Dropout Failure Experiements, and a call for Fork Donations

[John in CR]

Justin,

As always, great work that you so generously share. If Mexico ever gets safe enough for a north/south trek, you've got a place to stay in Costa Rica for as long as you like.

In the meantime, I'm sticking with deep steel dropouts modified to 1/2" thick and cut for an exact fit with the axle. Plus, just in case a nut ever does come loose, closed end torque arms bolt to the plate above the dropout giving me a full 1.25" of steel on the axle flats to resist spin with torque arms to hold the axle on no matter what. With Methods' overkill 100v100a controllers with regen, I want overkill in securing my hub motors too.

John

[Drunkskunk]

Glad to see someone doing this! I think that picture of the Torque arm needs to get stickied someplace as an example why not to get them backwards.

I have a couple forks laying around. I believe an Aluminum suspension, and a Mongoose like the one Dogman posted, though I need to dig through the shed and see. All yours if you want them.




On a side note, it amazes me. We here, collectively, are Pioneers in the sport of Ebikes. But electric hub motors are nothing new, having been used in India and China by the hundreds of millions for decades. Yet these problems were never addressed. We are a small comunity here, each contributeing in atleast some small way (If only by example of what not to do). I believe members of this forum have done more to advance eBikes with our various home grown designs and testing than the whole of the industry up to this point.

[gogo]

I'd like to see a test of a shear pin or cotter pin through the axle and nut using the nut and pin to transfer the torque to an arm.

Take a torqued nut/axle, drill a hole through both, insert pin, put closed five point wrench over nut and hose clamp wrench to fork.

R-Clip.jpg (27.09 KiB) Viewed 1464 times

[dogman]

Shipping a few forks won't cost me much. Well worth it and it will come back to me double later. If you must, send Justin money, if it gets to be a lot, he could give us free shipping for something we buy.

Justin has nearly done as much to advance Ebikes as any ten of the rest of us. But it is amazing to me how the Chinese have been content to put up with crap so long. A good example of why closed societies, lack of free market, etc warp stuff. Stalin created an entire society of criminals by making most everything illegal and sending somebody from every family to gulag. Look where that got them by 1970.

[davespicer]

I'd like to see a test of a shear pin or cotter pin through the axle and nut using the nut and pin to transfer the torque to an arm.

Something a bit bigger than a cotter pin has already been tried, on a setup where C rates have almost no meaning: the energy source was an ultracapacitor. Those things can charge and discharge incredibly quickly. The guy doing the development was twisting torque arms like taffy... the whole thread is lots of fun to read, but the torque arm (and bolt through the axle!) part starts here:

viewtopic.php?f=6&t=7511&hilit=ultracapacitor&start=30#p122326

[mwkeefer]

If you guys still need forks for testing....

PM me a list of brands, models, types, etc... if for stock bikes, than the source bikes make, model year.

I'll check the graveyard tommorow for spares... you guys are paying s&h right?

-Mike

[BLUESTREAK]

HI ALL: The idea of drilling a hole through the nut and axle and putting a keeper pin through is ok for keeping the nut from comming loose and releasing friction on the washers and torque arm and dropouts is good but the nut with the pin through can not take much torque as it will shear the pin. The best is a good tight fit of the torque plate hole to fit the axle all the way around and good flat friction surface like DOGMAN has been trying to pound in to everyone from the start will save most from having a spinout. If the torque plates fit solid on the axle and is squeezed tight on both sides of the dropouts that thing will stay put. In the test done by JUSTIN the axle has space on the top and bottom of the torque arm and there is room for the material to go into that space, if all the material has no place to go the axle can't spin. Good work JUSTIN.

[justin_le]

I cut up 8 (curbside bikes) bikes today so have 8 sets of forks laying here destined for the bin, pitty your in North America freight would be a killer...
KiM

Hey, so these are 8 random forks rather than 8 identical forks I presume? If it was possible to get 8 or 10 of the exact same fork, from some kind of bike parts liquidation happening somewhere in the world, then we'd be able to do some really good comparative science. Testing the exact effect of different torque arm types and material harnesses to quantify just those things affect the ultimate spinout strength, with actual variations in the fork itself being fixed.

Here is a pic of the forks from bikes I'll never reassemble. Turns out only four, I put together some of the junk bikes and sold em the first week of school at the university.
From left to right, cheap bmx forks, Cheap roadmaster mtb forks, Steel suspension mongoose wallbike mtb forks, and some vintage but quality cromoly QR hub forks from an mtb.

