"Bad Ast" Frame and Suspension Design

[astroracer]

I've gotten a lot done in the last couple of weeks. Namely just verifying dimensions on hard parts and virtual geometry.
I've replaced the Astro van UCA Cross Shaft with one from a "G" Body, gotten a roughly modeled 2" dropped Astro Spindle in place and started designing control arms.
As you can see I've got a good start on the frame rails, front and back, with more work to do for crossmembers, engine and body mounts.
The rear frame rails are the tough nuts... I talked to a company in Detroit about mandrel bending them but, at $295.00 dollars EACH... PLUS material, it isn't going to happen. Cutting and welding isn't an option so I am talking to a couple of guys who have CNC Plasma and laser cutters about doing all of my brackets and the rails that way. Making .DXF files isn't a problem...

[Matt@RFR]

Have you made any progress with mandrel bending that rect tube?

Nevermind...I went straight to the drawings!!

[jakespeeds]

Chris Alston of Alston chassis can take your drawings and make rails right from them. He has a big frame bending machine that is CNC operated.

Jake

[Salt Racer]

Looks good Mark.

Just curious...What is your UCA/LCA length ratio? I've never messed with Astro spindles so I don't know what kind of UCA/LCA ratio those spindles prefer for good RC migration, but LCAs seem to be bit short on your modeling.


K

[astroracer]

K,
The upper arm is 8.52" long and the lower is 11.85". That is a 1.39:1 ratio.
The roll center at design is 1.99" above ground
At full Jounce it is -1.47" below ground and
At full Rebound it is 6.69" above ground.
This works out to a little over 8 inches of RC migration throughout suspension travel. I wasn't real concerned with this as I will probably limit total suspension travel to around 5" or less during shock/spring tuning. Is there a target I should be looking to hit?
Running the geometry through a motion program gives me 2.61 degrees of Camber Gain at a full wheel travel of 3.75 inches in Jounce.
Camber Loss is 1.2 degrees in Rebound.

I utilized Corvette Z06 geometry points and wheel center travels as a start and then revised the Upper and Lower Control Arm pivot points to better match the C5 Corvette Steering Rack for bump steer and ackerman. I did narrow up the LCA pivot points considerably to do this. I have less then 3 degrees of toe in at full Jounce and around 3 1/2 degress at full Rebound. With my planned travel limits I was pretty happy with these numbers also.
Thanks for the input and let me know how my numbers sound to you...
Mark

[Salt Racer]

Mark,
You have a PM.

[BlazerSpeed]

damn mark drawings look better everytime I see 'em. I remember what you were planning on doing for body/suspension, but what were your plans for the interior?
DEREK

[astroracer]

Thanks Derek!
I've got some ideas rolling around in my head for the interior stuff but I haven't really thought about it too much. I've still got a lot of design issues with the front suspension so, until I get those worked out, I'm not going to worry about the rest of it....
I do have a pair of Neon buckets that I may use or I may go with a full set of Fiero seats a buddy can get for me. Resculpting the dash is a probability with all aftermarket gauges and what not...
Mark

[astroracer]

A big thank you to Salt Racer for his help in getting my front suspension optimized. He helped me with a lot of input on what I needed to achieve with all of my settings. I spent a lot of time on the initial design but, without any clear goals in mind as far as bump steer and roll center migration, I was leaving a lot of it to chance. With his guidance I've relocated the upper and lower control arm points and pushed the brake corner farther outboard for a deeper offset rim. We both feel this will be a killer set up and should handle very well... Which is what you want it to do, right? Thanks again Katz...
This is what I ended up with.
Initial settings:
Track = 32.24
Wheel mounting face = 34.24
Rim = 10" wide with 7" B.S. (2.00" offset)
275/40x17 tire.
Scrub Radius = 1.80"
Side scrub at 3" dive = .07"
Anti-Dive = 51.2%
SVSA Length = 98.4"
Bump Steer @ 3" Dive = 0.00 deg.
Bump Steer @ 3" Rise = 0.08 deg. (never see it)
R/C height @ design = 1.31"
R/C hgt in left turn (3 deg Roll/10.55 deg Steer) =1.30"
R/C migration in left turn (3 deg Roll/10.55 deg Steer) = 0.23" from Center
R/C migration in right turn (3 deg Roll/10.55 deg Steer) = 0.23" from Center
R/C in Off Camber Right turn ( 3 deg Roll Left/ 10.55 deg Steer Right) = 3.33" from Center.
R/C in Off Camber Left turn ( 3 deg Roll Right/ 10.55 deg Steer Left) = 3.33" from Center.
Bump steer and Roll Center Migration are pretty important. This should be a very stable and predictable suspension.
Mark

