Welcome to the North American Subaru Impreza Owners Club Thursday March 28, 2024
Home Forums Images WikiNASIOC Products Store Modifications Upgrade Garage
Click here to visit TireRack
Brakes & Suspension Forum sponsored by The Tire Rack

Losing traction? Need new tires?
Click here to visit the NASIOC Upgrade Garage...
Go Back   NASIOC > NASIOC Technical > Brakes, Steering & Suspension

Welcome to NASIOC - The world's largest online community for Subaru enthusiasts!
Welcome to the NASIOC.com Subaru forum.

You are currently viewing our forum as a guest, which gives you limited access to view most discussions and access our other features. By joining our community, free of charge, you will have access to post topics, communicate privately with other members (PM), respond to polls, upload content and access many other special features. Registration is free, fast and simple, so please join our community today!

If you have any problems with the registration process or your account login, please contact us.







* As an Amazon Associate I earn from qualifying purchases. 
* Registered users of the site do not see these ads. 
Reply
 
Thread Tools Display Modes
Old 11-04-2012, 05:12 PM   #26
AndyRoo
Scooby Specialist
 
Member#: 20952
Join Date: Jul 2002
Chapter/Region: MAIC
Location: Baltimore, MD
Vehicle:
BRZ & Datsun
White & White

Default

Quote:
Originally Posted by EarlQHan View Post
Oh and to anyone who still thinks the kinematic roll center needs to be above ground to shorten the moment arm, thereby reducing the roll moment, because the chassis rolls about the KRC, please read:

http://www.neohio-scca.org/comp_clin...namics2007.pdf

Long story short: the KRC is irrelevant
I was going to post that.

- Andrew
* Registered users of the site do not see these ads.
AndyRoo is offline   Reply With Quote
Sponsored Links
* Registered users of the site do not see these ads.
Old 11-04-2012, 06:35 PM   #27
EarlQHan
Scooby Specialist
 
Member#: 90215
Join Date: Jun 2005
Chapter/Region: MWSOC
Location: Where am I not?
Default

Quote:
Originally Posted by rbaldi View Post
I'm a little surprised that the kinematic-roll-center-doesn't-exist/matter/below-ground-is-okay notion hasn't caused an uproar yet; after all, NASIOC is not the place for facts
I am as well. But I don't think those who believe in it have a strong grasp of what it is or how to argue it.

Thanks for the tips on the loading conditions. As for ANSYS, I'm very limited with its use in Workbench. I'm in a 500 level FEA class, but we've mostly been setting up everything manually through the product launcher as the focus is on the theory behind FEA. So a lot of matrix algebra All my previous FEA experience has been with SolidWorks Simulation with very limited use on assembly analysis.

Since it's out of my scope to do account for bushing deflections and there's no way for me to get proper K&C data, I'm going to try and get as much camber gain/reduce camber loss as possible, and try get a linear ride-steer curve. It's really limited to what WinGeo tells me by moving the pick-up points within the packaging constraints. I hate WinGeo... if any of you have used it before, you understand the pains caused by the stupid "loop of death." I can't wait to start my masters and start using ADAMS.

I was going to model heat transfer and account for the stresses on the upright (both convection and conduction) from braking, but I hadn't thought of brake torque. Do you know how I could best model that for analysis?

jdblock - I am not worried, because there isn't going to be that much adjustment. Maybe an inch or two. I can also modify the pick up points for the strut to correct the KPI. And this is just for research, I'm not actually going to machine this... probably
EarlQHan is offline   Reply With Quote
Old 11-04-2012, 06:41 PM   #28
EarlQHan
Scooby Specialist
 
Member#: 90215
Join Date: Jun 2005
Chapter/Region: MWSOC
Location: Where am I not?
Default

Quote:
Originally Posted by AndyRoo View Post
I was going to post that.

- Andrew
You work for RCE, correct? One of the reasons you guys have my respect.
EarlQHan is offline   Reply With Quote
Old 11-04-2012, 08:41 PM   #29
AndyRoo
Scooby Specialist
 
Member#: 20952
Join Date: Jul 2002
Chapter/Region: MAIC
Location: Baltimore, MD
Vehicle:
BRZ & Datsun
White & White

Default

Quote:
Originally Posted by EarlQHan View Post
You work for RCE, correct? One of the reasons you guys have my respect.
Thanks.

Once I started reading your post I thought FSAE, then I thought FAPs.

