Hey guys,How do you adjust your fsae car's center of gravity?

[lcy1989]

I kown 2 ways now?
1. lengthen or shorten the pull/push rod
2.change the initial suppresses of the suspension spring


I don't kown whether these are right or not
please guys tell me more about this

many tks

[lcy1989]

I kown 2 ways now?
1. lengthen or shorten the pull/push rod
2.change the initial suppresses of the suspension spring


I don't kown whether these are right or not
please guys tell me more about this

many tks

[woodsy96]

Are you sure you don't mean ride height (the distance from the ground to the lowest point of the sprung mass(i.e. undertray, chassis))?

[lcy1989]

In my opinion,the ride height and the center of gravity are almost the same. Because you can easily adjust one to modify the other one


but want i'd like to know is how to adjust either one of them?

can anyone tell me??

[Mike Cook]

Oh, in that case, I would like to run my chassis underground please. Kthanksbye.


You should be running your car at the minimum ride height (1").

When you are adjusting your suspension, you usually don't want to preload your spring...So if you are trying to raise ride height, you don't want to keep jacking up the perches until the spring is preloaded. Spring preload takes away rebound travel. In general, you don't want to do this.

Usually, the best way to adjust ride height is with the pushrod. The reason you do it this way is because your bellcrank remains in the designed position. If you move the spring perch the BC moves and you might end up at a different spot on your wheel rate curve.

However, when testing, I will always adjust the spring perches, for two reasons. The adjustments are easier to make, and are easier to measure. Also, you can do the same adjustment to both wheels so you don't add any wedge to the car. Generally, after a test session, if we change the rake angle of the car a lot, I will go back and put the spring perches where they are suppose to be and change the pushrod length to compensate.

Mike

[GianVioli]

There is a big problem to adjust the CofG (itself) of a F-SAE car: The lack of minimun weight like in F1.

Since there is no limit for your cars weight you always try to make it as light as possible and we dont use ballast on the bottom of the car to reduce your CofG.

You do change your ride height according to your suspension system set-up (and the methods you said are correct) but not with the proper intention to reduce nor increase your CofG.

[Wesley]

I use a warp bubble set at factor 9 for maximum COG reduction.

[MalcolmG]

this is one of the methods we've used in the past

http://i3.photobucket.com/albums/y51/all4s/8329_159364017315_763677315_3607875.jpg

[JamesWolak]

I have seen teams with bell cranks that have two attachment points for the push/pull rods on their bell cranks so that they can quickly and dramatically adjust the ride height (ie CoG) of their car for the acceleration event. The placement of the attachment could affect your motion ratio though but for acceleration I don’t know how much that really matters.

[flavorPacket]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by JamesWolak:
I have seen teams with bell cranks that have two attachment points for the push/pull rods on their bell cranks so that they can quickly and dramatically adjust the ride height (ie CoG) of their car for the acceleration event. The placement of the attachment could affect your motion ratio though but for acceleration I don’t know how much that really matters. </div></BLOCKQUOTE>

Jamie, the motion ratio change is actually the primary reason for using that kind of bellcrank. Making the car softer in ride will help with traction more than a small increase in CG (for a typical FSAE car).

[DART-CG]

If you really mean adjustment of the CoG: Just use a simple undertray made of 20mm thick deuterated uranium sheet alloy with a density of 25 like F1 did some years ago http://fsae.com/groupee_common/emoticons/icon_smile.gif

Works fine if you only care about the CoG though http://fsae.com/groupee_common/emoticons/icon_wink.gif

[lcy1989]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by Mike Cook:
Oh, in that case, I would like to run my chassis underground please. Kthanksbye.


You should be running your car at the minimum ride height (1").

When you are adjusting your suspension, you usually don't want to preload your spring...So if you are trying to raise ride height, you don't want to keep jacking up the perches until the spring is preloaded. Spring preload takes away rebound travel. In general, you don't want to do this.

Usually, the best way to adjust ride height is with the pushrod. The reason you do it this way is because your bellcrank remains in the designed position. If you move the spring perch the BC moves and you might end up at a different spot on your wheel rate curve.

However, when testing, I will always adjust the spring perches, for two reasons. The adjustments are easier to make, and are easier to measure. Also, you can do the same adjustment to both wheels so you don't add any wedge to the car. Generally, after a test session, if we change the rake angle of the car a lot, I will go back and put the spring perches where they are suppose to be and change the pushrod length to compensate.