Super. To Dogman and all the others who have forks (or rear dropouts) they'd like to contribute and see destructively tested, the shipping details are:

Attn: Justin
The Renaissance Bicycle Company
4570 Main St
Vancouver, BC, Canada
V5V 3R5

Try to keep the list posted on what was fired off, just so we know when enough of a certain type has been sent.
I think it will be in the area of suspension forks and aluminum forks in particular that we'll be most interested to get a range of results, as this is where most failures are happening. There is always the caution about 'cheap' alloy suspension forks, and I think we'd all love to know how expensive suspension forks rank by comparison. So if anyone has old quality downhill mtb forks that are out of commission for whatever reason, those would be golden.

[justin_le]

The best is a good tight fit of the torque plate hole to fit the axle all the way around and good flat friction surface like DOGMAN has been trying to pound in to everyone from the start will save most from having a spinout. If the torque plates fit solid on the axle and is squeezed tight on both sides of the dropouts that thing will stay put. In the test done by JUSTIN the axle has space on the top and bottom of the torque arm and there is room for the material to go into that space, if all the material has no place to go the axle can't spin. Good work JUSTIN.

Hi Bluestreak, this seems "intuitively" correct to a lot of people and so that's probably the main reason why it hasn't been challenged. But once you actually spin an axle through a dropout plate and watch the metal smear out of the way, you realize that it doesn't make much of a difference if the original slot was a dead perfectly tight fit or a little sloppy. Once you hit the yield point of the metal, it just starts to move no matter if it started snug. The failure is quite localized at the contact point, the rest of the torque plate often doesn't suffer any deformation at all.

A super tight fit does help reduce the amount of play when you have an axle with both regen and forwards torques, but even then it will still wiggle back and forth just a little, and eventually start to loosen things up.

In any case, this is one of the other things I'd like to include in the testing. ie. having two identical setups, but in one of them the torque plate is a little loose and with the other it is fit quite tight on the axle. We'll let the conclusions speak for themselves when the test happens, but I'd wager a bet that there won't be any difference. Or I might have to swallow my words! We'll see.

-Justin

[gogo]

The idea of drilling a hole through the nut and axle and putting a keeper pin through is ok for keeping the nut from comming loose and releasing friction on the washers and torque arm and dropouts is good but the nut with the pin through can not take much torque as it will shear the pin.

This idea has been dismissed on ES previously, but deserves to be quantitized. Many shear pin applications are intended to be mechanical fuses of a specific failure value. Is it not possible to use a shear resistant material and round off the axle and nut holes to maximize the shear failure value? If I recall correctly the shear value is 75% of the tension value?

[BLUESTREAK]

Yes shear pins made of certain hardness can be like a fuse. but in this case the problem is not the torque on the nuts that hold it's the torque on tha axle. in something much larger in size the shear pin can hold a lot of torque.and JUSTIN may be right this needs more testing.

[gogo]

Yes shear pins made of certain hardness can be like a fuse. but in this case the problem is not the torque on the nuts that hold it's the torque on tha axle. in something much larger in size the shear pin can hold a lot of torque.and JUSTIN may be right this needs more testing.

Yes, that's why I'm proposing to use the pin in an unconventional way to transmit the axle torque through to a closed end wrench on the nut that would then be clamped to the fork. This would be a fairly simple implementation and, as you pointed out, have the additional benefit of keeping the nut tight on the forks.

[johnb]

The best is a good tight fit of the torque plate hole to fit the axle all the way around and good flat friction surface like DOGMAN has been trying to pound in to everyone from the start will save most from having a spinout. If the torque plates fit solid on the axle and is squeezed tight on both sides of the dropouts that thing will stay put. In the test done by JUSTIN the axle has space on the top and bottom of the torque arm and there is room for the material to go into that space, if all the material has no place to go the axle can't spin. Good work JUSTIN.

Hi Bluestreak, this seems "intuitively" correct to a lot of people and so that's probably the main reason why it hasn't been challenged. But once you actually spin an axle through a dropout plate and watch the metal smear out of the way, you realize that it doesn't make much of a difference if the original slot was a dead perfectly tight fit or a little sloppy. Once you hit the yield point of the metal, it just starts to move no matter if it started snug. The failure is quite localized at the contact point, the rest of the torque plate often doesn't suffer any deformation at all.
-Justin

Not just intuitive I think. A loose fitting spanner will quickly round off a nut with only a little torque. With a tight fitting spanner you can apply much more torque to the same nut. Why is it not the same with torque plates and axle flats? From a physics point of view, I would say that the loose fitting plate will apply a greater pressure at the corners of the flats than a close fitting one given the same torque. This is because the force is applied over a smaller area.

