Wild Dog Adventure Riding

Technical Section => Make / Model Specific Discussions => BMW 1200 LC => Topic started by: OomD on May 03, 2016, 03:26:21 pm

Title: R1200GS - drive shaft, why universal joints?
Post by: OomD on May 03, 2016, 03:26:21 pm
Was chatting the other day and we wondered why they use universal joints on the drive shaft and not CV joints. Probably a cost thing, but would there be any other reason?
Title: Re: R1200GS - drive shaft, why universal joints?
Post by: Beebop on May 03, 2016, 03:47:26 pm
Universal is sealed. CV joint would need to be sealed which increases risk of contamination if the seal is damaged  ???
Someone else got ideas ?

Title: Re: R1200GS - drive shaft, why universal joints?
Post by: ratrap on May 03, 2016, 03:53:44 pm
Maybe because the drive shaft only moves in one plane a universal is sufficient.
CV has to cope with movement in two planes.
Title: Re: R1200GS - drive shaft, why universal joints?
Post by: Parkinoff on May 03, 2016, 07:03:08 pm
If I can get a CV small enough I'll change/modify  to CV.
Title: Re: R1200GS - drive shaft, why universal joints?
Post by: Welsh on May 03, 2016, 07:18:39 pm
Absolutely no idea. :biggrin:
Title: Re: R1200GS - drive shaft, why universal joints?
Post by: TheBear on May 03, 2016, 07:20:35 pm
Was chatting the other day and we wondered why they use universal joints on the drive shaft and not CV joints. Probably a cost thing, but would there be any other reason?

I am not sure, but CV Joints are much more expensive and their advantage is they allow more movement than universal joints.  Why use them then, when a universal will manage the movement?

If I can get a CV small enough I'll change/modify  to CV.

Why?
Title: Re: R1200GS - drive shaft, why universal joints?
Post by: OomD on May 03, 2016, 07:39:23 pm
Was chatting the other day and we wondered why they use universal joints on the drive shaft and not CV joints. Probably a cost thing, but would there be any other reason?

I am not sure, but CV Joints are much more expensive and their advantage is they allow more movement than universal joints.  Why use them then, when a universal will manage the movement?

If I can get a CV small enough I'll change/modify  to CV.

Why?
Well, a universal joint does not have constant transfer of power, so a CV is more efficient. Only reason, we were just wondering.
Title: Re: R1200GS - drive shaft, why universal joints?
Post by: SmuGS on May 03, 2016, 07:46:26 pm
The canbus flux capacitor makes the CV joint obsolete so us mere mortals of the force have to make do with the tried and trusted universal...
Title: Re: R1200GS - drive shaft, why universal joints?
Post by: Parkinoff on May 03, 2016, 07:54:11 pm
Was chatting the other day and we wondered why they use universal joints on the drive shaft and not CV joints. Probably a cost thing, but would there be any other reason?

I am not sure, but CV Joints are much more expensive and their advantage is they allow more movement than universal joints.  Why use them then, when a universal will manage the movement?

If I can get a CV small enough I'll change/modify  to CV.

Why?

Smooth power transfer as OomD says. The Parelever with the 2 UJ out of phase is a relatively good solution because each UJ cancels the other out but the drive shaft still accelerates and decelerates between the input and output ends and i dont think the 2 angles are always the same so some of that acceleration and deceleration wants to go to the rear wheel. I think that's the reason for the rubber cushion between the 2 drive shaft sections? Put your bike on centre stand start with rear wheel up and put into first gear, you'll hear the backlash clearly. Must be real bad on Monolever bikes it think.
Title: R1200GS - drive shaft, why universal joints?
Post by: Sláinte Mhaith on May 03, 2016, 07:56:58 pm
To link to the above.
A CV joint cost more.
A CV jount is just that: A constant velocity joint.
With a universal the output velocity is not constant depending on the angle it is at.  Now put two universal in series and both at the same but opposing angle the the final output is constant speed again. Thus your input and output shaft must be in line while the drive shaft can be at an angle. The input shaft will be at a constant speed while the drive shaft will have a slight speed fluctuation and the output shaft will have a constant speed again. That is part of the reason they use a parallel arm withe the final drive to keep the angles correct.

