Well on other brands I have personally machined them and the case hardening was done after machining. I’ve never worked on a MakerX brand motor. As a factory, it would also be dumb to do metalworking on something after you’ve case hardened it. So I am 99.7% sure that’s the case.
5 Likes
No one in their right mind is machining the shaft after case hardening it. The shaft would be machined on a lathe first, keyway cut, then case hardened.
4 Likes
They are breaking. I haven’t killed one myself but have def seen 8mm pop. And the stress concentration of a 10mm shaft stepped down to 8mm is worse than just an 8mm through shaft. If you want some theoretical calculations I can do them. But the general take away is as soon as you introduce any marking on the shaft (that can include a deep scratch) you create an area where the shaft will be more prone to failure. This could be mitigated by adding a chamfer or filet to the shaft, but no one seems to do that.
As we move to higher torque setups using parts like 5000w motor and run it in 1/5 gearing with GD’s stuff like motor shafts are going to become the next weakest link.
1 Like
I’d love to see details about all these supposed breakages and how they were being used… and which curb they accidentally banged their motor pulley on…
I’m not buying any motor without an 8mm shaft unless things drastically change. And I’m fat and use single drives a lot and stress my motors more than 90% of you do.
6 Likes
That’s not good enough proof for a manufacturer to care “they are breaking” is not a concrete quantity in percentage. If I had to guess I would guess that less than half a percent of all their motors have ever seen a broken shaft
In terms of raw stress concentration you are not wrong. However, even I don’t believe 1.5x more force on the actual material will cause these breakages. Stepped shafts have their downsides, and one of those is that stress concentration at the step. If you were to have a fillet there to reduce the harsh concentration, sure, it might help some, but then the problem becomes that the pulley never actually sets flat against the step, which I would argue would be worse.
There is no way a gear drive is more stressful than a belt
Besides, why would we want 10mm shaft when all the pulleys are 8mm, and our AXLES are 8mm? Like how does that make sense. Sure, you can make the argument for 10mm axles, which I would want on a mountainboard that gets jumped and experiences a lot more stress, but not on a street board.
I’ve been the victim of bending axles, but they were on cast trucks. Since riding the BN trucks with the higher quality axles, I have not experienced this at all.
Edit: I’m more than happy for you to go professor shartisis on me with math but maybe this isn’t the place to do it lol
2 Likes
It’s not many, for sure, but large motors have already had 10mm shafts for a long time, so that probably plays a role. I will dig up evidence, I remember it on the old forum.
I dont think that’s the real purpose of the step. People use loads of diff size pulleys, especially when you consider GD, belts or chains.
It’s not about being more stressful, it’s about fail points. I believe a belt is gonna snap under stress before teeth sheer off a gear, especially now that people are venturing into steel on steel GD’s. Now will the gear tooth break off before the shaft does, more than likely, but I’m not even sure about that.
First, your wheel axle shafts are not rotating, the stresses are not comparable. Second, there’s gonna be a select few people running this large of a motor on a urethan rkp board, I don’t expect people to run 10mm shafts on normal boards just like I don’t expect people to run 1/5 ratios on those boards. Lacroix, Flux, and more use 10mm shafts for a reason.
I’m not arguing 10mm shafts should be in 6354 motors. Big motors need big shafts, and imo stepdowns are unnecessarily adding a fail point when 10mm pulleys are available.
2 Likes
Hmm I guess this is probably true, bar the circumstances where the main gear is POM or some other plastic.
Well sure obviously, are you suggesting that the motor shafts you speak of broke from torque?? I would not expect the torque number to be anywhere near the shear number…
I’d need to see a broken shaft for sure though to say if it broke to torque or shear but my bet is that it’s shear from an improperly setup belt. You really shouldn’t even have very much shear loading on the shaft if you do it right
We really are getting off topic here, this should be in its own thread. Granted, I don’t think this motor post should be in DIY Builds anyway but still.
1 Like
I would say with this statement we can stop to derail this thread more.
Everybody can decide by it’s own what big motors are and what big shafts are, so everybody is right in a way.
I personally would prefer to not have a step down shaft on my motors if there is the choice…
2 Likes
Pretty sure a better solution for longer shaft life is adding more bearings than making the diameter larger
1 Like
Stepped down does not do anything for torsional forces i believe. So the whole shaft should be a single diameter.
2 Likes
Redundancy tho
2 Likes
This makes no sense. Motors have mechanical RPM limits, especially outrunners.
At 100v it will spin over 18k RPM; the bell will literally fly away from you. 
I would argue you don’t need that much power in the woods. It would be geared for high torque since you’re not gonna do 70km/h offroad anyways.
For a street pnum-pnum board on the other hand, there’s never enough power. I got bored with dual 6380 @ 100 amps cause it didn’t pull hard enough. 
I had a slightly bent 8mm motor shaft once, would rather have an unbent 10mm one.
Don’t see a lot of downsides to 10mm shafts except small pinions on geardrives not being possible.
8 Likes
hahaha this is exactly why I just bought the FS 6374 motors last week. I was defeated by a hill yesterday, that is unacceptable. I also feel like it’s not as spunky as it was with urethane, even though I sized my gearing appropriately.
Anyway, I’m looking forwards to @YUTW123 motor developments. Congrats on the new territory.
Also this lol I wanna see this motor at 100v
4 Likes
As long as the motor is well balanced such that you’re not overloading it for quick heat buildup before it can dissipate, then high rpm shouldn’t really be an issue provided the bearings can handle it. 100V might be a bit on the high side, but esk8 shouldn’t be that taxing on a motor of that size and KV (obviously dependent on how much current and gearing you’re pumping through) but it’s nothing too unreasonable I would think.
I’m stuck with a 2:1 gearing atm so would ideally like a little less KV
At those rpm you will probably melt the motor by core losses alone, it will something on the neighborhood of 300 to 400 W just to spin the motor And all that has to be dissipated
3 Likes
It’s a linear relationship between voltage and loss for the same amount of current, so you will be getting double the losses at 100V compared to 50V (ignoring bearing losses and drag) but that aspect alone shouldn’t be dangerous for the motor provided the current supplied isn’t too much when the motor is under load
I’m not talking about current (copper) losses, it’s core, this is extrapolating from my test in 6355 190Kv motor running 16S
After 1 minute running on the bench, no load, I couldn’t even touch the can
Once you put the copper losses by actually running it into a board it will get even hotter
2 Likes
It may be that your motor uses 0.3 silicon steel sheets…
Using 0.2mm silicon steel sheet, it will not be very hot at high speed. It has less iron loss
2 Likes
I used to run the outer rotor 5065 of the KV270 at 75v. It spins like a wild horse🤣
6 Likes
0.2 also
It may be a interesting test for you to do, run it a 18S or more at full battery charge and see the power draw
2 Likes