Hub motor shell split in half.

Q

qwerkus

10 kW
Joined
Jul 22, 2017
Messages
794
I was lacing a RH212 motor, when this happened:

11.jpg

Motor shell literally split in half. Since it's the first time I witnessed this, I wonder if any of you had a similar experience.

A careful inspection of the outer shell revealed many tiny pores in the shell, some of them more than 2mm deep. I suspect they weakened the outer ring, which is already super thin because of the back iron, and allowed a crack to form.


15.jpg
 
3ah9v4.jpg
 
I hope it's not a common problem. I have one of those new in a box to lace up soon. Will be extra careful !!

Are those 12 gauge spokes?

You probably had to get that from Grin since I think it's a special 9C build for the store. Let us know what they say....
 
BlueSeas said:
Are those 12 gauge spokes?
Click to expand...

Not even. Butted 14G. Since the spoke came in too long and I was lacing a fat rim anyway, I chose to lace them with elbows outwards - maybe that added even more stress?
Yet I think Spoke tension has little to do with this crack since I wasn't even close to the usual tension I put on hub motors. Usually, the rim is failing way sooner than any hub flange I've seen. I also hope for a 1 time defect, as I was counting on this motor to match a mac in terms of torque, when laced into a 20" wheel.
Didn't get it from GRIN though, as shipping from canada is just insane. Ozo in france also sells ( https://ozo-electric.com/en/rear-wheel-hub-motor-bike/140-direct-drive-motor-1000w-1500w-rh212.html ) though given the long lead time mine probably comes directly from china.
 
And if was just the elbows out thing it might just broken off the spoke hole tab, but the all the way across crack seems like it's just not designed for straight outward pull. That, and too much spacing between the sideplate screws.
 
qwerkus said:
BlueSeas said:
Are those 12 gauge spokes?
Click to expand...
Ozo in france also sells ( https://ozo-electric.com/en/rear-wheel-hub-motor-bike/140-direct-drive-motor-1000w-1500w-rh212.html ) though given the long lead time mine probably comes directly from china.
Click to expand...

Didn't know that!

The new GMAC without the freewheel was a runner up. The torque on the 10T is very close to the 9C212 STD. But costs quite a bit more, and heats up a little faster. According to the Grin simulator.

I was planning to lace elbows 1/2 inside, 1/2 outside in an attempt to reduce the differential spoke tension required to offset the rim. Is that a bad idea? Never laced a wheel from scratch before, but have taken the wobbles out of many. Mine is going on a 29" MTB rim, so there will be a cross pull. Only 9 degrees though. Hopefully that helps.
 
BlueSeas said:
I was planning to lace elbows 1/2 inside, 1/2 outside in an attempt to reduce the differential spoke tension required to offset the rim. Is that a bad idea? Never laced a wheel from scratch before, but have taken the wobbles out of many. Mine is going on a 29" MTB rim, so there will be a cross pull. Only 9 degrees though. Hopefully that helps.
Click to expand...

Depends on the rim. Small diameter and narrow rim kind of forces you to lace with elbows inwards. In my case the rim is 47mm wide but with holes punched at a very strange angle which actually made lacing elbows outwards easier on the nipple angle. Ebikes.ca recommends lacing all elbows out, to maximize spoke triangulation. Most bike manufacturers (shimano) recommend alternating in / out as it's supposed to be strongest, though given the large flange most hub motors have, you need to dimension the outwards going spoke up to 2mm longer espcially on smaller rims. Once you move to 29er, the difference gets insignificant, though I'd never lace a hub motor into such a large wheel. I've never done one complete flange in and the other out. Don't remember who told me it was a bad idea though...
 
qwerkus said:
Once you move to 29er, the difference gets insignificant, though I'd never lace a hub motor into such a large wheel. I've never done one complete flange in and the other out. Don't remember who told me it was a bad idea though...
Click to expand...

Is the large wheel/hub motor combo a concern about hills? In Florida we don't have hills, unless you count bridges. The highest spot in the metro area, about 20 miles from us is a whopping 110 ft. I actually ordered a 26" wheel donor bike, but it was incorrectly advertised, and had 29" wheels when it showed up. Decided not to send it back.

I purchased a new rim for lacing:

https://www.ryde.nl/andra-40

Advertised as built for hub motors, and other heavy duty applications. Great reviews from regular long distance cross country campers. I will just have to look at the geometry since the spoke holes are drilled at an angle and offset a bit. Then take a shot at it. Relative to the 9C212, I should be able to angle all the spokes to pull toward the strong side of the lacing holes.
 