[dogman]

I suspect the scales don't lie on the previous tests. There may be a difference between tight fit and loose fit, I'ts just less than you'd Intuitively think it would be. Once the nuts got loose though, a sloppy fit in the dropout would allow the axle to rock back and forth with more force, but with loose nuts, the tests show you are screwed already.

Re the cotter pin idea. At one point i considered welding a steel bar to the end of the axle, after the nut and washer were on it. Then strap to the forks. At that point, 1 week into ebiking, I had no idea what a tourqe arm was.

On the aluminum forks, I'd like to see some real tests on those too just to prove what we think we know. The problem with those is that if you tighten a too big washer down on the cups, you make a hairline crack in the drops. I bet even with tight nuts, that hairline crack comes back to screw ya. If a nut gets loose, I bet the rotation of the axle smears and cracks that metal at really low forces. Too many ways to break both collarbones again for me! Once was quite enough!

[Ypedal]

Whoa.. how did i miss this thread....

* Brews fresh cup of coffee before diving neck deep into archive of pictures

[mwkeefer]

No offense.... but Canada...

Maybe someone in the states should duplicate the experiment to reduce overall cost (S&H)?

I'm still down for gathering a few up but to ship to canada could cost (I guess it really is "Replacement Parts") for customs!

-Mike

[justin_le]

No offense.... but Canada...
Maybe someone in the states should duplicate the experiment to reduce overall cost (S&H)?

Hey Mike, that's kindof a downer comment.

I'll HAPPILY pay the shipping for anyone who has some interesting forks that we'd like to see tested for whom that's an issue. It's a nothing compared to the overall time and labor and space cost of doing a set controlled lab experiments like this. I just thought it would be fun and useful, given the fairly lively debates that go on here about dropout strength, to give people a chance to contribute forks that they particularly want to see tested.

In any case, I was just down at the community co-op bike store and bought from them a handful of chromoly/steel forks of various vintages, so between those and the ones from Dogman we should have the steel side of forks covered. But it's certainly on the alloy and suspension front at this stage that we don't have anything useful yet.

Surely somebody converted a suspension bike and given the advice from this list, replaced the original suspension forks with solid steel ones, and now has this extra pair of forks and a nagging question in their head about whether they would have been strong enough? Now you can find out!

[philf]

Surely somebody converted a suspension bike and given the advice from this list, replaced the original suspension forks with solid steel ones, and now has this extra pair of forks and a nagging question in their head about whether they would have been strong enough? Now you can find out!

I can just see it now...

"Damn! They WOULD HAVE been strong enough! Now I want 'em back... Oh."

I've always had two worries about putting a motor on suspension forks. Spinout is one, but the other thing that doesn't sit well is the notion of pulling the bike along through the shocks. Other than during braking, they're mostly used to going up and down. There is such a huge selection of suspension forks out there, and of widely varying quality. I can't help but wonder if sudden spectacular shock failure might not creep into the equation here...

[OneWayTraffic]

This thread really, really needs to be stickied.


Who is the appropiate mod?

[justin_le]

The best is a good tight fit of the torque plate hole to fit the axle all the way around

Hi Bluestreak, this seems "intuitively" correct to a lot of people and so that's probably the main reason why it hasn't been challenged. But once you actually spin an axle through a dropout plate and watch the metal smear out of the way, you realize that it doesn't make much of a difference if the original slot was a dead perfectly tight fit or a little sloppy. Once you hit the yield point of the metal, it just starts to move no matter if it started snug.

Not just intuitive I think. A loose fitting spanner will quickly round off a nut with only a little torque. With a tight fitting spanner you can apply much more torque to the same nut. Why is it not the same with torque plates and axle flats?

If by spanner you mean an adjustable crescent wrench, I don't think that's really a good comparison because they also have a lot of mechanical play in the adjustment mechanism and that's why you need to snug them tight to be of any use. If you look at an ordinary wrench, they don't fit super tight on the nuts. They are actually pretty sloppy, so even if the nut is dinged up or of poor tolerance the wrench will still fit over it, and that doesn't cause problems.

