I would not bother with an XRF. You are not trying to do a PMI here. Strength in 4140 comes also from carbon (which normal XRFs can’t detect as it is non metallic) not to mention heat treatment.
Of course there is always the chance that somebody mixed the 4140 rod with something else (mild steel etc) in which case the XRF would detect that. Maybe a PMI is not such a bad idea after all.
@slerm i’m a little confused. was it a “soft” hit? what force are you saying made the wheel & 12mm axle move upwards? a 12mm axle has more than double the cross section area of a standard 8mm axle.
If I looked at the board without knowing any thing I would think one of the following:
I am not a mechanical engineer or anything, so probably don’t know what I am talking about.
Only one axle is bent. He could’ve just hit a rock at speed. Wouldn’t feel like much more than a bump, but could do damage. Say he hit a rock and it angled the truck, The normal force would be directed to the leading edges rather than distributed = greater torque applied. In addition, you’re moving at some velocity so when you initially hit a pebble, it will prob apply force in some direction directed towards axle at some angle to ground. So you have normal force and the x component of that acting towards back of board. So resultant would be greater than normal, acting at angle above ground, AND applied at the edge. Idk difference in strength between 8-12mm. I’d assume they would’ve calculated to cover this scenario. Disclaimer: With limited self taught physics background, I could be way off. And if I am, please correct. That’s Part of teaching myself. Haha
Its interesting to see that despite the larger spec 12mm axle for this new generation that it has failed though the failure is a bend this time and not a fracture.
From memory the past failure was possibly down to cutting of the truck in vicinity to the axle?
Would be good to see some more pics.
The bent axle is no problem and getting a harder steel axle in there in the future and I have extra can give if anyone were to bend one in the meantime no questions asked
I’m here on it and for these 5 sets it was a slowdown w the glue fuckup as I said. I’ll get the postage costs at least figured by tonight n out tomorrow. They’ll all be done in a couple hours and I’ll pack them up n get a pic up with address on them tonight. Neeext batch I won’t fuck it up w the glue. I don’t want to use metal magnet placers/shims with an obsession about reducing eddy currents but it’s super minor n will use them next batch unless anyone has another non-conductive non-warping material at 250f. Used all kinds of print materials n it’s no good n too thin at like 1.3mm. Nylon fishing like warps unfortunately and kicks up the glue while still curing at a hair over 250f I found.
Totally on schedule to get these all done this week. I’m not working this week again n on it over full time
Found magnetism sneaks out of the bell if the magnets aren’t lined up ironically right in front of the gaps between teeth on the outside. After looking at a magnetic simulation even a 1mm thick mild steel wall would contain like 98% of the field. J and b magnet tools. But it makes a big difference and if not in position with the gap behind I can stick iron to the outside. Not so if in position. Counter intuitive that u want the thick back iron on the sides of the magnet for best field reflection. People’s outrunners have a thin back iron at maybe 1mm thick max and probably for use in light weight plans as if the iron were thicker behind the magnets …could ultimately have stronger magnetic strength from the magnet side and then can compensate on the winding side with less current needed keeping cooler generally. That’s why it has 14 teeth on the outside for the 14 magnets
@Hummie consider it success the axle bent rather than snapping cleanly off-- in my opinion much safer compared to the failure mode of other hub motor axles, which generally break into 2 separate pieces.
Prof is right, I think all of us would take bent axle any day over getting ejected. Gotta wait to see if it happens to anyone else or if it’s isolated incident anyways.
jason had at least one failure with the R2 even after this test
and thats 10mm axle
@slerm
Theyre too soft and will be changing them for sure. I dont even care to see it. Thinking cheapest n easiest would be for me to send u a couple hangers and all u need is an 8mm allen wrench n a 10$ two-pin green bike tool. Theyll probably let u borrow it at the bike store for the minute ud need it. I hope u get back on them and tell me more! Its not a true 12mm axle n with the threading at its biggest diameter it’s 12mm but goes all the way down to 9.8mm. I didn’t realize how thin and with the long span and milder steel for sure it would bend. Good to know! I have like 200 of these hangers I had to get made. IF u bend it I’ll send u two. 
I’ve got at least 5 sets done n just waiting on power supply to be returned to charge my lipo for testing. 
zeroing in on done. more in the oven now. have a lot done but didn’t feel up to going to the po piece by piece.
@Blix changed his address and wrote me. if you change your address do the same.
I know I keep saying almost done…but almost done. on it all day tomorrow and really think by the end of the weekend done.
When are you starting the kick starter ?
two weeks! always two weeks. no im kidding but finally getting these motors out by this weekend and then will throw together a kickstarter.
So just to confirm is this the UK orders also?
Yes. Almost all the USA went out and been racking them up over here to go out
I’m still in disbelief that a truck bent. I have pushed these pretty hard, and I’ve always manage to find failures that no one else has had in past versions. The fact I’ve had zero issues with these makes me surprised.
I guess the easy solution is to use a stronger steel. I guess if it had to be done in the future, there is more space for an even larger axle. I think we could do a 16mm even with no issues.
Now that I’ve got a great way to protect with painted silicone I’m getting close to done with all the motors. The last couple I swear I’m waiting till then and get those myself as I will know how to put them together by then. This saved like 12 hours of fighting w crazy strong glue. Kapton tape doesn’t work. Silicone caps custom made nope. Some other high heat tapes. Epic resin I asked and they didn’t have any ideas. Silicone is the shit. Stripped the motor leads too early here u can see. Next time
So you apply the silicone in the bearing seats and then dip in resin and bake?
paint on silicone, sink in pot of resin in a vacuum chamber, then bake. supposedly air bubbles trapped in the windings, if you were to just dip the stators in the resin, get hotter.
Thanks, not sure how will do this step in mine, have you tried running some without dipping to see if the insulation really shorts over time?