Can someone explain whip effect on driveshaft.

[laser05]

Hey everyone. My friend is in his 3rd year as a machinst and in his book it states that on a 3 part drive shaft ( like a 3 ton truck ) the middle part spins approximately 64 rpm faster then the other two because of something called the whip effect? I've been searching on the net unable to find anything about this, and i find it pretty hard to believe that the middle shaft can spin faster when its connected to the front and rear drive shafts by u joints. Am i missing something? any thoughts or a link to a good site would be awesome, thanks.

[aristocrat]

sounds like a load of shit to me. Maybe when it first starts it will be whipped by the first driveshafts and start off at a quicker speed for like a tenth of a second but other than that?

[ianmcc]

It's called critical speed vibrations. As the speed of rotation approaches the object's natural frequency, the object begins to resonate which dramatically increases vibration. The shorter the driveshaft, the lower the critical speed. Basically, it starts to resonate and bends like a skipping rope and can actually fall out if it has a slip yoke on one end.
I think your friend is thinking if torsional vibrations caused by not having both u-joints phased. Imagine a torsional vibration as a twist occurring twice every rotation (one forward, one backward). The rear u-joint is playing catch up with the front u-joint and that can cause it to rotate faster. Now imagine a three-piece u-joint not in phase. You could see torsional vibrations twisting the hell out of the middle piece if the entire unit resonates.

[Darell_n]

It's common for big tire Dodge truck owner to throw in 4.56 gears in the rear end and then wonder why the driveshaft blows up on the dyno or while hitting 100+ mph on the track (=highway).

[Tik-Tok]

Originally posted by ianmcc

I think your friend is thinking if torsional vibrations caused by not having both u-joints phased. Imagine a torsional vibration as a twist occurring twice every rotation (one forward, one backward). The rear u-joint is playing catch up with the front u-joint and that can cause it to rotate faster. Now imagine a three-piece u-joint not in phase. You could see torsional vibrations twisting the hell out of the middle piece if the entire unit resonates.

But you wouldn't see a RPM difference. OP's friend is not understanding what he's being taught.

[rob the knob]

could you scan the page(s) from your friends book that refer to this and post the images up here?



Originally posted by laser05
Hey everyone. My friend is in his 3rd year as a machinst and in his book it states that on a 3 part drive shaft ( like a 3 ton truck ) the middle part spins approximately 64 rpm faster then the other two because of something called the whip effect? I've been searching on the net unable to find anything about this, and i find it pretty hard to believe that the middle shaft can spin faster when its connected to the front and rear drive shafts by u joints. Am i missing something? any thoughts or a link to a good site would be awesome, thanks.

[Iqoair]

Originally posted by rob the knob
could you scan the page(s) from your friends book that refer to this and post the images up here?





The more the drive line angle is the more "whip" you will have. The less of an angle, the less it's trying to throw the driveshaft outward. Pretty simple really.

[revelations]

Originally posted by laser05
Hey everyone. My friend is in his 3rd year as a machinst and in his book it states that on a 3 part drive shaft ( like a 3 ton truck ) the middle part spins approximately 64 rpm faster then the other two because of something called the whip effect? I've been searching on the net unable to find anything about this, and i find it pretty hard to believe that the middle shaft can spin faster when its connected to the front and rear drive shafts by u joints. Am i missing something? any thoughts or a link to a good site would be awesome, thanks.

From my days of working with gas turbine engines, whipping was a serious problem with tight tolerance components. Engineers used various solutions to combat this (eg. oversized shafts, testing different metals, etc.)

I dont think its 64 RPM but rather Hz. ie. unit mistake? :dunno:

That number might be one resonant frequency of the rotating group.

[laser05]

well i won't be able to scan the pages anytime soon. but it was out of one of those industrial handbooks i believe, like the machinists handbook that has a bunch of misc facts. I do remember him mentioning the number 64 and was pretty sure he said rpm, i may have misheard him tho.:dunno:
and yes after reading a bit on the net i finally found some more great info. thanks for all the replys.
heres the link, scroll down to driveshaft vibrations for great info. specifically torsional vibrations.

http://www.machineservice.com/technical.htm

[Canyonero]

That's a pretty thorough description laser. The base principle is that U-joints do not transfer power at a constant speed unless the two sides are perfectly aligned (in which case you wouldn't need the joint). Wikipedia has a good explanation and illustrations of this effect.
http://en.wikipedia.org/wiki/U-joint

Using two aligned U-joints in the shaft matches the input to output speeds, but the section in between is still going through that cycle of positive and negative acceleration creating a torsional vibration. The more angle you impart, the greater the acceleration and thus the worse the vibration.

[Rat Fink]

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