Mike </div></BLOCKQUOTE>


hi mike
I have something disunderstand to your reply.

when change the pushrod,how can u remain the bellcrank in the designed position?
ie,if you change the length of pushrod,the force affact on the spring should change accordingly. so the spring changes, and the bellcrank changes too. is that right?
or u just ignore the changes caused by this ?

[lcy1989]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by GianVioli:
There is a big problem to adjust the CofG (itself) of a F-SAE car: The lack of minimun weight like in F1.

Since there is no limit for your cars weight you always try to make it as light as possible and we dont use ballast on the bottom of the car to reduce your CofG.

what do you mean by the proper intention to change the cog?
can you tell me your method?
You do change your ride height according to your suspension system set-up (and the methods you said are correct) but not with the proper intention to reduce nor increase your CofG. </div></BLOCKQUOTE>

[lcy1989]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by DART-CG:
If you really mean adjustment of the CoG: Just use a simple undertray made of 20mm thick deuterated uranium sheet alloy with a density of 25 like F1 did some years ago http://fsae.com/groupee_common/emoticons/icon_smile.gif

Works fine if you only care about the CoG though http://fsae.com/groupee_common/emoticons/icon_wink.gif </div></BLOCKQUOTE>


come on man, who want to increase his own weight if he could keep a fitting body?

We actually don't want to add another weight on my car!

[lcy1989]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by flavorPacket:
<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by JamesWolak:
I have seen teams with bell cranks that have two attachment points for the push/pull rods on their bell cranks so that they can quickly and dramatically adjust the ride height (ie CoG) of their car for the acceleration event. The placement of the attachment could affect your motion ratio though but for acceleration I don’t know how much that really matters. </div></BLOCKQUOTE>

Jamie, the motion ratio change is actually the primary reason for using that kind of bellcrank. Making the car softer in ride will help with traction more than a small increase in CG (for a typical FSAE car). </div></BLOCKQUOTE>


can I understand like this:
the motion ratio actually relates to the suspension ratio(ie. the stickness of suspension)?

[lcy1989]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by MalcolmG:
this is one of the methods we've used in the past

http://i3.photobucket.com/albums/y51/all4s/8329_159364017315_763677315_3607875.jpg </div></BLOCKQUOTE>

sorry
I don't actually understand the pic you posted.
I can't see clearly how u change the cog.
can you explain it clearly,better with pic

thanks guy

[MalcolmG]

what you've got there is 20kg of steel bar bolted to the roll hoop. It changes the CoG height, if you don't understand how then give up.

[Mike Cook]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by lcy1989:


when change the pushrod,how can u remain the bellcrank in the designed position?
ie,if you change the length of pushrod,the force affact on the spring should change accordingly. so the spring changes, and the bellcrank changes too. is that right?
or u just ignore the changes caused by this ? </div></BLOCKQUOTE>

Icyhott,

Generally, when you change the pushrod length, you are doing so on the left and right side of the car (so that you jack the car up or down, without adding any cross weight (wedge)). If this is true, then changing the pushrod length doesn't change the load on the tire, which means the spring will not deflect any more or less.

[JamesWolak]

Damn Ryan. I had no idea that was why. I feel a little silly for thinking that now.

Icy, keep looking at MalcolmG's picture. I missed it the first time i looked at it because it looked like a part of the trailer. Look at what is attached to the roll hoop. Obviously Malcolm is joking around with you.

Edit:I didn't notice that Malcolm posted on this until after i posted. What is that attachement really for? Transporting the car?

[lcy1989]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by Mike Cook:
<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by lcy1989:


when change the pushrod,how can u remain the bellcrank in the designed position?
ie,if you change the length of pushrod,the force affact on the spring should change accordingly. so the spring changes, and the bellcrank changes too. is that right?
or u just ignore the changes caused by this ? </div></BLOCKQUOTE>

Icyhott,

Generally, when you change the pushrod length, you are doing so on the left and right side of the car (so that you jack the car up or down, without adding any cross weight (wedge)). If this is true, then changing the pushrod length doesn't change the load on the tire, which means the spring will not deflect any more or less. </div></BLOCKQUOTE>


but the angle between pushrod and bellcrank changes?which means the arm of force changes,and the load on tire is constant (I kown this),so the force of spring will have to change

[lcy1989]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by JamesWolak:
Damn Ryan. I had no idea that was why. I feel a little silly for thinking that now.

Icy, keep looking at MalcolmG's picture. I missed it the first time i looked at it because it looked like a part of the trailer. Look at what is attached to the roll hoop. Obviously Malcolm is joking around with you.

