New for 2009 - frame rules

[URracing]

So we are basically having to build a new frame since our one that has been in progress has been built quite crooked and is next to impossiblt to attach a proper suspension to. So anyway, we've been initiating a new design for 2009 whereas I just received this info from the rules committee:

I was in contact with the FSAE rules committee about building our new frame for 09. We have our templates cut out that are specified in the 2008 rules but then they said they are not allowing any tubing or steering rack components to be directly mounted in front of the driver's shins. I've seen quite a few designs where teams run a cross member between the points that the front bulkhead supports are mounted to. This is either for structural support or offering a solid place to mount a steering rack. Supposedly we cannot do this anymore. A quick n dirty diagram of what I mean is below

http://s268.photobucket.com/albums/jj16/cdnbacon85/?act...nt=fsaeframespec.jpg (http://s268.photobucket.com/albums/jj16/cdnbacon85/?action=view&current=fsaeframespec.jpg)

The diagram represents a couple of different ways that I've seen the front role hoop braced while the area in the red sections are where the cross brace or steering rack is usually attached to. Basically it was clarified to me that the vertical template must pass either over top of the steering rack or underneath it and still have adequate room in order to reach within 4" of the (undepressed) pedals.

Since our uprights are already milled out and corner assemblies are all put together, I just have one question to ask some of the suspension/steering guys out there since I'm still learning this stuff:

Our uprights are designed so the front-left one is the same as the rear-right one and vise-versa. The steering links are designed to be attached to the top of the upright and in-line, parallel to, (and out front) of the upper a-arm link. Now since we cannot mid-mount our rack anymore, I'm just curious what effects we will get if we simply turn the upright upside down and run the steering link behind the bottom-rear a-arm and attach it to the back of the upright while placing the steering rack down low. I realize it reverses our usual motion to our steering box (meaning the steering wheel turns left in order for the car to turn right) but I'm more interested in what effects it has on handling to mount the steering links low instead of high.

[URracing]

So we are basically having to build a new frame since our one that has been in progress has been built quite crooked and is next to impossiblt to attach a proper suspension to. So anyway, we've been initiating a new design for 2009 whereas I just received this info from the rules committee:

I was in contact with the FSAE rules committee about building our new frame for 09. We have our templates cut out that are specified in the 2008 rules but then they said they are not allowing any tubing or steering rack components to be directly mounted in front of the driver's shins. I've seen quite a few designs where teams run a cross member between the points that the front bulkhead supports are mounted to. This is either for structural support or offering a solid place to mount a steering rack. Supposedly we cannot do this anymore. A quick n dirty diagram of what I mean is below

http://s268.photobucket.com/albums/jj16/cdnbacon85/?act...nt=fsaeframespec.jpg (http://s268.photobucket.com/albums/jj16/cdnbacon85/?action=view&current=fsaeframespec.jpg)

The diagram represents a couple of different ways that I've seen the front role hoop braced while the area in the red sections are where the cross brace or steering rack is usually attached to. Basically it was clarified to me that the vertical template must pass either over top of the steering rack or underneath it and still have adequate room in order to reach within 4" of the (undepressed) pedals.

Since our uprights are already milled out and corner assemblies are all put together, I just have one question to ask some of the suspension/steering guys out there since I'm still learning this stuff:

Our uprights are designed so the front-left one is the same as the rear-right one and vise-versa. The steering links are designed to be attached to the top of the upright and in-line, parallel to, (and out front) of the upper a-arm link. Now since we cannot mid-mount our rack anymore, I'm just curious what effects we will get if we simply turn the upright upside down and run the steering link behind the bottom-rear a-arm and attach it to the back of the upright while placing the steering rack down low. I realize it reverses our usual motion to our steering box (meaning the steering wheel turns left in order for the car to turn right) but I'm more interested in what effects it has on handling to mount the steering links low instead of high.

[Landreneau]

just be cautious of:

-camber change (if we switch our uprights, we'll get the opposite camber than what we designed for)

-bump steer

-flip your rack around so turning left turns the car left

[benjo]

Looking at the picture you posted, if that is what your designing your frame around you will run into trouble with bulkhead support. Check this link out for some clarification. There's a download at the bottom of the page.

http://www.formulasae.org/forums/formula/dispatch.cgi/r....6.2%20Triangulation (http://www.formulasae.org/forums/formula/dispatch.cgi/rules/docProfile/100158/d20071016135451/No/3.3.6.2%20Triangulation)

[URracing]

Sorry to take so long replying, but thanks for the input on the uprights. Our uprights are completely symetrical whereas originally hoping to attach rack links to top of upright. I was more curious as to how handling and steering "feel" is changed when basically flipping the upright 180 deg so the steering link attaches to the bottom instead. From the looks of it though, being we already have the uprights done and assembled, we'll be using a high-mounted rack with drop links out front of the forward suspension mount (to enable the rack's drop links to clear the frame at full travel - about the only way we can do this).

