Drive Shaft Twisting

[Tim.Wright]

Wow that is a manly shaft. I think 100mm is too big. The assumed wall thickness of 25mm seems a bit too manly too. Finally, I think they are all titamium shafts too which will increase the deflection angle.

because I like that number (one) and it is a Formula One shaft.

[youtube]http://www.youtube.com/watch?v=tFUJjm0yXNc[/youtube]

Tim

[Ciro Pabón]

Agreed, while you were posting I removed some smart comments and decided to use a 0.5 cm thick tube, so we were thinking more or less the same. There you go. If it were made of titanium the deflection would be twice as large, that is 1 tenth of a degree, give or take.

Anyway, it's a very small angle, not noticeable with your eyes.

I think that the idea of twisting around itself three times is a misunderstanding. Perhaps when starting the axle takes three times the design load or something like that, so they have to be replaced frequently. Who knows? Anyway, as stated, the idea is preposterous.

I find hard to believe that exists a structural material that can be twisted three complete turns without breaking first.

[ringo]

Seems far fetched at first...

At first, at second and at third.

Let's see.

Shaft length, exaggerating, 1 meter (L).

Twisting moment (T) of 274 N-m, which I find in the Wikipedia article on Formula One engines.

Let's make the shaft of structural steel so I don't have to google for the modulus of rigidity (G), which I know is around 80 GPa (twice the one of titanium, btw).

I would like to have a manly shaft of 10 cm in diameter (D) and let's make the hollow part 9 cm in diameter (d).

So, torsional deflection (θ) is:

θ = 32 L T / (G π (D4- d4))

θ = 32 * 1 m * 274 N-m / (80000000000 N/m2) * 3.14 * ((0.1)^4-(0.09)^4))

θ = 0.0010 rad

θ = 0.06 degrees

That's around 6 hundredths of a degree. Am I mistaken? Thanks for any check.

Who would have thought that? Everybody seems to be wrong (probably, me too).

My verdict:

10cm?

too manly.

hows about 4cm with 3.4cm bore. with a 700mm length? seeing as though an F1 car is just 1.8m wide.

θ = 32 * 0.7 m * 274 N-m / (80000000000 N/m2) * 3.14 * ((0.04)^4-(0.034)^4))

θ = 0.0199 rad

θ = 1.144 degrees

still pretty small even with a tiny little 4cm tube.
It would take 43,256 Nm to turn this thing 180 degrees.

[ringo]

I find hard to believe that exists a structural material that can be twisted three complete turns without breaking first.

i guess you haven't read the 2013 regulations. Look in the KERS section.

[Mikey_s]

=D> Ciro, another excellent lesson in sanity...

Being a simple chemist (albeit one who has metamorphosed slightly into rheology from time to time) I was trying to think this through in rational terms.

What is the drive shaft turning?... the wheel!
What is the part of the wheel that is attached to the track?... the tyre!
what is the tyre made of (and what is the relative stiffness of it)?... rubber (albeit carbon/kevlar reinforced)!

If anything is going to deform significantly it is the tyre (you can clearly see it on dragsters at the start;
http://static.wix.com/media/6264ffa5f9a ... wix_mp_256

Intuitively there is no way (particularly at the start when there is no downforce on the wheel) that the half shaft is winding up through three, two, or even one turn. Furthermore, it would be highly undesireable to have such large deformations in the shaft as this would inevitably change the length of the shaft (when all the other components are held in place by the wishbones) and lead to substantial hysteresis in the drivetrain... can you imagine the thing winding up under braking (car travelling another 2-3 wheel lengths as a result of drive shaft elasticity...?)

In fact I would be interested in some specualtion on when the shaft is under the most stress.. it has to be a low gear and/or heavy braking my guess is when there is significant downforce on a hot (sticky) tyre... in to/out of a slow corner??? Can anyone recall a specific incident of a drive shaft failure and where it happened? (My sense is that they also probably happen when the forces on the shaft are not purely axial)

[strad]

I see,,,I see...
In drag and off road racing the axle does slowly get twisted and must be replaced...perhaps that is what they were talking about...We used to paint a line on the axle and after use you could see the line twist,,,but it was a slow continual process.

