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Hollow bore motor bearing failure Thread


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How many have failed?  I saw one post on here of a failed from the factory bearing.  Looked like the seal had come off and dirt got in.  In general the larger size means they are much stronger than smaller bearings, but countered by the fact that they are being sourced in China as cheap as possible.  A European bearing of that size would be a couple hundred Euro.  I'm sure these are $30 max.

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Good consideration indeed, a counter point is that the more balls, the less weight pressure per ball.

Edited by null
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On the EX the circumference of the bearing is 566 mm.

On the MSP the circumference of the bearing is 180 mm.

So the EX bearing has ~3 times the area in which debris can enter and is ~70 mm closer to the ground.

The 6832-2RS bearing that the EX is using, already has two rubber seals - one on each side of the bearing. Perhaps an improvement could be made to the seals, like on these triple sealed waterproof, dustproof bearings: 
https://www.nsk.com/common/data/ctrgPdf/e1234a.pdf

 

Overall, there's no quick, cheap solution to this issue. The manufacturers are going to have to pay for higher-quality bearings, the cost of which they'll happily pass onto consumers.

 

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14 hours ago, Asphalt said:

Hollow bore/centreless/hubless motors will always wear out faster than traditional axle motors, given the same bearing material for the following reasons:

  1. Being further away from the centre, each ball bearing has to travel further and faster for every rotation of the wheel
  2. More ball bearings are required as you increase the bearing distance from the the centre of the wheel. Increasing the number of required ball bearings increases the likelihood of one of them failing.
  3. With the bearing being located closer to the tire, there is a greater likelihood of water and debris entering the bearings - don't go through puddles deeper than your tire [EDIT - this should have said "don't go through puddles deeper than your bearing"]

Let's calculate how far a ball bearing in the EX has to travel each wheel rotation assuming a bearing diameter of 180 mm (halfway between the 160 mm inner diameter and 200 mm outer diameter):

  • C=2πr
  • C=2*3.1415*0.090 m
  • C=0.5655m

Now how far a ball bearing in the MSP has to travel each wheel rotation assuming a diameter of 57.2mm (halfway between the 17 mm inner diameter and 40 mm outer diameter):

  • C=2πr
  • C=2*3.1415*0.0286 m
  • C=0.1797m

The EX is spec'd with a wheel diameter of 508 mm:

  • C=2πr
  • C=2*3.1415*0.254m
  • C=1.5959m

The MSP is spec'd with a wheel diameter of 482 mm:

  • C=2πr
  • C=2*3.1415*0.241m
  • C=1.514m

The EX is spec'd with a no load speed of 86 km/h:

  • rpm = speed / C
  • rpm = (1433 m/min) / 1.5959 m
  • rpm = 898

The MSP is spec'd with a no load speed of 80 km/h:

  • rpm = speed / C
  • rpm = (1333 m/min) / 1.514 m
  • rpm = 880

Each ball bearing in the EX will be moving at:

  • 898 rpm * 0.5655m
  • 507.9 m/min
  • 8.465 m/s = 30.5 km/h = 18.9 mph

Each ball bearing in the MSP will be moving at:

  • 880 rpm * 0.1797m
  • 158.1 m/min
  • 2.636 m/s = 9.5 km/h = 5.9 mph

So the ball bearings in the EX have to move more than 3 times the speed and distance compared to ball bearings in the MSP.

 

The MSP uses the 6203-2RS bearing with 8 balls:
https://www.nationalprecision.com/ball-bearings/6000-series/6200_light/detail/6203-2RS/

The EX uses the 6832-2RS bearing with 9 balls:
https://www.bearingscanada.com/6832-Bearing-Deep-Groove-6832-Ball-Bearings-p/6832-deep-groove-6832-ball.htm
 

 

Possible Fixes:

Improve bearing quality - bearing quality can vary widely. The ABEC rating system for machine parts doesn't necessarily mean it's a good fit for EUCs. Check out this article by Bones Bearings, a company revered in the skateboarding world.
https://bonesbearings.com/support/abec/#:~:text=The ABEC rating system includes,at 20 to 30%2C000 RPM. 

Improve bearing material - ceramic bearings, used in racing bikes, are faster, lighter and more durable. They are also more expensive and more prone to debris contamination due to lighter seals.
https://www.cyclingweekly.com/news/latest-news/do-you-need-ceramic-bearings-in-your-wheels-197145#:~:text=They are more corrosion-resistant,less friction is a bonus.

