Hollow Bore Motors, Friend or Foe?

[Finn Bjerke]

Hollow motors will have bearings problems and be shortlived wheels, first we had axels problems now its the bloody bearings in hollow motors that causes problems.  The idea is not mine really, inspired by American friends. I saw this video and some dissable pix that made me think hollow motors are problematic for the Chinese producers.   - Its too complex for the Chinese EUC producers perhaps?   The axels were pissy weak on Gotway Monster.  If the new thang is hollow motos maybe there is hope for Korean wheels ? If axels on traditional motors are a problem and bearing on hollow motors are a problem too - then we got a lot of DIY repairing to do?  


More info below. (oh if you dont like my sarcasm - its not really my problem)



DUF talks about it here: 

 

Demonstrated here for tech ppl: (the wonderfull EUC bros my favorite EUC madness, love these guys: 

 

 

Edited December 10, 2020 by Finn Bjerke

[xiiijojjo]

I prefer just buying a new higher quality Japanese bearing once instead of having to buy a new motor when my axle eventually snaps. Also i won't have to tighten the axel nut to stop the pedal hangers from being loose. Also when a bearing fails you are still able to ride the wheel home(with a bit of noise to accompany you) whereas when an axle snaps you will have a potentially catastrophic crash.

As euc enthusiasts we have become accustomed to opening these wheels and fixing them and honestly changing a bearing in an RS is much easier and less time consuming than changing any motor on any non-hollow wheel. That's my 2 cents.

edit: Overall i think the durability of the hollow motors are far superior as the only parts that can even potentially be damaged is the bearing and the pedals hangers. 

Edited December 12, 2020 by xiiijojjo

[Finn Bjerke]

Interesting: I got new bearings + wheel + motor from Inmotion.  They had to do that because they bought to cheap bearings ?  Gotway have the same bloody problem it seems: 
 

GotWay RS HS Update:

So... after 5 hours trying to get this thing apart without breaking anything, I finally understand my bearing problem I was having (I think). Basically the bearing was either low quality or defective and something caused it to start grinding itself apart. There are two bearings. Only one of them had this issue.

Now, this doesn't mean the bearing has failed completely. It still works and before taking this thing apart I was riding all day, but the sound it makes is just not right. It sounds like a constant rubbing and it's pretty noticeable even when you're not the one riding it.

I did contact eWheels before this and they said that the sound was normal for the RS. Maybe the video I sent didn't illustrate the sound good enough, because I've heard nothing but good things about them.

Either way, I'm not sure what the next step should be. Contact gotway or eWheels and try to get some replacement parts that may or may not fail again, or replace the bearings with custom ones (probably better quality).

On the bright side, I now know why it's called the RS. It's the name of the ball bearings

 

[Flying W]

@Finn Bjerke try to take video or record the sound free spinning by picking it up, the bearing noise will be the only sound heard in a quiet room. eWheels had been great for all my wheels so the sound must have not come through well on the recording. 

If.....no I mean when my bearings go south on my rs I'm just replacing them with higher quality bearings. The only way I wouldn't is if gotway has better one to fix the issue. It try those out under warranty. 

If it's the same ones to replace these though I'd rather get better ones vs using the warranty.

I'm loving the wheel so far, mine the torque model. 

[Finn Bjerke]

Been ressearchnig the topic a bit more, hollow bore motors need huge bearings off course. Inmotion V11, GW RS, The New GW MOnster have hollow motors Sherman Does not.  High quality Bearings that size aint cheap  Here is Gotway RS motor 

[Flying W]

The bad part is not knowing what is enough, and what is overkill. I saw japanese rubber shielded bearings for $80 a piece that might do the job, I also saw crazy expensive bearings that I'm sure are overkill for $500 a piece. 

I'd spend 160....maybe 200 after tax and shipping to put the problem to bed, but spending a grand, damn near half the cost of the wheel, would be a no go for me. 

Hopefully sub $100 bearings from a good manufacturer will work plenty well in our wheels.

 

[mhpr262]

I wonder why they went so overboard with those hollow bore motors that need those giant specialized bearings. If they had just used ordinary style but slightly oversized axles, lets say between 3cm and 4cm diameter, they would have been robust enough for the heaviest riders and the toughest use, they could have used motor wires as thick as they liked and at the same time they could still have used standard size bearings for just a couple of dollars apiece.

[shellac]

On 12/10/2020 at 4:34 PM, Finn Bjerke said:

Hollow motors will have bearings problems and be shortlived wheels, first we had axels problems now its the bloody bearings in hollow motors that causes problems.  The idea is not mine really, inspired by American friends. I saw this video and some dissable pix that made me think hollow motors are problematic for the Chinese producers.   - Its too complex for the Chinese EUC producers perhaps?   The axels were pissy weak on Gotway Monster.  If the new thang is hollow motos maybe there is hope for Korean wheels ? If axels on traditional motors are a problem and bearing on hollow motors are a problem too - then we got a lot of DIY repairing to do?  
 

