Anti-Roll Bar [Torsion] Nm/deg --> N/m

[Carlos289]

I am an old man of 56 years.

I am not involved in the FSAE world but I follow as much as I can, to learn things about the dynamics of cars.
I have made a 3D design with [SW] in an Spanish Open forum a Lotus 7 replica, all the drawings are free for the members.
http://trackdaycars.freeforums...yecto-lcct-t624.html (http://trackdaycars.freeforums.org/faq-y-galeria-del-proyecto-lcct-t624.html)

I have learn a lot during the design.

At this moment I am using the OptimumG PDF's files to define the ARB and did put the information in an spread sheet so that the members can adjust to suit their corners weights.

But at the end I came to a problem.

I get the result of ARB twist of 2621 Nm/deg

Using other formula I can dimensioning the diameter of the ARB but the result of this formula is an spring parameter give in N/m


I am trying to design an ARB [Anti-roll bar]
- It has a "U" shape
- The short legs have a length o 0.1344 m
- Length between the legs is 0.840 m

So my question is:

How can I convert the Nm/deg to the N/m.

Sorry for my ignorance.
I wish I could seat on the school!

Thanks in advance for you time.
Regards,
Carlos

[Carlos289]

I am an old man of 56 years.

I am not involved in the FSAE world but I follow as much as I can, to learn things about the dynamics of cars.
I have made a 3D design with [SW] in an Spanish Open forum a Lotus 7 replica, all the drawings are free for the members.
http://trackdaycars.freeforums...yecto-lcct-t624.html (http://trackdaycars.freeforums.org/faq-y-galeria-del-proyecto-lcct-t624.html)

I have learn a lot during the design.

At this moment I am using the OptimumG PDF's files to define the ARB and did put the information in an spread sheet so that the members can adjust to suit their corners weights.

But at the end I came to a problem.

I get the result of ARB twist of 2621 Nm/deg

Using other formula I can dimensioning the diameter of the ARB but the result of this formula is an spring parameter give in N/m


I am trying to design an ARB [Anti-roll bar]
- It has a "U" shape
- The short legs have a length o 0.1344 m
- Length between the legs is 0.840 m

So my question is:

How can I convert the Nm/deg to the N/m.

Sorry for my ignorance.
I wish I could seat on the school!

Thanks in advance for you time.
Regards,
Carlos

[Tom W]

For each mm that your wheels move your anti roll bar will rotate by a certain amount, the force required to move the wheels by 1mm (and rotate the anti roll bar by whatever angle) will be the spring rate style of number in N/m, the torque required to rotate your anti-roll bar by 1 deg will be your Nm/deg number, this is the more useful number to specify a tube for your anti roll bar. The two will be related by whatever motion ratios exist between your wheel and anti-roll bar. A few free body diagrams should allow you to work out the relationships that you are chasing.

[Carlos289]

Hi Tom,
Thanks for your response!
Please allow me to be ignorant.
Lets say I am not convinced. If I understand you correctly it means that K[wheel] x MR[arb]^2 = K[arb]
If that is so simple, why is OptimumG making such calculations taking in account the K[tire] and the 5% magic number of the TLLTD.

I see it this way:
Weight transfer, generate a force at the wheel via the spring, etc. etc. and the ARB counteract in the other direction by a determined amount, that is dependent of the bar diameter, material and dimension of the ARB.

If the diameter of the bar has been selected the wrong way, we still, will have a K[arb] and it will moves according to the MR relation to the wheel, only we will not get the TLLTD that we expected.

OK I re-formulated the question,having calculated a Nm/deg of an ARB how should I calculate the diameter of the bar????

You mention:
<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">A few free body diagrams should allow you to work out the relationships that you are chasing. </div></BLOCKQUOTE>
I am sorry if I left the impression that I am looking for any relationship. That was not my idea.
I am trying to make my design the best that I can so that others people can enjoy a good balanced car.
You can see an information thread of our project at the Spanish forum with pictures of the design and from the real car that my son and other 30 people are building.
Lots of pictures, but the text is in Spanish, but you are smart enough to interpret the Google translations.
http://trackdaycars.freeforums...yecto-lcct-t624.html (http://trackdaycars.freeforums.org/faq-y-galeria-del-proyecto-lcct-t624.html)

[SNasello]

The roll stiffness distribution depends on the roll stiffness of the front axle/total roll stiffness, in Nm/deg. The TLLTD is based on the amount of load transfered on each axle, which will be affected by the tire stiffnss and frame stiffness. If you take these out of your calculation then you are looking at roll stiffness distribution, which will probably get you close.

To size the ARB, google search for torsional stiffness of a tube, or wikipedia torsion (mechanics).

[billywight]

Yikes!

www(DOT)cobratech(DOT)nl/BUILD/BUILD_LCCT481.JPEG

[Carlos289]

Hello!

I think that now I understand what you guys are telling me. [Sorry I am to slow]

The founded Nm/deg is the torque that should be used in a torsion formula.

I hope that this what I have done is right, can some one confirm [Please]

Knowing that my total ARB roll rate needed to increase the roll stiffness is [Nm/deg] and changing the radians to degrees, the torsion formula will look like this:

http://www.cobratech.nl/LCCT/D=ARB_01.JPG

Best regards,
Carlos

[Drew Price]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by billywight:
Yikes!

</div></BLOCKQUOTE>



I don't have a problem with it..... http://fsae.com/groupee_common/emoticons/icon_wink.gif


Carlos, I think you've basically got it. Just make it as adjustable as you can, it'll be the easiest and quickest way to tune your handling balance.


Drew

[Carlos289]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by Drew Price:

I don't have a problem with it..... http://fsae.com/groupee_common/emoticons/icon_wink.gif

Carlos, I think you've basically got it. Just make it as adjustable as you can, it'll be the easiest and quickest way to tune your handling balance.

Drew </div></BLOCKQUOTE>
Thanks for the replay.
It is a very low budget car [7500 euros] but with some old and thick anti-roll bar we will make a blade to have some adjustability.

I like your Saab project!

Regards,
Carlos