Edit:I didn't notice that Malcolm posted on this until after i posted. What is that attachement really for? Transporting the car? </div></BLOCKQUOTE>

I didn't understand the pic either. the trailer u thought is attached on the roll hoop,so the car is not suspended. I thingk Malcolm's pic is posted on the wrong place and has nothing to do with the topic.

what do you think ?

[MalcolmG]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by JamesWolak:
Edit:I didn't notice that Malcolm posted on this until after i posted. What is that attachement really for? Transporting the car? </div></BLOCKQUOTE>

We really used it to change the CoG height of the car, as part of a series of tests to establish the importance of CoG height and longitudinal location in different scenarios (slaloms, constant radius corners etc). We also used a 6mm thick steel undertray to lower CG, and a 20kg bucket of lead either on the front bulkhead or hanging off the diff to shift weight forward and back.

[Simon Dingle]

This reminds me of a discussion we had a few weeks ago about how high our CoG would need to be for the car to wheeley in the accel. event.

I can't remember the exact figure, it was something like 5kg on the end of an 18ft pole :s Disappointingly high

[JamesWolak]

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

We really used it to change the CoG height of the car, as part of a series of tests to establish the importance of CoG height and longitudinal location in different scenarios (slaloms, constant radius corners etc). We also used a 6mm thick steel undertray to lower CG, and a 20kg bucket of lead either on the front bulkhead or hanging off the diff to shift weight forward and back. </div></BLOCKQUOTE>

Wow. You guys from the down under don't mess around. I couldn't get my suspenion team to adjust their sway bars let alone have a DoE like that.

[lcy1989]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by MalcolmG:
<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by JamesWolak:
Edit:I didn't notice that Malcolm posted on this until after i posted. What is that attachement really for? Transporting the car? </div></BLOCKQUOTE>

We really used it to change the CoG height of the car, as part of a series of tests to establish the importance of CoG height and longitudinal location in different scenarios (slaloms, constant radius corners etc). We also used a 6mm thick steel undertray to lower CG, and a 20kg bucket of lead either on the front bulkhead or hanging off the diff to shift weight forward and back. </div></BLOCKQUOTE>


hey bro?MalcolmG
I think I can kown your idea now.what you did in the pic is your design stage?and what do you get from your test?
can you share your result with me?
you can gmail me: lcy111989@gmail.com
Be easy,Our team have no conflict with yours?

[MalcolmG]

I'm not going to share the intimate details of what we discovered, but I will say that CoG height was nowhere near as important as I thought it would be, which makes sense if you look at the load sensitivity of typical FSAE tyres (got TTC data?). Maybe this is why our 2009 car had only a 1m track width...

[lcy1989]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by MalcolmG:
I'm not going to share the intimate details of what we discovered, but I will say that CoG height was nowhere near as important as I thought it would be, which makes sense if you look at the load sensitivity of typical FSAE tyres (got TTC data?). Maybe this is why our 2009 car had only a 1m track width... </div></BLOCKQUOTE>

wwao you are still online?
isn't it too late?

but still thanks for reminding,

[Zac]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by MalcolmG:
I'm not going to share the intimate details of what we discovered, but I will say that CoG height was nowhere near as important as I thought it would be, which makes sense if you look at the load sensitivity of typical FSAE tyres (got TTC data?). Maybe this is why our 2009 car had only a 1m track width... </div></BLOCKQUOTE>

What was your wheel base?

[MalcolmG]

1.53m

[Kirby]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by JamesWolak:
Wow. You guys from the down under don't mess around. I couldn't get my suspenion team to adjust their sway bars let alone have a DoE like that. </div></BLOCKQUOTE>

I doubt very few people outside of their team have any comprehension of the sheer amount of data Auckland collect during testing and indeed competition (and not just on their car http://fsae.com/groupee_common/emoticons/icon_wink.gif )

On that topic: Malcolm, can you please forward me all your test reports for the last few years I would like to try and apply your very specific test data to my own car. hah.

[woodsy96]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by Kirby:
I doubt very few people outside of their team have any comprehension of the sheer amount of data Auckland collect during testing and indeed competition (and not just on their car http://fsae.com/groupee_common/emoticons/icon_wink.gif )
</div></BLOCKQUOTE>

You make us sound so much more awesome and organised than we actually are, Kirby.

You are right, though: we do gather data on other teams cars as well as our own. Some other teams may have noticed our "Timing Team" up on the hill, recording all of the lap times from endurance.

