steering effort

[MSA]

I want to calculate the torques and forces applied to steering system from wheels to find out how much torques our drivers should apply to steering wheel to turn it(steering effort).And I want it to design shafts and tie rods and etc.but I havent found any equations about it.can anybody tell me some information about it .where I can find these equations?
And I want to know what is the range of steering effort in your cars?

[MSA]

I want to calculate the torques and forces applied to steering system from wheels to find out how much torques our drivers should apply to steering wheel to turn it(steering effort).And I want it to design shafts and tie rods and etc.but I havent found any equations about it.can anybody tell me some information about it .where I can find these equations?
And I want to know what is the range of steering effort in your cars?

[kwancho]

Look at aligning moments in your tire data, and then back calculate through your steering ratio.

[markocosic]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">I want to calculate the torques and forces applied to steering system from wheels to find out how much torques our drivers should apply to steering wheel to turn it(steering effort).And I want it to design shafts and tie rods and etc.but I havent found any equations about it.can anybody tell me some information about it .where I can find these equations? </div></BLOCKQUOTE>

Numerically it's all classical physics/mechanics 101:

http://www.vectorsite.net/tpecp.html

The best text ever written on the subject:

http://en.wikipedia.org/wiki/The_Feynman_Lectures_on_Physics

Fill gaps with assumptions in the abscence of data, but keep track of which ones you make/why and try to tally wiht existing data as you are doing:

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">And I want to know what is the range of steering effort in your cars? </div></BLOCKQUOTE>

[Jersey Tom]

You want the suspension/tires to give enough force feedback to the driver that he can feel out the car's grip, but not so high that its a full body workout every lap.

You tell me. Figure out roughly how many footpounds of torque you want the driver to be resisting mid-corner.. take a look at self-aligning torque from the tires and how much additional resistance you need from mechanical trail.

Of course you'll have to kind of guess how much the footprint moves around from lateral and longitudinal tire stiffness.. and good luck with that.. but it'll get you in the ballpark.

[MSA]

hi tom .The problem is that I dont have any tire data and also I dont know how much torques is reasonable!It is our first car and I have recently started studing about steering.can you help me what I should do ?can you tell me some useful web sources?I dont know what is the procedure of steering design!

[ad]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by MSA:
hi tom .The problem is that I dont have any tire data and also I dont know how much torques is reasonable!It is our first car and I have recently started studing about steering.can you help me what I should do ?can you tell me some useful web sources?I dont know what is the procedure of steering design! </div></BLOCKQUOTE>

I'd be guessing RESEARCH, im entering this field myself (i.e. steering design) and im going to start by reading books, searching web, critique other designs, and physical testing http://fsae.com/groupee_common/emoticons/icon_smile.gif

sorry thats all i got...

[JHarshbarger]

You can get tire data by donating to the Tire Testing Consortium (TTC). Search for it on here and you find the links to it.

If you want to find out what forces are reasonable, create a testing rig, do some calculations, and VIOLA, your very own personalized steering force preferences.

[Jersey Tom]

Whether you buy it or not is up to you and your financial situation, but buying into the $500 tire test data is one of the best and most educational investments you could make.

[Marshall Grice]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Of course you'll have to kind of guess how much the footprint moves around from lateral and longitudinal tire stiffness.. and good luck with that.. but it'll get you in the ballpark. </div></BLOCKQUOTE>

now correct me if i'm wrong, but doesn't the moment data for the tire tell you exactly where the contact patch has moved too?

[Jersey Tom]

Does it? To be honest the self-aligning moment data I haven't really looked at, I spent all my analysis time on lateral and longitudinal modeling.

The moment data tells you how much the tire wants to right itself just from the nature of the elastomer having being squashed down and rotated.. independent of the aligning torque created by mechanical trail and lateral force. Knowing lateral and longitudinal sidewall stiffness at varying loads and pressures is well beyond me or anything I've seen from the TTC data.

[Kurt Bilinski]

I built a mid-engine Mini, 1800lbs loaded, 40/60 weight distribution, and the steering effort is really light. I can't imagine how you'd have tiresome steering in a vehicle that's 30% my weight. Granted you're on really sticky tires, but still.

Are you asking because you want to make sure the driver doesn't tire out, because the design judges expect you to know, or because you need the numbers to determine suitably strong pivots and brackets? Regardless, I thought tire data was free to you guys.

