what exactly causes an axle to break?

[acannell]

fine minus the tires but either way your calculation is incorrect.

no its not

 

[acannell]

what is this math good for?

haha! love it

 

[AIbandit]

ahh, i think i see the mixup


yes it does output around 200ft lbs at the flywheel

Gotcha that and the w/o tire

 

[kastein]

So are you asking us a question or telling us... what?

I'd like to note that I warned you about this axle sucking here: http://www.naxja.org/forum/showthread.php?t=1045933

and again in this thread.

Your own math says it sucks too, and for some reason you're asking if you are right and then telling anyone who disagrees that they're wrong... so I'm a little confused on where you are going with this.

 

[AIbandit]

But tire size does effect the torque placed on the axle shaft. It would add to it immensley


Taking the force from 47" down to a 1" axle shaft

 

[kastein]

The force applied by the motor shouldn't change depending on tire size unless I am mistaken, but the shock loading (which is far above the force applied by the motor) from wheeling definitely does.

In short, sell that locker and axle on craigslist for as much as you can and get a real axle

 

[AIbandit]

The force applied by the motor shouldn't change depending on tire size unless I am mistaken, but the shock loading (which is far above the force applied by the motor) from wheeling definitely does.

In short, sell that locker and axle on craigslist for as much as you can and get a real axle

Think about holding a ratchet on a bolt and I have a 3' breaker bar on the nut we're both applying force from both sides. Not only will I out power you but that little bolt is going through hell


The bolt = the axle shaft.

 

[acannell]

The force applied by the motor shouldn't change depending on tire size unless I am mistaken, but the shock loading (which is far above the force applied by the motor) from wheeling definitely does.

In short, sell that locker and axle on craigslist for as much as you can and get a real axle

what exactly is "shock loading"

 

[acannell]

Think about holding a ratchet on a bolt and I have a breaker bar on the nut we're both applying force from both sides. Not only will I out power you but that little bolt is going through hell

agreed.

if the ratchet is 1 foot long and the breaker bar is 4 feet long, and the bolt isnt turning, then you are applying 1/4" the force that I am applying.

but what does this have to do with what actually breaks the axle?

 

[kastein]

what exactly is "shock loading"

It's not usually the spinning that breaks a shaft, it's the stopping. It shock loads the shaft when the tire spinning slams into something or gets traction and abruptly is doing 1 mph again.

When the torque load exceeds the axle shaft, it breaks. This can be from too much torque when the tire is bound up, or from spinning then stopping suddenly.

The heavier your tires are, the more kinetic energy they contain spinning at a given RPM, and therefore the worse the peak impulse torque / shock load is when they abruptly regain traction and stop spinning while the drivetrain is still trying to keep them spinning at the same speed.

 

[AIbandit]

what exactly is "shock loading"

an example would be spinning on mud then having your tire hook suddenly


I believe that's what he is refering to anyway.

 

[acannell]

So are you asking us a question or telling us... what?

I'd like to note that I warned you about this axle sucking here: http://www.naxja.org/forum/showthread.php?t=1045933

and again in this thread.

Your own math says it sucks too, and for some reason you're asking if you are right and then telling anyone who disagrees that they're wrong... so I'm a little confused on where you are going with this.

i originally asked exactly what breaks axles. then people started saying gears dont multiply torque. yikes.


so now that thats straightened out maybe we can all figure this out without using general terms that arent well defined.

 

[AIbandit]

agreed.

if the ratchet is 1 foot long and the breaker bar is 4 feet long, and the bolt isnt turning, then you are applying 1/4" the force that I am applying.

but what does this have to do with what actually breaks the axle?

It has alot to do with breaking an axle say you're climbing a hill and your vehicle is causeing resistance from it's weight. your __ " tire is multiplying that weight resistance down to that 1._" axle.




Edit: now you're applying force to both sides as you were in the wrench example.

 

[acannell]

The heavier your tires are, the more kinetic energy they contain spinning at a given RPM, and therefore the worse the peak impulse torque / shock load is when they abruptly regain traction and stop spinning while the drivetrain is still trying to keep them spinning at the same speed.

if its the drivetrain spinning intertial forces (like all the drivetrain pieces up to the axle) acting as a flywheel breaking the axle when the wheel suddenly gains traction, then what difference does the wheel diameter make if its just the fact the wheel is stopped?

maybe its that the larger wheel (regardless of wheel mass) makes it easier for the traction surface to "stop" the wheel?

 

[kastein]

Tell ya what... go wheeling with that axle and figure out empirically what causes an axle to break.

I guarantee you it is shock loading in your case, or even constant loading from the locker while turning. You will discover that general terms that aren't well defined will still be very relevant...

I know you like numbers, I do too, but this is pretty intuitively obvious even though I'm not a mechanical engineer versed in statics and dynamics.

 

[AIbandit]

so if your formula = y

y+ (resistance x tire) = force on axle


If axle = 1" I think that would be true^


Edit: changed to Y to avoid multiplication confusion.

 

[AIbandit]

resistance numbers would be impossible
traction, incline, vehicle weight would all matter

 

[acannell]

Tell ya what... go wheeling with that axle and figure out empirically what causes an axle to break.

I guarantee you it is shock loading in your case, or even constant loading from the locker while turning. You will discover that general terms that aren't well defined will still be very relevant...

I know you like numbers, I do too, but this is pretty intuitively obvious even though I'm not a mechanical engineer versed in statics and dynamics.

im not a mechanical engineer either. i think we can all figure this out. there doesnt seem to be any real explanations of it on the web.

i think its valuable because ultimately, its a cylinder of steel, and it has very well definied characteristics.

if we can figure out the precise reason the axle breaks, we could make a calculator that takes into account many variables, like vehicle weight, engine output, gear ratios, tire speed, tire diameter and weight, and then determine what exact situations are 90% likely to break the axle, and what other situations are safe..i think that would be very interesting dont you

 

[AIbandit]

we could make a calculator

If resistance possibilities = infinity you would be making alot of calculators.

You could do one for say 100% traction on a set grade and this would almost represent "shockload" but even that could vary and be 99.9999997 or 98% or well... sideways 8 (yeah that's right my pc sucks to hard to open character map)



Edit: Though you could get Maximum possible shockload

 

[kastein]

im not a mechanical engineer either. i think we can all figure this out. there doesnt seem to be any real explanations of it on the web.

i think its valuable because ultimately, its a cylinder of steel, and it has very well definied characteristics.

if we can figure out the precise reason the axle breaks, we could make a calculator that takes into account many variables, like vehicle weight, engine output, gear ratios, tire speed, tire diameter and weight, and then determine what exact situations are 90% likely to break the axle, and what other situations are safe..i think that would be very interesting dont you

I think it would be interesting, but there are a whole lot of variables. The condition of your motor, how hard you're hitting the gas pedal, how sharply you shift, what clutch you use, how much play there is in the spider gear teeth from wear, the tread on your tire, the air pressure you're running, temperature, suspension design (leafs have some rotational "give" to them), trail slope, exact trail composition, shaft size and material, how badly the shafts have been abused in the past (are the splines already twisted?), open or locked (and what type of locker), vehicle weight, etc all come into play.

In general people go with a generally known rating and derate or overrate depending on all the factors above, plus stupidity (see also gas pedal.) Generally accepted for a d35 is "no larger than a 31" tire, locked or not" but like I said before I have evidence for them failing well before that point.