Double the rows - The 6832-2RS bearing used on the EX is a single-row bearing, meaning that there is one row of ball bearings around the circumference of the bearing. A double-row bearing would distribute the load across more bearings and be able to bear radial and axial loads in both directions. The drawback is that they need better alignment than single-row bearings. You're also doubling the chance of a single ball bearing failure.

 

EX specs:
GW-EX100V.jpg

MSP specs:
http://www.begode.com/productinfo/406993.html

 


 

 

 

 

Great post! 

Here is my next question then, assuming no factory defects, on average, how long do these bearings last before they need a replacement in other applications? 10000 miles? Less?

Given a broken axle on the old style EUC motors means you are basically getting a new motor, One would surmise replacing the bearings would be a cheaper (and easier) undertaking than replacing a whole motor. 

Also some links/discussion relating to suitable bearing replacements for these motors would also be greatly appreciated! 

Your feedback is invaluable! 

Edited by Ben Kim
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11 minutes ago, xiiijojjo said:

Nice vid! I dont even own an RS, but had to watch. I am SHOCKED that they put the circuit boards on the bottom and he has puddles in there. WTF were they thinking? I'd be drilling me some tiny drain holes!

Edited by ShanesPlanet
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A 61824 bearing is rated for like 6000 lbf of load and 130 mph continuously lol. It's specced more for size/fitment and well beyond the needs of the device, and a decent bearing should last well beyond the life of any EUC. Can anyone with a failed bearing take a pick and pop off one of the side seals and see how much grease is inside? I'm curious if they were just too lazy to pack enough grease in there from the get-go. 

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Edit: lol oops @xiiijojjo posted the same one.

----------

This looks like a pretty good video that walks through the bearing replacement process from a couple of guys in the Seattle crew. (Btw lots of good offroading vids on this channel too.)

 

Edited by brockj
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On 11/19/2020 at 2:43 AM, ShanesPlanet said:

Nice vid! I dont even own an RS, but had to watch. I am SHOCKED that they put the circuit boards on the bottom and he has puddles in there. WTF were they thinking? I'd be drilling me some tiny drain holes!

Same, I put my trust in the weather man this weekend and went out for a 30 mile ride. Got rained on, not heavy, but def more than a drizzle. When I got home I put and air mover aimed at it for 30 min. When I opened it there was small puddles inside.

There is a appears to be a vent on the case as well that may allow water in.

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Thanks for posting the teardown of the bearings.

It's crazy the conditions of those bearings AFTER the EcoDrift waterproofing service - standard Begode bearings stand no chance.

From this picture we can see that there are 24 ball/cylinder bearings (or groups of double-bearings, it's hard to see through all that grease). No wonder these bearings are so expensive!

Monokoleso-Begode-RS-rzhavyj-podshipnik-

 

It also looks like the bearings were already sealed (or at least shielded):

Monokoleso-Begode-RS-rzhavyj-podshipnik-

I'm not sure there's much that can be done to remedy the situation.

I'm hoping that there's a bearing manufacturer out there who've found a robust way to seal them, but it's going to be a challenge with high speed moving parts and pressure fluctuations due to motor thermals, as mentioned by EcoDrift.

If possible, it will be an expensive solution.

While I love the idea of hollow bore motors, I think there's a reason they're not more common.

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11 hours ago, Asphalt said:

Thanks for posting the teardown of the bearings.

It's crazy the conditions of those bearings AFTER the EcoDrift waterproofing service - standard Begode bearings stand no chance.

From this picture we can see that there are 24 ball/cylinder bearings (or groups of double-bearings, it's hard to see through all that grease). No wonder these bearings are so expensive!

Deep groove ball.  

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Could switching to ceramic bearings help with the issue?
There is still the long gap to be sealed but at least it shouldn't rust..

Edited by null
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34 minutes ago, null said:

Could switching to ceramic bearings help with the issue?

Bearings are designed to run with clean lubricant, or run clean and dry (special ceramic applications). But here, they can't stay clean.

And ceramic is a bit of a false choice here: it would be relevant if a commercial ceramic product were offered in this bearing size at an affordable price... today, there isn't.

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