Are we clamping our axles too tight

http://endless-sphere.com/forums/viewtopic.php?f=3&t=40785&p=596561#p596552

I just thought I would create a link with this title but point you to a link where I started discussing this idea.

I may be way off the mark, but it is a thought i have had in my mind for a while now, and it was only when a local engineer friend suggested this very thought that maybe it had some merit. See my snapped axle thread linked to above.
Or if you are a mod and you think this should have its own thread, feel free to move my post from the link over to here.

Interesting though.

With bolt on torque arms, I guess you could oversize the bolt hole in the arm and fit a compliant bush to allow a small amount of rotation. Whether the bolt/screw would survive though I don't know, as you wouldn't be able to torque it properly without crushing the bush. Unless you used a bush with a steel tube in the middle (like a car suspension bush).

I've been thinking of a torque damper dropout system since my first hub motor.

The insane power thing using a bicycle hub motor is inherently problematic. Did you ever see Luke's flaming dicks high power hub effort? JohnCR pull's it off but he's using scooter/moto hubs to start with. The stuff we're dealing with is intended for bicycles not emotos so be prepared to re-engineer the entire hub motor package if you continue to take it to the insane extreme.

I understand the need for speed/power but much above 4kW a mid motor chain/belt drive is probably the way to go. Many more proven options to control and deliver massive power to the rear wheel. Do applaud the effort to fabricate a much improved axle but considering the intended use of these motors, 'wonder if that's the best use of your time/resources?

On my flaming hub motor video, you will notice it doesn't even have nuts on the axle.

fully agree, a clamping solution is the best way to go.

the failure on neilP's axle looks like the thin stainless was cutting into the softer metal of the axle near the frame..

Ypedal said:

fully agree, a clamping solution is the best way to go.

the failure on neilP's axle looks like the thin stainless was cutting into the softer metal of the axle near the frame..

Click to expand...

No, not at all.
The stainless torque plates were...I think 7mm thick so twice the thickness of the commercial ones. the failure occurred well away from the torque plate. Torque plate was on outside of frame drop outs and there was a spacer between inside of dropout and end of axle.

The failure was a good 10mm away from the edge of the torque plate.

Looks like this thread has gone totally the wrong way, I was obviously not exact enough when I wrote it the first post...The intention of putting this post was for you all to see the title, see the link on the first post and then go to the linked post and make comments there.

Moved from other thread:






Here is another idea to throw into the mix that I have not see mentioned before. It has been on my mind for a while and I am wondering if this is part of the cause of the problem

I know it is a bit heretical to say it as it seems to go against what every one it is trying to do...but..here goes






ARE we clamping our torque arms too tight?

I am thinking that with the axle clamped very tight, all the shock going from acceleration to cruise and braking is all being transmitted to the axle.

Would we not be better to have a shock absorber collar between axle flats and the torque plate/ clamping mechanism...You et what I mean..a shock drive/cush drive type collar that takes some of the initial shock when torque reverses.

Am thinking something like a bushing that you see in a vehicle chassis at the pivot points of leaf spring suspension. OK, so they are round section...need to find a square section type, and make the axle the same size as the internal diameter of the bushing centre

What I should have said was please go to the linked post and make coments there about my thoughts...but since we are all posting here now...I shall copy that part of the post here.

What I was thinking was that we are clamping the axle TOO TIGHT and not giving it any flex, so all the shock is being transferred to the axle


this sort of think in square section. Ok the one pictured here is a vibration mount, not designed for rotating loads..but it would be a matter of seeing if there is anything out there

http://www.avproductsinc.com/bushing/mounts.html

does anyone have more thought on this? neil, what you are saying makes sense to me. i think it is also likely that some axles are weaker than others. clamping on a hollow axle definitely seems like it could be problematic.

Not done any more on it. My re built axle is holding up well.

i was trying to tighten my spokes/adjust my disc brake because my tire and wheel were both rubbing slightly. imagine my surprise when i saw what had happened! i am just thankful that i was riding slow because of the rubbing!

where the axle sheared, it is slightly twisted. the patterns of the axle in the first picture are hard to see, but they also seem to twist or swirl. as you can see, it broke about 1/8" after the start of the recess for the wiring.

i have been running 20s with about a 50 amp limit. there have been some timing/syncing issues with my sensorless crystalyte controller - this might have been part of the problem. if you go full throttle, the motor will lose sync and lock up or jolt for a fraction of a second. however, this happens very rarely. i have never taken the bike off jumps (other than the occasional curb) and only have done very moderate offroading - but mostly street riding.

i do have about 7000 miles on the motor so im not completely disappointing...but im sure you guys know how this kind of stuff can be frustrating. has anyone else managed to break a hs3540 axle or replace one? is it possible to fix or is it basically trashed?





so to return to the question: are we clamping our axles too tight?

jansevr, I don't know if that is a case of the axle being too tight. I think your torque arm design and that sync issue likely had lots to do with the snapped axle. In fact, I doubt axle clamp tightness is really an issue for anyone.