[MalcolmG]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by woodsy96:
<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by Kirby:
I doubt very few people outside of their team have any comprehension of the sheer amount of data Auckland collect during testing and indeed competition (and not just on their car http://fsae.com/groupee_common/emoticons/icon_wink.gif )
</div></BLOCKQUOTE>

You make us sound so much more awesome and organised than we actually are, Kirby.

You are right, though: we do gather data on other teams cars as well as our own. Some other teams may have noticed our "Timing Team" up on the hill, recording all of the lap times from endurance. </div></BLOCKQUOTE>
I was thinking that too, but I didn't want to make people realise that we were not awesome, damn you Paul!

[Kirby]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by MalcolmG:
<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by woodsy96:
<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by Kirby:
I doubt very few people outside of their team have any comprehension of the sheer amount of data Auckland collect during testing and indeed competition (and not just on their car http://fsae.com/groupee_common/emoticons/icon_wink.gif )
</div></BLOCKQUOTE>

You make us sound so much more awesome and organised than we actually are, Kirby.

You are right, though: we do gather data on other teams cars as well as our own. Some other teams may have noticed our "Timing Team" up on the hill, recording all of the lap times from endurance. </div></BLOCKQUOTE>
I was thinking that too, but I didn't want to make people realise that we were not awesome, damn you Paul! </div></BLOCKQUOTE>

I was allowed to rummage through your "filing cabinet" at comp last year...I was pretty impressed. Way more than I 'see' other teams doing.

[woodsy96]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by Kirby:
<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by MalcolmG:
<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by woodsy96:
<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by Kirby:
I doubt very few people outside of their team have any comprehension of the sheer amount of data Auckland collect during testing and indeed competition (and not just on their car http://fsae.com/groupee_common/emoticons/icon_wink.gif )
</div></BLOCKQUOTE>

You make us sound so much more awesome and organised than we actually are, Kirby.

You are right, though: we do gather data on other teams cars as well as our own. Some other teams may have noticed our "Timing Team" up on the hill, recording all of the lap times from endurance. </div></BLOCKQUOTE>
I was thinking that too, but I didn't want to make people realise that we were not awesome, damn you Paul! </div></BLOCKQUOTE>

I was allowed to rummage through your "filing cabinet" at comp last year...I was pretty impressed. Way more than I 'see' other teams doing. </div></BLOCKQUOTE>

Note to self: hide filing cabinet in Melbourne this year http://fsae.com/groupee_common/emoticons/icon_wink.gif

[benny41]

i hear geelong is a wonderful place to leave filing cabniets.......

[student_racing]

Hii mike, we are taking part in FSAE for the second time in this car we are looking forward to install inboard suspension system with a push rod bell-crank system.
if we change the push rod length do we have to change the spring mounting to have same spring characteristics ?
Will there be any change in the angle of bell crank and force transmitted to the spring and angle b/w push rod and bell crank?
Can you please direct us to a comprehensive technical paper which deals in detail about changing the ride heights in a push rod, bell-crank actuated inboard suspension system ?

Pritham
Camber Racing,
SRM University,
Chennai,INDIA

pritham.reddy9@gmail.com
www.camberracing.com (http://www.camberracing.com)
Can you
Is there any other methodology to change the ride height
<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by Mike Cook:
<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by lcy1989:


when change the pushrod,how can u remain the bellcrank in the designed position?
ie,if you change the length of pushrod,the force affact on the spring should change accordingly. so the spring changes, and the bellcrank changes too. is that right?
or u just ignore the changes caused by this ? </div></BLOCKQUOTE>

Icyhott,

Generally, when you change the pushrod length, you are doing so on the left and right side of the car (so that you jack the car up or down, without adding any cross weight (wedge)). If this is true, then changing the pushrod length doesn't change the load on the tire, which means the spring will not deflect any more or less. </div></BLOCKQUOTE>

[Dash]

I'll answer your question with Mike's words that you already quoted.


<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">
Generally, when you change the pushrod length, you are doing so on the left and right side of the car (so that you jack the car up or down, without adding any cross weight (wedge)). If this is true, then changing the pushrod length doesn't change the load on the tire, which means the spring will not deflect any more or less. </div></BLOCKQUOTE>


Unless you change the length of the pushrod a significant amount ( probably more than an inch ) it should act in the same way it always has.

[Crispy]

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

Can you please direct us to a comprehensive technical paper which deals in detail about changing the ride heights in a push rod, bell-crank actuated inboard suspension system ?

</div></BLOCKQUOTE>

I believe that the book "Hands-On Race Car Engineer" has a nice chapter on vehicle set up.