JJLudemann's Design Thread

[RobLav]

Interesting graph - thanks for sharing. It's good to see the independent variable (tire movement) on the X-axis and the dependent variable on the Y-axis - makes it easier to understand.

Also interesting that the curved line does not cross the origin (0,0). With changes in geometry, you can move that curve where you want. It might be worth trying to decrease the effect of the falling rate geometry at greater displacement - ie - move the curve to the right a bit. Also, the more linear section in the middle illustrates a range of movement from roughly -15mm to +10mm. That's only about an inch of travel. Can you try to add more linear displacement?

Lastly, I'm assuming that the graph does not show the effect of spring compression. It'd be cool to do that too - like show the effects with a 500#/in spring and then a 1000#/in spring.

I've enjoyed following your progress.

[nulrich]

SolidWorks is great software. However, using Motion to develop suspension geometry can be very time-consuming. You might look into some of the specialty suspension design software, which will allow you to iterate much faster, and report exactly the parameters you are trying to modify. I use SolidWorks to develop a draft geometry, work in OptimumK until I get the desired suspension characteristics, then finalize the packaging in SolidWorks. (OptimumK is fairly pricey, but I know there are simpler and cheaper packages.)

You probably want to plot motion ratio rather than force/displacement. Based on your example graph you have massive changes in motion ratio, even though the force curves don't show it clearly. There is no reason you can't get very close to a motion ratio that is constant (or rising/falling if that is your objective) by the appropriate rocker design and damper mounting...independent of pushrod/pullrod angle. Here's a graph from OptimumK.

Nathan

[JJLudemann]

Just a few things I was thinking about. A motion ratio of 0.8 might be ok, this is for the wheel/damper movement MR. I know some people say it should be the other way around but this is the definition I've always used.

I find it easier to visualize output/input, or dependent variable / independent variable.

How big is the distance between the rear upper outer a-arm point and the toe link? It looks a bit small to me. Try to increase it as much as possible, it will reduce the toe compliance and make the car more stable. Are you using the same uprights front and rear? Could you post an image of the upright with hub and brakes attached?

The position of the rear toe link isn't finalized. I think you're right-- it needs to be moved forward, away from the A-arm attachment. Front and rear uprights will be similar, but not identical. Attached is a view of the upright with hub & brakes.

http://s103.photobucket.com/albums/m...tLF_Assy02.jpg

The distance between the rear sprocket and the frame tube looks a bit small. I have been surprised a few times with how much the chain moves when driving.

My plan is to enclose the chain in the mandatory chain guard, with teflon chain ramps to control the flailing as in Porsche 911 cam chains.

The upper mounting for the right diff holder will put a fair bit of bending on the tube. You might want to try to fit a tube going to the node where the upper a-arm front pick up is attached.

Fixed. This is an area that will receive special attention as I screwed this up in designing the Princetion '81 Mini-Baja car causing a DNF the following year .

http://s103.photobucket.com/albums/m...onrear2_03.jpg

I can't see how the front of the engine is attached, but there is a risk you will put a bit of bending on the tube holding the upper rear engine mounts.

Pending finite element analysis

I'm also not too sure about the mounting of the rear dampers. Are there going to be some triangulation around there?

Redesigned to improve motion ratio:

http://s103.photobucket.com/albums/m...onRear2_04.jpg

And tested:

http://s103.photobucket.com/albums/m...Member2_01.jpg

I would really consider losing the clutch pedal. Or actually I would never design a race car with a bike engine with a clutch pedal. It can be nice when driving slowly in the pits or when spinning. But a well-placed and well done hand clutch works just as well. And from my point of view driving with tree pedals is just more uncomfortable and there is more risk of getting stuck when moving your feet around. I know a few people who have a really hard time driving with only two pedals in a formula car, but it shouldn’t be that hard to learn. Most people don't have a problem driving carts.

