JJLudemann's Design Thread
I guess I'd better start a design thread before I finish the design... I'm working on it full time, seven days a week. The frame is largely done but not tested yet, including mounts for A-arms, suspension rocker arms, anti-roll bars, steering rack, shocks, pedal cluster & master cylinders, front ARB adjuster, engine, differential, steering column, and all the associated brackets and jingly bits.
Here's a recent rendering of the frame:
http://s103.photobucket.com/albums/m...ssisTop006.jpg
And here's the front end with some of the hardware attached:
http://s103.photobucket.com/albums/m...artop005-1.jpg
And here's a early version of the body:
http://s103.photobucket.com/albums/m...t=Body0019.jpg
-Jim
Concentric/sq.tube adjustable Stabar...!
:thumbsup: OK; just skip the "Concentric/" in my subject reference... :eek:
http://i103.photobucket.com/albums/m...arFront004.jpg
Tube flex under braking...
Richard,
You mean the upper rear a arm attachment to the chassis is the one that may flex, correct? The front one appears to have a chassis cross-member directly behind it, fixing it pretty damned substantially (laterally). Isn't it the upper rear a-arm attachment point that's suspect?
Chris Crowe
PS: A very cool redering of a very cool design effort, Jim. (Although I DO share in Rob's opinion concerning the 1" floor-deviation rule being violated between bulkheads A and B. The deviation pictured looks to be about three or four inches ot so).
Connector visualization trouble; please help
Quote:
Originally Posted by
RobLav
- Citations use steel male and female cone shaped threaded connectors to join the rear tubular structure to the rest of the chassis. The rear structure goes back to the exact same spot upon re-assembly - always. The male fitting is welded to the chassis tubes perpendicular to the chassis tube, and the female end goes inside the rear structure tube. An advantage to this is also that you can place the engine bay structure exactly where you want it, regardless of small welding tolerances. Weld the perpendicular bosses to the chassis first, then place the female connectors inside the engine bay structure loosely with rosette weld holes in the tubes. Put the rear where you want it, then weld the rosette holes inside the tubes. Minimizes stresses too. This method will be much better than trying to raise and lower the engine / chassis.
Rob,
I have trouble visualizing this connector's layout, :confused:; are the connector's male and female cone centerlines perpendicular to the tubing centerlines?
Do you have any pictures of these Citation connectors?
Thank you,
Rick
Re: Square Tube Adjustable Stabar
Quote:
Originally Posted by
Rick Kean
:thumbsup: OK; just skip the "Concentric/" in my subject reference... :eek:
Yup. It's a cylinder with flat faces machined on it, slots milled down the sides and center drilled for variable torsional stiffness along the length of the bar. Stiffness is adjusted by sliding the bar back and forth between the torsion arms.
http://s103.photobucket.com/albums/m...llbarshaft.jpg
-Jim
Re: Front Upper A-arm Mounts
Quote:
Originally Posted by
R. Pare
Front upper a-arm inboard mounts : expect a lot of flexing under braking - mounting to a tube in that manner (untriangulated) will eventually fatigue and break the tube.
You're absolutely right. Modified as shown:
http://s103.photobucket.com/albums/m...=cartop008.jpg
Clearly, more frame mods to come. I have an idea for the rear bellcranks, but need to analyze the front motion ratio first.
Thanks,
-Jim
Thanks yet again, Richard ---
I think what I find confusing is the "stressed panel" on the floor-plan. That is, if the chassis floor is fully V shaped, and that V-shape is capped (on both ends) at the front, steering wheel and roll bar bulkheads... well, you no longer really have a "space frame" car, but a monocoque. (Actually a semi-monocoque; a semi-monocoque... fully stressed-skin V-shaped [or even U-shaped] structure with an open top. Like all the first Formula 1 monocoques of the mid sixties).
You've explained this to me before; one day I will hopefully understand. Another way of expressing my question is this: Could JJ's v-shaped floor be even a deeper V (or U) configuration than it is now? Say, a very deep v-shape, say six inches high and 10" wide? Is that still a "tube-frame" race car as F1000 is intended to be? Just how far can this gray area be pushed?
Thanks again -- and please anyone, give Richard a hand -- I've been pestering him for more than a year in this area of grand confusion for me.
Chris
PS: Also could have sworn there was a stricture against more than a 1" deviation in the stressed-floor panel. This would negate the potential for much of the craziness (deep V or U shapes) above. But if that 1" deviation rule doesn't apply to the catagory, why not exploit this gray area all the way? Will again scrutinze the GCR.
Re: R. Pare-- Shock & Bellcrank Mounting
Quote:
Originally Posted by
R. Pare
I'd also re-think the rear shock mounting - again, you have big loads fed into the mid section of long tubes.
Also - the long clevis adjusters mounting the rear shocks will be very prone to bending. Better to mount the shocks directly to the plate rather than hang them out in the air like that. There also needs to be some triangulation of the mounting points of the cross bracket or the shock loads will move the bracket and the tubes around a lot.
Correct again. I've moved the rear bellcranks forward and up, which allow me to use a longer arm to drive the damper & springs and gives a greater angle with the ground plane. My motion ratio (damper movement / wheel movement) is now 1.12, a significant improvement.
Here's a shot of the new location:
http://s103.photobucket.com/albums/m...ionrear002.jpg
I did an FEA of the entire region of the bellcrank mounts and the result was just as you suggested:
http://s103.photobucket.com/albums/m...ftrear2_02.jpg
Now looking at how to brace it...
Thanks,
-Jim
Citation style conical connectors
Thanks Stephen and Dan for the references to Sean's blog.
My take-away: To successfully incorporate Citation style conical connectors into a subframe design, all of the connectors must be fab'ed up with their centerlines parallel to each other.
The trick is how to deal with subframe warping from the weldout, and Rob's suggested 'loosely fit female connectors + rosette welds' sounds like it works fine.
Rick
Re: Motion Ratio Linearity
R. Pare asked how linear are my motion ratios, but it looks like the post was deleted. Anyway, here's a plot of the rear suspension motion ratio. It looks like I have to reposition the zero point as I have only about 1" of useful linear wheel motion in bump.
-Jim
Tire Force vs. Tire Movement
I figured out how to make SolidWorks plot vertical tire force versus wheel displacement. It apparently blew SolidWorks 2009's little mind permanently and I had to upgrade to 2010.
For those people I haven't yet replied to, I'll get to it...
-Jim