VibeZ worse on one motor

I have been doing some vibration testing today on my Tarot 680Pro hexa (setup in hexa-x layout), with Sunnysky x4108s kv690 motors. 5 of the motors are almost vibration free with VibeX, VibeY and VibeZ all under 2, when I spin the motors individually upto 80% of full. One motor however (motor 5) has its VibeZ reading shoot upto 15 - (mean value is 7), but strangely the graph shows regularly changing spikes between 2 and 15, whilst all other motors give fairly smooth lines.

So wondering what could cause this rapidly changing vibe reading on the Z axis of this one motor. These are the things I have tried so far:

  • I have switched 3 props on this motor, all statically balanced to perfection. Made no difference!
  • I have tested for bell end-float on this motor and there is none.
  • Checked bearings are are in perfect condition
  • I have tried balancing the bell by adding tape and moving it around, but see no real improvement on the Zvibe reading, so thinking its not a bell balancing issue.
  • I checked the motor timing value set on the X-Rotor 40A ESC and it is correctly set to intermediate timing ( I don’t hear any timing issues to be honest, but thought I’d check this one was set as per the others).

I realise that these are very low vibe readings and I probably shouldn’t be concerned, but I am just curious why this one motor is so different from the other 5. (to the point where I have just ordered another motor!

Any thoughts would be gratefully received. I’ll post to report results of the new motor once it arrives - could be 4 weeks from GLB in China.

If you have the 680Pro with the stock mounts, that will likely be your problem. Those mounts are utter sh*t. If you do have the stock mounts, I’d suggest at the very least you replace them with these:

Anti vibe motor mounts red

The black ones are part number tl68b34 I believe.

If it were the mounts, then the other 5 motors would surely show signs of vibration, but they are perfect. Those anti vibration mounts got tested on YouTube vid and showed worse vibes than the stock mounts

But I didn’t say it was ALL the mounts…

Also, you can try your luck with the stock mounts. You’ll be replacing them at an alarming rate. All my issues went away as soon as I dumped them and used the anti vibe. I wouldn’t place much stock in youtube reviews. I tested myself and they were far and away better than those crappy stock mounts.

I probably should have said - this isn’t a new build. I have been using the stock mounts for over a year now without any issues, and as I said, the vibes are extremely low - the wiki says upto a value of 30 is within limits and my bad motor is only giving a peak of 15, whilst the others are around only 2 on the z axis. I’m really only trying to determine what could be the cause of the huge z axis difference on this motor compared to the other 5, I’m talking 15 vs 2, so changing the mounts does not really address the underlying issue, but would only serve to mask it. I would change the mounts to vibration dampening ones if they were as practically designed as the stock ones, but they don’t provide a platform for holding the ESC, and my setup is very tidy in this respect. See the pics here:

Is it possible that you have more movement in the outer bell-housing movement, compared to the other 5 motors?

I second that about the mounts, if they’re the same as the 650sport, they’re absolute junk. The antivib mounts are much better, if only because they’re made of aluminium and much stronger so they don’t keep breaking.

Have you tried tightening the motor bell?

Leonard Hall posted a great post on diyd about the bells and vibration.

1 Like

Yes I checked the bell play (actually commented to this effect in my Op :grin:
I actually did adjust the shaft on this problem motor to remove a tiny bit of play but it made no difference to the zVibe reading.
I agree that the plastic mounts aren’t very strong and aluminium would be better, but the design of the originals gives a tray for the esc which I have used very tidily in my build and so switching motor mounts would involve new ESC mounts too.
In any case the purpose of this post is trying to determine why one motor would have fluctuating zVibe readings when the others have virtually none. They all use the original mounts which are fully tightened in the same way as each other.

Ops sorry didn’t see that. Try swapping the position of the bad motor with a good one (ie swap 2 around) and see if the problem follows - that will tell you at least if it’s the mount or the motor?

The ones I got, if you tightened the screws just a little too tight, the brass inserts that those screws threaded into would separate from the plastic. Junk. I’m pretty sure the 650 and 680 mounts are identical.

Actually, the aluminum mounts had a decent space under there for my ESCs (I have XRotor 40 ESCs as well, but not the big heatsink, just regular one) and worked just fine how I had them.

Yup that’s exactly the same as I found, and the plastic would split. I went through a dozen of them before declaring them junk…

Strangely I haven’t had that experience and the screws are pretty tight on mine. I wrapped the carbon tube with a single layer of selotape before sliding on the motor mount to provide grip.
fnoop - good call on switching the motor around. I will do that.
One other mod I carried out yesterday is to remove the pixhawk mounts I had made and replace them. Before I had 1cm x 2cm oblong pieces of the orange HK foam with a piece of double sided foam tape on either side - one of these in each corner of the pixhawk - this gave excellent vibration dampening, but at the expense of the flight controller not being solidly held in place - My impression was that a twitch on the frame would likely cause the FC to be thrown excessively in the direction of movement, so excessive movement on the part of the FC. So I decided to stiffen up the mount by using some thinner and firmer 4.5mm foam, which is sticky on one side only, which meant some double sided tape on the non-sticky side - I have added a 1cm strip of this along the full width of the FC at each end. Hoping it will maintain vibration dampening whilst providing more stability for mora accurate IMU measurements. I took it for a flight tonight - it was a bit windy, but it was clear that the PIDs are far too high now. They were a tad high before (since my auto-tuning at the weekend) but this flight demonstrated that they were a tad beyond acceptable limits, so need some manual tuning to get the best results. Just waiting for a calm day!

guys, do you have your ESCs mounted on the underside of the anti-vibe motor mounts? Would be interested to see any pics if this is the case. Trying to figure how an X-Rotor 40A ESC would fit under there. really don’t want to rewire to put the ESCs under the central frame if I were to get these mounts.

This is the YT video I was referring to in an earlier post:
he refers to the anti-vibe mounts as “vibration inducing”!

fnoop - I followed your suggestion…, swapped my vibey motor with the least vibey one, and the vibes stayed with the same arm/mount. I then swapped the props between this vibey motor with one from a motor with no vibes and again, the vibes stayed with the arm/mount position, so I can only conclude that this arm is somehow attracting more vibration than any of the others. The vibey arm is front right, and on this same arm I have the GPS mounted on a pole, so wondering if the gps is getting vibes induced from the motor, and this in turn is amplifying those vibes into the arm. Its also one of the folding arms for which the hinge point lies directly under the front right corner of the pixhawk, so wondering if this is where the IMU is located and perhaps it just reads more vibes from this arm due to the locality of this inboard end of the arm.

In any case, I think I’m going to give up trying to solve an issue which is probably not relevent. My overall vibe readings peak at around 25 whilst in flight, which is under the recommended limit of 30, so I’m hoping this is good enough. I get zero vibe clipping in flight.

Fnoop - would you be willing to attach one of your dataflash logs from your 680Pro? Is your’s running on 4s or 6s? If 4s, then it could be a good comparison - I’d like to compare the vibe values to see how mine stacks up. I’ve seen really varied vibe levels on the logs in posts in this forum, some super low and some crazy high (although these tend to be logs from copters with issues!)