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Feb 01, 2016, 05:43 PM
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NorCalMatCat's Avatar
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Need help fine tuning 450 with kbar


Just a little background on this bird, was a cheap Chinese eBay 450 Pro V2 clone, I replaced it's ESC and motor on arrival, I also switched out it's head for a HK FBL head with chinese yellow kbar for control. I haven't really flown it much, it sat for a good year and only got flown once and mainly because I never got around to fully fine tuning the kbar. Got me another micro heli to practice on and started itching to get this 450 running again (it developed a strip servo somehow sitting on the shelf), so all the cyclic servos got replaced, leveled and centered as best I could (seems pretty good). Now I am back to the issue of getting it all dialed in. My main issue is that as it stands right now if I give fairly aggressive left yaw (nose left) the elevation tends to pitch up, and if I aggressively yaw right the elevation tends to pitch down,though not as bad when yawing left. I am really curious as to what is causing this and how I could resolve it. Also I noticed that the vibrations are pretty bad, it has a bit of a spool up wobble but that seems to go away at head speed, I had the blades tightened enough to stay put unless you jolted them, so I tried loosening them and the max vibration parameter dropped from maxed out 3393 to a still maxed out 2680.

Attached is VStabi screenshot of settings.
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Feb 02, 2016, 11:49 AM
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2Doggs's Avatar
Bad vibes are like the enemy, dude!

Seriously, with a cheap clone 450, high vibration will be quite likely, and will compromise the performance of the Kbar.

First thing you should do is check the Kbar Event Log. On a well balanced and properly set up heli, you will see mainly "Good Health Message" entries, but it's hard to achieve that even with a high quality 450. Instead, you may see "Raised Vibration Level" alerts. That's OK, and the heli can still fly well.

If you see lots of "High Vibration Level" entries, however, you need to do more work on the heli, and if you see lots of "Extreme Vibration Level" you shouldn't try flying it.

On the bench, you can spool up the heli with the main blades removed and the tail control rod disconnected, and check vibration using the "Live View" feature.

Most of the time, you will see vibration peaks for the tail rotor, generally around 12000rpm or so on a 450. You need to try to get the peaks below the yellow line in the graph.

Cheap clone 450 mainshafts can be bent when new, so it's handy to have a few to hand to see if they help reduce vibration around 3000rpm.

Cheap motors can also be unbalanced. You will feel motor vibes as a buzz when you touch the heli close to the motor, and they are the kind of vibes that can easily cause screws to come undone and wires and soldered joints to break. I balance my 450 motors using a process of trial and error with Scotch 3M Magic tape, stuck to the can.

Good luck!
Feb 02, 2016, 11:55 AM
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NorCalMatCat's Avatar
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I can't seem to find this event log feature.
Feb 02, 2016, 12:46 PM
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2Doggs's Avatar
With the controller connected, and initialised, click on "Info" in the top left of the main window, and then select "Event Log". In the Event Log window that then opens, you can then click on either "Get All entries" or "Get 100 Entries".

You also have the option to save the log as a pdf file if you click on the "Save Log" button.
Feb 02, 2016, 02:11 PM
Registered User
What I did....
Add stuff one at a time
Motor only, look at vibes
Add mainshaft collar and maingear - play with motor mesh a little to get least vibes but still good mesh
Add tail gear/drive - play with mesh again
add boom and tail drive (but no blade holders) - again play with mesh if TT drive
Add head but no blades and see where that gets you

I then spent some time getting the blades - main and tail - as close to the same weight as each other and in balance

Mine only shows good health when nothing is moving

under normal hovering it's always showing raised vibration

spoolup and landings/spooldowns usually give a high vibe or 2, sometimes it goes to extreme vibe

It /seems/ to at least hover OK like this despite the logs
Not really "flown" it though, still waiting for fields to dry up and it to stop blowing a gale and me to man up

There is a feature where you can see the vibration "live" which is interesting to play with

If I press down slightly on the FC's case my vibes die down quite dramatically (obviously only attempting this without blades installed )
maybe this suggests I could use a different density foam pad- I have tried 2 different types but both seem to yield similar results
maybe its just my finger damping what vibration there is

I did try and add a velcro tie down to put pressure on the FC but it didn't do anything as I couldn't get it very tight
I may try adding a ziptie in a length of silicone fuel tube to see if that helps any as I feel I have got meshes and balances as good as I can
(all bearings are new smooth and un-dinged!)

I think the cheap yellow ones must be ultra sensitive
I had a right long chat with a fellow from here using skype - and his complete 450 was putting out less vibes than mine with just its motor installed IIRC...
His was a blue one, mine the yellow one

Regards
Rob
Feb 02, 2016, 02:19 PM
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From my understanding (and granted I have not looked at the hardware for myself to tell) the only difference is that the blue version has the governor.

As far as touching the device your body has much greater mass and any application of pressure will create a nice sink for vibes to go into you and get dampened, so touching it is not good for measuring vibes . Personally for something like this don't even try to use a soft anything that could cause harmonic oscillations from existing vibrations, much better to have it more of a firm attachment.

