Dropout Failure Experiments, and a call for Fork Donations

[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 dan]

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.



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.

View attachment 1

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.



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

 

[justin_le]

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.

For a system with regen, or when you have a bad hall signal / blown controller mosfet etc. and have heavy motor chugging action, then this is totally true.

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.

This is something I am very curious about too, since it would help quantify how much the 'friction' between the axle shoulder and the inside of the dropout contributes to the spinout strength.

As far as round axles and using only a torque arm for spinout prevention, that has a lot of merit. One of the real challenges in trying to design a 'universal' torque arm is the many dropout angles that are present. If your axle was round then this wouldn't be an issue, and you could more easily make a rugged single piece torque arm that would fit in almost any frame. Though there is something to be said for the redundancy in having both the axle flats and a torque arm involved.

-Justin

 

[justin_le]

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..

Ha, thanks for reminding me, I should go to bed! No never been an early bird, but I did just finish a bunch more spinout experiments, including some using thicker torque plates. Will get some rest first and then post the results after. -Justin

 

[justin_le]

Setup was the same basic setup and apparatus as the last post. I did a total of 6 more spinout tests with various torque plates and axles. Torque plate #1 and #6 were both from 1/8" mild steel from when I had the dropouts cut. Plate #2 was made from 1/8" stainless but without much metal width around the hole (just 5mm), while #3 is the same tight fitting 1/8" unit from eZee that was discussed in previous post. The 3/16" plates in #4 and #5 are both units from our current crop of torque arms. Here are the results:

[pre]# Material Thickness Axle Yield Force Yield Torque
1 mild steel 1/8” 12mm 8.1 kg 24 N-m
2 stainless 1/8” 12mm 7.8 kg 23 N-m
3 stainless 1/8” 12mm 10.9 kg 32 N-m
4 stainless 3/16” 12mm 18.8 kg 55 N-m
5 stainless 3/16” 14mm 40 kg* 118 N-m*
6 mild steel 1/8” 14mm 12 -16 kg 35 N-m[/pre]

Comparing #2 and #3, we can see that the torque plate with only 5mm or metal around the hole (#2) was able to stretch out and deform, and hence spun out with about 1/3rd less torque than more or less the same plate from eZee that had a lot more material around it (10mm).

Comparing #1 with #3, it would seem that stainless steel is a little better than mild steel at resisting spinout.

Comparing #1 with #6, going from a 12mm to a 14mm axle with an 1/8" torque plate did improve the spinout strength, but not by as much as we would have expected. The 12mm axle spunout with 24 N-m. The 14mm axle had mostly given way at 35 N-m, but in order to make it do a full 180 degree rotation I recorded a peak of 16kg or 47 N-m

Comparing #3 and #4, increasing the torque plate thickness by just 50% from 1/8" to 3/16" had a significant effect on the spinout strength. Even with a 12mm axle the plate resisted 55 N-m before giving. When we then went to a 14mm axle with the 3/16" plate (#5) the torque was so strong that I couldn't actually get it to give way completely. At 32kg or 94 N-m the axle was starting to really deform the plate, but by 120 N-m which is all I could really apply it still hadn't spun all the way around. Here's what it looked like at that point:

View attachment 1

And here is what the whole collection looked like after the test:

 

[Doctorbass]

Great results Justin! very interesting!

Something to consider with rear dropout problem and hub motor axel i sthat some rear dropout on many bike frame have a part of the dropout that is made of aluminum with less thickness.. usually this is the part that hold the rear derailleur pivot, so when you thighten the nut on the axel, the nut tend to exit the dropout due to the variable thick o fthe dropout on the circunference under the nut

These new dual piece dropout complicate the tightening job..

Doc

 

[dogman dan]

Axles that spit out of the dropout as they are tightend are a sure sign something doesn't fit right. You say it gets thinner towards the open end of the dropout? That would indicate to me that the design is only intended to be used with the smaller shoulder surface of the QR hub skewers. The larger size of the hub axle puts the shoulder out on the thinner part of the dropout, and the nut will want to squirt out to the narrow end. Some kind of shimming might fix it but I would look at cheaper frames with flatter dropouts for a rear hub. Something in the price range of bolt on wheels. If you need the quality bike, then custom machined combination tourqe plate and derailur hangers are the solution.