What I am saying is that if you look at the diagram below, I wouldn't expect there to be any notable difference in the spinout torque between case A and case B, but obviously if you take this to further to the point where you are changing contact angles an appreciable amount, as in C, then of course that would be a lot less effective.

Example of torque plate fitting

Spinout Diagrams.jpg (18.91 KiB) Viewed 1929 times

[Ypedal]

ok.. i'm not finding the pictures in my archive... ( i know they are in there.. somewhere )

But, torque arms, after alot of pondering and various experiments, 2 things to mention..

-Needs to clamp onto the axle, not just fit over the flats, i had an ampedbikes torque arm ream itself thru the axle on an X5 ( ok.. 80v and 80 amps was a tad much ... but still.. )

- Does not have to be clamped inside the axle nuts.

A torque arm that can be secured to the end of the axle ( assuming the axle is long enough to allow this, and longer axles are an easy thing to request and even kenny at clyte was able to do this for me ). 2 piece, clamped solidly onto the axle then secured to the fork eliminates all slop, forward and backwards..

Torque arms that fit inside the axle nuts tend to be too close to the fork tubes ( considering all the various shapes and sizes of forks out there ) and add another layer that tends to slip and give way..

*crappy ms-paint time.. brb

[dogman]

I'd say that's correct assuming that the nuts are tight. Once the nuts are loose, any slop allows some momentum to be created before the metal makes contact. With loose nuts, the rocking motion between braking and motoring could increase the damage.

An interesting test would be to take a damaged axle after testing, grind it round, and see what it takes to spin a round axle in the dropouts, with and without tourqe arms. Mabye we should be using round axles at the point where the axle contacts the frame, and using tourque arms to prevent spin. This approach would prevent damage to expensive bike frames.

[justin_le]

What I am saying is that if you look at the diagram below, I wouldn't expect there to be any notable difference in the spinout torque between case A and case B,

In any case, those were my expectations, here is what testing showed.

I happened to have a stash of eZee torque plates that are factory made to be almost an exact fit over the eZee axles, virtually no play at all. They are wire cut from 1/8" stainless steel. One of these was left as is, the other one I filed the slots wider and deeper so that there was appreciable play over the axle. In this case, the width was increased from 9.90mm to 10.12 mm.

eZee torque plates before slop test.jpg (64.4 KiB) Viewed 1932 times

These were each fitted over a fresh 12mm axle, sitting freely (not sandwiched between nuts) and a 30cm arm with a load cell was used to apply torque until the plate started to yield and spin around the axle.

Torque Apparatus.jpg (40.88 KiB) Viewed 1932 times

With the unmodified tight fitting plate, the metal started yielding at 10.8 kg and pretty much gave way completely at 11kg. That's a tad over 30 N-m.

With the loose fitting torque plate that I filed larger so that there was a 0.2mm gap between the axle flats and the opening, the metal started yielding at 10.4 kg, though it didn't give way completely until almost 12kg.

eZee torque plates after slop test.jpg (20.5 KiB) Viewed 1940 times

So that's that, not much difference really between a tight as can be fit, and what the average person might whip up with a drill press and file. There is nothing wrong with making it super snug, but it's not AS crucial to the spinout strength as some posts would suggest.

Justin

[Ypedal]

the thickness is key i think, i'd make this torque donut thing at least 10mm, more = better..

Justin, it's 9am out here. so 5am in BC ??? holy crap dude.. been up all night ? or an early bird ? lol..

[justin_le]

Spinout is one, but the other thing that doesn't sit well is the notion of pulling the bike along through the shocks. Other than during braking, they're mostly used to going up and down.

Hey Phil!! Will send a PM.

I've heard this concern about 'pulling' on forks come up a few times, often with our customers as justification for going for a rear rather than a front hub motor conversion.

But really ?! The horizontal pulling forces present on the fork from a hub motor barely compare to what is generated when you slam on the front brakes and come to an abrupt stop. That is what they are engineered to take. And since their design is basically symmetrical, whatever they can take in a braking force should be more or less the same as the pulling force. The only possible exception is that the dropouts are sometimes mounted in front of the fork tubes, and perhaps the front end of the dropout arm might break off more easily from pulling than the rear would from braking.

Another way to put it in perspective. A powerful 5304 running 48V with 35A controller has a pulling thrust of about 55 pounds. That's roughly the same thing that the fork would see when you hang the ebike up by the front wheel in the garage at the end of the day, with the battery removed.

-Justin