The second picture you posted paints an interesting picture. There are only a few ways that piece of angle steel or whatever material could have gotten that bend in the middle. I think what I am suggesting is pretty clear. But you may have been radically better off either not having the piece of angle steel, or having it on both sides. Is it possible something came loose? Is it possible things weren't aligned (improper hole placement) correctly? Hard to say for sure. But that angle steel, not something being too tight, is in my opinion the primary culprit in the cause for your broken axle.

I'd be surprised if you couldn't replace the axle some how.

I think you were on the right track for an interesting design on a torque arm. I think you would be better off having two pieces of angle steel run up along the length of the chain stay, clamping on the axle. You'd likely need to change the orientation of the dropouts though, which if you were going to do that, you may as well just make beefy dropouts to begin with unless torque arms are absolutely essential.

Are you familiar with nord lock? I see things like double nuts, but really I think the way to go is probably nord lock, maybe I just bought into their videos. http://www.mcmaster.com/#nord-lock-washers/=mfcz3q

I think that having a wider torque arm is certainly a good idea, but implementing it can sometimes be difficult.

Just to reiterate my opinion, study the bend in the angle steel. I think the angle steel snapped the axle off.

sorry bowlofsalad, i should have also included a pic of the complete clamping mechanism. you can see in this picture, there is another piece of angle steel that is actually clamping int he axle.



in regards to something being loose, this was absolutely not the case, everything was tight. i even put c clamps over the clamps on each side and directly over the motor axle. i dont have the best picture of this, but you can kind of make it out here:



regarding your comment about the angle steel bend causing the axle snapping - isn't this my question and the subject of this whole topic - (a question that you disregarded almost immediately)

maybe it was because i didn't include a picture of the complete clamp, but although the angle steel was slightly warped, the axle fit very snug and very tight without any play whatsoever. i believe that the slight bend in the angle steel was not a problem - if anything it seemed to hold the axle tighter.

These pictures do yield a different perspective. But the metal deformation in the angle pieces is still suspect in my mind.

It is possible that pinching metal can cause a sag or slackening in the material. The idea exists or occurs plenty of the time. You can witness this immediately by applying too much torque to wood with a nut and bolt. I've made washers sink into the wood when tightening a nut and bolt. This happens in metals as well, it's more subtle though.

There are a lot of dynamics here at play that can create several theories. When you mentioned the twisting appearance on the axle, a second theory came to mind after the idea of the axle being snapped off. The axle may literally have been twisted off due to the repeated stresses created by the loss of sync. This idea may also account for the deformation in the angle iron, a little play developed, then a little more, and instead of the angle yielding over all, the axle did instead. I don't know if thicker angle pieces would have helped at all.

All I can say for sure is, I'd consider ditching the sensorless setup.

Any regen in use? that puts lot of strain too. But the sync issue will cause a lot of sudden 'jerks'

My reason for asking the original question about clamping too tight may have been misunderstood.... maybe not. I was thinking the axle should MAYBE be clamped very securely within a clamping mechamisim that itself is allowed to rotate slightly within the frame. Like a damping mechanisim. Metalastic coupling/ cush drive type idea.


There is still some merit in what has been posted about the angle iron clamps causing some distortion to the metal of the axle too. Since the axle is not constrained on all sides, tightening of the angle iron clamps could cause the axle to squash outwards slightly... I know it can I have done the same on a much lighter axle, almost squashed the wire hole to such an extent the wire was stuck inside.
This is why I now make shaped alloy clamp blocks, that completely enclose the axle,



Is it possible to repair motor... YES
Is it posdible go repair old axle, again yes, but probably difficult

Easier in my opinion to make new axle
I see you have already seen my axle build thread and posted there, but here is the link again

http://endless-sphere.com/forums/viewtopic.php?f=3&t=40785&hilit=+Snapped+after

no regen in use. i like your idea about the cush drive idea i think this would solve almost all of the problems with axles breaking. the syncing definitely buts a lot of stress on the axle, but it hardly ever happens. it shouldnt be much more than the initial stress under heavy acceleration or of regen.

i can see with a hollow axle how clamping the axle too tight could cause a problem...but in this case i dont see how this could cause the axle to squash outwards slightly? from overtightening? the clamp was not this tight. just snug enough to not go anywhere. obviously the angle steel was weaker than the axle itself - since building these dropouts the angle steel had been warping slightly. every day i just check and make sure the screws are snug, some days i had to tighten them but it hasn't been moving much the past week or two.

