G500 Vibrations

[Striges]

Hi,

I had a crash a couple of days ago during takeoff and I think it could have been due to vibrations and the gyro going nuts. I hadn't enabled vibration logging unfortunately, so i cant be sure. However during playback vibration was about 10.

I have rebuilt the heli now and did a spoolup without blades and this is what was recorded: https://www.dropbox.com/s/u59ixjklue...LOG28.SKV?dl=0

There are two spikes that I asume are tail and the motor due to the high rpm, but are the vibrations to high?

Any help would be appreciated!

/Striges

[Luvmyhelis]

Originally Posted by Striges

Hi,

I had a crash a couple of days ago during takeoff and I think it could have been due to vibrations and the gyro going nuts. I hadn't enabled vibration logging unfortunately so i cant be sure. However during playback vibration was about 10.

I have rebuilt the heli now and did a spoolup without blades and this is what was recorded: https://www.dropbox.com/s/u59ixjklue...LOG28.SKV?dl=0

There are two spikes that I asume are tail and motor due to the high rpm but are the vibrations to much?

Any help would be appretiated!

/Striges

The fore aft vibes in the tail are excessive. Seeing the related up down/lateral vibes tells us something is amiss. I look to keep these under about 1.5 to 2 max on a heli to safely fly. But have flown with worse.
Maybe some motor damage also? Look at the fore aft and specifically up down there are rather high? Or? Has the up down been there all along? That could be attributed to bad timing pwm combo causing the up down can bounce.

[georgi UK]

=] just attach the file directly using HF......

[Striges]

Originally Posted by Luvmyhelis

The fore aft vibes in the tail are excessive. Seeing the related up down/lateral vibes tells us something is amiss. I look to keep these under about 1.5 to 2 max on a heli to safely fly. But have flown with worse.
Maybe some motor damage also? Look at the fore aft and specifically up down there are rather high? Or? Has the up down been there all along? That could be attributed to bad timing pwm combo causing the up down can bounce.

I dont know if it has been there all the time. Bought the heli used and tried to maiden it the other day when i crashed. Allthough he told me there where no problems with it, promised it had never been crashed and had been well maintained, but you never know.

I will try and lower the PWM and see if that helps.

[Striges]

Originally Posted by georgi UK

=] just attach the file directly using HF......

Ok, I have attached it using HF now

Edit:

Did another spoolup without blades in the livingroom with lower PWM and this is the result:

[georgi UK]

=] is the tail drive belt and pulleys all good, and belt tension especially, correct?



motor bearings all good?, any float in the can?

[Striges]

I have started taking the drive train apart, found that a pulley has some vertical play.

Spooled it up on the carpet i used yesterday and the vibrations where almost as bad with only the motor connected!
Ran it again, this time on a folded towel and the vibrations are only about 1.5-1.6 or so.

Im gonna try it again but with the motor belt connected and see what happens.

Could it be that the gyro mounting is to soft? I did was shown in the manual: heli mount plate||thick foam tape||metal plate||thin tape||gyro

[Luvmyhelis]

Originally Posted by Striges

I have started taking the drive train apart, found that a pulley has some vertical play.

Spooled it up on the carpet i used yesterday and the vibrations where almost as bad with only the motor connected!
Ran it again, this time on a folded towel and the vibrations are only about 1.5-1.6 or so.

Im gonna try it again but with the motor belt connected and see what happens.

Could it be that the gyro mounting is to soft? I did was shown in the manual: heli mount plate||thick foam tape||metal plate||thin tape||gyro

If the gyro mount is too soft it won't show higher vibes, but lower. The only drawback is the heli will feel spongy in hard moves as the gyro lags due to its flex on the padding.

[Striges]

Have looked over the drivetrain, managed shim all float out of the motor.
Thighten the motor and tail belts and its looking alot better now.
There's still some slop on the pulley connecting to the motor. But Bert says in the official build video that there should be a little bit, but not a whole lot... Whatever that means...
I have orderd some shims anyway and will try if that makes any difference.

Also played around with PWM and found that lower PWM = less up/down vibes.

Haven't taken the tail apart yet but there has to be something wrong there. Put a ~1" piece of tape on the blade grips (one at a time) and found that when i did that on one of them the vibrations went up to over 30. Shut it down before it hit max rpm on the bad one because it sounded really bad. While the "good" one got to about 19-20 at max rpm.
Maybe I should order new blade grips? Thinking there might be some weight difference?

I don't really know how to check the tail. Still sort of new to this so any pointers would be much appreciated.

[Luvmyhelis]

Individually weight match the blades, check them to make sure they are the same exact length from the bolt hole out to the end and such.

Check the tail shaft to make sure it is straight. Check the tail bearings to make sure they are smooth, with virtually no slop. Check the hub to make sure, (mic it) the hub stubs are equal length on both sides of the hub and the shaft hole is dead center. Then weigh the grips and compare. Mic the tail thrust and bearings to make sure the thicknesses are all identical from side to side. Check the grips for how much play they have when mounted on the tail hub. Not only side wag but end play when pulling on them. There should be little to none!

The singular best way to insure the entire tail assembly is matched and running true is to snag a Dubro prop balancer and then go through the process. I balance the assembled tail, sans blades. Then balance it with the blades until it is perfectly matched and neutral. Even on really good or close setups I mark the grip and blade that works the best, as simply changing balanced blades from one side to the other on a small heli can make a large difference. The tolerances are so small on these size and smaller helis it is crazy.

Much the reason I am a hardcore advocate on smaller helis in running abec 7 or higher rated tolerance bearings virtually everywhere on certain brands. We wont go there.

[Striges]

Could someone help me check this log?
Wanted to see how the vibrations were with the blades on so I took it to the field but it felt like the motor or esc shut down for like a second a couple of times.

The vibrations are massive in the tail. A buddy at the field helped me look over the tail. Didn't find anything wrong execpt that the bearings might be bad, so I changed them when i got home.

[Fruitbat]

Hi Striges,
I am no expert, but these vibes look almost exactly the same as I had on my G570 the other day (posted in the "New secondhand Goblin" thread).
I got rid of the worst of the vibes by loosening the tail blades. They were very tight in the grips so I opened the grips up the tiniest bit until the blades could slip in and out without force, then nipped the bolts up until the blades were firm rather than tight.
I still have some vibe chasing to do, so looking forward to sharing any fixes I come up with.
Hope this helps!
Cheers
Dave