I've got more than 30 years of experience pushing that clutch pedal when I spin . Plus, I hope to train drivers in Thailand, and that may be just too foreign. Maybe for the Mark II. The pedals and footwell are carefully designed for my size 11 1/2 feet.

I don't know if you have seen these master cylinders AP CP7854. It can be a bit more complicated to do the balance bar and package. But they are really nice and you can usually reduce the play and compliance compared with the normal balance bar.

My plan is to design & build the entire pedal cluster here. It'll be cheaper and lighter than I can buy elsewhere.

Other than that I would just try to move the suspension points as close as possible to the nodes on the frame.

There will be some of that when I do the overall FEA on the chassis.

Looking like it could be a really nice car. I wish I had the time to do more designing and building the car I have been thinking about/designing for the past years. I was hoping to work some on it tonight, but I wrote this instead.

Thanks! I had to "retire" before I could do this. I think it would be almost impossible to do while also working full time.

-Jim

[JJLudemann]

After some (OK, lots of) playing around with the design, I came up with one that gives me an almost perfectly linear spring rate for a full 50mm of wheel movement in bump. Here's a plot of the vertical spring force at the rear wheel versus movement of the wheel above nominal in bump. The offset at zero wheel movement is the static load required to support the car at rest. Spring force will just scale linearly with spring constant, which in this case is 1000 pounds per inch.

-Jim

[Billy Wight]

Jim,

First off, you've done a lot of good looking work here. Most people don't realize the number of hard hours this takes until they actually try it for themselves! I do have one cautionary statement for you though: be very careful with what results you get from FEA, especially with the SolidWorks software as they make it is very easy to create colorful glamorous looking plots with no absolutely no meaningful results.

For example, the plot of your latest rear shock member: It looks as though you are using solid elements. With such a thin walled body, solid elements are a very bad choice because you end up with one element across the thickness and very bad aspect ratios. This will give false results in deformation and stress (not even close to the actual numbers, especially stress) even though the elements are second order by default in SolidWorks. In order to get correct results with solids, you would need at least 3 elements accross the thickness with good aspect ratios. By my estimates from the lines in the plot, you will need 1/3 the element size to get the aspect reasonable, and 1/3 of that to then get the 3 elements across the thickness. Shrinking the elemets by a factor of 9 increases their number by it's cube (volume): you will need 729 times the current amount of elements to get a real soluion! I'm sure this will be beond your computers computational power.

A much better option would be to use shell (2d) elements. This will give a real solution and will actually solve faster than your current solid element setup. Have a look at the help for shell elements (you will need to create surfaces) if you are not already familiar with this. Good luck, and keep up the good work!

[JJLudemann]

First off, you've done a lot of good looking work here. Most people don't realize the number of hard hours this takes until they actually try it for themselves!

Thanks! It is an amazing amount of work. Fortunately, it's what I was born to do.

It looks as though you are using solid elements. With such a thin walled body, solid elements are a very bad choice because you end up with one element across the thickness and very bad aspect ratios. This will give false results in deformation and stress (not even close to the actual numbers, especially stress) even though the elements are second order by default in SolidWorks. In order to get correct results with solids, you would need at least 3 elements accross the thickness with good aspect ratios. By my estimates from the lines in the plot, you will need 1/3 the element size to get the aspect reasonable, and 1/3 of that to then get the 3 elements across the thickness. Shrinking the elemets by a factor of 9 increases their number by it's cube (volume): you will need 729 times the current amount of elements to get a real soluion! I'm sure this will be beyond your computers computational power.

A much better option would be to use shell (2d) elements. This will give a real solution and will actually solve faster than your current solid element setup. Have a look at the help for shell elements (you will need to create surfaces) if you are not already familiar with this. Good luck, and keep up the good work!

That's really important feedback. A whole new kettle of worms, as it were. OK, so I've spent a lot of time studying the SolidWorks documentation on meshing and watched some YouTube videos on mesh quality (that high-end software like MSC Nastran is unbelievably sophisticated, like what you might use to design a 747. Oh, right.) I think I'm coming up to speed on mesh quality.

