King Song S22 motor stator slippage issue: more severe than expected

[supercurio]

@Rawnei I believe they will make a public statement describing the issue, testing method and how they propose to solve the problem globally.

From what I gather and like we speculated earlier, they are not confident being able to afford a full recall of motors for almost all units already out here with air shipping, due to the scale of the accumulated shipping costs.
Depending on how reliable the motor validation turns out, and the test result failure rate to begin with, maybe a high percentage will still need to be replaced?
Then that might be feasible only at a slower pace, with more economical shipping methods like train and sea shipping.

 

On a personal note, I was offered to be sent a replacement motor and mainboard directly.
I initially refused since I don't want preferential treatment. They insisted mentioning that it will allow me to experiment with the validation test: good point.
After 5 days riding and 25 days waiting for parts with a broken wheel, I kind of forgot that I actually own this wheel.
So I'll share what the replacement parts look like as well the test results when they arrive.

[Planemo]

I can't see how the 'test' will comprise of anything other than applying enough shock load to the motor to try and break the stator free.

It's not like plugging in a dongle/diagnostic device.

A bit like the previous 'test' when trying to blow the board. In fact I wouldn't be the surprised if it was the same process (lift up the wheel, spin to near max speed, pull back sharply etc etc, rinse and repeat).

This kind of end-user stress testing isn't always conclusive and isn't exactly technical either. It would be a lot better if KS simply knew the serial numbers of the affected motors. Do they not keep track of serial numbers/build dates/source of motors etc?

[supercurio]

@Planemo I'm sure a non-negligible % of owners will hesitate to run any stress test because

• they think their wheel is working fine and are concerned about shortening the time before motor failure
• repair delays might be significant. more with some distributors than others especially
• might depend on their wheel for a commute to a school/job, choosing short term convenience vs long term risk - circumstances pushing them to make a bad bet.

Agree a stress test will not always be conclusive because it needs to be executed properly then interpreted.
I don't know if test means checking the motor code & serial number or a stress test tho. Let's see.

Edited September 7, 2022 by supercurio

[Rawnei]

Even so, if stress test passed, does it really mean motor is 100% ok? How can we be 100% sure? It's like home tests for covid that later turned out to be unreliable, oh great I don't have covid lets go out and party! Possible that passed stress test could also mean that the motor didn't break too easily, unless they tested it on a big sample of motors already and it was 100% reliable.

[Tawpie]

43 minutes ago, Rawnei said:

Even so, if stress test passed, does it really mean motor is 100% ok? How can we be 100% sure?

Death and taxes. Everything else is statistics.

If the failure doesn't leave behind physical evidence that allows the Engineers to identify the root cause, all you can do is see if you can force the end result. Very high torque that's beyond what's applied by the motor would seem a reasonable way to make a stator slip, it's not definitive but it's something.

Assuming the folks at KS have access to more failed motors than we riders do, I'm hopeful they can devise something that's reasonably effective at identifying motors that need to be replaced. It's a good sign that they think they know when the problem that allows the stator slippage was solved because that allows them to focus their diagnostic.

In the meantime, a periodic stress test isn't a bad idea. So far, slipping stators have happened pretty early in the motor's life so as one accumulates mileage I think I would gain confidence. I might add a UStride-like try-to-skip-magnets test to the pre-ride and maybe mid-ride checklist… when you're rolling along slowly and jumping up and down on the suspension like everybody likes to do to show off the suspension travel, try coming down on your heels, then your toes. Do that bouncing exercise in the Master test video where they disconnect 1/2 the battery pack (that's a pretty brutal test, and relatively safe—for the test conductor).

 

Edited September 7, 2022 by Tawpie

[Elliott Reitz]

On 9/5/2022 at 7:14 PM, supercurio said:

@Elliott Reitz the knocking typically comes from a loose fit of the bearings which end up moving, measurably misaligned due to poor manufacturing tolerances of the motor side covers, instead of being held securely in place by friction. 

...

It doesn't act like loose fit or even interference.  More like its loading up a spring and then the spring "pops" to knock.  

