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Hollow Bore Motors, Friend or Foe?


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32 minutes ago, mike_bike_kite said:

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!

I think that may be a tad unfair to the poor little hollow motors.  They are trying their hardest lol

Keep in mind these are the first renditions of these motor designs.  As far as im aware there has only been 3-4 sets of bearings used in these motors and 1 of them to this point has allegedly proven to be far more durable (the newest inmotion motors have had no documented failures that im aware of) 

So i think it is to soon to say for sure they are foe.  It may be a very simple solution that makes them the clear superior option.  However there is no guarantee we ever find a cost friendly solution so i can also see them becoming such a developmental headache that they are abandoned and we go back to standard axle mounts.  

 

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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

Very excited for this "2nd generation" of hubs and bearings! Having broken MSX axles before, I'm a believer in the future of hollow motors. Let's see if they improved the bearing fit this time

I think we can only comment on what's been produced already, the latest version of these bearings might bomb proof or it might not of been out long enough to fail. Is it too early to say whether it's

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30 minutes ago, mike_bike_kite said:

It's difficult for me to see what they offer: they allow for larger gauge wires but I don't recall reading about Inmotion motor wires burning out and Gotway still use the same gauge wires in the wheels that I've seen (that might of changed now). Even if they worked perfectly, they'd still be 10x more expensive than a normal bearing and 1.5Kg heavier. To me they just seem like a bad answer to a question that no-one is asking ;) 

Gotway's priority has alway been performance. Look to other manufacturers for reliability, ergonomics, longevity, durability and safety.

Apparently Gotway has pushed as far as they can with voltage (couldn't get 126V to work), so hollow bore motors are the next performance frontier. The larger the radius of the stator-rotor, the more torque the motor can generate.  This potentially translates to better acceleration, hill-climbing, and braking; compared to a traditional motor.

The added benefit of larger gauge motor wires, unencumbered by a motor axle, will allow them to push the current ceiling and not have to worry as much about motor cables melting, like on early Shermans.

If Gotway can figure out the bearing reliability issues and can tune their firmware so that their hollow bore motor wheels are more responsive (not requiring as much input force from the rider), they'd be in a good position to regain the performance crown.

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I don't see why any new motor has to be dependant on a hollow bearing, that's a bit like saying a car engine is dependant on it's wheel bearings. If they need larger cabling then just make the axle and bearing 50% larger.  It's not like these wires are huge. They could also have a slightly wider pedal hanger to seal in the new bearing and make it waterproof. Making a change like that would mean they wouldn't loose face by going back entirely to their original design. Overall that's a win, win, win.  

 

Having a slightly larger bearing

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21 hours ago, mrelwood said:

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

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. 

How would you know you got the new larger 6916 bearings? I got my wheel on 25th of November.

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1 hour ago, chroma said:

How would you know you got the new larger 6916 bearings? I got my wheel on 25th of November.

Someone said that the upper saddle brackets were changed at the same time. If the plastic on the bracket goes well beyond the edge of the bolt head, you have the newer ones.

 Whether this really changed at the exact same time has not been confirmed though.

 

 On the question of the benefits of the hollow bore motor, I think the physical space saved compared to the traditional axle mustn’t be downplayed. Both the EX as well as the V11 depend on the space that would otherwise be taken by the axle, for the suspension.

Edited by mrelwood
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 I am hoping the Hollow motor of Gotway/begode T3 has taken some of the issues to heart a little bit, looks very interesting, I wonder if they will use a  smaller diameter bearing for the hollow motor, being that it is just a 16" tire with even smaller rim diameter. If not, it would likely increase contamination by the smaller size rim pushing the bearing closer to debris, and higher rpm of smaller tire.  I guess we will find out soon, it is to be releasing in bulk likely early 2021.

T3.png

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2 hours ago, mike_bike_kite said:

I don't see why any new motor has to be dependant on a hollow bearing, that's a bit like saying a car engine is dependant on it's wheel bearings. If they need larger cabling then just make the axle and bearing 50% larger.  It's not like these wires are huge. They could also have a slightly wider pedal hanger to seal in the new bearing and make it waterproof. Making a change like that would mean they wouldn't loose face by going back entirely to their original design. Overall that's a win, win, win.  

 

Having a slightly larger bearing

I agree that this would have been the prudent approach:

  • slightly larger axle could have been made thicker at the same time to improve strength while accommodating larger gauge wires
  • slightly larger bearing
  • slightly wider pedal hanger (improving strength and with the extra room they could have designed a shim-less mount that didn't loosen so easily.)

I'm guessing they didn't take the prudent approach because:

  • 3500W motor spec looks awesome for marketing
  • Potentially a lot higher torque/performance ceiling
  • Room to fit a novel suspension system
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  • 2 weeks later...
Posted (edited)

2021-01-01-191752

2021-01-01-210407

2021-01-01-210416.jpg

Here you have the V11 bearings dissambled - not how do I get old ones out and new ones in. 

Heating gun and violence helpd. bearing-out-of-v11-whel

 

Edited by Finn Bjerke
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The is a video of RS bearing replacement. The same process will be the same on the V11. The video was posted about a month ago. The video was posted by" EUC BROS". They used a propane torch to heat the bearing plate to around 70C. The old bearing will drop out. Then using the same technique with the empty plate, once heated the new bearing will drop in. This technique is simpler than trying to press a large bearing.