- drew
AndyRoo is offline   Reply With Quote
Old 11-05-2012, 09:19 AM   #30
MSI
Former Vendor
 
Member#: 95419
Join Date: Sep 2005
Chapter/Region: E. Canada
Location: montreal
Default

I will chime in here before things go crazy out of proportion.
We have about 120 hours of FEA done on our model, it is significantly stronger than the OE part to the point that we have no worries about using it on a gravel car. Our current revision will take a lot higher loads than the cast IRON oe part, between 45 - 150% more depending what load and angle, etc.

We do have a gravel version that does not have an adjustable steering arm for increased strength. The steering arm for this model is mounted on a plate were the pin for the bearing goes on the lower pick-up point.

We do have a version that uses the OE ball joints as well as a steering arm that is mounted in double sheer. As far as the OE all joint, why would you want to use this when you are going so far as to use a billet upright? It is not worth it. Put a proper bearing in there and change the front arms.

I will also say, the less adjustment in the part the better. Our non-adjustable models are MUCH stronger than the adjustable ones.

-mark
MSI is offline   Reply With Quote
Old 11-05-2012, 09:30 AM   #31
stevenkelby
Scooby Newbie
 
Member#: 207569
Join Date: Apr 2009
Chapter/Region: International
Location: Adelaide, South Australia
Vehicle:
MY04 Forester XT
Red

Default

I'm following with interest, thanks for the input Mark

Quote:
Originally Posted by MSI View Post
Our non-adjustable models are MUCH stronger than the adjustable ones.

-mark
Isn't that point moot? If your adjustable models are "strong enough", what advantage is there in the non adjustable model being even stronger?

Just a thought.

I agree with ditching the OEM ball joint, surely it's a weak link, why leave it in place.
stevenkelby is offline   Reply With Quote
Old 11-05-2012, 09:35 AM   #32
vicious_fishes
Scooby Guru
 
Member#: 158864
Join Date: Sep 2007
Location: Aussieland
Vehicle:
2003 SOHC destroker

Default

i know i'm repeating myself here but again, what makes yours better than LIC's or MSI's or whoever else?


no better/different = no motive to buy
vicious_fishes is offline   Reply With Quote
Old 11-05-2012, 09:39 AM   #33
stevenkelby
Scooby Newbie
 
Member#: 207569
Join Date: Apr 2009
Chapter/Region: International
Location: Adelaide, South Australia
Vehicle:
MY04 Forester XT
Red

Default

Quote:
Originally Posted by vicious_fishes View Post
i know i'm repeating myself here but again, what makes yours better than LIC's or MSI's or whoever else?


no better/different = no motive to buy

Too lazy to read the thread?
stevenkelby is offline   Reply With Quote
Old 11-05-2012, 09:43 AM   #34
EarlQHan
Scooby Specialist
 
Member#: 90215
Join Date: Jun 2005
Chapter/Region: MWSOC
Location: Where am I not?
Default

Quote:
Originally Posted by vicious_fishes View Post
i know i'm repeating myself here but again, what makes yours better than LIC's or MSI's or whoever else?


no better/different = no motive to buy
Never said I was selling
EarlQHan is offline   Reply With Quote
Old 11-05-2012, 09:51 AM   #35
EarlQHan
Scooby Specialist
 
Member#: 90215
Join Date: Jun 2005
Chapter/Region: MWSOC
Location: Where am I not?
Default

Quote:
Originally Posted by MSI View Post
I will chime in here before things go crazy out of proportion.
We have about 120 hours of FEA done on our model, it is significantly stronger than the OE part to the point that we have no worries about using it on a gravel car. Our current revision will take a lot higher loads than the cast IRON oe part, between 45 - 150% more depending what load and angle, etc.

We do have a gravel version that does not have an adjustable steering arm for increased strength. The steering arm for this model is mounted on a plate were the pin for the bearing goes on the lower pick-up point.

We do have a version that uses the OE ball joints as well as a steering arm that is mounted in double sheer. As far as the OE all joint, why would you want to use this when you are going so far as to use a billet upright? It is not worth it. Put a proper bearing in there and change the front arms.

I will also say, the less adjustment in the part the better. Our non-adjustable models are MUCH stronger than the adjustable ones.

-mark
I didn't mean your uprights weren't strong enough. As I said, it was all just by guessing from eyeballing what I could see from pictures. Even though OEM is iron, it still has a modulus of around 160 GPa compared to 70 GPa of Aluminum (tensile strength is higher too), so I'm sure you can understand why I would think it to be weaker. I'm glad you guys have taken everything into account. I agree adding adjustability will weaken the part but we all make compromises. Mine goals are clearly stated and since this won't ever go into manufacturing, I'm not worried about it. I'm shooting for targets to be met on the computer.