[airrj1]

Mark,


Very cool. I understand half of what you posted, but I am catching more of it everyday. I am hoping to work on a custom suspension in Pro/E this winter. I'll have to hit you up for some tips. :icon996:

[astroracer]

Mark,


Very cool. I understand half of what you posted, but I am catching more of it everyday. I am hoping to work on a custom suspension in Pro/E this winter. I'll have to hit you up for some tips. :icon996:

No problem... Ask away...
I was pretty busy this weekend redesigning the whole front suspension to the new points Katz helped me out with... Here are a few screen shots of what I've got now...
This is a bottom view
Front View...

Front Iso View of the new Control Arms

And a view of the complete corner... Arms, Shock, frame and tire/wheel.

[astroracer]

This is a section I cut through the brake corner, tire and wheel. I sent this to Bill at Bonspeed to help him develope the front rims for "Bad Ast".
Even though I am using mostly stock Corvette parts I still wanted to verify Caliper to rim Clearances.

[Salt Racer]

Looks good Mark. Good call on checking caliper/spoke clearance with the manufacturer.

Good job!

[astroracer]

Thanks K...
After moving the Rack up last Thursday I re-optimized everything Friday and this suspension is ready to go now. I still have zero bump. The R/C actually moves inboard .31 inches @ 3 degrees Roll & 10 degrees Steer! And the outer tierod has plenty of clearance to the rim.
Anti-Dive is 51% and the Ackerman angles are near perfect... (.05 degrees of error at full steer...). Thanks again for all of your help. I still have a few things to work out but I hope to start developing welding fixtures in a week or so...
Mark

[TurboLark]

What program are you using for that? Solidworks? Is it too big to email?? :D

[astroracer]

It's not solidworks and it's way to big to email...
I have a beta version of Unigraphics V18. It's out of date now but it does what I need it to do so I keep it loaded. The big problem with it is it's NOT very user friendly. Ive been running UG since '92 so I am pretty proficient with it but anybody trying to learn it without training is not going to do well... Sorry
Mark

[astroracer]

Katz (Salt Racer) gave me some more direction friday concerning the Anti-Dive and Side View Swing Arm (SVSA) Length. I've re-developed all of the points and this is where I'm at. I think we've covered everything right Katz? Look this over one more time and let me know if you see anything else...
A few things I did while reworking the points was to bring the LCA pivot points parallel to ground AND Center of car and I also brought the UCA pivots in parallel to center of car.
I did another major move of the Steering Rack also. I moved it and the outer Tierod Point 1" rearward in car to gain more clearance to the rim.
This is what I ended up with.
Initial settings: (Specs in Black did not change)
Track = 32.24
Wheel mounting face = 34.24
Rim = 10" wide with 7" B.S. (2.00" offset)
275/40x17 tire.
Scrub Radius = 1.80"
Side scrub at 3" dive = .07"
Anti-Dive = 26.8%
SVSA Length = 97.7"
Bump Steer @ 3" Dive = -0.008" This is Bump out which is better then bump in. It actually starts bumping out (-0.001) @ 1.50" of Dive.
Bump Steer @ 3" Rise = 0.003"
R/C height @ design = 1.68"
R/C hgt in left turn (3 deg Roll/10.0 deg Steer) =1.66"
R/C migration in left turn (3 deg Roll/10.0 deg Steer) = 0.04" from Center
R/C migration in right turn (3 deg Roll/10.0 deg Steer) = 0.04" from Center
Outside tire Camber Gain in left turn (3 deg Roll/10.0 deg Steer) = -.41 degs

This suspension design is a far cry from the Corvette points I started out with... The Corvette doesn't even come close to pulling down these numbers... I just hope it works as well under a vehicle as it looks on paper...

[Salt Racer]

Mark,
It looks good to me. If anything, I'd try 10~30" longer FVSA and see if it decreases side scrub. If not, set in -1.0~-1.5* static camber and you're good to go.

[astroracer]

Katz,

I didn't update the Side Scrub in my last post... It should be 0.04 @ 3" of Dive. How does that sound?
Mark

[Salt Racer]

That's pretty damn good. Also, be sure to check scrub at every 0.5" suspension travel - both jounce and rebound. Typically the curve is not linear. More than likely the number will increase quite a bit when you go over 2" travel on rebound, but don't worry about that.