Nice work Justin. I'm really impressed with the effectivness of the thicker torque arms! I've been of the opinion that the thin ones were decorations, but clearly 3/16 makes a huge difference. This thread is really increasing my understanding of the subject! Forks will get shipped today BTW, including one set of aluminum rear drops from a cheap huffy.

I hate to admit it, but I'm starting to eye my giant mtb, with the alloy 120 mm travel forks for a light gearmotor. Must resist temptation!

 

[ZapPat]

I hate to admit it, but I'm starting to eye my giant mtb, with the alloy 120 mm travel forks for a light gearmotor. Must resist temptation!

I've done quite a bit of riding with a cheap alloy front suspension fork, dogman (it's a low end 100mm RST I got for a buck). No incidents yet even with lots of off-road riding... but I do have two of Justin's 1/8th torque arms on there (it's a 9C hub). I even use regen all the time for braking and it has never loosened up yet after the normal initial break-in period of a few rides. Mind you, that bike also has a rear 9C hub too, so maybe this releaves the front fork from doing too much work by itself?

Thanks for the great tests, Justin!

 

[dogman dan]

Part of the concern about riding a motor on aluminum is the terrian I have in mind. Think going down a rock staircase with steps 16" tall. Not a place to go over the bars. A lot of the trails I see on you tube look quite cushy compared to my local desert rock piles with cactus.

But the forces a good tourqe arm can take do give me a lot more confidence in thier usefullness. I really had the opinon that they weren't so effective before.

Forks have been sent, it was a bit expensive but worth it for SCIENCE!

 

[jag]

[pre]# Material Thickness Axle Yield Force Yield Torque
1 mild steel 1/8” 12mm 8.1 kg 24 N-m
2 stainless 1/8” 12mm 7.8 kg 23 N-m
3 stainless 1/8” 12mm 10.9 kg 32 N-m
4 stainless 3/16” 12mm 18.8 kg 55 N-m
5 stainless 3/16” 14mm 40 kg* 118 N-m*
6 mild steel 1/8” 14mm 12 -16 kg 35 N-m[/pre]

These torque values aren't very encouraging. Many hub motors do 100+nm.

Besides the thickness, the material plays a role. Tools made from crome vanadium alloy are much stronger than mild steel. What's the max torque of a good quality 10mm wrench? Maybe better material in the torque arms would be a way to go.

On my ebike I'm lucky to have 8mm thick forged dropouts. Probably the torque washers and arms don't add much to that.

 

[justin_le]

Forks have been sent, it was a bit expensive but worth it for SCIENCE!

Hey Dogman, that's super. We also got a paypal donation to go toward these tests so thanks for that whoever it was.

Otherwise though, there hasn't been much response at all as far as aluminum forks go. There is the one unit that Dogman is sending, and another one from a pretty decent downhill MTB with shot seals that my room-mate donated, so that makes two at least. I'll be doing the rounds of bike shops around Vancouver over the next week or so to see what we can collected as far as discarded alloy forks that still have dropouts in tact, and expect to start doing all the spinout failure tests at the beginning of December. So sit tight!

 

[justin_le]

Nice work Justin. I'm really impressed with the effectivness of the thicker torque arms! I've been of the opinion that the thin ones were decorations, but clearly 3/16 makes a huge difference.

Well, I think the results more or less confirm what had generally been figured out the trial and error way: that torque plates made from 1/8" steel ARE pretty much decorative, as they don't in-and-of themselves have enough strength even with 14mm axles to resist the stall torque of most hub motors.

The effect of going to 3/16" was impressive, and I see no reason now why we wouldn't go further to 1/4". The reason I didn't get plates made from 1/4" stock before was that as the metal gets thicker, the accuracy of the bore made with the waterjet cutter gets worse and worse, so the tolerances suffer (we saw this even in the difference from 1/8 to 3/16, and had to hand-file a lot of them). However, since we've seen that a really snug fit isn't nearly as beneficial as the extra thickness, then it's not so much of a problem anymore!

