What do you guys think of this tripod joint angle

[Spetsnazos]

It has worked flawlessly for a few runs and there are no visible signs of damage to the joints themselves. I checked with Taylor Race(Taylor Race CV joints+halfshafts) and they recommend nothing over 11-12 degrees.

Other sources say that up to 25 degrees is acceptable.

What is your opinion on the angle??

http://i295.photobucket.com/albums/mm133/liquidoleg/IMG_20110921_120757.jpg

[Spetsnazos]

It has worked flawlessly for a few runs and there are no visible signs of damage to the joints themselves. I checked with Taylor Race(Taylor Race CV joints+halfshafts) and they recommend nothing over 11-12 degrees.

Other sources say that up to 25 degrees is acceptable.

What is your opinion on the angle??

http://i295.photobucket.com/albums/mm133/liquidoleg/IMG_20110921_120757.jpg

[xxsportscar]

When companies rate the maximum angle for joints its usually the maximum angle and plunge that can be run before an interference issue occurs that would result in joint failure. The thing to remember with Tripod joints is that at angles like that the roller actually end up sliding on the joint instead of rolling. This sliding increase friction and thus heat generation which decrease driveline efficiency. From what I can see you have a very attractive design, if I were a judge I would ask if you could quantify the driveline losses due to your poor joint angle and how that trade off relates to other changes you would have to make to reduce the angle.

[Dash]

I'd have to say that looks pretty bad there. Our team has unfortunately run it in a similar fashion on the past two cars. We have had tripod bearings come apart on two of them. So I would make sure to check the bearings often!

[exFSAE]

1) Should have asked in the design cycle rather than after car is built.

2) Looks pretty questionable.

3) Really no reason for it is what I would say if I were judging

4) Time will tell. Run some hard launches and an all out mock endurance on it. See how it looks.

Biggest thing when evaluating durability of parts.. can't baby it.

[BillCobb]

Perhaps without flaws, but put it on a chassis dyno and see how much it wobbles in toe.

[Spetsnazos]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by BillCobb:
Perhaps without flaws, but put it on a chassis dyno and see how much it wobbles in toe. </div></BLOCKQUOTE>

The car is in the process of being fixed(engine issues). Its ran multiple times on the chassis dyno and it never had a problem.

I checked the bearings recently and they looked practically brand new. Of course the car doesnt have many miles on it but I haven't seen any major wear issues.

I'm not saying its ideal but someone here is telling me that this is the worst thing they've ever seen...I know its not ideal, and I'd prefer it to be inline but I don't quite believe it to be catastrophic...

Was wondering what you guys thought. We will be running some tests in the near future when the engine is done.

Cheers.

[swong46]

Hi CSUN =]
That angle does look quite extreme though

[exFSAE]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by Spetsnazos:
I'm not saying its ideal but someone here is telling me that this is the worst thing they've ever seen...I know its not ideal, and I'd prefer it to be inline but I don't quite believe it to be catastrophic... </div></BLOCKQUOTE>

Worst thing I've ever seen was a "BLT" pizza that used mayo as the sauce. It's hard to top that, but this does look pretty bad/questionable.

With regard to not seeing any major wear issues after a handful of miles.. of course you won't.

Tellin' ya, beat on it with all-out laps for 20-25 minutes. Check the wear. Do it again, check the wear.

If you're fine after that... you've dodged the bullet!

[PatClarke]

Hi all,

Thats almost 'good' enough to be Pat's Design Error of the Month on another site. http://fsae.com/groupee_common/emoticons/icon_biggrin.gif

The drive shaft angle is poor, but there are several other serious design errors on show here too. http://fsae.com/groupee_common/emoticons/icon_smile.gif

Certainly not a Design that would get into the Design Finals at any event I was in charge of.

Pat

[Bemo]

Our 07 car had quite a poor tripod angle, but still much better than this. Back then we had a "tripod graveyard" in our shop. If you manage to do some hundreds of testing kilometers you should order some tripods in advance...

Btw, happy birthday Pat!

[Xeilos]

The driveline inefficiency alone should be enough to make you cautious at angles above the 12 degrees.

Driveline manufactures may say you can use up to "angle X" but that is for non-extended length, low speed use.

From everything we have read as a team, anything above 11-12 degrees results in significant losses (think efficiency jumping off a cliff). We are going to be evaluating this in the next two months as we are have been running 11 and 16 degree driveshaft angles for years without real validation.

Also, we have had wear problems at 16 degrees though the root cause is up for some debate and/or speculation.

[Rex Chan]

Dear Pat Clark,

For those who don't have as much knowledge/experience, could you tell me if these are the other design errors you speak of?

