Steering Geometry, Fore of Aft Rack position/ Steering arm length

[mohamedabolezz]

Hello,

Currently, I'm working on our steering geometry.

I assumed the turning radius to be 3.5 m ( the min Radius in the autocross) then i calculated turn angle of the wheel on the inside of the turn and then Rack travel.

Here are the results:

maximum turn θi 28.99138701 deg
steering wheel movement 180
Steering Ratio S.R 6.208740546
Steering Wheel Radius r 130 mm
The steering wheel travel for one complete rotation 817.1428571 mm
Rack travel L 131.6116934 mm

I Need to know are these results reasonable for a FSAE Racing Car?


Also, I need to apply 80% Ackerman and i need to know how to measure the steering arm length and also need to know which is better fore or aft rack position?

Thanks in advance,
.................................................. ...............

[BillCobb]

The required steer arm length will depend on the steering gear's effective pinion radius (presuming you will use a R&P gear). The S.R. is (for all practical purposes) the ratio of the steer arm length to the pinion radius. Now go figure.

As far as leading or trailing tie rods, ask yourself whether it is better to pull on a chain or push on one. (and why this analogy applies).

Hopefully your Ackermann fraction was determined by taking into consideration the properties of the tire you have selected as well as the minimum turn radius requirement.

[Claude Rouelle]

Mohamed,

maximum turn θi 28.99138701 deg
Steering Ratio S.R 6.208740546
The steering wheel travel for one complete rotation 817.1428571 mm
Rack travel L 131.6116934 mm

You just made a classical mistake that irritates design judges. At least it irritates me: do you need that many digits after the "."?

One more comment: make sure you calculate the steering torque. It is an usual other FS mistake. Try to stay under 5 Nm. On passenger cars the maximum steering torque at the wheel is about 3 Nm.

[Z]

Claude,

Thank you for that. I wanted to say the same, but have only just stopped banging my head on the wall. How anyone could spend all that time typing in all those numbers, and not see the STUPIDITY of it, is beyond me!
~o0o~

Mohamed,

Do you realize how expensive it would be to manufacture a rack to 0.1 NANOMETRE PRECISION? Is that even possible???

So please enter a new post with sensible numbers.

Also, what do you mean by "turning radius"? Is it from corner-centre to car-CG? Or to inner-wheel? Or to outside of outermost-wheel (= "between curbs")? Or "between walls"?

And what is your definition of "Ackermann"?

Z

[BillCobb]

You ought to know that your value for Pi is low, too. Try 4*atan(1) in your spreadsheet instead of 3.14285714269231 that your pasted values indicate.