On 9/6/2022 at 1:39 PM, supercurio said:

@NErider I think you might be confusing the knocking and scraping sound as diagnostics.

@Elliott Reitz video shows a textbook example of knocking sound (bearings alignment, cause: poor side cover tolerances), and no scraping.

It makes the same knocking sound when hand-rotated slowly.  Same wheel position each turn. 

On 9/6/2022 at 1:07 PM, NErider said:

Yes. You should open the motor and look at what may be loose. You should probably stop riding unless you are willing to risk a cutout at any time. And factory installed glue is 100% ok and is the industry standard as long as it is...actually applied. 

The glue, or epoxy, whatever it is goes all over the aluminum hub on the exterior of the stator, and the plastic insulator that the coils are mounted to is the other surface. There is so much surface area there, that it will hold any and all forces that the motor torque could output. 

You mentioned screws to lock it in. I dismissed that at first, but looking at a spare S18 motor I have, it looks possible if done expertly. You would need to drill and tap thru the center of the coil, into the stator hub. Then be lock tite'd in place and make sure none protrudes out the top. 

But a new motor would be way easier. 

Nothing shakes or does anything strange except the 1x / some revolutions "pop" like knock sound.  And this morning on my commute it went away quickly as I exceed 25mph on 1st block.  Slowing down at intersections and in work-parking-lot I don't here it knocking now.  

So back to guessing - something sort of spring tension builds and releases inside the bearings (???).  

[supercurio]

New case in Germany, reported by @LeFotografion, who unfortunately got injured in the crash resulting.

@LeFotografion, is your dealer already in the loop on your S22 motor failure?

[Dubardo]

I've heard the EU batch was different then the NA one. Do we have cases in north america? I saw a knocking sound on my Facebook group. 

[supercurio]

@Dubardo yes at least one, EUCO customer who got injured in a crash on August 2.

This rider had both the knocking and scraping sounds, making the issue extremely difficult to identify (it was not known yet by the community and dealers)

[Rawnei]

3 minutes ago, Dubardo said:

I've heard the EU batch was different then the NA one. Do we have cases in north america? I saw a knocking sound on my Facebook group. 

The motors come from a 3rd party motor manufacturer so educated guess is that it's the same problem in all wheels for specific time period regardless of region.

[supercurio]

While pushing King Song hard to release a statement to inform all distributors and riders of the risks and what to look for (scraping sounds) - even before everything else is ready, some distributors have already prepared documents to alert and educate their own customers.

Starting with Voltride.com, in this letter:
https://drive.google.com/file/d/1eltE8FOJljYTqgS64h5oIJQfhPnb_yoZ/view?usp=sharing

[level9]

Quote

The stator has slipped in the braking direction in all the failure cases at our hands. Probably
the forces at play in braking are much stronger than in acceleration. But it can also happen in
other circumstances, riding stairs, curbs, or acceleration.

 

Yikes. @U-Stride 's updated theory may be right about the actual fire's root cause...

A cutout on braking (as opposed to acceleration) is also even more concerning IMO.

 

[supercurio]

48 minutes ago, level9 said:

Yikes. @U-Stride 's updated theory may be right about the actual fire's root cause...

A cutout on braking (as opposed to acceleration) is also even more concerning IMO.

It is not impossible that @U-Stride S22 NYC fire was caused by this issue but unlikely since no scraping sound was noticed back then.

The mainboard has its own issues without being shorted by defective motors, unfortunately.
I'll check the footage that was recorded again tho!

[level9]

38 minutes ago, supercurio said:

It is not impossible that @U-Stride S22 NYC fire was caused by this issue but unlikely since no scraping sound was noticed back then.

 

If I'm understanding the issue correctly, it seems to me hearing sounds ahead of time is not required. It's only that if you happen to hear certain sounds, then the slippage has likely begun - but not enough to sever wires/cutout.. yet; however it seems entirely possible to slip it to the point of severing wires all at once if you eg. brake it hard.

I'll wager a guess atm he hit the braking hard (edit: hit it hard twice in succession), motor slipped and wires severed all at once, then contacted metal which, in combination with a firmware issue (a condition KS didn't account for) caused the fire. KS then fixed the firmware but not the actual root cause.