1. Load path for the pull-rod&gt;bell crank activation&gt;damper is at too much angle

2. Camber change through spherical bearing rod ends, which puts a-arms into bending.

3. Too narrow a base for tie rod

4. Reaction force of damper is not reacted well into the chassis (force from bell crank goes up, but bracket is the wrong way - will shear/bend rather than be in tension/compression)

BTW, I'm an engine guy, so don't spend long looking/understanding suspension loads.

[coastertrav]

Rex,

The rod ends do not appear to be in bending as the forces from the A-Arms are co-linear with the rod end itself.

The toe base looks way too short, I've always thought you want it as large as you can fit in the wheel.

The load path through the suspension rocker looks miserable, and I hadn't noticed the shock mount till you said something, but that's definitely not how I would have done it.

But hey, I'm just the electronics guy.

[Spetsnazos]

Hey guys I forgot to put on my flame suit...not fair.

[wagemd]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by Xeilos:
The driveline inefficiency alone should be enough to make you cautious at angles above the 12 degrees.

Driveline manufactures may say you can use up to "angle X" but that is for non-extended length, low speed use.

From everything we have read as a team, anything above 11-12 degrees results in significant losses (think efficiency jumping off a cliff). We are going to be evaluating this in the next two months as we are have been running 11 and 16 degree driveshaft angles for years without real validation.

Also, we have had wear problems at 16 degrees though the root cause is up for some debate and/or speculation. </div></BLOCKQUOTE>

We have run up to ~8-9 degrees a few different years with acceptable results, though a few years back, one of the cars did have a nasty habit of ejecting halfshafts under load which was always entertaining...

I believe Taylor publishes a chart of efficiency loss vs angle? Then you can choose/limit/discover your driveline losses (though it wont tell you much quantitatively about reliability, you'll just have to test that)

Since its already designed and built, you might be able to get away with classifying it as a wear item, inspecting, and replacing regularly, depending on if testing indicates it could be a problem.

[Spetsnazos]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by wagemd:
[QUOTE]Originally posted by Xeilos:

I believe Taylor publishes a chart of efficiency loss vs angle? Then you can choose/limit/discover your driveline losses (though it wont tell you much quantitatively about reliability, you'll just have to test that)
. </div></BLOCKQUOTE>

Never seen that chart, do you have a link to it?

[PatClarke]

Quote Spetsnazos "Hey guys I forgot to put on my flame suit...not fair".

Sorry mate, but you posted the picture asking for comment. You have not been flamed, the comments have been critical about a fairly 'ordinary' design.

Most (but not all) of the shortcomings have been identified here. Unknownst to anyone here, there has been some back channel discussion between Design Judges about the picture and the feelings are mutual. (Oh, you didn't know that the experienced Judges maintain contact and discuss this stuff?? Darn, now I have let the cat out of the bag!)

So don't feel miffed, no-one (least of all me)is flaming you. Feel free to PM me if you feel aggrieved.

Cheers

Pat

[Spetsnazos]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by PatClarke:
Quote Spetsnazos "Hey guys I forgot to put on my flame suit...not fair".

Sorry mate, but you posted the picture asking for comment. You have not been flamed, the comments have been critical about a fairly 'ordinary' design.

Most (but not all) of the shortcomings have been identified here. Unknownst to anyone here, there has been some back channel discussion between Design Judges about the picture and the feelings are mutual. (Oh, you didn't know that the experienced Judges maintain contact and discuss this stuff?? Darn, now I have let the cat out of the bag!)

So don't feel miffed, no-one (least of all me)is flaming you. Feel free to PM me if you feel aggrieved.

Cheers

Pat </div></BLOCKQUOTE>

Oh I understand people are trying to help and I'm not upset or surprised. I wasn't part of the suspension design(was engine/drivetrain/sprockets/chain) but I will note what people are saying and pass it on to the other guys who were. I seriously didn't think the axle thing would be an issue because all the research I could find said it would be fine up to 20 degrees.

I knew there would be drivelosses associated with a huge angle but I didn't think it would be huge up to 20 degrees. Live and learn http://fsae.com/groupee_common/emoticons/icon_smile.gif

[Rex Chan]

coastertrav: sorry, when I said bending, I meant that if the threaded part of the rod end was made shorter/longer, due to the constrained ends, it will put the a-arm in bending in plane with the arms.In the extreme, if you could extend the rod ends by 1", then they should end up much further apart from each other. However, the brackets constrain the ends to be always a fixed distance apart.

