There is no nylon locknut holder on those? Looks like it does based on the angle I can see. Otherwise it would seem terrible annoying to assemble those wheels.
1 Like
Oh I see what you’re saying that is really annoying lol
It only aligns it on one side, doesn’t hold the whole nut in place
Half a nut holder…thats what she said.
2 Likes
No this is the usual appearance, of fastener slop (wobbling around in the thread bore). This looks like very loose tolerance fasteners, or incorrect interface of fasteners to the thread profile. Presumably this part is aluminum, which definitely will yield to steel in cold deformation scenarios, quite easily, i.e. every vibration or impact hammering inside the bore because it’s not immobile. Ironically with tight tolerances, steel fasteners will so thoroughly weld themselves to aluminum thread bores that you often have to destroy the part if specific anti-seize isn’t utilized when fastening, with any amount of torque. If someone used short fasteners, you wouldn’t see damage the full length of the bore, you’d see a conical profile with the fastened side showing the above oval profile. There’s pretty clear evidence here of heavy leverage as every impact or torque force caused the fasteners to move laterally like a crowbar against the bore.
If this hasn’t been a common issue, to me, this looks like an operator (installation) error frankly. I’m not familiar with these drives, this part, and how exactly it’s supposed to be attached, but presumably it should be firmly anchored, such that the fasteners have no potential for play.
All I can contemplate here without knowing much about the specifics, is that there are a number of very close “almost fitting” overlaps between metric and imperial thread profiles, some fasteners from either will “kind of fit”. Some are very tight and only thread in a portion (because of either the chamfered bore, or lightly tapered fastener end), but others will thread in easily, fully, but with very low thread engagement, which is almost assuredly destructive to the threads when any torque is applied. Otherwise, some component or action is causing EXTREME leverage between the two mating components here with the fasteners being the lever.
Slop in the wheel bearings would cause extra uneven preassure on the wheel adapter that is transfered through the bolts themselves. Seems like it would be better if they weren’t threaded at all to allow for such movement.
The holes are not threaded. It is a bolt that passes through a clearance hole. The fit is on the tighter side. It would be obviously silly to drill the hole any bigger than 4.0mm for an M4 bolt. I actually used a 3.9mm drill bit to account for the fact holes are always bigger than the drill.
I personally think there were forces other than repetitive torque that caused that to fatigue so badly. The torque alone wouldn’t be enough to destroy it like that. The moment arm is quite big and there are 5 bolts to share the load. The actual tangential force on those bolts is not a lot at all.
If the holes were overly big, such as 4.3mm clearance, then this would allow a lot more leedway for deflections (strain) on the hubs transfering over to the star. However, the big con is that there would be play and the bolt would be essentially hammering back and forth under acceleration and braking. As to whether bigger holes or a smaller hole would last longer is something that has to be tested.
3 Likes
Ok yeah that makes sense, but shows how much wear is taking place across this bore then.
Yes, drill sizes are always clearance, and of course never create a round bore.
The wear profile of this damage suggests very specific repetitive leverage, with lots of movement. I assumed this was threaded since the thread impressions are so uniform around the hole, but the extreme oval shape means it was mostly one specific motion. I agree that this isn’t just repetitive torque from the motors, maybe in 50 years, not in a short time period. I’m guessing there’s something specific going on here if you haven’t seen this before.
FWIW, if this part isn’t threaded, it’s screaming (to me) to be wire EDM’d in steel or grade 5 ti though, I know cost can seem high if you haven’t worked with this process much, but at scale it gets insanely competitive… (and if this is something you’re interested in looking into, hit me up, I can help, even “not at scale”).
There are a few better design solutions here:
- Make the part again but out of stainless steel (thinner, laser cut).
- Decouple the current rigid set up by implementing some sort of elastic component
I am favoring option 2. It makes more sense design wise. Forces on the wheel shouldn’t be able to make their way through the drive. They should instead be entirely taken care of by the hub bearings. The best way to isolate the two would be some sort of elastic coupling type thing.
5 Likes
but then there’d be a weird stretchy feeling when applying power/brakes no?
since there’s now a stretchy part between the motor gear and the wheel, which could also break
1 Like
hmm makes me think about how if you wanted to add a freewheel/one way bearing to this gearbox you would just bolt it on there, not sure for what exactly. Ebikes maybe idk.
No the original screws that came with the hubs where to short and got loose didn’t notice this until I was home. I mentioned this earlier in the tread and order longer screws.
Thats exactly what happend.
Weird and stretchy… like tires? Seems fine to me. I say Kevin keeps the aluminum but adds inserts for thick POM washers where the wheel bolts go into. That part gets worn out and we replace them from our bag of 100 we got for $10.
2 Likes
Got the motors to fit
Tomorrow’s goal…
Cut motor shafts and wheel bolts
Put gears on and Grease
thread locker
And some other stuff if the 2 year old let’s me 
16 Likes
@Boardnamics That sounds good . But what can we do in the short term… Because these are going to fail in the short run and I use my board nearly every day…
Where’s the build thread?
6 Likes
You may have an inch of clearance but boy you will have some flippin fine tourqe. What trampa rims you running?
1 Like
Damn son, that’s NICE!!!
I would say they wont fail if you assemble correctly and cut your bolts the right length and check for tightness before every ride. We gonna chock this up as an isolated incedent for now. How about if you ride really hard offroad check it more frequently like everytime you check your phone…check your board
Why are you assuming I didn’t ? This isnt my first gear drive and not my first board either… I do check my boards but I used it off-road a lot during my holiday. And with my other board it’s not like I have to check everything after every ride… I never had anything break like this before
1 Like