spring rate

[lafayette college fsae]

We are currently running risse racing shocks 200 up front and 300lb/in in the rear. there is much slop in the spring and we wanted to bump up the the spring rates to 350 and 400 front and rear respectively. The car is 1100 lbs w/ driver (180lb driver), we're using hoosier tires 20.5X7X13 and we have a install ratio of 1.225. Millikin specificies 200/300 front/rear, but the car doesn't like these rate. can anyone help, thanks

[kwancho]

Did the other 4 responses not cut it for you?

[lafayette college fsae]

i dont think that is an answer to the question at hand, I reposted to help people better understand what i was asking. NO IT DIDNT IT "CUT" IF FOR ME.

[pengulns2001]

theres no such thing as "slop" in a spring, what problems are you having? car bottoming out? to much lateral weight transfer? your springs seem like they should be stiff enough as is so your going to have to be more specific, not to sound like an asshole but how confident are you that your suspension guy got your motion ratio right?

[kwancho]

Well... in that case, it depends on a lot of things. First of all, we're still not sure what you're asking. As penguins said, there really shouldnt be any slop in your springs. Is the car bottoming out? Is it rolling too much? And what do you mean by the car doesn't like it? Those springs rates are effectively 300 and 450 wheelrates. I plugged that into my spreadsheet, with a guestimate of weight distribution, and that spring rate looks spot on.

[KevinD]

what are your corner weights and natural frequencies? i suspect you are running very very low natural frequencies if your car is that heavy with that soft of a spring. it would take a very very large motion ratio to get a decent nat.freq. with those springs. and if you have a large motion ratio then your suspension travel is going to be extremely limited assuming you are ussing a risse mountain bike shock (limited travel... 2.5 inches?).

find your natural frequencies and then report back, it should give you your answer.

[lafayette college fsae]

we're seeing a 40/60 weight dist. The car is not drivable yet but we did the fat guy test. This is where we get the fattest guy on our team to stand on one end of the car. We feel that the suspension is not stiff enough and anticipate lots of roll. we wont find out until the car is ready to hit the pavement. Alex are you saying that it would be neccessary to run 300 lb/in in the front and 450 in the rear??

Pengulns2001 how is motio calculated so i can check to see if my suspension guy is doing it right. (its shock travel/ wheel travel right??)

thanks

[kwancho]

Nono, I put the spring rate you have (200/300) and then multiplied by your motion ratio squared (1.225^2) and got 300 and 450. And yes, that's how you calculate motion ratio.

[lafayette college fsae]

thanks for the help,

by the way alex, your "stanford formula racing" link isn't working, would like to check out the car.

[pengulns2001]

just because your motion ratio is 1.25 (or whatever it is) at 1 point during your suspension travel (probably resting ride hight with a driver) assuming your suspension guy sets his car up like everyone else doesnt mean it will be 1.25 for your suspensions full travel, since the point on the bellcrank moves in an arc it will rise or fall based on where in the arc the point is, your suspension guy should know what im talking about im sorry i cant explain it better but make sure its not a rapidly falling rate (ie you step on the car and in jounce your motion ratio falls rapidly)

[pengulns2001]

btw when i stand on the back of our car (i weigh 200) our car bottoms out and the car handles great... just something to think about, we have sway bars so that has an effect on the springs we chose granted our car weighs less than half of yours but just becuase the car feels soft doesnt mean it will handle poorly... wait till you drive it then decide

[lafayette college fsae]

ok, will take that into consideration, we'll try the spring we have and if there is time look at sway bars. thanks

[pengulns2001]

i would almost go as far as to say you NEED sway bars with a car as heavy as yours, even if you half ass it due to lack of time its better than nothing, throw a 3/4" .028 tube with probably something like a 6" moment arm on it for a sway bar make slots in the moment arms so its adjustable... something like that can save you design time (which im assuming your lacking) and can be made in less than a day... i didnt run any calculations to come up with those sizes but its an educated guess and better than nothing

[kwancho]

Originally posted by lafayette college fsae:
thanks for the help,

by the way alex, your "stanford formula racing" link isn't working, would like to check out the car.
Fixed.

[PedalOnTheRight]

1100 lbs ! whoa

[Travis Garrison]

Out of curiousity, where is the weight coming from?

[lafayette college fsae]

massive overdesign, check out our website the pics will def. explain all the weight. Our goal was to look at anything that'll break and over design because this is our second car, and 1st. year competition. Also, no fancy carbon fiber, just plain old steel.