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In the application of an EUC, the bearings shouldn’t be subjected to any serious loads IMO. The rpm of the wheel is pretty low, the weight they have to carry is rarely over the 120kg they are designed to carry. Also, with the larger bearing in a hollow motor, any load is spread over a much larger surface area. I would guess the problems are caused by sub optimal bearing materials and the ingress of dust/ sand etc, or water. I’m sure that all the companies building euc’s to this design will quickly overcome these initial problems....None of them will want to dent their reputation. 

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I've seen something similar happen in the cycling industry. Once they depart from standard reliable bearing sizes, it becomes a whole new project to get reliability. Some have never ending problems and some don't.

I'm curious to know the motivation of jumping all the way to such an extreme diameter? There are diameters well below this that can hold a heavy rider going around the world. Is it because they want to avoid steel and stay with aluminum? The problem with that is that the bearings themselves become boat anchors.

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11 hours ago, alcatraz said:

I've seen something similar happen in the cycling industry. Once they depart from standard reliable bearing sizes, it becomes a whole new project to get reliability. Some have never ending problems and some don't.

I'm curious to know the motivation of jumping all the way to such an extreme diameter? There are diameters well below this that can hold a heavy rider going around the world. Is it because they want to avoid steel and stay with aluminum? The problem with that is that the bearings themselves become boat anchors.

Yeah the hollow motor was designed for a big cable to run thru, no need to make bearings with extreme diameters - Sherman veteran have axel still - 

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  • 2 months later...

A larger bearing would require more rotations of each ball per revolution of the wheel. If you think about the inner and outer races of the ball bearing rotating against each other, with the balls in between also rotating, the circumference of the races vs the circumferences of the balls is much greater in larger bearings.  The extra rotations of the balls would directly correlate to shorter lifetimes of the bearing, if the bearing is subject to more of the stresses described earlier in the thread.

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Your point is correct if the balls are the same diameter in both bearings. To my knowledge, they are not. I would imagine they are far larger in the hollow bearings..but then we are talking dubious Chinese design here...so I will use that as my get-out if I'm wrong ;)

 

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22 hours ago, Wei Zhong said:

The extra rotations of the balls would directly correlate to shorter lifetimes of the bearing

For wearing out, sure. But currently the bearings in hollow bore motor EUCs are failing as soon as in just a few rides. Getting the bearings to last as long as the natural wear would enable would be a magnificent leap forward from the current situation.

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  • 3 months later...
On 7/21/2021 at 5:50 PM, Asphalt said:

Not saying that Begode reads these forums, but it looks like they finally came to their senses.

I would say it's commendable they experiment:innocent1: Even if the experiment (or their version of it) fails. Given that IM has gone with a traditional axle on the V12 vs. the hollow motor of the V11, I would say Begode/Gotway aren't the only ones that learned a lesson.

In theory, a hollow motor could save weight (nothing instead of the motor stator spokes) if the big bearings don't negate the weight savings. And they could offer extra space on the inside that could be used for whatnot. So I'm a bit sad it seems the hollow motors are over, but at least the manufacturers tried.

The "mini hollow motor" new Begode motors are the best of both worlds imho. Better than an axle (more robust), not as susceptible as the big bearing hollow motors, even though the latter would be cooler if they worked.

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I wonder if this smaller hollow design has an effect on torque. I love the torque on my RS HT!

My bearings have been fine, lots of dusty off road and 1100 miles down. I avoid water like it's an allergy though. 

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5 hours ago, Flying W said:

I wonder if this smaller hollow design has an effect on torque. I love the torque on my RS HT!

My bearings have been fine, lots of dusty off road and 1100 miles down. I avoid water like it's an allergy though. 

Bearing size shouldn't have any effect on torque.
Torque will be influenced by stator-rotor radius, wire thickness, stator windings, and magnet size, as well as voltage and current.
 

Edited by Asphalt
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11 hours ago, RagingGrandpa said:

Let's see if they improved the bearing fit this time around... but it sounds like the huge-diameter boutique (expensive) thin-shell bearings from the RS/EX.N/MonPro are being phased out.

Well this change to a much smaller version of the "Hollow Motor" might mean that the EX suspension model also gets phased out from the line-up too?

There is Absolutely No Way GotWay/Begode will be able to retrofit/re-engineer that cumbersome, clunky, travel limited air suspension into these New motors!

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9 hours ago, fbhb said:

Well this change to a much smaller version of the "Hollow Motor" might mean that the EX suspension model also gets phased out from the line-up too?

I totally forgot about the EX suspension that needs a big hollow motor!

Might very well be the EX.N is the new standard EX now. Or they come up with a different suspension design (please just copy KS).

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9 hours ago, fbhb said:

Well this change to a much smaller version of the "Hollow Motor" might mean that the EX suspension model also gets phased out from the line-up too?

There is a re-design happening for the EX. I was informed that the units would start shipping in mid to late fall. I pulled my pre-purchase after receiving this news LOL. 

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On 7/27/2021 at 6:58 AM, Asphalt said:

Bearing size shouldn't have any effect on torque.

It does have a small effect. Friction torque in the bearing is friction coefficient times force times bearing radius. Doubling bearing size doubles friction torque.

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