use of apex joint in steering column

[RikyTheRipster]

As our steering column cannot go straight from the wheel to the rack I am going to have to run it through an angle of 20-40 deg. I am thinking of using an apex joint from pegasus or aircraft spruce to do this as they have been recommended here.

What do ppl think?

Also whats the best way of mounting either end of the apex to the upper and lower steering column? Was thinking welding but if you need to take it apart for any reason would be tricky.

How about a split pin?
The column would sleeve onto the apex(or visa versa) and the pin would go through both the column and the apex. Would this give any play?

What do people think?

Thanks

[RikyTheRipster]

As our steering column cannot go straight from the wheel to the rack I am going to have to run it through an angle of 20-40 deg. I am thinking of using an apex joint from pegasus or aircraft spruce to do this as they have been recommended here.

What do ppl think?

Also whats the best way of mounting either end of the apex to the upper and lower steering column? Was thinking welding but if you need to take it apart for any reason would be tricky.

How about a split pin?
The column would sleeve onto the apex(or visa versa) and the pin would go through both the column and the apex. Would this give any play?

What do people think?

Thanks

[BStoney]

First off..here is a link to a previous thread on the topic of the APEX U-joints...

http://fsae.com/eve/forums/a/tpc/f/125607348/m/34310687911/r/ (http://fsae.com/eve/forums/a/tpc/f/125607348/m/34310687911/r/46510778911#46510778911)

We had used them for the past few cars, in a dual u-joint design. It tended to be difficult to make sure the joints were in the proper phase and also to make sure that the angle each U-joint was at was the same as the other...

DO NOT weld the U-joint on both sides, you'll just be asking for trouble. You can weld one side, but I recommend either pinning or bolting the joint to the column. Pinning would probably be best as there would be less slop in the system if done correctly.

Just make sure that when and if you are welding at all to the U-joint that you keep that sucker as cold as possible, meaning the joint itself. You'll tear up the internal lube and the thing will be essentially worthless.

Hope some of this gets you pointed in the right direction.

We went to an upper mounted rack for this year, so we're not messing around with the U-joints again.

[scotty young Taylor Race]

We stock the following sizes in an Apex joint
3/8''bore
1/2''bore
5/8''bore
3/4''bore
7/8''bore
It is best to put the joint in cold water when welding on it.This is what we do to the shift linkages when we build them for the formula cars.

Scotty
Taylor Race

[adrial]

We are using the pin for our new car, along with 2 apex joints.

One of them has a nut/bolt going through it so we can remove the rack/steering shaft from the car if need be.

I have not noticed that the pin or bolt produce any slop.

[RikyTheRipster]

When you say double apex joint i take it you mean one of these:
http://www.pegasusautoracing.com/Images/M/1490.JPG
Does it matter what lengths the upper and lower steering columns are?
I was just going to have a short upper column then the apex(as shown) then the lower column running straight into a steering column coupling with the coupling being welded to the column at one end and attached to the pinion at the other.
How does that sound?
Thanks

[Ben Beacock]

with only one u-joint, you will introduce a non linear relationship between steering wheel angle and rack travel which gets worse as the angle increases. By properly phasing two u-joints at the same angle, you can cancel this out and have a linear relationship again.

[BStoney]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by Ben Beacock:
with only one u-joint, you will introduce a non linear relationship between steering wheel angle and rack travel which gets worse as the angle increases. By properly phasing two u-joints at the same angle, you can cancel this out and have a linear relationship again. </div></BLOCKQUOTE>

You beat me to the punch Ben, well stated.

[RikyTheRipster]

Right so the one pictured is classified as a single uj. You know what the next question is going to be..........
where do I place/how do I setup the second joint in order to phase the two correctly?

Thanks again

[UTA racer rikki]

Riky,

I know that some comments have been made about running the two U-joints to cancel out the phase change, but I ask this to all drivers.

Do you even notice that there is a phase change??? Do you account for it when you're driving??? Is it something to worry about???

My answer, having driven both set ups is that you won't realize the difference (provided you orient the u joint correctly). On top of that, though they aren't insanely expensive, if you're trying to cut cost, use one u-joint if it does the job.

[Garlic]

How do you know if a driver feels the difference? Test back to back? That's the only way I see. Steering and tire feedback isn't exaclty a linear thing to begin with.

That said I tend to agree, it's not necessarily a terrible thing. Make sure you are aware of it but it doesn't mean it's bad. If you are rrunning two joints it would be a good idea tomake suree you aren't doubling the problem, but I wouldn't run 2 joints just to make sure the rotation is exact. That's more weight, more complexity, and more places for steering freeplay which is always bad.