[RobbyObby]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by wagemd:
We have run up to ~8-9 degrees a few different years with acceptable results, though a few years back, one of the cars did have a nasty habit of ejecting halfshafts under load which was always entertaining... </div></BLOCKQUOTE>

This past year we ran ~10-12deg static misalignment that grew to about 15deg through full squat and had the tripod unseat from the housing at least 3 times during testing. We also had one eject on a dyno pull that created an lateral load so great it literally sheared the suspension bracket off the frame.
So you really also have to look at the housing depth as well. If it is too shallow, and the angle is great enough, the tripod rollers will actually exit the housing during part of a full revolution. Which is obviously not very ideal.
If you PM Scotty from Taylor Race or call him up im sure hed be willing to give some input.

[wagemd]

@Spetsnazos Still looking for that plot, I know its around somewhere, but I haven't seen it for at least a year...

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by RobbyObby:
This past year we ran ~10-12deg static misalignment that grew to about 15deg through full squat and had the tripod unseat from the housing at least 3 times during testing. We also had one eject on a dyno pull that created an lateral load so great it literally sheared the suspension bracket off the frame.
So you really also have to look at the housing depth as well. If it is too shallow, and the angle is great enough, the tripod rollers will actually exit the housing during part of a full revolution. Which is obviously not very ideal.
If you PM Scotty from Taylor Race or call him up im sure hed be willing to give some input. </div></BLOCKQUOTE>

Ah... Thanks for reminding me, that same car also did exactly that once. Ripped a spherical out of an a-arm, destroyed a few brackets, destroyed the tripod, and a few other bits here and there. I think that was my first or second year so I dont remember if it was before comp or after... Hey, formula wouldn't be any fun without the spontaneous catastrophic failures (and the nights fixing them)!

[coastertrav]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by Rex Chan:
coastertrav: sorry, when I said bending, I meant that if the threaded part of the rod end was made shorter/longer, due to the constrained ends, it will put the a-arm in bending in plane with the arms.In the extreme, if you could extend the rod ends by 1", then they should end up much further apart from each other. However, the brackets constrain the ends to be always a fixed distance apart. </div></BLOCKQUOTE>

Ah, gotcha. We manufacture our a arms with rod ends also, but just use them to take up any manufacturing error (if needed), and do all suspension adjustments with shims at the upright.

[xxsportscar]

Just for fun, the next time you run can you take a temp reading off the inner tripod and let us know how hot it gets after a few minutes of running?

[PatClarke]

Actually, before you take it for a run, snip the zip ties off the boots and see what happens when you slide the shaft fully in either direction. With the amount of spline that is showing, I think it possible you could lift the shaft right out! Or at the very least, think about how much spline engagement you will have at one end if (when) the shaft migrates.

Out of curiosity, how do you stop the lube coming ot between the boots and the splines?

Meanwhile, research 'precession' and think about it relates to the driveshafts.

Cheers

Pat

[Spetsnazos]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by PatClarke:
Actually, before you take it for a run, snip the zip ties off the boots and see what happens when you slide the shaft fully in either direction. With the amount of spline that is showing, I think it possible you could lift the shaft right out! Or at the very least, think about how much spline engagement you will have at one end if (when) the shaft migrates.

Out of curiosity, how do you stop the lube coming ot between the boots and the splines?

Meanwhile, research 'precession' and think about it relates to the driveshafts.

Cheers

Pat </div></BLOCKQUOTE>

The shaft will not come out unless we unbolt the uprights. The plan was to get better boots but we couldn't find any in the last moment.

[Simon Dingle]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by Rex Chan:

4. Reaction force of damper is not reacted well into the chassis (force from bell crank goes up, but bracket is the wrong way - will shear/bend rather than be in tension/compression) </div></BLOCKQUOTE>


Hmmm, I'm not sure I agree with this, so I'd be interested to hear some other opinions.

However, this is my take on it. I would have thought that the damper mount (on the chassis) is stiffer than the fore-wishbone mounts. Admittedly, the spherical is a bit far from the chassis which produces an unnecessarily long cantilever, but I think the concept is correct.

Having the loads directed perpendicularly to the chassis skin (see the fore-wishbone mounts) means that the chassis will flex (or breathe as I've heard it called before) as the skin is in bending. But, having the load entering the chassis near parallel places the skins in tension/compression which to my understanding would be stiffer.

And so as not to completely hijack the thread, I agree with most other posters that the driveshaft angles are very bad. Also, you've only posted a photo of the angle in one plane, what about when the wheel is in full droop/lift? What is the angle when viewed from the rear of the car? And what is the effect of having both of these angles at the same time?