I think a universal can also handle more power.

Edit:  I see Parkinoff beat me to it.
Title: Re: R1200GS - drive shaft, why universal joints?
Post by: Parkinoff on May 03, 2016, 08:05:59 pm
I don't think power is a problem on modern CVs. Some seriously big vehicles with fwd. And CVs are not that expensive. Replacement outer CV for my son's car was less than R1000. BMW should change their shaft design to a replaceable CV. Really the only weak point on the bikes in my opinion.

Wonder how the S10 deals with the oscilation as it's only got one UJ
Title: Re: R1200GS - drive shaft, why universal joints?
Post by: lecap on May 04, 2016, 11:08:11 am
The change of rotational speed of the universal joint is small as long as the deflection angle stays within limits. Only the high articulation angles of for example a front wheel drive car (up to 54°) require the use of constant velocity joints.

The BMW Paralevers kinematics do not constitute a parallelogram. The articulation angles of the two universal joints are NOT equal (they change as the suspension travels).

Because of the relatively small articulation angles of the bikes rear suspension even a single universal joint in the drive shaft works. This will typically be combined with some sort of elastic rotational damper either in the shaft itself or in the rear wheel hub or both.
Title: Re: R1200GS - drive shaft, why universal joints?
Post by: Frankrzzgp on May 04, 2016, 11:23:55 am
https://www.youtube.com/v/gmV4qwLfOMY

This explains it very nicely....
Title: Re: R1200GS - drive shaft, why universal joints?
Post by: Parkinoff on May 04, 2016, 11:31:49 am
https://youtu.be/gmV4qwLfOMY


Watch this short clip and see how much the output velocity oscilates even with a relatively small input angle. The relatively small output oscilations gets amplified hugely to the outside of the wheel when the 2 UJ's do not run exactly at the same angles and even then the drive shaft will accelerate and decelerate continiously.

And yes, the two UJ angles on the Paralever are seldom at exactly the same angles so there will always be a velocity difference at the wheel.

A CV will eliminate this. Overkill and unnecessary  maybe according to BMW but it would be nice to have a replaceable CV enstead of a UJ.

Don't know how to post the actual video
Title: Re: R1200GS - drive shaft, why universal joints?
Post by: DeepBass9 on May 04, 2016, 11:39:53 am
Interesting, didn't know that. So on a tractor PTO you should keep the shaft as straight as possible to avoid buggering up the UJs.

Also people with 4x4s who jack up their suspension to dizzying heights also run the risk of buggering up either the drive shaft or gearbox.
Title: Re: R1200GS - drive shaft, why universal joints?
Post by: Parkinoff on May 04, 2016, 11:40:53 am
OOps Frankrzzgp posted the video. The one I linked.
Title: Re: R1200GS - drive shaft, why universal joints?
Post by: Parkinoff on May 04, 2016, 11:45:28 am
Interesting, didn't know that. So on a tractor PTO you should keep the shaft as straight as possible to avoid buggering up the UJs.

Don't think the UJ's will get buggered sommer but whatever is driven will pump (or whatever the thing is doing) like a bike with an offset sprocket. Don't think it's a problem on a pump or something that does not mind some speed variation / oscilation. Metinks
Title: Re: R1200GS - drive shaft, why universal joints?
Post by: DeepBass9 on May 04, 2016, 11:50:41 am
Interesting, didn't know that. So on a tractor PTO you should keep the shaft as straight as possible to avoid buggering up the UJs.

Don't think the UJ's will get buggered sommer but whatever is driven will pump (or whatever the thing is doing) like a bike with an offset sprocket. Don't think it's a problem on a pump or something that does not mind some speed variation / oscilation. Metinks

Some implements have big flywheels like a baler for instance so the universals will probably be the weakest link. I see now at the end of that vid that as long as the UJs are in phase and the input and output shafts parallel you are OK, but in practice that doesn't usually happen.
Title: Re: R1200GS - drive shaft, why universal joints?
Post by: Sláinte Mhaith on May 04, 2016, 12:15:22 pm
Also people with 4x4s who jack up their suspension to dizzying heights also run the risk of buggering up either the drive shaft or gearbox.