Though it's a pain these joints are able to be dis-assembled and should be if you do any welding. This also allows welded joints on both ends if you like.

[UTA racer rikki]

Garlic,

You reinforce my point exactly. If you put it in the wrong orientation, the turn in on the car might be a little too quick, and hard to control. Other than that, I challenge anyone to go into a car blind and tell me the orientation of the U-joint, or if there is one or two.

As for welding, our welders here found some heat removing agent that they spread all around between the weld area and the rubber boot. You can't even feel the heat from a freshly welded part on the other side. Amazing stuff.

[BStoney]

Erick,
What's the "stuff" Denver is using down there? Just curious....

[Garlic]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by UTA racer rikki:
As for welding, our welders here found some heat removing agent that they spread all around between the weld area and the rubber boot. You can't even feel the heat from a freshly welded part on the other side. Amazing stuff. </div></BLOCKQUOTE>

We had welders too but they were the kind you plugged in the wall not the kind that spread stuff on parts for you! http://fsae.com/groupee_common/emoticons/icon_wink.gif

[Z]

Riky,

Non-linear steering ratio is OK. Many production cars now have it (via tapered pinion and "bent" rack). The idea is to have slow steering at "straight-ahead" and a faster ratio towards full lock. A single U-joint does it automatically (for less than 360 degree lock-to-lock), if you want it.

If using a single UJ one shaft has to be well supported by bearings at each end, and the other shaft should only have one bearing at the other end from the UJ (ie. only one bearing next to the UJ).

But why use UJ's at all? What's wrong with a steep steering shaft and almost horizontal steering wheel, like a go-kart or truck? Has anyone tested, and proved conclusively, that this makes for difficult or slow driving? Seems to work OK on go-karts. My bet is that this is another design decision that is based on nothing more than fashion - "err, real racecars have upright steering wheels, so we should too...".


Z

PS. A pin or bolt through tube/shaft might be ok for a few days of FSAE testing and comp, but in the long term it will develop slop.

[IsheeM]

Z,
Regarding the horizontal steering wheel, I hope you are joking. It is not good for ergomonics (depending on driver position in relationship to the steering wheel). I have discussed this with the appropriate people at work (Nissan), but I cant give away all my secrets. I dont have enough yet.

[Buckingham]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content"> PS. A pin or bolt through tube/shaft might be ok for a few days of FSAE testing and comp, but in the long term it will develop slop. </div></BLOCKQUOTE>

If you cut about an inch or so into the female tube with a good saw, the bolt will be able to clamp the tube and shaft together, creating a friction joint. Provided that the two shafts are closely toleranced, and that shaft you are trying to notch isn't hardened steel, this type of joint can be very effective.

[Z]

Michael,

Quote: ".. horizontal steering wheel... not good for ergonomics... I have discussed this with the appropriate people at work (Nissan)"

Yes, a completely horizontal steering wheel is a bit uncomfortable, but a wheel at about 45 degrees (like a go-kart) feels quite good to me. In fact, I reckon a 45deg wheel is easier than an upright one if you have very quick ratio steering. It works best if the wheel is just above your lap - not too high.

The old Mini's had ~45deg steering wheels and they worked ok. Quad-bikes have very quick ratio handlebars (&lt;90 deg lock-to-lock) working about an an axis of ~60 degrees. I know handlebars are not allowed in FSAE, but it is a similar action from the driver/rider.

I accept that Grandmother driving to church in her Nissan mightn't like a laid down steering wheel, but she's not going to be negotiating many 2G slaloms on the way. Well, then again...


Z

PS. Donavan,

Yep, that's the only way I've found to make them work, and they still get loose if you really load them.

[Moke]

Z,

The horizontal or 45deg steering wheel works on trucks, minis and go carts as the driver is sitting over the wheel, read approx 90deg back angle. A race car has a steeper angle as the driver is laying back say 45deg as with our car. A flat wheel won't provide the optimum mechanical advantage for "2G slaloms".

So this begs the question what are we making? Trucks or race cars?

[Z]

Moke,

Quote; "...what are we making? Trucks or race cars?"

So what are go-karts? Are you saying that they are NOT real racecars? The discussion on the "Design" thread suggested that go-karts, with about one third the horsepower of most FSAE cars (and a fraction of the cost), are about equally fast.

My point is that some team members are obviously finding an upright steering wheel a bit of a hassle - extra UJ's etc. So why do they complicate the linkage to get the upright wheel, rather than using a simpler straight shaft to a low-rear-rack and a ~45-60 degree (from horizontal) wheel?