This is of particular concern for myself as I do tend to brake wheels pretty hard but then also of course, don't want a sudden cutout during an emergency braking situation - which would be a particularly bad situation.

 

Listen starting @ ~9:00 about the braking and slipping.. 

 

Edited September 8, 2022 by level9

[supercurio]

28 minutes ago, level9 said:

If I'm understanding the issue correctly, it seems to me hearing sounds ahead of time is not required. 

There has been scraping sounds in all documented cases so far.

The tricky parts are confusing the light initial scraping for something else, then that the cutout can occur quickly after scraping: in one case, the rider reported that the cutout occurred subjectively "2 seconds" after the sound.

That's why I described it as unlikely. Believe me when you ride and hear that second bad sound, it's not discreet and clearly doesn't sound right.

 

@level9 you can listen for scraping sound on the raw footage here 🙏

Edit 2: I hear no scraping, only a bad sound when the wheel is already overleaned on the last hard braking. I don't know what that is. A component popping maybe?

 

Edited September 8, 2022 by supercurio

[level9]

1 hour ago, supercurio said:

@level9 you can listen for scraping sound on the raw footage here 🙏

Edit 2: I hear no scraping, only a bad sound when the wheel is already overleaned on the last hard braking. I don't know what that is. A component popping maybe?

Agreed. I only hear some kind of pop. It's hard to say if it's mechanical.

I do have to note that @U-Stride did say he felt motor slippage on the first hard brake ("something in there (motor) lost its ability to grip"). I don't want to put words in his mouth but that's not the same thing as pedal dipping from over powering - at least not how I would describe it from experience.

I understand from the information we have atm that all known reports have a sound proceeding them but to be fair, most users don't ride their wheels very hard at least from the EUC World comparison data I've seen and consequently are more likely to experience a slow failure condition (with related noise) as opposed to a sudden condition that a hard(er) rider might experience IMO.

I'm also starting to wonder if this issue is related to KS limiting torque on takeoff - one of their original issues. Could it be that whatever adhesion mechanism(s) they are using is simply insufficient for the amount of power available and the firmware "fixes" or workarounds were to basically cut back performance to keep the motor from breaking free. Just thinking out loud but I'm not so sure if this is a stretch at this point...

 

[Elliott Reitz]

2 hours ago, level9 said:

Agreed. I only hear some kind of pop. It's hard to say if it's mechanical.

I do have to note that @U-Stride did say he felt motor slippage on the first hard brake ("something in there (motor) lost its ability to grip"). I don't want to put words in his mouth but that's not the same thing as pedal dipping from over powering - at least not how I would describe it from experience.

I understand from the information we have atm that all known reports have a sound proceeding them but to be fair, most users don't ride their wheels very hard at least from the EUC World comparison data I've seen and consequently are more likely to experience a slow failure condition (with related noise) as opposed to a sudden condition that a hard(er) rider might experience IMO.

I'm also starting to wonder if this issue is related to KS limiting torque on takeoff - one of their original issues. Could it be that whatever adhesion mechanism(s) they are using is simply insufficient for the amount of power available and the firmware "fixes" or workarounds were to basically cut back performance to keep the motor from breaking free. Just thinking out loud but I'm not so sure if this is a stretch at this point...

The key is he felt something slip twice.  Its a ready speculation that the torque exceeded the strength of the magnets and "slipped a magnet".  But its entirely possible that the slipping was the stator and not the magnets.  Especially with a 126V wheel.  

Its also entirely possible that the corporation decided to hide the truth and cover it up while harvesting the company stock for the last bit of $ they can pump, then DUMP.  Its even reasonable to argue that firmware limits are an appropriate solution because they've not warrantied a testable torque spec for the wheel.   Further, this speculation explaines the 10-15% defect rate (latent discovery of torque exceeding product variation in glue applications, environmental conditions, etc).  