Yes. Some of the extra high lift kits come with adjustable trailing arms or offset bushes or whatever is needed to correct angles etc. depending on suspension setup.
Title: Re: R1200GS - drive shaft, why universal joints?
Post by: OomD on May 04, 2016, 12:37:17 pm
This has got me wondering about the new LC's, and GSA LC's... when riding with the suspension set any higher than "Rider only" mode, there is a constant oscilation from the rear suspension. Bavarian say this is normal, but my older (2008) GS never did this. Bothers me every time I set the suspension. I'm wondering now if it could not be related to the phasing of the propshaft?

Maybe worth it having a look?
Title: Re: R1200GS - drive shaft, why universal joints?
Post by: DeepBass9 on May 04, 2016, 12:50:45 pm
Also people with 4x4s who jack up their suspension to dizzying heights also run the risk of buggering up either the drive shaft or gearbox.

Yes. Some of the extra high lift kits come with adjustable trailing arms or offset bushes or whatever is needed to correct angles etc. depending on suspension setup.

And the cheapies just have a few rubbers and longer springs....
Title: Re: R1200GS - drive shaft, why universal joints?
Post by: TheBear on May 04, 2016, 07:06:42 pm
Was chatting the other day and we wondered why they use universal joints on the drive shaft and not CV joints. Probably a cost thing, but would there be any other reason?

I am not sure, but CV Joints are much more expensive and their advantage is they allow more movement than universal joints.  Why use them then, when a universal will manage the movement?

If I can get a CV small enough I'll change/modify  to CV.

Why?
Well, a universal joint does not have constant transfer of power, so a CV is more efficient. Only reason, we were just wondering.

I didn't know that.  Thanks.  Will it make a marked difference?
Title: Re: R1200GS - drive shaft, why universal joints?
Post by: eberhard on May 04, 2016, 07:30:57 pm
https://youtu.be/gmV4qwLfOMY


Watch this short clip and see how much the output velocity oscilates even with a relatively small input angle. The relatively small output oscilations gets amplified hugely to the outside of the wheel when the 2 UJ's do not run exactly at the same angles and even then the drive shaft will accelerate and decelerate continiously.

And yes, the two UJ angles on the Paralever are seldom at exactly the same angles so there will always be a velocity difference at the wheel.

A CV will eliminate this. Overkill and unnecessary  maybe according to BMW but it would be nice to have a replaceable CV enstead of a UJ.

Don't know how to post the actual video

Very informative video clip. Thanks for linking it.
Title: Re: R1200GS - drive shaft, why universal joints?
Post by: OomD on May 04, 2016, 09:24:40 pm
Was chatting the other day and we wondered why they use universal joints on the drive shaft and not CV joints. Probably a cost thing, but would there be any other reason?

I am not sure, but CV Joints are much more expensive and their advantage is they allow more movement than universal joints.  Why use them then, when a universal will manage the movement?

If I can get a CV small enough I'll change/modify  to CV.

Why?
Well, a universal joint does not have constant transfer of power, so a CV is more efficient. Only reason, we were just wondering.

I didn't know that.  Thanks.  Will it make a marked difference?
Well, based on the excellent video clip posted earlier it makes a difference if the 2 universal joints of the shaft are not correctly phased. Which got me wondering about the ever-present vibration (in sync with the rear wheel speed) when the suspension is set any higher than "rider only" mode. But then, I don't suppose the phasing must be exactly 90 degrees, so even if one opens the shaft assembly and inspects the shaft it would probably be impossible to tell if it is correct or not just by looking.

It is strange though that my previous GS (2008 model) didn't have this vibration that I could remember, when setting the suspension higher. If it did have it it is certainly not as pronounced as on the LC. And, both my LC and my current LC GSA both have the vibration. Which Bavarian say is normal.
Title: Re: R1200GS - drive shaft, why universal joints?
Post by: Sláinte Mhaith on May 04, 2016, 09:52:54 pm
Which Bavarian say is normal.

Get them to put that in writing.  ;)

Don't put too much trust in them saying it is normal.  They also told me something is normal but then I asked him how can it be normal if the play is almost three times more than what their manual say is allowable. Got met with a blank stare.