If we can no longer run a steering rack in front of the driver's shins then this is probably our best and only option.

[URracing]

So after thinking about it a bit, are we allowed to run the steering rack underneath the bottom frame rail at about the same position as the driver's knees in the longitudinal plane? Figured this would be a good alternative to get away from the new design paramater but now we will just have to flip the upright upside down so the rack attaches to the bottom instead of the top. Again, any ideas as to what kinds of effects are caused between attaching the steering links to the top of the upright vs the bottom of the upright? Much appreciated.

[Jeff Crane]

I think with the 2009 rules most teams will be running the steering rack at the bottom. this is just fine. you will probably need a u joint in your steering column to allow the steering wheel to be the right angle

In regards to the upright, flipping them upside-down may or may not change anything. It depends on the caster offset. The caster angle should stay the same though. Best case nothing will change. second best case is the steering effort might increase. and worst case is the steering effort might reverse as in the mechanical trail might go negative ( definitely dont want this). This worst case is probably the least likely though but better make sure.

Ackermann will probably change aswell going from top to bottom steer.

We tried to run drop links last year but they were incredibly sloppy and didnt work out.

[Jeff Crane]

now that i think about it. it will flip the king pin inclination from leaning in to leaning out. this will increase your srub radius. unless kpi is zero

[URracing]

KPI is zero. Thanks for the input. To get away from running drop links, are we allowed to mount the steering rack UNDER the cockpit's frame (just in front of the bottom forward a-arm link)? Or does it have to be completely contained within the "major stucture"?

[Michael Palaszynski]

Glancing through the rules, there is nothing stated of this in the steering. The frame is defined as:

3.3.1
"Frame - The "Frame"� is the fabricated structural assembly that supports all
functional vehicle systems.

And the close-out panel is only separating the driver from the pavement.


But my instincts tell me you cannot do that. Even though it's not written in the rules, I would expect this type of response from a judge: All critical components of the car (ie parts that dictate the motion of the vehicle) must be located within the main structure.

Limiting their damage until the car is in an accident causing the frame yield, but at this point the steering is the least of your worries. On the other hand, if you do it, you now have to raise the ride height of the front to compensate the the XX inch thick steering rack you have.

[MalcolmG]

i'd be pretty suprised if there was an issue with running the steering rack outside of your major structure, in 2005 and 2006 our rack was mounted underneath our monocoque, and I've seen a number of other monocoque cars doing the same thing

[URracing]

Yep rules committee said it's fine to run the rack and pinion under the major structure provided we show some effort in offering the pinion box some protection (wrap a thin steel strap around it with some mild re-enforcement.

This will be interesting, since our upright were originaly designed to have the rack attach to them on the top. KPI is zero so hopefully that will help our situation.

[Davo]

Will having the uprights flipped mean that the mounting positions of the brake calipers are flipped as well? It may not be an issue but it'd be worth checking how the brake torque will get transmitted through the wishbones and into the chassis.

[Casey Hahn]

Flipping your uprights around could, and most likely will, increase your mechanical trail thus, as said previously, increasing steering effort. It could also decrease your wheelbase by a little bit. Before flipping, how long is your camber offset and in what direction (ask if you need a better explanation of what I'm asking here)? Ackerman would change if the tie rod outer pivot arm and the (before flipping) upper A-arm outer pivot are not at the same lateral distance. If the lower and upper A-arm outer pivots aren't the same vertical distance from the wheel center, your original suspension design could be changed a little by the outer pivot points being at different heights. Also if you mount your rack underneath your chassis, make sure that the tie rod still points to the instant center in order to keep bump steer to a minimum (unless of course, you desire a certain amount of bump steer). If your camber adjustment is at your upright, flipping it could affect this. Also, if your upper and lower A-arm pivot mounts at your upright are different, think about what the force from the push or pull road might do to the strength of the upright. Last, as said before, you are likely going to have to use a U-joint in your steering column. U-joints output sinusoidal motion if the input is of constant angular velocity (see wikipedia for a good graph). Note what this might do to your steering linearity. Putting to phased in a certain way can cancel out this effect so I've heard. That's all I can think of right now.