I am working on a set of sway bars for the Temple formula SAE car. I have found some calculations for the torsion rate (strength) of the bar. But i am unsure what numbers i should be shooting for when using the calculation. Our car weighs roughly 500lbs. If anyone has autocad i can send them the drawing of the car if that would help.
The calculation i have is: R=5e6 x D^4 / (0.4244 x A^2 x L + 0.2264 B^3)

R = Torsion Strength of bar
D = Bar Diameter
A = Effective Length of Lever
L = Length of bar
B = Length of lever arm

i found this on http://www.swedishbricks.net/faq/swaybars.html
ive also been too http://www.mercurycapri.com/te....html

Basically i am a little lost on how i begin to fab these and determine the length, angles, and diameters i need for my car. Any help would be greatly appreciated.

 

I got AutoCAD 05...

but, unfortunately i have no effing clue what the hell your tryin to do.

 

i need to build some sway bars for the car. but i dont jst wanna use some random diamtere bar and just throw some random bends in the bar that work. this is for SAE and my Automotive Design project, so i need to backup my design with some calculations

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by RE- v8killa121 &raquo;</TD></TR><TR><TD CLASS="quote">I got AutoCAD 05...
but, unfortunately i have no effing clue what the hell your tryin to do.</TD></TR></TABLE>

would you like a copy of the cad file? if so pm me.

 

bump for help

 

Thanks to chrisw85, i talked to some people at suspension.com. They told me to use 4150, 8150 tempered steel for the sway bars. Mild steel does not have to stiffness and spring sway bars need (thou some companys still use mild steel). Does anyone know where i can get some of this steel, or have any info on working with it?

once again any help will be greatly appreciated

 

I think that might also be known as "tool" grade steel. Out here in Cali we have some pretty good metal yards, might be able to find them on the web and they probably ship. Check out Industrial metal supply (IMS) they are pretty big. Id google for other metal supply companies id bet money theirs something local to you.

 

I can try asking some of the SAE guys at my school. I think they did pretty good in 05, something like 4th overall and 2nd in design. I don't know how forthcoming they will be on information though (it is a competition after all).

What I can tell you is stop using autocad and get into a good 3D package. Autocad is more or less useless for such things. 3D allows you to then put your design in some good simulation and FEA packages and really figure out what is going on. All the teams in my school; solar car, mini baha, snowmobile, concrete toboggan, SAE..etc, use 3D. The other thing is get in the text books. There are probably a dozen text books in your library that talk in part about sway bar design and what all the numbers and calculations mean.

Cheers and good luck with your car.

 

thank you, as always any help will be appreciated.

I have tried searching our engineering library, and it turned up nothing unfortunatly.

 

yeah, good point.
i've been using autocad since i was a sophmore in highschool (01) and know how to draw in 3d pretty damn good on it, and i've used solidworks for one semester... it was so much better than autocad for 3d drawings

 

AutoCad for 3D is like taking your tricycle to the dirt bike track. So ******* hopeless. AutoCad is good for 2D but that's about it. Right now must industries work in 3D. Solidworks is very easy to learn. Just go through the tutorial and you should have it down in less than a day. The advantage is that a 3D package is like any other. Once you learn one you can pretty much use them all.

Even if you don't learn it for school learn it so that you can walk into a job interview and you know it that way you can get hired.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by old man neri &raquo;</TD></TR><TR><TD CLASS="quote">AutoCad for 3D is like taking your tricycle to the dirt bike track. So ******* hopeless... </TD></TR></TABLE>

yup, 'cept for people that know how to use it real good

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by RE- v8killa121 &raquo;</TD></TR><TR><TD CLASS="quote">

yup, 'cept for people that know how to use it real good </TD></TR></TABLE>

Sadly no. You can't input it into most other softwares (i.e. FEA packages and machine shops) Even if you are a real pro it just takes more time and you can't make modifications as easily.

AutoCad was/is great for 2D applications such as floor layouts and what not. But if you need 3D get a 3D package, that's my 0.02

 

ahmm... u win
i'm too lazy to argue..

 

well i think tongiht i am going to definetly look for a legal :: shift eyes :: copy of solidworks.