The answer is not for any rational, measurable reason (say, based on back-to-back testing of lap times, etc.). Or, at least, I've yet to hear any compelling argument based on testing in FSAE conditions. The real reason is that an upright wheel is more fashionable! That sort of brainless stick-with-the-flock mentality is ok for sheep, or if you're in the dressmaking industry, but I don't think it is good engineering.

There are a lot of features on these FSAE "real racecars" that add nothing to speed, but add a lot to cost and weight, so ultimately slow the cars down. I realise that real motorsport is mostly about being fashionable, but as a design exercise I don't see this competition producing many "well thought out solutions" to the given problem - namely "design a fast and simple Autocross car" (Rule 1.2).


Z

[Ben Beacock]

one of the benefits of using a u-joint setup is the "no steering shaft through your chest in an accident" argument, although I bet it would be pretty hard for it to happen with a straight shaft anyways.

[Marshall Grice]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content"> So what are go-karts? Are you saying that they are NOT real racecars? The discussion on the "Design" thread suggested that go-karts, with about one third the horsepower of most FSAE cars (and a fraction of the cost), are about equally fast. </div></BLOCKQUOTE>

You missed the point. So before you get off on another rant about how we should be building shifter karts, pay attention. His point was not that a kart isn't a real race car it was that the seating position of a kart is more upright and much less limited in elbow room so a compromised steering wheel angle can be made to work. This not the case for all fsae cars, so you put the wheel where the driver can still turn it.

Our "fashionable" steering angle was determined by testing many different wheel angles on our mock chassis and finding the angle that provided and acceptable compromise for our drivers between linkage complexity and driver preference. Driver preference being the more heavily weighted factor. I'll take .24lbs of extra weight for a car that doesn't take a day to figure out how to steer.

[Charlie]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by Z:
So why do they complicate the linkage to get the upright wheel, rather than using a simpler straight shaft to a low-rear-rack and a ~45-60 degree (from horizontal) wheel?

The answer is not for any rational, measurable reason </div></BLOCKQUOTE>

Z, I'm tired of your ranting, but more tired of your continuous assumption that all FSAE team members are totally incompetent lemmings that are all about style ahead of function.

Enough already. You've never been to a competition as a competitor, and I haven't heard you say that you've been to one otherwise. You are going off internet assumptions which is a bad idea.

Please give these competitors the respect they deserve and quit acting like a God, please. You don't know what's going on behind the scenes.

Anyway, back to your topic, we built a car with a straight shaft, and the steering wheel was less than ideal (2003). It was a bit cumbersome but it worked, and definitely better than putting a joint in for a few degrees.

In 2004, we used joints. Guess why? Because with a bottom mounted rack, under the drivers knees, made it IMPOSSIBLE to do a straight shaft. Yes, we did CAD modeling, different driver placements, CG comparisons, all to arrive at the conclusion, which of course you think we were following the flock. Give me a break.

It's a freakin U-joint. Not hydraulic steering. It adds about a quarter pound, brackets and all.

[Moke]

Don't like ragging people out but:

Z

Since you like quoting the rule try 1.2, the idea is the cars are to be sold. It's simple, what sells?? Sex and if the car is not sex on wheels who will "buy" it.

Also try rule 2.1, then think about the 1000's of us doing this for real. (re: Charlie)

but anyway my point was that the driver's angle makes a flat wheel unsuitable.

Now that said I'm off to think happy thoughts and start design of our car.

[Mike T.]

Charlie, thanks for being the first to get at your points about Z. Its been a long time coming.

Z, I have read your articles in Race Car Engineering since finding out who you actually are after my first 'get off your high horse' comments, and am curious to know what functional race cars you have ever designed and manufactured form scratch. Care to answer? You seem to be firmly rooted in theory, and tend to base many of your comments and conclusions on it rather than actual testing/physically and specifically tested quantitative results. I've appreciated most of your input on these forums, as it is generally insightful, but coming back to these types of generalized condescending comments is out of line. Way out of line.

After having spent many, many hours and even years devoting much of my life to this project, it is irritating to me that someone with as much appearant racing intelect would make such sweeping and absurd generalizations, and be so sure of them based on 'I've yet to hear any compelling argument based on testing in FSAE conditions'. I'm sure I speak for many people out there in saying that the reason for this is that we don't really have the time to spare to detail all of our design decisions on an internet forum. Please, don't continue on with such ridiculous comments, and consider the fact that you may not know eveything there is to know about our designs and our competition, and what's best for it. I'll trust the many, many hours of testing preformed by hundreds of teams over the years over your 'gospel word'.

Mike Trumbore
UWFSAE 2003-??

