor! nice work!