Anyone got any help with the equations. even a break down of the variables would be helpful. from what ive gatherd/guessed the effective lever arm is the part of the arm (bar) that isnt held down via the bushings to the frame. so the part of the sway bar that runs from the bushing to the control arm or whatever point i fasten it at is the effective length lever (A)? making the whole bar length the length of bar (L), but then theres the length of the lever arm (B), thats where i get lost. What makes a lever arm effective compared to regular arm length?

thanks for the autocad to solidworks advice

 

Ditch solidworks and get inventor, I think it's the best autodesk software i've used yet.

Also.. you can always ask Dr. Cohen, Basu, or Alaways which would be your most direct route

 

I would like to know this as well.

If you have no sway bars your controls move as much as the spring/dampers allow them to or as far as your vehicle pitches while on the course. You can figure out the g forces depending on the corners you are taking/pitch of the road/speed of the vehicle.
When you add the sway bar one side of the car limits the movement of the other side of the cars spring/damper.
Before getting into torsion, you don't have to design it to use torsion because it can done with a bar in compression.
Just to review torsion on a cylindrical component is similar to a spring with a very high spring rate which defines a force that is a torque around an axis. Also the movement is not very linear.
Well I will try to calculate it for you but you need to know the weight (its given as 500lbs) the cg (center of gravity). Forces will then be determined by the speed your running on the road course at a given point. (the straightaway)
The horizontal distance from the center of gravity to the point on the control arm or hub where the bar will be bolted.
This force can be used to calculate the torsion strength R that you are looking for. You can then get the diameter of the bar from the material you are using and the space you have to mount the bar for the "effective length" you are referring too. You can also tune your car to understeer or oversteer in this way.

cliffs:
Get the cg
the speed
weight
distance from the cg to the hub or sway mounting point
force can be found and your torsion can be tuned for your vehicles driving characteristic, i.e. oversteer
I will try to calculate it with this data.

 

thanks a lot, ive gotten a lil help with the effective length from some physics guys. i will get that data as soon as i can.

 

 

well the bar has been pushed back to next comps car. we are a little behind right now, we actually havent even driven it yet. we had some(alot) of wiring issues. So when i am able to drive the car and get speed, handling numbers i will post them. thanks to everyone for the help

 

Ok well if anyone is actually watching this, lol i have some updates. after combing through web sites, physics books, and making a few calls. here is what i have.

When designing a sway bar, their are some key variables to look at (refering to the previously stated equation). Diameter and A (effective lever arm length). Diameter is the crucial one. In the equation for strength (R), diameter is in the numerator, thus as the diameter increases so does the strength. since it is harder for the quotient to reach zero; zero being fragile and unusable.

another equation to look at it the Torsional Twist equation

TT(torsional twist) = (2xTorque)x(Length) / (PxDiameter^4xmaterial modulus)

In this equation diameter is in the denominator. thus, as the diamter increases the quotent approaches zero, and zero in this case is no torsional twist at all.

So, diameter is extremly critical. in order to determine how much stiffer your newly built/bought bar is over the existing bar is very easy. simply take:

(New Diameter^4 / Old Diameter^4) = %stiffer over old bar

ex. Old bar = 15^4mm New = 16.5^4mm
16.5^4/15^4 = 1.46
= 46% stiffer
*an increase of almost a half by adding 1.5mm
*add one mm more and the increase becomes 85% over original

Coming back to (A) the effective lever arm length, this is in the denominator of the strength equation. so we want to keep it as small as possible. This length is essentially the hypotnuse of a triangle drawn from the center of the bar to the end of the bend to the end of the link. A 90 degree bend is ideal, but space constraints make this almost impossible. so keeping the bend in the bar closest to 90 degrees is ideal for the strength of the bar.

-If anyone is interested in a copy of my paper, let me know. i will have it completed fully in a few days.
-Deoexmacchina i will have those numbers for you in a week or two.
-if anyone has any input or anything let me know

 

yeah i am watching.
Do you have any drawings of what you are referring to when you say the shape is not 90 degrees?
Post up a pic from your solidworks models or whatever you have. Keep it up.

 

i am going to have the drawings and the paper done sometime this weekend.

When i say not 90 degrees i mean ideally u want this shape |_____| for a sway bar, in
application this does not work so well. so trpically you get something that looks like this
\____/ , sometimes with even more bends or a varying angle.

 

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Hey I am interested with your work, could you please send me your workings to pranavjb@gmail.com. I am currently stuck with the calculation of forces acting and how to get the corresponding torsion rate

 

I bet he watches all his nine year old posts like a hawk...