SK720 vibrations help please

[Colin Broughton]

Hey Vibration gurus

I recently picked up a sk720be and installed it on my Goblin 700 v1 with the old tail system (none dampening).

Im trying to make use of its awesomeness and need alittle guidance on diagnosing my logs. By the looks of it I have a major issue

[dcope17]

Looks like you have fore/aft and up/down vibes in the 21K rpm range.
Sounds like motor to me. Pull off your main drive belt off and do a test of the motor spinning only. Post up that log and we'll go on from there.

[Colin Broughton]

Thanks for your time and suggestion dcope17

I removed the main belt and have this log now.

[SpeedTape]

Originally Posted by Badhelipilot

I removed the main belt and have this log now.

Many of us here are happy to help (come back Georgi, we miss you!) but you do know that the free version of the data viewer that is included in the standard install package allows you to view vibration logs, right? You would have even installed it on your computer when you installed the SK720 setup software on your computer.

The "Pro" data viewer is only required if you want to view playback logs (.SKL files).

There is even a page on the Skookum Wiki that will help you learn how to interpret what the data viewer software is telling you about your heli's vibrations. You can find it here: http://www.skookumrobotics.com/wiki/...ng_for_Dummies

[Colin Broughton]

Originally Posted by SpeedTape

There is even a page on the Skookum Wiki that will help you learn how to interpret what the data viewer software is telling you about your heli's vibrations. You can find it here: http://www.skookumrobotics.com/wiki/...ng_for_Dummies

Thanks for the link I'm gunna read threw this

I have the pro viewer and use it alot, I'm just new to vibration logs with a 5 flight old sk720

[omerco]

Yep its your motor. Scorpion? If so check the bearings they tend to die fast without consistent oiling.I have changed mine to regular grease ones.

If the bearings are good then see this:

In depth video how to balance brushless motors using a vibration meter and tape - Ontaerial (25 min 35 sec)

[Colin Broughton]

Thanks for posting the video omer.

As for the motor it's a Quantum 4530 500KV I noticed it has a slight up and down play once I removed the belt. I may remove the motor and check the shaft and bearings first?

[omerco]

you have very low up-down vib. most of them are side to side and for-aft: shows balancing or bearing problem. start with checking the bearings.

While you are at it try to get what scorpion uses: small spring rings to be used between both bearings and the bell - they eliminate the up down play.

but again - that is not your main issue. most probably balancing (I have winded a quantum not so long ago and it has nice bearings).

[dcope17]

I've had great luck with Quantum motors being well balanced. never had an issue but I haven't worn bearings out yet either.
I agree with Omerco, your vibes are NOT up and down so it's not magnetic resonance issue ( Other threads show this and sometimes its hard or impossible to remove )
looks like a simple vibration. Get that motor rebuilt and you'll probably be good to go.

[Colin Broughton]

Perfect, thanks for the information Omer. I will start by unmounting the motor and checking the bearings, then go onto the balancing method you shared

[Luvmyhelis]

Get a cheap Dubro balancer and source some also economical balance putty off ebay. It doesn't take that long really to balance a can if that is the issue.

[omerco]

Originally Posted by Badhelipilot

Perfect, thanks for the information Omer. I will start by unmounting the motor and checking the bearings, then go onto the balancing method you shared

Check mainly the upper bearing - That motor has a pair of bearings at the bottom and are unlikely to be worn, and most of the side force goes to the upper bearing. If its good than you are left with balancing.

[Colin Broughton]

Got a chance tonight to change the bearings in the quantum motor and pulled a quick log. Seems its still an issue, physically its feels better now vibration wise while running and the can of the motor has 0 up and down play now

How much vibration is tolerable? Im never going to use the self level and probably shouldnt have used the skookum anti vibration kit?

[omerco]

This log show great improvement. I have seen many Ultimate motors with the same level of vibes.
But if I understand that is a bench test? if so send another log after a flight. If you are not planning on the SL you should have no problem i believe.

[Luvmyhelis]

Am I missing something here? The up down are perfect. Fore aft look great. But the lateral vibes? Still horrible. Is the motor engaged here or free wheeling?

[A VIKING]

I have a Quantum 4530-450 that had similar vibe issues.
I had great luck with sticking a 1/4" square piece of clear boxing tape at random points on the exterior surface of the can then running up and checking the vibe level to see where the greatest improvement was. Once this was known, I applied small half drops of 5 min epoxy in the same spot as the tape, one small half drop at a time, letting it harden and checking the vibe level with each application. The vibe level came down with each additional application of the epoxy half drops until I reached a point when the next drop of epoxy made the vibe level climb once again. I removed that last drop of epoxy by getting under the edge with a sharp box cutter and flicked it off.

I now knew my vibe was as good as it was going to get with this method which was 2 as recorded by the Skookum.
I too have no vertical vibe but unlike you my vibe is all fore and aft with no lateral vibe.
I am also running 19,000 RPM which is slower than your speed and will have an effect on vibe score as well.
I have hundreds of flights on the motor with the epoxy drops which have never slung off. Motor temps hover around 150 degrees.
Since you have the smooth sided Quantum like mine and I already know this works and is reliable you may want to give it a shot.

Just experimenting with the tape will tell you it's simply a balance problem which can be corrected.
I just did the first bearing change on this motor a while back and with the can removed, I noticed the balance putty applied at the factory was in the same place that I had applied the epoxy to the outside of the can...had they put just a little more, they would have nailed it but they came up a little short. It was an "awe that's good enough" moment from the guy doing the balancing at the factory.
If you have questions, let me know.

[omerco]

Just small addition - its easier done with a zip tie instead of a tape: put a small one around the can and just turn it around a little each time until you find the sweet spot. there you need to find the weight with another material.

[A VIKING]

Originally Posted by omerco

Just small addition - its easier done with a zip tie instead of a tape: put a small one around the can and just turn it around a little each time until you find the sweet spot. there you need to find the weight with another material.

Sounds like an easy thing to do as opposed to the tape method. From the forums I know many go that route but I am a bit of a chicken putting the weight of the zip tie head, even a small one on a motor can turning 20,000 rpm. Seems like it would be way more weight than would be necessary at that RPM creating its own out of balance making it difficult to determine where the imbalance actually is.

It seems the zip tie method is done so much here, I may have to grow a pair and try it out.
The tape coming off a can turning 20,000 will get your attention also.

[Colin Broughton]

Originally Posted by Luvmyhelis

Am I missing something here? The up down are perfect. Fore aft look great. But the lateral vibes? Still horrible. Is the motor engaged here or free wheeling?

It's free wheeling with the pinion installed only.

What is lateral vibes? Meaning left and right?

[Colin Broughton]

A VIKING thanks for the information I may have to try the drops on the can for a more permanent application over the tape, once I find the problem areas that is lol.

I've never read about the zip tie trick yet, sounds interesting