steering column design

[Hansel]

What other options are available besides using a universal joint for the steering column?

Go the gunners

[Hansel]

What other options are available besides using a universal joint for the steering column?

Go the gunners

[Andreas]

No joint at all.

Andreas

Chalmers University of Technology

[Hansel]

I should have explained our current scenario. We are currently mounting the rack on the "floor" of the car. Therefore we are using two shafts connected by the uni joint for the steering column.

Go the gunners

[James Waltman]

Rag joints. There aren't very elegant but they work. Most are probably too big for a FSAE car but I suppose you could make your own pretty easily.

What do you have against U-joints?

James Waltman
http://dot.etec.wwu.edu/fsae/
Vehicle Research Institute at
Western Washington University

[Matthew]

a gearset

-Matthew Hetler
hetl0020@umn.edu

[Hansel]

I don't really have anything against U joints I'm just looking at other options which could minimize the slack.

Go the gunners

[Kirk Feldkamp]

Maybe instead of a U-joint you could use an apex joint. It's essentially the same size piece, but it doesn't 'pulse' like the traditional U-joint does. They are also permanently oiled/sealed. We got ours locally, but I know that Aircraft Spruce sells them at a killer price.

Where's the slack? Rotational play in the shaft?

-Twig

[Hansel]

What do you mean by 'pulse'? The slack comes from the shafts and the pinion as well.

[Didier Beaudoin]

<BLOCKQUOTE class="ip-ubbcode-quote"><font size="-1">quote:</font><HR>Originally posted by Hansel:
What do you mean by 'pulse'? The slack comes from the shafts and the pinion as well. <HR></BLOCKQUOTE>

Hmm, I believe a better quality universal joint should do the trick then, because we don't have any slack in our steering, except a slight one because of the quick disconnect, and we are using a universal joint.

[MikeWaggoner at UW]

<BLOCKQUOTE class="ip-ubbcode-quote"><font size="-1">quote:</font><HR>Originally posted by Hansel:
What do you mean by 'pulse'? The slack comes from the shafts and the pinion as well. <HR></BLOCKQUOTE>

U-joints aren't constant velocity joints. At higher angles, there is a noticable angular velocity difference between input and output (fast slow fast slow = pulsing). That's why people usually use two (at the same angle), so that the shaft with relatively low inertia pulses in velocity, but the output drive remains constant.

That said, it's probably not signifigant in a steering system; people don't rotate fast and learn to adapt. Some car company was using 2 u joints 90 degrees apart in phase for a long time (doubling the pulsing) and nobody noticed for a few years.

[duckei]

Has anybody with adjustable steering had problems with the U-Joint angle?

[duckei]

Let me clarify: Adjustable steering column for ergonomics.

[Patrick]

I suspect that the use of U-joints would make adjustable steering much easier to implement. I guess one "problem" I could foresee is that as your range of adjustment caused higher mis-alignment angles in the U-joints, you may start to see this cyclic pulse. But as was mentioned above, this effect is probably so minute that the driver would never notice. In speaking about ergo, however, I've had conversations with some CU folks regarding the elimination of U-joints in their steering system. They claimed that driver feel was significantly improved by designing a steering system with no U-joints at all. Has anyone else experienced similar results?

-Patrick
RPI Alum
NASA - Jet Propulsion Laboratory

[Christopher Catto]

All University of Hertfordshire FSAE cars from 2005 have had the steering at the top, inline with the top wishbone. Although you can get good UJs and eliminate all play by using good components, we found that placing the steering at the top had many advantages. I hope future teams do not go back to "rack on the floor" designs just to move the weight lower.

The rack position and length and the steering arms on the uprights had the effect of making the steering nice and light, without detracting from the feel the driver needs for when the front tyres are losing grip.

[Patrick]

I thought future rules were going to mandate the rack be on the floor....

-Patrick
RPI Alum
NASA - Jet Propulsion Laboratory

[Steve O]

Steering rack on the floor decreases your moment arm between your KPI/centerline srub radius promoting driver feel without burning out your driver from the pavement fighting back. It also allows for better movement about the KPI as you will have more leverage on it due to force application angle vs king pin. Most books that go deep into suspension kinematics will tell you that a lower steering link balljoint position will give you better road feel with a lighter steer.

Steve

[Christopher Catto]

Steve. Welcome to the board http://fsae.com/groupee_common/emoticons/icon_smile.gif

good observation there about the moment arm. of course, this is quite important. I used the same explanation for having my toe link on the bottom wishbone for the rear suspension of a sportscar since i was worried about rear toe change that was making the car oversteer at high speeds during emergency manoeuvres (i mean double legal motorway speeds, and yes, we were quite crazy). Also because it fitted well with the packaging since the front wishbones were quite small.

I havent read anywhere in books about this though. Then again, i maybe don't own many traditional american books on racing (just some of Carroll's and the rest typically academic SAE books, the rest maybe more from europe). I d be interested to know if you find where exactly the info is written.

I know that many books explain the effect of steering rack in front or behind wheel axle but that is for production cars with elastomer bushes.

mathematically one might agree about the "lighter steer". however, practically i wonder (due to the addition of universal or other kinds of joints) how big the effect might be. its a statics/dynamics problem vs a physical/friction problem.

i think most teams should really do some back to back tests before making a decision. i read some great articles in Race Car Engineering about how people have made theoretical designs (like lowered the CG in some new LMP car putting dampers or other things in what i think is damn awkward locations). yet when I think about other cars (F1 even), i know that many sensible designers (including the crazy but great Gordon Murray believe it or not) give more priority to usable and practical designs which can save you weight once you develop them further (just like basic composite car vs evolved spaceframe when having the same expenditure). F1 cars now have steering on the top wishbone for aero reasons but dont doubt that they have also historically come to this design because of the beauty and simplicity of the design (straight carbon column, good upright design and stiffness etc).

anyway, i think it's great that teams do stuff different ways. makes it so much harder to design your winner. you just cant copy that much so it's more satisfying when you find something that works for you.

[DEAD_MAN]

Hey.....
We've designd our new steering system with all the geometries n stuff....But now our chassis team has requested us to... if possible lower the steering wheel position ie reduce the column length as they wanna get the front roll hop down by a couple of centimeters....
I just wanted to know what effect would it have on my column geometry(All the angles would remain the same..the only change would be the overall vertical length of the columns)...and the forces it would be transmitting...???

[The_Man]

Put it this way. Why would anything change?

You are just changing the length and position of the steering wheel. If you still turn the steering by a certain angle the pinion will turn by the same angle. So kinematically there should be no change. Why would the forces change by too much either? They will not unless you are changing the wheel radius.

[DEAD_MAN]

Thnkx a lot bro.....