I saw those same videos. The hollow bore motors are a new thing, so there’s bound to be some growing pains as they figure out which bearings work best and also keep costs down for the consumer. I don’t think there’s reason to despair that they will always have bearing problems or be short lived wheels. Your casual sinophobia which you call sarcasm aside I think Begode will figure it out and as early adopters of the RS we should anticipate such things. 

I haven’t had bearing issues on my RS but they did switch out the control board already. The warranty service from ewheels is pretty solid so I’m not all that worried about it. I admit having to send the wheel there and get it back was a minor inconvenience. I’d say just buy from a place with good service, not from say aliexpress. 

[Flying W]

Gotway has bey the farm on these motors so I'm sure they will figure it out...if not they will be hurting since every new release from them has a hollow motor. 

Mine RS is fine so far but only 70 miles on it. I will put another 40 or more miles on it tomorrow. 

I am loving this wheel so far though!

[GoGeorgeGo]

Many of you may have seen by now that the new hollow bore motors being used on a few brand new wheels have had some growing pains.  It appears to be an issue with the ball bearings wearing out abnormally fast most notably. 

For the sake of transparency, i am invested in this topic as i own a wheel with one of these newer motors.  I am happy to report that over 800 km so far, my bearings have been perfectly fine 👍 and its important to note for the sake of this conversation, im not the only one with a machine without issues. The majority of peoples wheels seem to be unaffected by the bearing issue.

But to me that just makes the issue even more interesting. What is different between my wheel, and a wheel thats bearings gave after 100km?

But why are the bearings failing? Two seperate companys have had the same issue in at least 3 different motor configurations.  At least one company has changed the bearings they used to no avail.  Another individual claims they had replaced the bearings in 2 hollow core wheels with higher quality ones (quality unknown) and they still wore down quickly allegedly on his machines.

Hollow Bore motors, although new are not exclusively used by unicycle companies however.  As an example, here is a link to a motor made by Mitsubishi, it is a hollow bore direct drive electric motor capable of spinning about 50 km/h

https://us.mitsubishielectric.com/fa/en/products/drive-products/ac-servos-melservo/melservo-j4/direct-drive-motor/j4ddm

It is designed for industrial use meaning constant run time so longevity is a must. I can only assume they are crazy expensive since you need a quote to even get the price.

So is the answer as simple as quality of parts? And not even neccesarily the bearings themselves but could the entire housing be to flimsy leading to minor flexing and compressions damaging the bearings? Could it be an issue with how long we run them in one direction? Are they being damaged during installation? 

The hollow motors have many benefits, but are those benefits worth the headache?

If anyone has ideas on hollow core motors i thought this would be a great place to share them.  Anything from how to fix the problem, what the problem exactly is, or if anyone knows of any other companies using hollow core direct drive motors for heavy duty applications that might have some insight on what the issues with this iteration of unicycle motor design could be.

I am confident its something that will not be an issue for long, but i thought it was interesting that both companies introducing these new motors had the same issues (unsure if they are using the same producer or not)

Edited December 23, 2020 by GoGeorgeGo

[houseofjob]

The curious thing is, hollow bore motors don't seem to be new by any means, but I can't find one instance where it's used in a car, truck, bike, or any other commercially available vehicle that must operate out in the elements / outdoors. Perhaps someone can provide an example?

Also peculiar, we've seen the SoloWheel Orbit and Fastwheel Ring back in 2015 (the closest things to hollow bore), come and go without ever being released.

Maybe there's a good reason for that 🧐🧐

 

Edited December 23, 2020 by houseofjob

[mrelwood]

This is indeed an interesting situation. Can’t wait to hear how things pan out.

Quote

Another individual claims they had replaced the bearings in 2 hollow core wheels with higher quality ones (quality unknown) and they still wore down quickly allegedly on his machines.

A few more details on this: The bearings that were used cost 12.5€ per piece. SKF bearings in 6816-2RS cost 70€ each (83€ for the 6916-RS), which they recently used on one V11. The future of the SKF in the V11 will be very interesting to watch, as it might indeed be about the tolerance of the large bearings that cause the whole issue. Tolerances vary, which would also be a reasonable explanation for others having an issue while others remain free.

While looking at the prices of said bearings, I noticed that all of the bearings - SKF included - were just ABEC-1, “standard tolerance”, or both. What it means for each manufacturer surely differs, so jumping to bearings many times the cost of the original may turn out to be the only solution.