[Travis Garrison]

That's just it, I don't see 1100 lbs, I see an unfinished car...how confident are you in that number?

[lafayette college fsae]

well those pics are a bit outdated and we still have a bite of work to do. keep posted we'll have some new pics by next week. We have heavy steel rims, 1/2" cast iron rotors, big brakes, and all usable stock trim from the bike. The car very large, and wide. I can go through a list of things but check back later it'll better answer your question.

[kwancho]

1/2" brakes. jeezus.

[fade]

you might look into a different material for your body
http://www.ces.clemson.edu/~canoe/canoe1993/pics/SF_concrete_2.jpg

[lafayette college fsae]

what material is being used??

[RiNaZ]

it looks like one of those concrete canoe competition http://fsae.com/groupee_common/emoticons/icon_biggrin.gif

[lafayette college fsae]

so is this kid fade trying to be funny or something??

[Micko..]

Hi lafayette,

I know it is hard for 1st year guys, but I have to ask why your Chassis CAD and actual chassis look so different.

I have to agree with the other guys and say that I can't see the 1100lbs (430Kg minus driver) in your car, what do you have left to add? Are you using steam pipe for the chassis? Personally I would wait until your car is driving to see how your suspension calcs pan out, and then maybe start to throw stiffer springs at it. I don't' know if the "fat man" test is really going to tell you that much, I mean how fat is the fat man?

Also how much flex is in that bar the rockers mount to? Can it be measured in inches?

And how did your car put on 100lbs between this post and your last?

Miko

[RiNaZ]

lafayette, what kind CAD program do you use? I dont know about others, but if you use CATIA, it can calculate how much the car will weigh and based on my experience, it comes out pretty close.

My car has more triangulation that your car and even with me in it, it's close to 500 lb, and im 215lb!.

[kwancho]

500lbs with you in it? That would make your car the lightest by far...

[lafayette college fsae]

the cad drawings dont show this year's car, our webpage guy didnt include this years cad drawings. We use inventor. I have several springs coming so we'll test with what we have and tune after that. A roll bar is def. in the works. If everything goes well, the car will be under our estimate. That 1100 lbs came from last years car it was 956lbs. i personally think it will come out to be 800lbs w/ driver.

[lafayette college fsae]

we're planning on weighting the car next week, i will keep everyone posted.

[lafayette college fsae]

rinaz,
I would really like to see your car, are you guys finish?

[Mexellent]

Yeah rinaz, I would like to see the car as well. We were proud when we got our into the 480's with aero. 300 is insanely light. http://fsae.com/groupee_common/emoticons/icon_eek.gif

[RiNaZ]

took this picture about a month ago i think. I dont have any latest pictures. Right now, we're trying to tune the car with that infamous haltech ECM.

If you need an updated picture, send me an email, and i'll send it to you. I dont feel like taking pictures anymore since ive been told that im getting distracted and spend more time taking pictures than working on it (what can i say, i waited a very long time for this ... veryyy longgg timeee).

[RiNaZ]

Okay ... that didnt work. I know you have to host it and everything. Ive been using this forum eversince it started and i still dont know how to attach a picture http://fsae.com/groupee_common/emoticons/icon_smile.gif.

lafayette and mexellent ... give me your email add, and i'll send it to you guys.

[TG]

Originally posted by RiNaZ:
Okay ... that didnt work. I know you have to host it and everything. Ive been using this forum eversince it started and i still dont know how to attach a picture http://fsae.com/groupee_common/emoticons/icon_smile.gif.

lafayette and mexellent ... give me your email add, and i'll send it to you guys.

click on the little square of what appears to be mountains or something that is above the comment box. then paste the url location into the space (you find this by right clicking on the image - properties - image location (and copy the address for the image location))

[kwancho]

roflcopter. I'd advise imagestation. If you're emailing, I'll take a gander.

[kwancho]

Looks standard. How is it 500 lbs with driver?

edit:
put url tags around the link you put.

[RiNaZ]

http://www.imagestation.com/picture/sraid204/p2eb0bf878b337f3965260baa1d2ff5b5/ef53f449.jpg

i think i got the numbers wrong ... 700 with the driver is more like it i think. I just found out that our scale isnt working right. We're just using a 10 dollar bathroom scale.

I think by the time we got our body back, everything will total up to 600lb and our driver is a 105lb girl, so 700lb with driver i think.

Sorry for the mistake http://fsae.com/groupee_common/emoticons/icon_smile.gif

[Jersey Tom]

Got any close up shots of that rear wheel assembly? Somethin don't look right.