Two things: 1. would you mind explaining how you set up your loading conditions for FEA?
2. could I get a picture of a fully-assembled tarmac version of your upright in the specification you mentioned? I haven't been able to find one yet.

Last edited by EarlQHan; 11-05-2012 at 09:59 AM.
EarlQHan is offline   Reply With Quote
Old 11-05-2012, 01:12 PM   #36
Dmochowski
Scooby Guru
 
Member#: 306478
Join Date: Jan 2012
Chapter/Region: South East
Location: chattanooga, TN
Vehicle:
2016 Focus RS
stock

Default

Based off the title I thought it was gonna be something silly like "bc it lets me pick up chicks!"
Dmochowski is offline   Reply With Quote
Old 11-05-2012, 03:39 PM   #37
jamal
Scooby Guru
 
Member#: 71875
Join Date: Oct 2004
Location: Montana
Default

I just haven't felt like getting into this big internet argument.


Just because the roll center is an imaginary point and doesn't do as accurate of a job as forced based analysis doesn't mean it's a worthless term and should be ignored. If put a big ball joint extender on the car and keep everything else the same (ride height, alignment, spring rates etc), the car is going to handle differently and you will change the amount of roll.
jamal is offline   Reply With Quote
Old 11-05-2012, 08:21 PM   #38
rbaldi
Scooby Newbie
 
Member#: 312567
Join Date: Mar 2012
Vehicle:
2012 STi

Default

Quote:
Originally Posted by EarlQHan View Post

Since it's out of my scope to do account for bushing deflections and there's no way for me to get proper K&C data, I'm going to try and get as much camber gain/reduce camber loss as possible, and try get a linear ride-steer curve. It's really limited to what WinGeo tells me by moving the pick-up points within the packaging constraints. I hate WinGeo... if any of you have used it before, you understand the pains caused by the stupid "loop of death." I can't wait to start my masters and start using ADAMS.

I was going to model heat transfer and account for the stresses on the upright (both convection and conduction) from braking, but I hadn't thought of brake torque. Do you know how I could best model that for analysis?

I feel your WinGeo pain; I've used it in DOS As far as mass-market suspension analysis programs go, ADAMS is my favorite. Optimum K is also pretty good, but is limited to only kinematics. I would say that ADAMS is the Catia or Unigraphics of kinematics/basic simulation programs, and Optimum K is more like Solidworks....if that comparison makes any sense.



To model brake torque, just constrain your upright at the UBJ (well, where it bolts to the damper in this case), LBJ, and at the steering arm and apply loads at the brake caliper mounts. You just need to work backwards from the contact patch into the upright to figure out the loads - think about what would happen if the pads were welded to the rotor and you applied a longitudinal force at the contact patch - how would that force be reacted into the chassis? To figure out how much longitudinal force you need at the contact patch for a given deceleration, you will need rotor/pad/caliper geometry to figure out the brake bias. Then just move the force (net moment=0, and make sure you get your forces applied in the correct direction; it's easy to get something backwards here) from the contact patch to the pad/rotor interface, then to the brake caliper mounts on the upright. Here's a hint for calculating the effective radius of the pad friction force - the pad face centroid is a not-perfect, but really close approximation. The actual radius is effected by many things, including pad compound, clamp load, rotor rpm, temperature, and pad wear, etc; but that's a different thread.
rbaldi is offline   Reply With Quote
Old 11-05-2012, 09:09 PM   #39
rbaldi
Scooby Newbie
 
Member#: 312567
Join Date: Mar 2012
Vehicle:
2012 STi

Default

Quote:
Originally Posted by jamal View Post
I just haven't felt like getting into this big internet argument.


Just because the roll center is an imaginary point and doesn't do as accurate of a job as forced based analysis doesn't mean it's a worthless term and should be ignored. If put a big ball joint extender on the car and keep everything else the same (ride height, alignment, spring rates etc), the car is going to handle differently and you will change the amount of roll.
I think I probably got a little carried away with my hatred of the kinematic roll center in my first post, but I do believe that it is the most over and incorrectly analysed kinematic parameter, at least with regards to influence on lateral g capability and lap time. For a given roll gradient, the FAP's effects are felt much more in transient conditions (ie: how fast the load transfer builds up in reaction to lateral g, and how much the dampers can control it) than in steady state. In terms of adjustablilty/tuning, this is one of the areas where a lower roll center is better - the springs contribute more to the roll stiffness, so the dampers have more control on the load transfer distribution build rate. However, it's easy for this to make the car feel lazy on turn in, as yaw moment will build slower - so, as with everything, it's a trade off.