Attached are the latest plots of the part in question. I used shell elements for the tube and solid elements for the bracket. I meshed it using the curvature-sensitive mesher with some mesh controls on problematic edges, and made a few minor changes to the design by adding some small fillets to replace some sharp edges.

The first one is the stress plot on the deformed shape:

http://s103.photobucket.com/albums/m...Member2_03.jpg

then the new mesh:

http://s103.photobucket.com/albums/m...Member2_04.jpg

Aspect ratio mesh quality check:

http://s103.photobucket.com/albums/m...Member2_05.jpg

and the Jacobian mesh quality check:

http://s103.photobucket.com/albums/m...Member2_06.jpg

I haven't been able to find any way to view the internal structure of the mesh in SolidWorks.

-Jim

[rickb99]

......high-end software like MSC Nastran is unbelievably sophisticated, like what you might use to design a 747. -Jim

BOING does a lot of their design work in CATIA and ENOVIA (which likes to talk to CATIA) as their manufacturing aid. CATIA was used for the 777, newest 737 and the Joint Strike Fighter.

Saw some of the CATIA work for the 777. It's beautiful. I'm still a fan of AutoCAD for simple stuff. BUT your Solidworks leaves me drooling too

[Billy Wight]

Jim,

Looks like you're making progress, here's some more info to chew on:

You will want to use a shell mesh for that entire structure. With the smaller elements you show there, you could get good results, but it will take a long time to solve. You can get the same results from a shell mesh that will solve in less than 10 seconds. This is vital for quick iterations on design.

Aspect ratio ahould be less than 5 for a good element. It is ok to have a few worse than that as it is impossible to get perfect elements for every shape, but you want to have a very small portion of your mesh with bad elements (<2%).

I'm not sure what the Jacobian value in your plot is referring to, it should range from 0 to 1 with 1 being a perfect element, 0 a very badly distorted one, and negative numbers being essentially inside out or self intersecting. A value greater than 0.7 is preferred. Maybe SolidWorks is using some other scaling in the jacobian report.

You might be able to see the internal elements by doing an iso-clipped plot of your element quality contour. This is a good way to see the overall number of bad elements you may have.

It looks as though you have incompatable mesh between the shell meshed tube and the solid bracket portion (the nodes are not coincident between the two). Another reason to go for the full shell mesh structure.

Be careful designing in small filleted edges. Remember that it's really easy to insert a perfecly round dillet in CAD, but in actual manufacturing those will probably be done by hand with a deburring tool or similar which leaves much to be desired on surface finish.

Sharp corners and small fillets are problematic for simulation convergence. Sharp corners represent a singularity in the matrix leading to infinite stress and small fillets are similar - you will need to keep refining your mesh until you no longer see appreciable changes in the stress result. A h-adaptive (or p-adaptive) method is an automated way to accomplish this.

Good luck!

[JJLudemann]

Today I bit the bullet and tried a finite element analysis of the entire frame. Used beam and shell elements to keep Billy happy . It produced displacement and strain plots but no stress plot, or rather a stress plot on only the shell elements, which is not so useful. Still working...

Here's the displacement plot showing 4.1 mm maximum displacement with the frame supported at both ends and a 1000 pound load at the bottom of the main roll hoop:

http://s103.photobucket.com/albums/m...rameTemp01.jpg

-Jim

[Billy Wight]

Today I bit the bullet and tried a finite element analysis of the entire frame. Used beam and shell elements to keep Billy happy .

Uh-oh, now you're going to get me started on proper constraints for a finite element torsion test...

And don't worry about stress plots on your overall chassis, if you hit your stiffness targets you will not be overstressed anywhere (at least not at this large scale of analyisis). You may want to look into a modal analysis though...

[JJLudemann]

When I look at your side view drawing, I'd raise the roll hoop. It's marginal at best. As noted by others it does not appear robust enough. A bit more height will give you some of the egress you seek. The Citation roll hoop is a good example of the ridgity you seek.