FWIW, my wheel ran great on the commute today. The klunk noise subsided within 50 yards while exceeding 20mph.   Thankfully I've never felt it magnet/other slip in this wheel with >500 miles so far.  The over-torque curb/root climb cutout did not exhibit a sense of slip first (instant, firmware cut-out).  So that fits with firmware protecting the slip limits of physics and the underlying stator mounting (without screws).   

What is the point of slippage?  Is it between:

• {+Per Pic from $univehje on P1}: wire-windings and the frame (maybe we could add screws?)
• {+ NOPE}:  frame and hub/bearing part (have torches could solder/braze it? then replace seals?)

Edited September 8, 2022 by Elliott Reitz
{+}

[supercurio]

@Elliott Reitz the point of slippage is between the motor base and the stator, to be a bit more descriptive:

1. Hub to which the suspension frame is attached to
   Internal "spokes"
2. stator: 
   motor windings
   the frame they're wrapped around

[supercurio]

In terms of coverage, big thanks to

@U-Stride who published an extended Q&A in this video

 

And Adam of Wrong Way just posted on Instagram as a signal booster

 

 

Edited September 8, 2022 by supercurio

[supercurio]

Progress update:

King Song started mentioning the issue to repair shops handling wheels with burned mainboard:
Suggesting them to replace the motor as well, after looking inside the motor for torn wires or slippage of the stator.

[Rawnei]

25 minutes ago, supercurio said:

Progress update:

King Song started mentioning the issue to repair shops handling wheels with burned mainboard:
Suggesting them to replace the motor as well, after looking inside the motor for torn wires or slippage of the stator.

This was my suspicion that burned boards were actually due to the motor issues as it wasn't evident what would cause the board to burn.

[onkeldanuel]

26 minutes ago, Rawnei said:

This was my suspicion that burned boards were actually due to the motor issues as it wasn't evident what would cause the board to burn.

Besides the 4 Boards from Shibby, but thats different story, or perhaps he should open his motor and have a look......

Edited September 9, 2022 by onkeldanuel

[Rawnei]

26 minutes ago, onkeldanuel said:

Besides the 4 Boards from Shibby, but thats different story, or perhaps he should open his motor and have a look......

Exactly.

[supercurio]

@Rawnei @onkeldanuel I relayed the question to Rev Rides.

My assumption is that a motor capable of burning a board would keep making loud scraping sound afterwards and burn nearly instantly replacement boards. But it's true that might be worth checking anyway.

 

Progress update:

King Song announcement will not be completed until next week, as King Song is still working on details to make sure that everything can be clearly understood by riders.

IMO: I wish it was faster, but at least it's coming. The existence of multiple odd sounds from the motors (vibrations, knocks, 3x scraping types) probably doesn't help.

[Yamanator]

15 hours ago, Elliott Reitz said:

The key is he felt something slip twice.  Its a ready speculation that the torque exceeded the strength of the magnets and "slipped a magnet".  But its entirely possible that the slipping was the stator and not the magnets.  Especially with a 126V wheel.  

Its also entirely possible that the corporation decided to hide the truth and cover it up while harvesting the company stock for the last bit of $ they can pump, then DUMP.  Its even reasonable to argue that firmware limits are an appropriate solution because they've not warrantied a testable torque spec for the wheel.   Further, this speculation explaines the 10-15% defect rate (latent discovery of torque exceeding product variation in glue applications, environmental conditions, etc).  

FWIW, my wheel ran great on the commute today. The klunk noise subsided within 50 yards while exceeding 20mph.   Thankfully I've never felt it magnet/other slip in this wheel with >500 miles so far.  The over-torque curb/root climb cutout did not exhibit a sense of slip first (instant, firmware cut-out).  So that fits with firmware protecting the slip limits of physics and the underlying stator mounting (without screws).   

What is the point of slippage?  Is it between:

• {+Per Pic from $univehje on P1}: wire-windings and the frame (maybe we could add screws?)
• {+ NOPE}:  frame and hub/bearing part (have torches could solder/braze it? then replace seals?)

I think it's also worth mentioning that the NYC S20 incident was after a fairly substantial collision with an ebike. Regardless, shouldn't have happened, but for the purposes of using it as data in the current circulation issues it might be completely unrelated.