EDIT: I haven’t yet seen a report of failed bearings on a V11 that would be confirmed having the new larger 6916 bearings of the latest batch. 3rd batch V11 yes, but the bearing size was only changed in the midst of the 3rd batch. 

Edited December 23, 2020 by mrelwood

[Planemo]

Theres absolutely no reason why a bigger bearing should be any less reliable than a smaller one (assuming the same operating conditions). The only issue with bearings is that cost goes up exponentially with size if you want to retain the same quality.

I used to supply ballraces for industrial use that were around 25cm internal bore and 5cm wide. They weren't cheap, but would run forever if properly lubricated and not subject to water etc which would ruin them in minutes. 70 to 80 Euro for bearings of the V11 size sounds perfectly reasonable to me, but the best bearing in the world won't like water...

 

[meepmeepmayer]

Watch this video by Vee. Contains some horror footage from the Gotway factory, which might very well explain why some bearings fail and others don't.

(Timecoded at 8:02, Begode footage begins at 8:24, but watch her commentary too, it's very good)

Now this pertains only to the manufacturing side. To be fair, Begode are pausing production to figure the hollow motor bearing question out, and I expect them to have this fixed when they restart production. Same for Inmotion, they will (or already did) fix this.

-

Whether these big bearings are susceptible to water and dirt is another question. Would better quality bearings hold up? Is it a fundamental thing with these size bearings? I don't know.

Edited December 23, 2020 by meepmeepmayer

[fbhb]

9 hours ago, meepmeepmayer said:

Whether these big bearings are susceptible to water and dirt is another question. Would better quality bearings hold up? Is it a fundamental thing with these size bearings? I don't know.

The Only real issue with All these hollow bore motor bearing failures is very likely Just down to the very poor quality Non-branded, Chinese bearings that have been used so far by both manufacturers to keep the costs down.  Added to that, then there is the fact that the Begode/GotWay bearing install method of using a "Mallet" rather than a press is compromising the (suspect quality) bearing even further! (so the crappy bearings are likely to be faulty even before a New wheel gets to be ridden!)

IMHO, I Do Not believe there is a fundamental issue with the sizing per se, especially when compared to the much smaller, standard axle bearings we are more used to seeing, that cope with the EUC's load requirements just fine!  

Granted that water and dirt can also play a part in the premature failures, but there are also cases of bearings failing in very short order due only to the poor quality!  A good quality bearing, with rubber seals should be more than capable of taking the same, if not greater load considering it is Now being spread over a much larger surface area!

Again, IMHO If well established, reliable brands such as any of the following were to be used: TIMKEN SKF NTN KOYO NSK THK FAG, then we would Not have seen bearing failures on this huge scale, but unfortunately the cost of the wheels using them would most definitely have increase substantially!

Edited December 23, 2020 by fbhb

[null]

I was very glad to see them arrive, solving broken axis, allowing for thicker cables and using the unclaimed space (EX).
They have introduced new issues though, with the larger gap / seal area, beefy weight, higher RPM for the balls (wear?)

I guess they will find a fix but weight will be difficult to address. Maybe an in-between would do, a smaller diameter hollow bore. 

Edited December 23, 2020 by null

[meepmeepmayer]

edit: not true unfortunately

8 hours ago, fbhb said:

A good quality bearing, with rubber seals should be more than capable of taking the same, if not greater load considering it is Now being spread over a much larger surface area!

The bearings only hold the motor covers anyways, there isn't even any load worth mentioning on them.

I guess the actual balls/disk inside are crap material. Or something is so uneven that they quickly get grinded away.

So I believe you're right, better quality/brand bearings is probably all that is needed to fix this. And an assembly process that doesn't endanger them.

Edited December 23, 2020 by meepmeepmayer

[Asphalt]

1 hour ago, meepmeepmayer said:

The bearings only hold the motor covers anyways, there isn't even any load worth mentioning on them.

Not sure where you got this information, but the bearings have to support pedal hangar forces in the RS.

If anything, the way the pedal hangars are mounted with four screws, causes load "hotspots" on the bearings, whereas the traditional axle bearing will have the load more evenly distributed around the whole bearing.

Most industrial uses of hollow bore motors have a consistent, predictable load.
EUCs subject the bearings to varying torsional, axial and vibrational loads through carving, jumping, twisting, accelerating and braking.

Most industrial uses of hollow bore motors have a consistent operating environment.
EUCs subject the bearings to varying environmental operating conditions: humidity, temperature fluctuations, dust, mud, rain, snow, slush, sand, salt.