I guess I will have to strip down the heli a little to figure out my exact vibrations, bleh, such a PITA to do, I much prefer flying then tinkering .
Feb 02, 2016, 02:43 PM
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I just did some analysis using the spectrum and event logs. Logs from in flight show that during spool up the vibrations reach extreme level, though stay a constant high vibration level during actual hovering around. I proceeded to take the blades off and watch it with the spectrum, Without the blades it doesn't reach extreme but stays about raised vibration level status and sometimes hits extreme, I can clearly see there is a rotor wobble so I think the shaft isn't perfectly straight (I have NO IDEA what shaft to even replace it with), and the primary vibration of problem can easily be seen changing frequency with throttle which would indeed indicate a wobbly head .

Here is a screenshot of the spectrum after doing a fairly slow spool up to 100% throttle, note that vibration MAX increased with throttle, the giant primary peak at 237hz is during 100% throttle.
Last edited by NorCalMatCat; Feb 02, 2016 at 02:49 PM.
Feb 02, 2016, 03:25 PM
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I just ordered a 3pack of align main shafts, surely I will get a good straight one out of it
Feb 02, 2016, 03:26 PM
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Found when stumbling round the net

"The blue Kbar uses an ITG-500 on the yaw axis like an actual Vbar but uses a 2 axis ISZ-650 for the aileron and elevator axis (this is the same chip that the ZYX-S uses) with an amplifier to boost the signal amplitude to the same voltage range as the signal from the ITG-500. The yellow kbar uses a single three axis chip (probably an Invensense MPU-3050) and a small microprocessor to convert the combined three axis signal from that chip into three separate axis signals that mimic what the main Vbar CPU expects."

So blue and yellow "according to someone on the internet" are using different sensors....

I do wonder if the yellow ones /are/ simply more 'sensitive'

IF my ESC didn't look after gov I'd be looking at buying a blue one to see if this was the case
(I may still do this out of sheer curiosity)

Regards
Rob
Feb 02, 2016, 08:05 PM
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2Doggs's Avatar
Those are massive vibration peaks, way more than you should be seeing. The 273Hz one is obviously from the tail. The one around 430Hz may be from the motor. You should balance the motor and concentrate on sorting out the tail. Vibration from the mainshaft will show up at 50 - 60Hz.

There is a whole lot of nonsense talked about the different sensors in the various Kbars. In practical terms, they make no difference, and you certainly would not see appreciably lower vibration in the Live View screen if you were using a GV8000, which uses the same analog sensors as the mini Vbar.
Feb 02, 2016, 08:15 PM
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NorCalMatCat's Avatar
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Quote:
Originally Posted by 2Doggs
Those are massive vibration peaks, way more than you should be seeing. The 273Hz one is obviously from the tail. The one around 430Hz may be from the motor. You should balance the motor and concentrate on sorting out the tail. Vibration from the mainshaft will show up at 50 - 60Hz.

There is a whole lot of nonsense talked about the different sensors in the various Kbars. In practical terms, they make no difference, and you certainly would not see appreciably lower vibration in the Live View screen if you were using a GV8000, which uses the same analog sensors as the mini Vbar.
What makes you think the 237hz peak is the tail? I can physically see the wobble of the head, and I can see and feel it increase as I throttle up, I really don't see how the tail could be doing it based on my observations.
Feb 02, 2016, 08:51 PM
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NorCalMatCat's Avatar
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Quote:
Originally Posted by 2Doggs
Those are massive vibration peaks, way more than you should be seeing. The 273Hz one is obviously from the tail. The one around 430Hz may be from the motor. You should balance the motor and concentrate on sorting out the tail. Vibration from the mainshaft will show up at 50 - 60Hz.

There is a whole lot of nonsense talked about the different sensors in the various Kbars. In practical terms, they make no difference, and you certainly would not see appreciably lower vibration in the Live View screen if you were using a GV8000, which uses the same analog sensors as the mini Vbar.
well damn it if you are right! I disconnected the belt (its belt driven) to the tail and the only vibrations detectable left where about 60hz, picture attached.
Feb 02, 2016, 10:56 PM
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2Doggs's Avatar
It's all about the frequency. The tail will rotate at around 12000rpmand more, which is 200Hz and up, tho there can be harmonics too.

Main rotor is 2800-3000rpm, which is 70 - 75Hz.

The highest frequency vibes come from the motor.
Feb 03, 2016, 01:44 PM
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Damn, pulling my HAIR out to find the tail parts!!! This is the tail set my bird came with http://www.ebay.com/itm/450-Metal-Ta...3D321954836264

But I don't trust it to use again, very pour quality metal and very soft. I looked over all the parts sellers of Align but cannot find all of the required parts for a complete tail assembly! So I am thinking of this set http://www.ebay.com/itm/Tarot-Metal-...KlUtpactLD20xA, as far as I can tell it should work fine, but I have no idea, and regardless of what tail I go with I am going to have to order from China anyway as I cannot find any US suppliers with a complete tail set, ugh
Feb 03, 2016, 02:34 PM
Registered User
Have you tried with the blade holders not fitted so see if its the shaft that's bent?

One of my tail shafts caused hell and just replacing that part seemed to cure it
(I'm on TT, but same principal)
Also the mesh between the maingear and tail drive was a tad tight and making the holes that hold the tail into ovals and getting that mesh as smooth as possible also helped

Like I say - I added one bit at a time starting with just motor to see how the vibes reacted and what parts caused what level

(still convinced the yellow ones are more sensitive than the blues ;p )
I genuinely cant see anyone selling the blue ones that state they have a working gov - so likely all the blue ones I'm seeing are actually yellow ones in a blue casing at a slightly raised cost
If I find one for not too much I'm willing to do a back to back comparison

Regards
Rob


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