BlueSeas said:
In Florida we don't have hills, unless you count bridges. The highest spot in the metro area, about 20 miles from us is a whopping 110 ft. I actually ordered a 26" wheel donor bike, but it was incorrectly advertised, and had 29" wheels when it showed up. Decided not to send it back.

I purchased a new rim for lacing:

https://www.ryde.nl/andra-40

Advertised as built for hub motors, and other heavy duty applications. Great reviews from regular long distance cross country campers. I will just have to look at the geometry since the spoke holes are drilled at an angle and offset a bit. Then take a shot at it. Relative to the 9C212, I should be able to angle all the spokes to pull toward the strong side of the lacing holes.
Click to expand...

In that case you'll probably be fine with a hub. Depeding on your requirements, a RH212 might be an overkill, as 500W are plenty already to move a bike on a flat lane. Shengyi makes a dwg9c DD which is only 5KG. The andra 40 is great - I have one here. Super sturdy. If you don't do cargo, the andra 321 is enough and weights less.
 
The design goal is 35mph/56kph without overheating. Not that I will travel quite that fast, but I still wanted some headroom at normal cruising speed.
 
BlueSeas said:
The design goal is 35mph/56kph without overheating. Not that I will travel quite that fast, but I still wanted some headroom at normal cruising speed.
Click to expand...

Wooooot - that's a fast moped you are building! Can't help with those, as all systems I build are designed for 30-35km/h cruising. ebikes.ca simulator is your friend though. Try different models. It gives you a pretty good idea of what you actually need.
 
Re large wheel and hub motor... It's not a structural concern, but the large diameter makes the rpms lower at the motor for the same speed, which makes it struggle to climb hills. For a personal experiment one time, I laced the same motor into a 20", a 26", and a 700c rim, and with each size increase ran hotter and slower on hills with more battery drain, with a minor speed increase on the flats that didn't seem worth the overheating at other times.
 
Voltron said:
Re large wheel and hub motor... It's not a structural concern, but the large diameter makes the rpms lower at the motor for the same speed, which makes it struggle to climb hills. For a personal experiment one time, I laced the same motor into a 20", a 26", and a 700c rim, and with each size increase ran hotter and slower on hills with more battery drain, with a minor speed increase on the flats that didn't seem worth the overheating at other times.
Click to expand...

I sort of saw that on the simulator. Acceleration suffers too. But since we don't really have hills, I decided to not send it back to the seller in Los Vegas. I have a 26' rim I could lace it to. So I could probably get a new front rim/tires and try it out. Not sure if the geometry would work OK.
 
miro13car said:
good that it broke during lacing
instead
braking during riding
QC is job #1 in China brand factory LOL.
Click to expand...

Totally true. My first reaction was: sh***t, $350 for nothing. The second one was: puuhh - glad it didn't happen when zipping down the hill!
 
qwerkus said:
Motor shell literally split in half. Since it's the first time I witnessed this, I wonder if any of you had a similar experience.

A careful inspection of the outer shell revealed many tiny pores in the shell, some of them more than 2mm deep. I suspect they weakened the outer ring, which is already super thin because of the back iron, and allowed a crack to form.
Click to expand...

Easy to fix, just put a couple large hose clamps around the outer circumference of the rotor, between the flanges. Three if they'll fit, but probalby only two will. Put the clamp connection point of each on opposite side from each other.

It'll probably hold up fine....probably. ;)


(I used a hose clamp to hold the clutch together on a geared hubmotor after it cracked quite a ways from home, the main problem I had was the clamp was too wide and rubbed on the motor housing, but it did work to get me home).
 
That would work. This one reminds me of a crazy expensive, French, (then) alloy kick stand I bought when I was 13. Snapped on the first use. It had bubbles in the casting.
 
I'd need 2x 14mm hose clamps, around 220mm diameter. Found 12mm ones. Not convinced by this option though. Are you sure 2 thin stainless steel bands can withstand the tension of 36 butted spokes ? Methinks spoke tension will just stretch the clamps and open the gap further.
The back iron ring seems to be intact, but now that the shell integrity is compromised, won't this produce a slight wobbling ? Also water is going to seep in and cause problems. Not sure if I can seal it properly. I guess ferrofluid cooling is also out of the question.

EDIT: If I am to go down the "clamping solution", I think it would be smarter to make my own clamp. 2 pieces of 3mm stainless steel cut to the right length, with bent corners. 6mm holes + 2 bolts opposite each other so the motor stays balanced.
 
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