I haven't done any kinematic analysis on a Subaru, so this is just hunch, but I'm guessing that most of the "improvement" that comes from a roll center adjuster kit comes from fixing the bump steer curve.
rbaldi is offline   Reply With Quote
Old 11-05-2012, 09:35 PM   #40
speedyHAM
Scooby Specialist
 
Member#: 48377
Join Date: Nov 2003
Chapter/Region: MWSOC
Location: "They eat fish soaked in lye"
Vehicle:
1996 Gutted, built
XP class Impreza L

Default

Quote:
Originally Posted by rbaldi View Post
I haven't done any kinematic analysis on a Subaru, so this is just hunch, but I'm guessing that most of the "improvement" that comes from a roll center adjuster kit comes from fixing the bump steer curve.
Most of the improvement actually comes from improving the camber curve.

The only reason I would not want the roll center below ground is that it contributes to weight jacking. I don't know how many people here have an Impreza that has been on the verge of grip rolling, but mine was before I redesigned the subframes and suspension geometry to improve the dynamic response both in roll center and weight jacking.

I highly recommend starting with "Race Car Vehicle Dynamics" by Milliken and designing from there. Designing anything based off internet forum advice is not the best approach.

That said, I would plan on a few FEA case runs to account for different loading conditions such as- 3G bump with 2G cornering, 10G bump by itself, 3G cornering, 3G braking with 5G bump, and so on and so forth. Without knowing the final application of the car it's hard to tell what the limiting condition is. This is the method I used for the design of my suspension pieces.

Good luck with your project.
speedyHAM is offline   Reply With Quote
Old 11-05-2012, 10:51 PM   #41
EarlQHan
Scooby Specialist
 
Member#: 90215
Join Date: Jun 2005
Chapter/Region: MWSOC
Location: Where am I not?
Default

Thanks guys. Have RCVD, as well as a few of Dixon's books and use them frequently. There's just not enough time left in the semester to get into the nitty gritty of the geometry and I'm not aiming for the "perfect" solution. I'm taking 25 hours, as well as being the FSAE treasurer and compliance engineer, and working on top of all that (not much sleep these days ) I'm aiming for a solution that can be applied to a wide range of ride heights, since there's a business aspect to consider for the project. I was merely using the title to get some eyeballs in the thread to help out.

That being said, with textbooks, there's a conspicuous lack of information on vehicle dynamics, and response from a driver's perspective. Everyone models vehicle dynamics in terms of an open-loop system, but in reality, the driver closes the loop. I'm hoping I'll be able to utilize state-space equations to model a vehicle/driver system in order to create a simulation to get a better idea of how sensitive a driver is and how sensitive the vehicle needs to be because there are human limitations to reaction time and different driver preferences on feel. I think it could mathematically determine a driver's capabilities as well. A bit more out there, but the most important topic in my opinion and it is an underdeveloped topic in my opinion. Maybe it's because engineers don't like to think about the "loose nut." I'm hoping I can do this as the topic of my masters thesis next year.
EarlQHan is offline   Reply With Quote
Old 11-06-2012, 12:01 AM   #42
rbaldi
Scooby Newbie
 
Member#: 312567
Join Date: Mar 2012
Vehicle:
2012 STi

Default

Quote:
Originally Posted by speedyHAM View Post
Most of the improvement actually comes from improving the camber curve.
Sorry, should have been more specific; I was referring to the "My car drives so much better on the way to NOPI now that I have my roll center in the perfect location for my mad tyte hellaflush setup" type of improvement.


Agreed 100% on the RCVD recommendation, and since it sounds like you are on an FSAE team, the Optimum G seminars by Claude Rouelle are pretty good and affordable - ~36 hrs of classroom instruction crammed into 3 days for ~$500, just dont take everything he says as gospel, use it like any other resource. It may sound like a lot, but it's probably cheaper per hour than almost all respectably universities. And Claude has some good jokes too.
rbaldi is offline   Reply With Quote
Old 11-06-2012, 12:25 AM   #43
Suba_Roo
Scooby Specialist
 
Member#: 5691
Join Date: Apr 2001
Chapter/Region: BAIC
Location: Redwood City, CA
Vehicle:
2001 2.5 RS
Silverthorn

Default

Interesting discussion. Obviously MSI and LIC have spent a lot of time and effort working on the geometry designs. How about thinking about something totally different. Track Subaru's kill wheel bearings really fast. Track Subaru's overheat brakes super fast. What about a liquid cooled knuckle, cooling the knuckle would protect the bearings. Spraying liquid onto the rotors for cooling is illegal in most race series, but instead of taking TIC's approach of putting titanium spacers between the rotor and hub to reduce heat transfer between the rotor and hub, why not cool the hell out of the knuckle and try to use that as an approach to cool the rotor and thereby improve brake life as well?