 

In order for riders to enjoy the benefits of hollow bore motors, with similar reliability to traditional motors, manufacturers are going to have to do the following:

1. Design shielding around the bearings to protect them from ingress (traditional motor bearings were small enough to be covered by the pedal hanger)
2. Use higher quality materials that can operate under the loads and environments that EUCs are subject to.
3. Distribute pedal hanger load more evenly around the bearing to prevent "hot spots".
4. Follow bearing manufacturer guidelines for installation (use a bearing press instead of a hammer)

[meepmeepmayer]

42 minutes ago, Asphalt said:

Not sure where you got this information, but the bearings have to support pedal hangar forces in the RS.

Can you elaborate?

What I see in the picture you posted, which is what I had in mind:

The pedal hangers are screwed into the stator. The rest of the wheel and rider sit on the pedal hangers. The bearings only hold the black "gotway made in china" cap (plus the rotor/tire assembly) that rotates over an internal stator that doesn't. So the bearings connect everything that rotates and everything that doesn't (naturally), but in the end there's not much that rotates (the outer tire/rim/magnet ring plus that cap extending towards the middle).

Right?

-

Do you mean that impacts from the tire travel into the bearings? I always thought the motor's magnets/windings catch that (they don't rub, after all, but maybe that's only due to the bearings?).

-

If the stator is shitty and bends and puts uneven loads on the bearings... for me that's not a bearing problem, but a stator problem But you could make a point that this distinction doesn't matter because you got a problem either way.

-

42 minutes ago, Asphalt said:

Design shielding around the bearings to protect them from ingress (traditional motor bearings were small enough to be covered by the pedal hanger)

That's a really good point. Maybe expecting bearings to be waterproof doesn't make sense. So you'd just need an extra cap.

Edited December 23, 2020 by meepmeepmayer

[Chriull]

1 hour ago, meepmeepmayer said:

Right?

The rim, motor shell sits (rotor) on the ground - the tire "puts" the whole rider plus wheel weight on the ground.

The rider stands on the pedal hangers which are fixed on the stator (inner part with coils)

Rotor and stator are connected only by the bearing - so this bearing takes the whole rider and stator weight.

And the "full rotation" of the wheel!

1 hour ago, meepmeepmayer said:

Do you mean that impacts from the tire travel into the bearings? I always thought the motor's magnets/windings catch that (they don't rub, after all, but maybe that's only due to the bearings?).

No. Magnets and coils only create/take the rotational force - no "impacts from the tire"! Once that happens (dead bearing) the stator smahes against the magnets and everythings over...

[Asphalt]

@Chriull  beat me to it, in a much more succinct way, so I'll spare everyone my long winded response

@meepmeepmayer it would be very cool if electromagnetic forces were utilized as some sort of suspension.

Bearingless Motors use electromagnetic forces to replace the mechanical bearings. Maybe a solution for that $40,000 EUC InMotion was hinting at?

 

[GoGeorgeGo]

58 minutes ago, Asphalt said:

@Chriull  beat me to it, in a much more succinct way, so I'll spare everyone my long winded response

@meepmeepmayer it would be very cool if electromagnetic forces were utilized as some sort of suspension.

Bearingless Motors use electromagnetic forces to replace the mechanical bearings. Maybe a solution for that $40,000 EUC InMotion was hinting at?

 

Very interesting concept but im not so sure it woyld work in a EUC.  He says the bearings are stabilized passively laying on its side like that, but wouldn't they be super unstable if you tried to stand on a floating bearing like that? Even a little shift of weight would have it make contact with the housing.  (Completely ignoreing the potential development cost factors also lol)

Edited December 23, 2020 by GoGeorgeGo

[Asphalt]

1 minute ago, GoGeorgeGo said:

Very interesting concept but im not so sure it woyld work in a EUC.  He says the bearings are stabilized passively laying on its side like that, but wouldn't they be super unstable if you tried to stand on a floating bearing like that? Even a little shift of weight would have it make contact with the housing.  (Completely ignoreing the potential development cost factors also lol)

Yeah, they would need additional electromagnetic forces to constrain the axial forces.

An additional drawback is that in the event of a power failure your axle is likely to fly off and get jammed somewhere, seizing the entire wheel. Who would have thought that there was a worse way to cut-out?

[meepmeepmayer]

1 hour ago, Chriull said:

No. Magnets and coils only create/take the rotational force - no "impacts from the tire"! Once that happens (dead bearing) the stator smahes against the magnets and everythings over...

Well, in that case it makes sense that all the stress is on the bearings.

Somehow I expected the magnetic repulsion to do all that work, but it's the bearings!

[mike_bike_kite]

Friend or foe? The issues we're getting with hollow motor bearings are just too frequent. They make the wheels more expensive ($300?) and they add an extra 1.5Kg to the weight of the wheel. Gotway Monsters and the like had issues with their axles but that was just due to the poor axle mounting design. Kingsong have a much better design and don't get any issues. It's bad enough having to worry about the electrics when you ride in the rain without having to worry about the bearings failing. I'd say foe!