Done

If you watch videos of actual chain function, the amount of whipping going on can be quite surprising. Allow enough clearance.

This was the best one I could find:
http://www.youtube.com/watch?v=UYoRDFBD_Sc
Admittedly, not as good as I'd like. Apparently "chain whip" and "chain flail" have other meanings . Does anyone know of a better video of chain movement?

You don't need multiple centimeters of pedal adjustment. Having the driver's heels unencumbered by all those longitudinal rails will make foot movement smoother. A flat floor with basic heel rest will be easier to drive.

The driver's feet will have a flat, smooth floor to operate on. The large amount of pedal adjustment was a freebie which might come in handy when I teach my daughters to drive.

Check out the steering on the new RFR1000, it may make a simplier steering solution than those two joints being maxed out. You do not want the steering shaft hindering the driver's foot movement.

The manufacturer's specs for the steering u-joints are a maximum angle of 32 degrees and a maximum recommended operating angle of 20 degrees, which is what I'm running them at. Those purpose-built formula-car steering racks are $expensive$. I've carefully positioned the steering column and pedals so that the driver's feet will never interfere even under left-foot braking.

Another advantage to being able to "split" the chassis... you can, in time, build multiple configurations of rear chassis for both automotive and motorcycle engines.

Noted. If I have time maybe I'll get around to investigating a split chassis. Right now it looks like I'd have to make major concessions on chassis rigidity.

Where are you mounting the fire-bottle? Battery? The Tatuus mounted the fire bottle under the fuel cell. But it was a very special fuel cell, with an exagerated lower pickup. Putting the fire bottle under the fuel cell does raise the C/G a bit with a full fuel load.

The fire bottle goes under the driver's thighs. I expect the battery will be at the very front of the car to improve weight balance, but we'll have to see how heavy the battery cables would be. I might end up using a minimal stack of radio-control car batteries or the like, which would be light and allow the battery to be located wherever necessary. The fuel cell will be flat against the crossmembers below the driver's compartment.

Thanks for the feedback!

-Jim

[Alex Pate]

Look into ballistic batteries they weigh less than 2 lbs I think

[Nicholas Belling]

We have been building wiring looms for all our geartronics car harness's.

source spec 55 wire.. ultra light weight. same stuff Formula 1 use. find a gauge from there specification that flows your current demands.

[JJLudemann]

For those who think I don't have enough diagonal bracing, I present... A slight software glitch.

http://s103.photobucket.com/albums/m...rameTemp02.jpg

Apparently my CAD SW agrees with you. Luckily this disappeared the next time I meshed the frame.

-Jim

[iamuwere]

Looks pretty stiff. Hell getting in and out though...

[Evl]

I like the dual push-rod arrangement in the suspension too.

[JJLudemann]

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.

The belly pan is indeed a stressed skin, flat from the driver's knees back, transitioning from the driver's knees forward to a V shape which goes to the front-most suspension attachment point. As I understand it, SCCA FB requires a flat bottom from the back of the front tires to the front of the back tires. It also allows a stressed-skin belly pan back to the rear axle, but it doesn't say the belly pan has to be the bottom of the car. If the belly pan had to be the bottom of the car, shadow plates would be illegal, pretty much eliminating all cars from the class, wouldn't it?

The GCR uses the terms 'pan' and 'undertray'. 'Undertray' is technically not a word, but from dictionary.com:

tray

1. a flat, shallow container or receptacle made of wood, metal, etc., usually with slightly raised edges, used for carrying, holding, or displaying articles of food, glass, china, etc.

pan

1. a broad, shallow container of metal, usually having sides flaring outward toward the top, used in various forms for frying, baking, washing, etc.


So it seems normal usage of those words means that the tray or pan is not flat. Here's a view of my belly pan. This is one I'm using for the finite element analysis; the actual design will be flush with the bottoms of the tubes.

http://s103.photobucket.com/albums/m...rameTemp04.jpg

-Jim

[JJLudemann]

Jim,

I was looking at the the side view of your chassis with the driver inside and was thinking what would his knees do if it was backed into a wall at a high rate of speed. Make sure that your dash is not mounted so solidly as to become a knee cap remover.