[RiNaZ]

http://www.imagestation.com/picture/sraid204/ped98288426a411e9b59acc38df7d5371/ef53a9d4.jpg

i dont have any updated pictures, so this is the look of the rear without the sprocket, brake etc. Even the axle isnt cut according to the track width. So you'll see some extra tube sticking out of the tyres.

and yes it's not properly alligned. We had to put everything together for team picture. I think we got rookie award for our central florida section, so our advisor wanted the car to look like it's almost complete. We didnt make it, so we just slapped every single thing on there.

what doesnt look right? (besides everything http://fsae.com/groupee_common/emoticons/icon_smile.gif, technically i mean).

p/s: i have a bad feeling my other teammates wont like me putting pictures up here, so im going to take it down in a couple of days

[Jersey Tom]

Hm. Interesting suspension setup on the rear, will be interested to see how that works out.

What looked funny to me is how far those rear wheels are cantelevered on those axles from the uprights.

[RiNaZ]

it's been done before and it's been done a lot in baja. So it shouldnt be that interesting http://fsae.com/groupee_common/emoticons/icon_smile.gif.

that's your ex-advisor with a blue shirt. He's trying to make our machine shop look like CU boulder's.

So far, he's doing a very good job http://fsae.com/groupee_common/emoticons/icon_smile.gif

[lafayette college fsae]

Originally posted by RiNaZ:
took this picture about a month ago i think. I dont have any latest pictures. Right now, we're trying to tune the car with that infamous haltech ECM.

If you need an updated picture, send me an email, and i'll send it to you. I dont feel like taking pictures anymore since ive been told that im getting distracted and spend more time taking pictures than working on it (what can i say, i waited a very long time for this ... veryyy longgg timeee).

[Drewbe]

is that a solid axle? or is your diff mounted on one of your.. "uprights". Speaking of which how is your drivetrain connecting to your axle, it must be there somewhere but i cant see the sprocket. Aside from that it looks like a well packaged car. Best of luck

[RiNaZ]

it's a solid axle and there is no diff on the car. We're a first year, first car team, so our main goal is to get it done.

You can see a shaft behind the pushrod, that's where the gears/chain going to be and the sprocket is going to attach to the axle. Just like a baja car.

[Nigel G.]

that's your ex-advisor with a blue shirt. He's trying to make our machine shop look like CU boulder's.

Is that supposed to be a good thing?

[RiNaZ]

from what you guys are saying on this forum ... the answer is yes!!! http://fsae.com/groupee_common/emoticons/icon_biggrin.gif

he already got us a $150K worth of mill and lathe, CNC plasma cutter, all these nice tools and most important of all, a space big enough to work on a car, even with fits 2 baja cars and one formula car ... something i could never dream off when i started with the program in 99!!! http://fsae.com/groupee_common/emoticons/icon_smile.gif

[Test Driver]

Hey RiNaZ,

What is the latteral constraint on the rear assembly? Is it the mono-shock bell crank? Are the birdcages possitively connected to each other? Is there designed-in flex in those connections? Is that a jack-shaft?

C'mon man. You can't expect to show such a different approach without giving us more pics.

Ramon

[kwancho]

Originally posted by RiNaZ:
from what you guys are saying on this forum ... the answer is yes!!! http://fsae.com/groupee_common/emoticons/icon_biggrin.gif

he already got us a $150K worth of mill and lathe, CNC plasma cutter, all these nice tools and most important of all, a space big enough to work on a car, even with fits 2 baja cars and one formula car ... something i could never dream off when i started with the program in 99!!! http://fsae.com/groupee_common/emoticons/icon_smile.gif

*jealousy*...

[RiNaZ]

hey ramon, the axle just snap in two today, so i hope that answer most of your question http://fsae.com/groupee_common/emoticons/icon_smile.gif. The axle is actually big enough for our drivetrain ... the only problem with it is, is that we pin our hubs/sprocket on to it. So i guess we didnt take the hole diameter into consideration.

So when we did the testing, with accel. and brake testing ... it put a lot of stress on the hole that it snap in two. So now, we're just going to weld the axle in with the hub/sprocket instead of pinning them.

Yes the mono is bell crank. If you can see a square tubing right at the bottom of the shocks, that's one part of it.

what is a birdcages? and yes that's a jackshaft. Which connections?

like i said, it's not a different approach, at least not for a first year team. It's simple and even this simple, we're still having problems.

I could show you more, but it's going to be the same pictures that i've put on here. So i dont think you'd benefit from it any more.