[mep]

In fact I would be interested in some specualtion on when the shaft is under the most stress.. it has to be a low gear and/or heavy braking my guess is when there is significant downforce on a hot (sticky) tyre... in to/out of a slow corner??? Can anyone recall a specific incident of a drive shaft failure and where it happened? (My sense is that they also probably happen when the forces on the shaft are not purely axial)

Oh yea I know of a incident during Imola race 2005. Kimi was going for the race win after a very frustrating 2004 season. It turned to one of the saddest races I have seen when he suddenly became very slow and went back to pits. Later Haug said one of his half shafts broke. He also said that Kimi did some start test before the start and this might have put to much stress on the shaft causing it to fail later on. He can slowly continue to drive because just one of the shafts broke and the limited slip diff transmits a low amount of power to the remaining tire.

[youtube]http://www.youtube.com/watch?v=mV8lXnCx ... re=related[/youtube]

A part doesn't need to fail immediately when it once became overloaded. It might still take many load cycles where cracks grow or dislocations move trough the metal. The strength of the metal will reduce by this until it will finally fail.

[bettonracing]

Ciro,

Your calculations neglect gear and final drive ratios. Even with a 20:1 total ratio (roughly estimated from the 660mm diamater for 1st gear), we're talking 23 degrees max.

Regards,

H. Kurt Betton

Edit: This assumes the car could get maximum traction and has maximum power output in 1st gear(...). In the higher gears where it does have maximum engine output and full traction, the gear ratios are lower and therefore the multiplication factor is reduced by whatever the relevant gear ratios are.

[mep]

I see,,,I see...
In drag and off road racing the axle does slowly get twisted and must be replaced...perhaps that is what they were talking about...We used to paint a line on the axle and after use you could see the line twist,,,but it was a slow continual process.

You load the shaft beyond the yield point either for longer time and get the material into plastic flow or repeatedly and add up the plastic deformations.
This is possible part of the explanation because you can do this just a couple times. Also even with plastic flow I doubt this story. A drag racing car possible uses the shafts harder than F1. It just has to do 1 or a couple of starts until you can replace parts but a F1 car will load the shafts many laps until a race is finished. You must take the amount of load cycles into account in the design of the shaft and don’t load it up to the yield point.

[domdogger]

if it turned 1080 degrees you could use it as a form of kers.

[smaldj]

First post, so be gentle...

About 5 minutes down the road from me is a company which designed (must've been 20-ish years ago now) a drive shaft for the Jordan Team that twisted. I was a bit skeptical but apparently it was a form of manual traction control for the start of the race, at a time when traction control systems was banned.

Basically, the shaft stored up the tension and released it like an elastic band...

These drive shafts, so i've been told, have never been used in an F1 race due to the inability to effectively test them to destruction - they couldn't be broken. Therefore, there was no way to know what would happen if / when it snapped and so they couldn't be safely deployed.

Apparently, the company has a couple of these drive shafts lying around, unused - even though millions were spent on their development. All of this information is hearsay though and should probably be treated as such - although 'RH1300S' mentioning Eddie Jordan does corroborate the story a little.

[xpensive]

There are times when it's actually enjoyable to be an old school mechanical engineer, such as this one.

Wonder how urban legends such as the above can get spread with this kind of credibility?

Twisting the rear axle like a rubberband, yeah, sounds like Eddie Jordan that.

[Jersey Tom]

First post, so be gentle...

About 5 minutes down the road from me is a company which designed (must've been 20-ish years ago now) a drive shaft for the Jordan Team that twisted. I was a bit skeptical but apparently it was a form of manual traction control for the start of the race, at a time when traction control systems was banned.

Basically, the shaft stored up the tension and released it like an elastic band...

These drive shafts, so i've been told, have never been used in an F1 race due to the inability to effectively test them to destruction - they couldn't be broken. Therefore, there was no way to know what would happen if / when it snapped and so they couldn't be safely deployed.

Apparently, the company has a couple of these drive shafts lying around, unused - even though millions were spent on their development. All of this information is hearsay though and should probably be treated as such - although 'RH1300S' mentioning Eddie Jordan does corroborate the story a little.

What's this company's name? So I never work with them in the future...

[xpensive]

...
What's this company's name? So I never work with them in the future...

Indeed JT, good to see that we can see eye to eye once in a while btw, I can see the mechanical possibilities of building a half-shaft like a torsion-bar, but what would be the point of a flexing drive-train anyway? Never heard the like.

[smaldj]

Fair enough, must've been an urban myth then - my mistake. Just thought i'd say, incase there was any truth in it.
I'll see if the guy who told me this can get some proof - or at least an explanation of how it would work so that you guys can rip it to shreds.