It's kinda gross but...

It's not kinda gross, it's the designer's job to consider worst-case scenarios. My background as a computer designer is useful in that we had to explicitly consider what happens in situations as rare as 1 in 4e13, or 1/40,000,000,000,000. I think that the inside of the car will be paneled and padded, all rounded edges, no exposed screws, etc. I'm not a big fan of pain.

-Jim

[Christopher Crowe]

-- and if your "floor pan" is legal... it's a terrific exploitation of the letter of the rules.

I've been thinking along the same lines, in fact we're in construction... but I'm very nervous about this area. For instance... what (in the regulations) would prevent you taking your v-shaped floor and capping it with a flat sheet atop the vee? With no 1" deviation rule in FB, what prevents this?

I wish the GCR were a clearer document. I think in spirit the idea was to simply mandate that keep "lower main chassis tubes" would be right on the deck at 10" wide (inside dimension) with a flat bottom sheet attached. But the rules as written seem to allow for pushing things like mad in this area. My question is how far things be pushed... You've wisely taken it quite far... but the "feel" is still completely "space frame."

Again, thanks for the response and good luck with your extrordinary design effort. Just put big radiators on that thing for operation in Thailand!

Christopher Crowe

PS: My son and I are still laughing at the computer's take on chassis triangulation. What a machine that would be -- just straddle it and ride it like a horse!

[starkejt]

source spec 55 wire.. ultra light weight. same stuff Formula 1 use. find a gauge from there specification that flows your current demands.

Probably not terribly relevant to this thread, but while the spec 55 wire is nice, the whizziest wire I am aware of is MIL-W-22759/92 with nickel plated conductors, which is a tad lighter than spec 55 and carries a 260 deg C rating, meaning you can use as small as half the CMA as you can with spec 55 in some cases.

[JJLudemann]

My girlfriend saw the video of Lauda's horrifying crash and burn. She says, when I finish building the car, I'm not allowed to drive it . That would be a shame...


Having to find a new girlfriend, I mean.

-Jim

[R. Pare]

JJ:

Just curious as to where the design stands now. Hope you've made good progress.

[JJLudemann]

JJ:

Just curious as to where the design stands now. Hope you've made good progress.

Sorry, it's well past time for an update. I feel like I've redesigned just about every component in the car, some of them 3, 4, 5 times since the last update. I extended the nose to the FB max for more crush space, which required resculpting the front nose line, which allowed me to raise the front upper frame rails, which allowed me to raise the front suspension rocker arm to get a better angle for a higher motion ratio. I redesigned the front and rear wings using a higher-lift profile; rear wing went to 3-element upper and 2-element lower wing. Redesigned rear wing endplates to mate nicely with the diffuser, and included boundary-layer-sucking louvers above the upper wing. Resculpted the sidepods for cooler shark-mouth inlet and made the outlet more undercut at the bottom. Raised the point at which the middle side frame tube meets the main rollover hoop so the fuel cell can come out the side of the car by removing only one frame member; rescuplted the side of the car to match this. Designed the rear upright assembly, which was previously just a placeholder. Fixed front suspension caster angle which had gone wrong somewhere along the way. Did initial design of the seat; more design of the fuel cell. Did a lot of mirroring of suspension parts so the car now sits on 4 wheels. Designed the headers. Added engine air intake NACA ducts, also driver cooling NACA ducts. Redesigned rear anti-roll bar assembly for new location after changing routing of the suspension pushrods. Widened the flat bottom beside the rear diffuser, raised the flat bottom along the sides a tiny bit (still within the rules). Modified pushrod lengths so the suspension can move in bump before rockers reach the middle of their range-- makes motion ratios more constant. Removed the rearward braces from the main rollover hoop pending more FEA tests. Did a lot of finite element tests of the chassis. And there's probably lots more I've forgotten.