I'm suspicious that an engineer is about to jump in kick my butt in terms of cooling capacities, but its something I've never seen done, seems really hard to implement on a castknuckle, but wouldn't be difficult on a machined knuckle.
Suba_Roo is offline   Reply With Quote
Old 11-06-2012, 12:38 AM   #44
stevenkelby
Scooby Newbie
 
Member#: 207569
Join Date: Apr 2009
Chapter/Region: International
Location: Adelaide, South Australia
Vehicle:
MY04 Forester XT
Red

Default

Good idea, maybe just finning the hell out of it would help too, we used to cool engines that way.
stevenkelby is offline   Reply With Quote
Old 11-06-2012, 03:59 AM   #45
Counterfit
Scooby Guru
 
Member#: 124254
Join Date: Aug 2006
Chapter/Region: NESIC
Location: Rhode Island
Vehicle:
2006 06 SGM Slowbaru
"The Scoobinator"

Default

Quote:
Originally Posted by stevenkelby
Good idea, maybe just finning the hell out of it would help too, we used to cool engines that way.
50 years later, Porsche moves to liquid cooled knuckles and "purists" get their panties in a wad.
Counterfit is offline   Reply With Quote
Old 11-06-2012, 04:26 AM   #46
stevenkelby
Scooby Newbie
 
Member#: 207569
Join Date: Apr 2009
Chapter/Region: International
Location: Adelaide, South Australia
Vehicle:
MY04 Forester XT
Red

Default

Quote:
Originally Posted by Counterfit View Post
50 years later, Porsche moves to liquid cooled knuckles and "purists" get their panties in a wad.
stevenkelby is offline   Reply With Quote
Old 11-13-2012, 09:31 PM   #47
naSTI N8
Scooby Newbie
 
Member#: 194923
Join Date: Nov 2008
Location: south florida
Vehicle:
2006 gg evo iX

Default

Here's a link from the dark side that you guys might enjoy..

http://forums.evolutionm.net/evo-tir...uantified.html
naSTI N8 is offline   Reply With Quote
Old 11-29-2012, 01:52 PM   #48
jamal
Scooby Guru
 
Member#: 71875
Join Date: Oct 2004
Location: Montana
Default

A real chassis engineer seems to think the roll center is still relevant. motoiq just published this:

http://www.motoiq.com/magazine_artic...ll-center.aspx
jamal is offline   Reply With Quote
Old 11-29-2012, 04:12 PM   #49
vicious_fishes
Scooby Guru
 
Member#: 158864
Join Date: Sep 2007
Location: Aussieland
Vehicle:
2003 SOHC destroker

Default

Quote:
Originally Posted by stevenkelby View Post
Too lazy to read the thread?
too sick actually. obviously missed it

Quote:
Originally Posted by EarlQHan View Post
Never said I was selling
if you were to start producing them, even if they're exactly the same as the LIC's then providing they don't cost the same fortune i think you'd have more than a few keen buyers.
vicious_fishes is offline   Reply With Quote
Old 11-29-2012, 04:22 PM   #50
stevenkelby
Scooby Newbie
 
Member#: 207569
Join Date: Apr 2009
Chapter/Region: International
Location: Adelaide, South Australia
Vehicle:
MY04 Forester XT
Red

Default

Quote:
Originally Posted by vicious_fishes View Post
too sick actually. obviously missed it
Apologies, hope you're feeling better
stevenkelby is offline   Reply With Quote
Reply

Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Forum Jump

All times are GMT -4. The time now is 06:03 AM.


Powered by vBulletin® Version 3.7.0
Copyright ©2000 - 2024, Jelsoft Enterprises Ltd.
Powered by Searchlight © 2024 Axivo Inc.
Copyright ©1999 - 2019, North American Subaru Impreza Owners Club, Inc.

As an Amazon Associate I earn from qualifying purchases.

When you click on links to various merchants on this site and make a purchase, this can result in this site earning a commission
Affiliate programs and affiliations include, but are not limited to, the eBay Partner Network.