Food for thought this. I'm not going to add a pinch bolt now. I'm cutting the slot by eye and trial fitting you see. If I then pinch the axle you can actually guarantee I apply a bending force to it. My plate will be loads stronger than the axle, It won't deform around it. My axle would move in to position instead. Sod that. My decision is made. My dropout reinforcement plates will be snug, and if there not, then it is no loss, I'm not using regen. The axle only wants to turn in one direction, and will soon reach it's limit of rotation.

I have realised pinching can be bad unless super accurate. Thank you.


I could devise a work around, but I'm going with a pacman design that only seats in one position. I don't even trust my frames dropouts are parallel enough with each other to allow a lot better

As I see it: The sharp corner of the wiring groove cut into the axle is always going to act as a stress raiser and probably initiate the crack that causes eventual failure.

It's whether the crack is propagated due to torsional flexing (motor drive/regen), or radial flexing (weight of the bike). A damped torque plate mounting would help with the former.

I still think clamping type plates are intuitively a good idea if you use regen. I can't decent ones bending the axle to a significant degree. Even if they do, it's only a very small bend made once...

Punx0r said:

I still think clamping type plates are intuitively a good idea if you use regen. I can't seedecent ones bending the axle to a significant degree. Even if they do, it's only a very small bend made once...

Click to expand...

I agree, with a word added in RED

A small bend or squash is going to cause less issues than the flexing and 'turn and stop' caused by loose torque plates or clamps

Do them strong, thick,flat and straight with a perfect fit... They will last with high power and hard riding.
The dropouts on my Demo have lasted 40 000 Km so far. They show no sign of wear, nor the axle.
Open dropouts on my V10 are reaching 10 000 Km, still perfect with very high torque and aggressive mountain riding.



You don't need one foot of angle steel and 20 bolts to hold it, you need to make them right and that's all.
I use 5/16 steel, making sure of perfect fit and alignment. You hardly notice any difference from the original dropouts. I have nothing against building overkill, but doing so doesn't make any better a job that is not straight.

i will admit the angle steel could have been thicker - but there wasn't any thicker available at the hardware store. its hard to see the dropout in the picture that you posted - but i am still very certain that my dropouts were very secure and a perfect fit as well.

i still need to get better pictures...but it looks like the axle just sheered from too much force. clearly the axles could be stronger.

the dropout attachment itself is a bit overkill...but it was all scrap/free materials from a friend. it was what i could think of with what i had to attach the motor. (the original dropouts have 20mm axles that go through the frame).

Yep, sorry, Neil, I missed the word "see" out of that sentence...

jansevr, how long where you running the clamping angle iron torque arm before the failure? I recall at least one or two others who have managed to break the HS/HT series axles. One guy was running dual HS3540 and ended up in the hospital after snapping his axle at high speed. Can't recall the user name at the moment.

I've got the same type of torque arm in place using 1/4" angle. I've got 190 phase amps, 90 amp battery and 100v into my HS3540 and regen on moderate. I've been running this for the past 2 months or so and I'm accelerating and braking hard with regen. So far it's held up to all my abuse. It's surprising your axle broke without even using regen. You're not even using excessive power 20s and 50 amps, you'd think the motor should be able to handle that and many others are pushing that kind of power and more through these motors without the axle breaking. I doubt the sync issue could do that, I can't see that exerting more force than regen or accelerating hard. My guess is the axle was clamped too tight and put a strain on it. In the picture it looks like you've got a steel plate sitting between the angle iron and the frame and they're not perfectly parallel, maybe that had something to do with it?

jansevr, just thinking out loud, I'm wondering if the clamping style could have not been square.
Or as the clamping bolts were tightened one side was tight locking in the axle and then when the other
side was being tightened it shifted the shaft down or up and put a constant strain on the shaft.

jansevr said:

i will admit the angle steel could have been thicker - but there wasn't any thicker available at the hardware store. its hard to see the dropout in the picture that you posted -

Click to expand...

It is hard to see because nothing is added. It is an exact copy replacing the original, except that it is made out of steel with an open dropout instead of the original alu through axle.

I have had an X5 axle failure on my first build. The torque plates bolted on top of the dropouts were very strong and thick, but they were not perfectly perpendicular to the axle axis. Every time the motor torque force was applied, it would force the axle to a slight curve or twist, repeatedly until metal fatigue created the axle failure. The difference from the perpendicular was measured, less than a mm on the whole length of the swing arm, yet it was enough to to cause axle failure after 2 000 Km of hard acceleration and fast trail riding. The ones I make now are not any thicker and they are even much smaller in size, but they are very precise on all 3 axis.

adrhinio - could you possibly post a better picture of your through axle dropout modification? i am interested to see what you have done...and might want to do something similar.