Besides the thickness, the material plays a role. Tools made from crome vanadium alloy are much stronger than mild steel. What's the max torque of a good quality 10mm wrench? Maybe better material in the torque arms would be a way to go.

I will be picking up a 10mm wrench on my next hardware store visit and will do a spinout test on that too, since it seems to be a popular makeshift arm.

Justin

 

[Ypedal]

Likely different in different locations but here in Moncton the local landfill has a dumpster bin dedicated to bicycles, when full they crush them into a cube.. not sure how willing they would be to let someone do this but with a cordless sawzall or a regular with an inverter you could quickly hack apart the forks instead of wasting a bunch of time fighting with rusted bike parts.

 

[mwkeefer]

Dogman,

Earlier I noticed you relating your intended test to riding down a staircase of 16" stairs.

I can attest that i have ridden my 26" Hard Rock not only down the Philadelphia art museum steps but, I rode down after I had ridden up!

This is with a Rock Shox Tora RS (with Lockout) I believe they are 100mm travel forks aluminum alloy (may be magnesium, not 100% sure) 100% unmodified (I ground the axle to fit the fork) and using nothing more than a single of Jason from ebikekit's torque arms.

Motor was 9C FH205 in 26" rim -after 100mi of breakin riding and re-adjustment
Suspension was set for max travel/give

Ride up required some tactical pedaling to maintain traction, and honestly was more like bunnyhopping 100s of curbs in a row - I guess this is how mountain bikers traverse rocks, I've seen videos but this was my first real attempt at anything resembling rockhopping - until then I had stuck with just crazy offroad trails. It wasn't super fast going up (adding a rear hub would have helped that considerably).

Coming down.... that was fun... About 4x as fast as going up, have no idea how quick but the suspension ate up the steps like they werent even there... actually it felt like a canter for anyone who rides hoarses, only way I know to describe it.

I did wear a helmet for this but didn't get any video... I only did the run once for a test (figured if somthing broke, like me... I didn't want that idiocy on video), police showed up before I could do a second run and I wasn't about to push my luck that night.

I ride the same bike now with 100s more miles on it and im still running through the woods, hopping (more like running over at a good clip) curbs, etc.

No fork fatigue or breakage (yet).

-Mike

PS: I will at some point... do the run again on video, I may have to do it at night though to avoid trouble... would be even better if I could get a cop to "dare" me, since they are all interested in the eBike and want to try it... I could play it off as if I was demonstrating how useful it could be to a bike officer? Actually... that might work. = )_

 

[mwkeefer]

Guys,

What types of Aluminum forks are you looking for to do testing on?

I know I can get you 3 or 4 models of Sr Suntour and some others I haven't a clue the manufacturer but are there some specifics your lookign for... models, years, with/without disc mounts?

Where do they need to be shipped to?

I thought I had posted already, I can and will source as much as possible for this purpose... less failure = less physical injury = better public perception of ebikes and better safety for all of us.

I also see the torque ratings above... kinda scary.

I can't remember the hardening level on the torque arms carried by ebikekits and justin from ebikes.ca but I have tested them well over 3000w without modification and now > 5000w with a JB Weld filler (to take all slack out of them - they had perhaps 1/2mm of play in the fit prior to the JB Weld fil) - it didn't crack either (I expected it might).

Hope it helps!

-Mike

 

[icecube57]

Im not plugging or anything but the test data is making me feel a little bit more at ease with my GM front motor. I have two ComCycle Torque arms. They are 3mm thick. I doubled them up on one side of the motor. This is a total torque arm thickness of 6 millimeters = 0.236220472 inches which is almost 1/4 inch. With my current setup fresh off the charger my dropouts and torque am see about 95N stall force. Although youve mention that torque arm snugness doesnt matter. Mines super snug. I almost had to file them. The axel is 14mm .

Have you did data to includes torque arm length. Some torque arms are long like mine and then some are very small that you can use the rack mounts to secure them. Also are there any weakness in using a solid arm vs an adjustable one... like the ones that have the any angle cog in the middle of them.

 

[steveo]

since we are on this topic; I thought i might show you my toque arm ..

These are from a set of steel trainning wheels ... the slot in them was perfect size for my x5 shaft...

-steveo

 

[justin_le]

Guys,

What types of Aluminum forks are you looking for to do testing on?

