Rotor 3D+ broken crank

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maquisard
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by maquisard

highdraw wrote:You are at least 3 standard deviations to the right of mean in power output.


I see your points. But what is the mean power output you are talking about. My numbers are not extraordinary, they really aren't! Do you honestly consider an FTP of 330W to be 3 SD to the right of average in any cyclist who races...

by Weenie


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Marin
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Location: Vienna Austria

by Marin

Agreed, the OPs values are good, but nothing out of the ordinary. Any crank on the market should be able to last longer than 2 summers for him.

A 100kg rider who might be a lot slower but does a lot of loaded touring will stress a crank at least as much.

That said, I've seen threads about broken Dura Ace cranks too.

Raineman
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Location: Kent, UK

by Raineman

Any metal part, subject to a load, had to be designed with fatigue in mind. Rotor will have parameters such as force and load cycles (over a range of forces, Miner's law if your interested) and then introduce a margin for tolerances. All companies do this, it's the reason your washing machine fails the day after the warranty ends for example.

So your crank will have been designed for a given life and either through an unlucky stack up in tolerances (though unlikely give this is the second time) or the unique way you load the cranks has taken them beyond this life which has lead to failure. It is clear you have found the limit of the design but that doesn't mean it is an objectively bad design or indeed a dangerous product for the average user, but rather it may be unsuitable for you and why you would be in titled to think it is a bad design.

FWIW I am a masters student in material science and would be happy to discuss the mathematics of fatigue in more detail, but I don't think a public internet forum would tolerate this too well.

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prendrefeu
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by prendrefeu

Raineman wrote:FWIW I am a masters student in material science and would be happy to discuss the mathematics of fatigue in more detail, but I don't think a public internet forum would tolerate this too well.


Seriously: please do this. Either here or in a new thread. WW used to be heavy with this type of education/information. Lately it's all been "look what toy I bought but I don't understand!" type stuff.

Please, please share your knowledge with others here!!! :beerchug:
Exp001 || Other projects in the works.

maquisard
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Joined: Thu May 01, 2008 8:51 pm
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by maquisard

Yeah, completely agree, I am a semiconductor engineer, I love mathematics, physics and engineering science.

Discuss away!

On another interesting note, Rotor's warranty is 2 years, so I am bang on it.

mattyNorm
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by mattyNorm

I'm on my 3rd year of a mechanical eng undergrad and I learn more here than in some on my lectures...

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Mario Jr.
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by Mario Jr.

I am no engineer but has a lot of experience with the Rotor cranks, having distributed them for 7 years.
We have sold over 1000 cranks in that time, and the only crank we have seen broken, is an "old" 3D, which broke at the pedal thread. Actually, the same guy broke two, but he is a former rowing champ so a big and very powerfull guy and having broke a Specialized, a Campa Carbon crank in the same place, I would say that the track record is quite good for the Rotor cranks, and by no means dangerous.
We are supplying for the danish track team, and these guys are putting serious watts down without any problems.
My guess is a flaw in this particular crank rather than a general design flaw. Or maybe it has sustained an injury at some point.
I am sure you will be taken good care of by Rotor, otherwise contact me and I'll sort it out.

Butcher
Shop Owner
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by Butcher

It looks like it has been cracked for sometime. I guess we all can learn to check that stuff when cleaning our bikes. Finding the crack before you go out on the ride would have been beneficial.

Raineman
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Location: Kent, UK

by Raineman


maquisard
Posts: 3772
Joined: Thu May 01, 2008 8:51 pm
Location: France

by maquisard

Was removing the pedals from the crankset today to return the bike to the local bike shop in order to get it replaced under warranty.

Unfortunately my Look Keo 2 Blades have also been a victim of the incident. The left pedal struck the ground when the bike fell to the left ripping off the pedal platform and wrecking the left hand edge of the pedal.

Thanks Rotor!

Image

Grill
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Location: Oop North

by Grill

Given the right set of circumstances, everything will break. Absolutely nothing wrong with Rotor, just unfortunate. As has been mentioned it's most likely due to fatigue. http://pardo.net/bike/pic/fail-009/000.html

sm4100
Posts: 57
Joined: Wed Apr 09, 2014 4:33 am

by sm4100

Material failure, porosity or hardening or machining process. This is no way related to fatigue. This crank should be able to take 2000 watts for thousands of miles.

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Marin
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Location: Vienna Austria

by Marin

Power isn't relevant in this case, only torque is. The two are related through cadence, but if you produce your power through pedaling at a high frequency, your complete drivetrain will last a lot longer compared to someone how rides at low cadence out of the saddle all the time.

joongsun
Posts: 25
Joined: Mon Aug 24, 2015 3:17 pm

by joongsun

sorry to hear that,

i've never seen this situation...

wangsanegara
Posts: 63
Joined: Tue Sep 01, 2009 10:10 am

by wangsanegara

Sorry to hear about what happen to you. I have been using Rotor Crank since 2009 and nothing happen to me.

Looking at the picture, I am quite sure that the crank was cracked half way for some time. The blackened part was oxidized, which means air was present. The white part just happen split second so that no oxidation occur. I suspect that the crank has a "hairline crack" not long after production, which propagates during repetitious load before 16k Km. Until one day, it cannot handle anymore load it cracked under load. Without a hairline crack to start, it almost impossible things like this to happen. By bringing the crank to the material science lab, you can determine if the crank has a hairline crack or not.

Working at aerospace industry, and doing Non-Destructive Test on parts is part of my job. I need to catch "hairline crack" right after production so that it will not go into Assembly.

A.W

by Weenie


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