[Kirk Feldkamp]

Free? Nope. Last time I checked the available tire data was $500 per team.

[MSA]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by kb58:
I built a mid-engine Mini, 1800lbs loaded, 40/60 weight distribution, and the steering effort is really light. I can't imagine how you'd have tiresome steering in a vehicle that's 30% my weight. Granted you're on really sticky tires, but still.

Are you asking because you want to make sure the driver doesn't tire out, because the design judges expect you to know, or because you need the numbers to determine suitably strong pivots and brackets? Regardless, I thought tire data was free to you guys. </div></BLOCKQUOTE>
I want these informations to make sure the driver doesnt tire out and also the design judges expect us to know and i wnat to make sure the shafts and other parts are strong enough.these are more important for me because I want to use kart steering system not rack &pinion.And I think in this system steering effort is higher .

[John Valerio]

kart steering...interesting. i always wondered how a go-kart mentality fsae car would do at comp. on this particular issue though you have to be careful because go karts don't have any suspension travel. we need at least 2" so you will probably run into some major pro/digressive (yikes) bump steer problems due to the cantilever on the steering column karts use to actuate the tie rods (since they pivot on a shaft the inboard pivots sweep up and down...goodbye instant centres). and also as you steer through the range of motion your effort is going to change dramatically as you approach the "inversion of a four bar linkage" on the column. i think it will be really hard, if not impossible to satisfy all system requirements, that is:
a) enough steering lock
b) acceptable (LOW) amounts of bump steer
c) linear (and acceptable levels of) steering effort

also you're asking about shaft (tie rod) design. look in any static physics textbook and it takes 2 equations and 5 minutes once you know the forces involved to calculate if your tie rods will buckle (key word here).

and as far as the judges go, if you go outside the box on any design you really need to back yourself up, especially when you're not really saving huge amounts of weight or getting any other big advantages.

[PatClarke]

MSA,
If your intent is to use a kart style steering system, the smartest thing you have done is to ask on here.

Over the years there have been many cars at FSAE/FS with kart steering so it is nothing new.
Considering the low cost, simplicity and lightness in such a system, have you asked yourself why the fast guys don't use it?

I suggest you get hold of a kart and carefully analyse the steering geometry in ALL planes. Then do the same thing with a standard FSAE car. Keep in mind what the wheel weights are on the two different cars.
Keep safe
Pat

PS, Read carefully what John had to say in the previous post.

[Ashley Denmead]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by kb58:
I built a mid-engine Mini, 1800lbs loaded, 40/60 weight distribution, and the steering effort is really light. I can't imagine how you'd have tiresome steering in a vehicle that's 30% my weight. Granted you're on really sticky tires, but still.

Are you asking because you want to make sure the driver doesn't tire out, because the design judges expect you to know, or because you need the numbers to determine suitably strong pivots and brackets? Regardless, I thought tire data was free to you guys. </div></BLOCKQUOTE>

kb58, our little open wheel race cars are quite different to your mini. due to the course constraints it is advantageous to go to full lock with just 90deg of steering wheel rotation, add this to a fair whack of caster, sticky tyres and the fact that the driver is lying on his back without as much leverage on the steering wheel (also small) and the steering can become quite a handful quite quickly! From experience, make sure your tie rods are as straight as possible to the upright to minimise force vector losses. If your going for a kart style car....remember that having no diff will also significantly increase steering efforts!

Well said pat, we had similar thoughts back in 2004 but after thinking about the compromises introduced to the system as a result....the idea was quickly trashed!

Ash

[Jersey Tom]

Putting in a very large mechanical trail or having a very soft construction can make steering effort herculean on steady state cornering or combined braking and cornering, kb. You can have as much or as little force feedback as you'd like.

[Marvel]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by Pradeep Jadhav:
Scrub radius is crucial part in steering design. more the steering force require if the scrub radius is high. also wheel get toe-in or toe-out at breaking or acceleration due to scrub radius. causes the tension or comp. of tie rod. </div></BLOCKQUOTE>
More than that, I think it largely depends upon the position of tie rod and rack with respect to wheel center line.That is, front steer or rear steer.
(Someone please correct me, if it is wrong.. http://fsae.com/groupee_common/emoticons/icon_eek.gif )