Anyway, here are some pics:

http://s103.photobucket.com/albums/m...Corners36A.jpg

http://s103.photobucket.com/albums/m...Corners40A.jpg

http://s103.photobucket.com/albums/m...xploded02A.jpg

http://s103.photobucket.com/albums/m...ameTemp03A.jpg

http://s103.photobucket.com/albums/m...ameTemp05A.jpg

http://s103.photobucket.com/albums/m...ameTemp06A.jpg

http://s103.photobucket.com/albums/m...eTemp07A-1.jpg

http://s103.photobucket.com/albums/m...ameTemp09A.jpg

[Billy Wight]

Looking good, very nice renderings too!

[Christopher Crowe]

-- thank you for sharing all of it!

Chris

[JJLudemann]

Although I haven't been posting on ApexSpeed, I've been hard at work all along. The build has started, and I started a website where I've been documenting everything. I didn't want to bring it to people's attention until there was some worthwhile content, but now it's getting there:

www.LudemannEngineering.com

To make a long story short, I've built the chassis table, added the jigs, and have completed the frame back to the front roll hoop. Also, I've completed ordering most of the things that I need to finish the car. The rest I can have shipped by air one piece at a time, I hope.

[Christopher Crowe]

Damned happy to see the project wasn't still-born, Jim. Great work, please keep posting.

Chris

PS: Toward the end of the design phase, I believe you were a projected ten lbs (chassis only) overweight. Did you get that 10 lbs out before embarking?

[ghickman]

I do this stuff for a living and have hundreds of thousand of dollars wrapped up in fancy machinery. What you've done is very impressive to say the least.

Jim.... you display a knack for turning the learning curve from years into what appears to be days. It makes me tired just looking at all you've done in such a short time. Living in Thailand has to make doing this even more difficult I would think?

Wish my kids were young enough for a swing set.... I'd be snagging a set of plans from you.... pretty impressive.

[Billy Wight]

Looking good Jim. You should revisit your suspension arm loading, though, as your constraints are not corfrect in the analysis. You really need to add in a push-rod (or pull-rod) to react the vertical loads and apply the necessary beam end releases (or whatever SolidWorks calls it) to represent the spherical bearings at the ends of the arms and upright. You should not see any bending in the arms, only tension and compression. Also look at various other loadcases besides braking, and add some additional safety factor for dynamic loading and fatigue. I think you'll find you need much larger rod ends and spherical bearings than what you're planning on now.

[RobLav]

This is really cool stuff. Rodends and sphericals seem about right to me... What does Solidworks say the weight of the chassis will be?

Thanks for posting.

[Billy Wight]

Rodends and sphericals seem about right to me...

Indeed, I was mostly referring to the 1/4" rod ends. The others seem about right.

[RobLav]

Yes Billy - agree. 1/4 rodends are a bit on the small side. The problem will likely be the shank. Better to go with 5/16 and sleeve down for a 1/4" bolt or the more expensive 1/4 oversize shank type.

I recall my first FB mechanical shift system with round tubes. I had calculated that 3/16" rodends would easily suffice the mechanical advantage of my hand on the shift lever. Nope! One of them failed at the shank leaving me stuck in 3rd gear. You have to think about shock loads. I ended up using 3/16 oversize shank rodends and have not had a problem since.

Given that 1/4" shanks are required on my hand operated shift system, I cannot imagine how 1/4" shanks would suffice in a loaded suspension member on the car.

[problemchild]

Heavy duty workbenches!

[Christopher Crowe]

What is your (tube only) finished chassis weight, Jim?

Thanks,

Chris

[JJLudemann]

Damned happy to see the project wasn't still-born, Jim. Great work, please keep posting.

Chris

PS: Toward the end of the design phase, I believe you were a projected ten lbs (chassis only) overweight. Did you get that 10 lbs out before embarking?