[John Fratello]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content"> Originally posted by Simon Dingle:

However, this is my take on it. I would have thought that the damper mount (on the chassis) is stiffer than the fore-wishbone mounts. Admittedly, the spherical is a bit far from the chassis which produces an unnecessarily long cantilever, but I think the concept is correct. </div></BLOCKQUOTE>

I think the bigger issue being brought up about this is the fact that the pull rod is out of plane with the damper, which will induce bending loads into the bellcrank mount, damper and damper mount.

Another suspension issue I noticed is how many threads are revealed on the fore lower control arm rod end. Due to the welds in the control arm, longitudinal loads at the wheel should induce bending in the control arm tubes. This will be reacted as bending and shear on the threads of the rod end.

We ran a pretty steep halfshaft angle 4 or 5 years ago, but I don't remember it being quite this harsh. We did tests to measure efficiency variation with angle, which I would highly suggest doing to justify your choices. Also, keep a very close eye on the tripod bearings as several people mentioned. I am also assuming that you have the engine as far back as possible to take advantage of that extra space. This could do wonders for your weight distribution. If that is the case and you can justify the angle in design, then I really like the way it's set up.

[RollingCamel]

Cambridge had less angle than this last year, yet it failed.

[Dash]

And I had to jinx myself. We drove our car over the weekend after having it sit idle for some time. After about an hour of driving and letting some new guys drive we yet again broke a tripod end. :/ Hopefully we can fix it before our local Autocross this weekend!

[Dash]

Thought I would bump with a picture.

Edit: For some reason the pictures aren't working on this forum. You can right click the broken picture block and open it in a new tab and it should work.

http://www.flickr.com/photos/dsr92/6218783649/in/photostream/lightbox/

http://www.flickr.com/photos/dsr92/6218783843/in/photostream/lightbox/

[Dunk Mckay]

Yup, that's a broken tripod joint. We broke one when our chassis came unbolted from the engine and flexed a little too much. The tulip came out and flung bearing needles everywhere.

Needles to say the joint was never quite the same again, had to make and extension for it and it kept falling apart due to sheared bolts(housing made in two parts).

[Drew Price]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by Dunk Mckay:
We broke one when our chassis came unbolted from the engine and flexed a little too much. </div></BLOCKQUOTE>



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[Warpspeed]

http://i295.photobucket.com/albums/mm133/liquidoleg/IMG_20110921_120757.jpg
Some hopefully constructive ideas.....
If this was my car, I would increase the wheel base to straighten up the drive shafts.
That could be done with some new asymmetrical wishbones, without moving the existing inboard chassis mounting points.
The toe control arm on the hub carrier needs to be made much longer for greater stiffness, and better toe control.
And as others have already pointed out, the rocker arm geometry needs to place everything in the same plane.
It is just a matter of moving a few things around, and the changes should not be too difficult to fabricate.

[wagemd]

Just realized that the perspective in this picture looks like you're running 18"x10" rims and even more enormous tires.

Anyway, on the more helpful side:
The plot I was talking about months ago was in an actual SAE paper, you should be able to find it in their library with a few quick searches. Remember, your advisor can request something like 25 papers per year.

The next question is:
Presumably you've been running this for a while now... Failures? Thrown shafts? Temperatures? Maybe everything's peachy? IE, is it working for you?

[Drew Price]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by wagemd:
Just realized that the perspective in this picture looks like you're running 18"x10" rims and even more enormous tires. </div></BLOCKQUOTE>



Maybe the photographer just has very small feet.


Someone from the CSUN team may correct me, but I believe this car was only driven for a few hours of testing, and did not run at competition. It was not driven again after that. It is going to be stripped for parts and won't be used, so I don't think they'll get any information about reliability or integrity of the design of this car.


Unfortunate.

[wagemd]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Maybe the photographer just has very small feet.


Someone from the CSUN team may correct me, but I believe this car was only driven for a few hours of testing, and did not run at competition. It was not driven again after that. It is going to be stripped for parts and won't be used, so I don't think they'll get any information about reliability or integrity of the design of this car. </div></BLOCKQUOTE>

I wondered, but didn't say anything... http://fsae.com/groupee_common/emoticons/icon_wink.gif

That's too bad. Were there some other big issues or why would it get stripped? A DNF is almost always better than a DNS... It looked like the damper could have been fixed with some creativity (through the halfshafts weren't going anywhere soon).

[Warpspeed]

I think most of us at one stage or another, have fabricated something, and then thought of how it could have been done much better.

Oh the joys of iterative fabrication.....

But as the sage once said "man, if you ain't improvin you'r dead".

[Tickers]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by Drew Price:
<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by Dunk Mckay:
We broke one when our chassis came unbolted from the engine and flexed a little too much. </div></BLOCKQUOTE>
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Yeah. Funnily enough, the car was never quite the same after that...

[Drew Price]

Haha, you don't say!