[Z]

Marshall,

"Shifter karts"? No thanks. I'd rather not have gears. (FSAE is one of the few formulae that doesn't mandate gears.)
-----------------------

Charlie,

I have been to an FSAE event, and I am aware of what goes on behind the scenes (both in FSAE and wider motorsport).

Re: "acting like a God". If anything, I'm like the small boy shouting "the Emperor isn't wearing any clothes!". If you're tired of hearing that then perhaps you should have a lie down. Unlike you, I enjoy hearing other peoples unusual opinions, especially if they're well thought through and can be backed up with data. But I suppose yours is the only true faith? I notice that you are interested in being a judge - should give you a good opportunity to "act like a God" yourself, hey?

Anyway, if you think that a lot of the features on FSAE cars are NOT based on fashion, then you're dreaming. Maybe with time you'll realise how easily people can delude themselves. Or maybe not? (BTW, have they found those Iraqi WMDs yet?)
-----------------------

Moke,

Do you drive a Moke? I owned two of them (a good example of the British motor industry in free-fall, but they were fun).
----------------------------

Mike,

There are countless people writing race engineering articles based on their "practical experience". I write my articles based on numbers to provide some balance. If I get the maths wrong, then I have egg on my face. If someone gives you practical advice that doesn't work in your case, then "Hey, it worked for us, you must be doing something wrong...".

Do I have any practical experience? I've got plenty of callouses. I built my first V8 road going sports car, from the ground up, pretty much by myself, when I was a teenager (1970's). Since then I've built plenty of other stuff, including a few racecars. But one thing I've learnt in that time is that people who brag endlessly about their "extensive experience" are invariably covering up for a lack of ability. That's why I avoid doing that. I reckon that if the reasoning is good then the reputation is irrelevant.

Most of my "absurd generalizations" are actually questions along the lines of "Since you are finding your current design to be hard work, why don't you use another simpler method that works well in other forms of motorsport?" I think good engineers should be able to look at a problem from a broad perspective. But I'm seeing many closed minds on this forum.

Oh, and finally, regarding the "many, many hours and even years devoting much of my life to this project" - well, in a decade or three they're going to be "the good old days". I suggest you enjoy them as much as you can, while you can.


Z

[Denny Trimble]

Z,
Let me know when your sons build their first car, so I can harrass them about why it's not a brown go-kart.

[Charlie]

Z, I don't disagree much with your direction (simplicity), I do agree there is a lot in FSAE done for the wrong reasons. Certainly not as much as you do, but I agree it's there.

I disagree with your attitude about competitors. I take great insult when you say that if people don't do what you think is right, they must have no valid reasons, in fact, they must have a 'brainless stick-with-the-flock mentality!' That is not bringing sense into the equation it's pure lashing. Not something I see from people I respect.

[Mike T.]

Z, in response to your comments to charlie, there isn't anything wrong with 'other peoples unusual opinions', but if you think that is what you are bringining here with your insults, you are wrong. I think you are mistaking our comments towards you as attacks against the 'unusual' when they are not. All we're asking of you is to show a little more respect.

As for your comments about 'extensive experience', I agree. Reputation is irrelevant if there is solid reasoning behind what you are saying, but I don't see any reasoning behind your 'stick-with-the-flock mentality' comments. If these are questions, keep them in the form of questions and avoid the condescending tone. They are questions worth asking, I've got nothing wrong with that and am glad you ask them, but insults doing nothing to get your point across.

And trust me, I do enjoy them, otherwise I wouldn't be doing what I am doing. You get a hell of a sense of satisfaction seeing a car come together function like you've designed it to.

[Z]

Guys,

NO INSULTS WERE INTENDED!

The comment re: "stick-with-the-flock mentality" is a general one applying to all H. Sapiens. We are a gregarious, social, flock-like animal. Most people would rather die than be cast out of the flock. Very few people make a deliberate effort to "walk their own path", even if it leads to a better place - "What, go over to the other side of the hill to that lush green grass? Are you mad? I'm sticking with the flock and grazing on this gravel!"

Consider this. You ask one of your fellow students "Why did you get that ring/stud through your ear/nose/nipple/etc...? Is it the latest fashion? They answer "No way! I'm a free-thinker, a rebel! I'm expressing my individuality! Do you believe them???

Guys, I've been there myself (though no lip-studs, just other silly stuff - lots of silly stuff). Although thinking back, it is probably pointless for me to try to sway you away from that sort of thing...


Anyway, there have been many posts by students expressing how hard it is to build the "standard FSAE car". I have just tried to explain, in my usual tactful manner, that there are easier options. These easier options can give better engineering insight, and should ultimately be more enjoyable. If you think I've been harsh above, you should hear me coaching the local junior rugby league side! And the most important thing there is, again, TO HAVE FUN.

