Steering Geometry

[potter]

hey guyz...i've recently commenced my work on the steering system and i've to design a steering which is amply suited for our formula race car. So can u plz tell me something about the steering geometry which could be of some help to me in designing the steering.

[Mehul Botadra]

Yea, make sure that when the driver turns the steering wheel, the wheels turn as well! http://fsae.com/groupee_common/emoticons/icon_cool.gif

[The AFX Master]

I ought to add....

In the same direction would be useful

[BillCobb]

Not necessesarily, some drivers hold the wheel at the bottom to reduce net aero drag. This also helps them when backing up the trailer.

[The AFX Master]

A while ago i´ve read an article where a bunch of lab coats tested a driver with an inverted steering rack...

Since steering is largely a force controlled thing (instead of a position controlled), the driver had no problems at all to adapt. Obviously, almost got killed way home in his "too-lame-and-conventional" car :P

[Mehul Botadra]

Hahaha! Last year the manufacturing guys made the whole rack and pinion housing inverted which made the wheels turn in the opposite direction!

We did think it was a good idea to test the driver's concentration and confidence! :P

[MegaDeath]

Our suspension leader was "cure time" away from bonding the custom rack I manufactured this year into our car upside down, which thus would have made the car opposite steer. Luckily I caught it less than an hour into cure. I thought it was hilarious, he didn't.

[Adambomb]

I must admit, one year I developed dyslexia and set the car up with an inverted rack. We thought it was pretty hilarious. Luckily it was a pretty standard system so all we had to do was un-bolt it and flip it over. At that point we decided we would be better off just calling it a night and getting some beers.

[The AFX Master]

Seriously guys..

Is there anyone who did not put the rack inverted??.. We did too, couple of times, out of pure exhaustion and being bumpsteer "that last s&$)= i don´t want to check"

@MegaDeath

Awesome, didn´t know a rack could be bonded in place.. What if you break the thing?, do you replace internals or something?

[MegaDeath]

The rack is removable from the car. Just the mounts on the rack that bolt to the frame are bonded to the rack.

[Dash]

We definitely did this in 2009. After not sleeping for like two days straight I started putting the steering system together at like 4 in the morning. Once I got it done I decided pretending to drive the car was the next best thing. I think I died a little on the inside when the wheels turned the wrong way. Since I've made sure to check several times to not do that again.

[Mehul Botadra]

@ Megadeath

More details please. What kind of glue was it?

I tried bonding it this year using some grade of Araldite. It did turn. But after 3 lock to locks, the bond broke and the housing started moving instead of the wheels! :P

[MegaDeath]

We use Hysol 9396. There are better glues out there, but we did testing to find the proper clearance that was suitable for that application. The clearance is very very critical. If you can't get the clearance correct, don't even bother with it.

[Mehul Botadra]

Clearance as in?

[Chapo]

In 09 we did the backwards rack thing too. It was late at night and we finally got the rack in. One of the other senior guys were stoked that the wheels were turning, then one of the first years pipes up "ummm guys, I think something is wrong...." (insert awkward turtle here)

[MegaDeath]

Originally posted by Mehul Botadra:
Clearance as in?

The distance between the two surfaces being bonded. For example, if it's two circular parts being bonded, the difference in diameters of the bonded surfaces.

[rmk36]

You mean this kind of clearance?

http://www.fruitmachineworld.com/ekmps/shops/darrenlink/resources/Design/clearance-sale-yellow.jpg

[Mehul Botadra]

Originally posted by rmk36:
You mean this kind of clearance?

http://www.fruitmachineworld.com/ekmps/shops/darrenlink/resources/Design/clearance-sale-yellow.jpg


Lame.


@ Megadeath
Any idea about the ball park figures?
We had two circular surfaces with the same diameter! So I'm guessing the clearance is in microns. Will check though anyway.

[MegaDeath]

Originally posted by Mehul Botadra:


@ Megadeath
Any idea about the ball park figures?
We had two circular surfaces with the same diameter! So I'm guessing the clearance is in microns. Will check though anyway.

I won't tell you the figures that we came up with through our testing, but I will tell you that 0 clearance is not one of them. http://fsae.com/groupee_common/emoticons/icon_smile.gif

[Adambomb]

Yeah, I can imagine clearance being really touchy. As far as having a close-tolerance item split in half, I can think of the problem being similar to that of a con rod cap.

[Adambomb]

Scratch that...more like a main cap, since you've got a couple circles that also need to be concentric.

[Mehul Botadra]

@ Megadeath

Doesnt it depend a lot on bond area too?

[MegaDeath]

The total strength of the bond, yes. If you're asking if the clearance depends on the total area, I would have to think it doesn't, but I could be wrong. But to me it wouldn't seem to make any sense that it would change it.

[Adambomb]

Plus I believe some glues have a tendency to shrink when they cure...

[Rotary Sprocket]

Originally posted by Adambomb:
Plus I believe some glues have a tendency to shrink when they cure...

This is more of an issue if the epoxy is cured at an elevated temperature but the main problem is with the bonded components. Once cured the epoxy won't change shape much, but the metal that is being bonded will shrink as it returns to room temperature causing cracks to form in the epoxy especially if the temperature change is fast. Controlling how quickly the parts cool down will reduce the severity of this problem.