I know I can get you 3 or 4 models of Sr Suntour and some others I haven't a clue the manufacturer but are there some specifics your lookign for... models, years, with/without disc mounts?

Hi Mike, and thanks for the offer. I did the rounds to local bike stores yesterday and actually scored much better than I was expecting. In suspension forks, we've got vintage Rock Shocks (that are actually magnesium), SR Suntour CR850, RST 281R, an old BAM quality downhill fork, and a pretty cheap Logan fork. With these plus the units that dogman has sent and the various chromo forks collected previously I think we've got a good representative sampling.



What would still be nice though is if we can get a couple suspension forks of identical model, so that we can test the same fork with/without a torque arm for instance, and quantify the different that is made without the different fork being a variable. Would these SR suntour models be of the same family as far as their dropout goes? I've already got the one CR850 so any more of those (or equivalents) would be really useful.

Justin

 

[Affliction]

I think it's great you are failure testing all these forks. One question tho, how are you going to account for the effect that regen braking has on the dropouts? If you tourque a dropout in one rotational direction only it will fail at alot higher torque than a fork fatigued at two rotational torque directions. This is why I stopped using electric braking. I estimate the failure rate at 10 times more if using E-braking. It was mentioned that thicker torque arms worked better but I think the effect has to do with more than the thickness. The proper torque of the nuts and a proper 10mm keyway is the key to this. If you hold the axle in only one axis of clamping force then it rips open the dropouts; if you clamp the axle down by the other axis by the axle nuts with improper dropouts then again it rips the dropouts. The solution to this is indeed 3 dimentional.
All metal is maluable so the goal is to prevent deformation on all axis. Think of a cube... if you deform two sides you have to increase pressure on the other 4 to correct this. A dropout is no different. Thickness prevents spreading; 1st axis. tourque of the nut prevents the same in the axis equal to the axle; 2nd axis. and the combined forces of the two prevent the axle from spinning out of the dropout; 3rd vertical axis and this is due to friction from the other 2.

 

[justin_le]

I think it's great you are failure testing all these forks. One question tho, how are you going to account for the effect that regen braking has on the dropouts?

Hey Ben, in this set of experiments we won't be accounting for that. I am very explicitly testing only the failure strength of the dropouts (and torque arms) when stressed to the limit in a single direction. The strength I am sure would be identical in the reverse direction. But the situation of regen in an ebike where you are repeatedly torquing the axle one direction and then the other direction, causing it to wiggle back and forth, loosening the nuts, impacting the torque plate. etc. etc. is a totally different set of tests, and may be subject to another thread here in the future.

 

[mwkeefer]

Justin,

Nice find on the assortment of stock shocks!

Let me know which you need dupes of (if you can't source them lbs).

You are dead on about regen too... the issue is more that the axle on most hub motors have the flats at 9.94mm and the keying of the torque arms and torque washers is 10mm... .06mm may not sound like squat but its the wiggle room provided by that small absess (or a hub which wasn't properly installed - square dead on, flush in the dropouts) that can cause higher dropout (front and rear) failure rate on regen equipped eBikes...

Since non regen is only loading up in 1 direction (for the most part, exception normal braking) of force if the torque nuts are tight enough it may slip that .06mm but in a proper install it won't because it's preloaded, tensioned, positioned - whatever into the loaded position and has no where to go under highest force (dead stop to WOT with load).

1mm of proper material, adequate in length (perhaps 3-4") and with a 9.95mm flat keyway - were talking hardened stainless here.. no more problems with any dropouts (methods, liveforphysics, ypedal, dnmun, myself, etc excluded - comeon were idiots running 3kw and up all resting on what 5mm of total overlap (the girth of total clamping surface holding shit together) to an alloy frame - ha

Now I'm thankful, to be alive (I must remember to stop thinking).

Happy turkey day!

-Mike

 

[patrickza]

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.

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

This is a fantastic thread, I've had this question in my mind for quite a while now as I have a fraction of play in my torque arms and I've wondered what effect that had. Hopefully I'll be good with a 6mm arm on each side! Let me know if I can send a few dollars to your regular paypal account as for the cycle analyst, or if you have another one I should send it to?