We are way off-topic. I stand by my comments that a ~45 degree steering wheel, on the right sort of FSAE car, would be no great handicap.

Z

PS. Denny, they'd use a tin of that chrome spray paint. It is easy to make a car look sexy.

[Underthefloor]

Unlike most people, I like to read and am not offended by what Z has to say. I think he has a point with his sheeple comments. I admit that most of the design I did on the drivetrain was just following the flock. There are worse things than doing what everyone else is doing.

Z, instead of "gravel" you should have said "slightly less lush green grass"

[UTA racer rikki]

Z,

To bring the topic of this conversation back to where it was to begin with, there is data backing up an upright steering wheel. It's not traditional math based equations or theory about what steering angle provides the optimum force vector output from the human arm, but it comes from countless hours of research. And this research was done by people who had Ergonomics in mind.

Why do you think that the Fighter Plane designers spend billions upon billions of dollars to figure out if a switch is close enough to flick without the pilot having to lean forward in his seat. We were able to speak with a gentleman that works for Lockheed in their Human Interaction department where all they do is set up tests to find out if a cockpit window has too much curvature that it distorts the pilot's vision. Is there an equation for that???

Before we even design our car, we do an ergonomic study to find out where our driver's want the steering wheel, shifter, and any other controls that are in the cockpit. There is a hell of a lot that goes into that planning. If a simple U-joint allows me to put the rack where I want it, at the angle I need it for mounting and get the steering wheel where driver's want it, I would be a fool to say, "We're following the flock on this one."

Furthermor, there are studies done, which we use for our design, that show the optimum angles for arms and wrists for controlled outputs and "comfort" when seated in various positions. What all of these guys/gals, my peers, are telling you is that we have considered all of this and have come up with the optimum solution. That is what engineering is, the optimum. If it were a perfect world, I wouldn't have a driver and I would program the track into the car. After all, the most unreliable part (inconsistent) is the loose nut behind the wheel.

Having said all of this, I do appreciate a fresh look at an FSAE car. And I appreciate the open and free rules that this competition brings to our imaginations. It does take people such as yourself to challenge the ideas and designs we use, but bear in mind, we do have data to back up our choices.

Pardon My Rant,

[Sam Zimmerman]

This is first I've read this thread. It is kind of funny, really.
I have preached simplicity in our designs for three years now, sometimes more successfully than others. Not coincidentally, our simplest car was our fastest car. It was also the easiest to drive. There needs to be a balance there.

Z seems to think that if it isn't on a kart, it is excessive. I think Z's thinking is seriously flawed. The area on any race car with the least sex appeal is ergonomics. I applaud anybody who doesn't just pay it lip service and then move on.

As far as a "correct" steering wheel position, exists in the same universe as a "correct" suspension geometry, driver position, intake design, etc., etc. Even when equations exist, they only guide us to possibilities and not definitive answers. I am quite sure neither the builders of karts nor FSAE cars have found the correct answer, but I have a pretty good guess which have put more research into the matter, and isn't that what we are really supposed to be doing here?

UTA and UMR cars have wings. Their cars go fast. Therefore FSAE cars with wings are faster than those without. http://fsae.com/groupee_common/emoticons/icon_rolleyes.gif

[Kevin Hayward]

Ergonomics of the driver has definitely become a primary concern within our team. When all is said and done in a FSAE car it is the ability of the driver to get the most out of a car that determines a winning car or not. Countless simiulations will show that there is very little in the design of the cars that account for some of the time differences seen between different drivers.

In studying ergonomics and trying to make each of our drivers fit well within the car has thrown up a few surprises. First despite the fact that our driving team is almost exactly the same height (freaky actually) the different limb proportions cause havoc with designing the car. Most people would be aware that there is no such thing as an "average" person. We found that drivers were particularly sensitive to steering wheel position in their ability to control the vehicle. Both the angle of the wheel and the distance from the driver ended up being very important.

In our first couple of cars we had an adjustable pedal box. Now we have simple stationary pedals and an adjustable steering wheel. The adjustable steering wheel was much easier to design and build than the pedal box. So the car has got simpler overall but much more suited to our drivers.

I would imagine that in order to achieve the steering position that Z suggests the whole car would have to designed a certain way. Notably with a lot more elbow room than most FSAE cars. Which in turn affects the chassis construction. The driver would have to be more upright. Roll hoops would have to be taller. In fact the extra weight of the roll-hoops would probably exceed the weight of the UJ assembly. Admittedly the complexity would be less.

Cheers,

Kev