I'm not too worried about the weight of the frame at the moment as I consider the first car a prototype, and there's nothing to run against yet in Thailand anyway. Also, I haven't been able to get the exact wall thicknesses I want in Thailand. Maybe the next car will be built with tubing imported from the US. Right now I can't even get Solidworks to tell me the weight as most of the tubes have been replaced in the model with the thin slit tubes as explained in the tutorial on my website.

Thanks for the encouragement!

-Jim

[JJLudemann]

I do this stuff for a living and have hundreds of thousand of dollars wrapped up in fancy machinery. What you've done is very impressive to say the least.

Jim.... you display a knack for turning the learning curve from years into what appears to be days. It makes me tired just looking at all you've done in such a short time. Living in Thailand has to make doing this even more difficult I would think?

Wish my kids were young enough for a swing set.... I'd be snagging a set of plans from you.... pretty impressive.

Very kind words, indeed! I'm still smiling about your learning-curve comment. The work I've done makes me tired, too. Some days I give up at the end of the day with a headache and nausea . While I sometimes complain about the difficulties of doing this in Thailand, I'm pretty sure I never would have attempted it in the US. Just too danged expensive! When building the body buck, for instance, I think I'll be able to find qualified help for very little money. I dream someday of having lots of expensive machinery like you, or like the Diasio car factory photos I've seen...

-Jim

[JJLudemann]

Looking good Jim. You should revisit your suspension arm loading, though, as your constraints are not corfrect in the analysis. You really need to add in a push-rod (or pull-rod) to react the vertical loads and apply the necessary beam end releases (or whatever SolidWorks calls it) to represent the spherical bearings at the ends of the arms and upright. You should not see any bending in the arms, only tension and compression. Also look at various other loadcases besides braking, and add some additional safety factor for dynamic loading and fatigue. I think you'll find you need much larger rod ends and spherical bearings than what you're planning on now.

At your suggestion I added in the pushrod and ran a bunch of additional load cases on the model. The bending is just because it's a quick & dirty model, and I assumed the bending stiffness is minimal compared with the compression/tensile stiffness. Even with 5G braking performed entirely by the front tires (2500 lbs), combined with 4G bump also performed by the front tires only (like the rear wheels are in the air)(2000 lbs), I still can't generate enough load on the pushrod or upper A-arms to break a 1/4" rod end. In fact, I still have a 70% margin of safety. I had to think about this for a while to be sure it made sense, but eventually I figured out it's entirely determined by geometry, and the loads on the upper A-arm are what I would call a second-order effect.

Does anybody know of a catastrophic failure of one of these rod ends (of any size) in actual use? I sure would like to know before I get too far along.

Thanks,

-Jim

[JJLudemann]

This is really cool stuff. Rodends and sphericals seem about right to me... What does Solidworks say the weight of the chassis will be?

Thanks for posting.

I can't get a weight from Solidworks right now as most of the tubes have been replaced by thin slit tubes to get the end profiles (see the tutorial on my website). Solidworks has the nasty habit of completely losing the plot when you change the weldment profile, so I won't be changing them back until the last tube is cut. The last number I remember was about 105 pounds, but that will change some as I chickened out and used slightly thicker tubingin the lower front longitudinal frame rails to protect my legs a little better in a crash... I keep thinking about how Ayrton Senna wrote off six formula Fords in his last year of racing before graduating to F1. It's not IF I crash, it's WHEN I crash . Especially if I get out on the track with some young Thai guys, because they're completely incapable of dieing. Or so they think.

-Jim

[JJLudemann]

Heavy duty workbenches!

You mean the solid concrete ones? Actually the chassis build area is sunk into the machine shop floor, which automatically gives me 360 degrees of solid concrete benches. I highly recommend the concept. The other workbench is something I made in the USA and imported to Thailand, made with 4x4's and 1 1/2 thick plywood top. I hate wobbly workbenches.

-Jim

[RobLav]

Jim,
Front upper A-Arm rear leg rodend is critical.