Computer Aided Design tools used in the industry

[Bob_Sheaves]

Ohayo goziamasu! (that means "Good Morning" in Japanese):

I have followed the link-coil discussion vs. leaf (hotchkiss) suspension design with great interest.

I have a question of some personal relevance (I am a vehicle dynamics engineer by trade) directed at the industry reps on this board, "What CAD tools (if any) do you use and why or why not?"

The second half of this question: "Is there any interest in utilizing the same design tools the 'Big 3' use for your projects?"

Best regards,

Bob Sheaves

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[Donahoe]

DRE uses Autocad...Turbo cad .......... Solid works....... But mostly I use chalk & concreate...

NEVER LIFT!!!!!

[Bob_Sheaves]

I appreciate your answers to the first part of the question. Judging from the tools, it seems that cost is an issue. Is this true? Being in the industry for a number of years, I know what I have invested in my personal CATIA and DADS software and hardware. Which leads me back to the original post...

How do you do your preliminary analysis to ensure you haven't made an unforseen "oops" in the design of the vehicle? A/Cad, nor the others has even the slightest analysis capability (by this I am NOT referring to FEA- Finite Element Analysis- but rather dynamic analysis of the handling characteristics you have designed in). Experience can cover a great multitude of sins, but not performing some dynamics on a design seems to be "unusual". Could you please explain in more detail?

Arigato goziamasu! (formal "Thank you"- accompanied by a bow)

Bob Sheaves

[Donahoe]

The problem comes down to veriables... And LOTS OF THEM... In and off road car you have so meny unforseen things that can throw a wrench into the best laid plans... As far as stress.. Most of the time I will consult with outside engineers. We are actually working on the rear arms for a new truck we are building now and we went over and over what we thought how thick the arms should be at the shock piviot points... Its a 51" long arm with 2 shocks riding about 30" from the piviot point... We went over it and over it.. Then called our engineers to get the tech answer as to what the loads will be and how thick to build the arms... Before we called I came up with 8" thick at the shocks.. We called them and after a few hours they called back with the answer... 8" thick.. Now keep in mind they started not knowing what I thought ...Just the facts... So they will take all the info we give them and start running analisis programs on the computer... My caculation came from looking at the span and thinking about it for a second and saying to myself... HMMM? I think about 8" ...Total guess..with a little bit of past knowlage... But whats funny is... Its happens 9 times out of 10... We go hmmmmmmmmmm?? I would stick that hiem about there... They come back and say it goes right there... We say oh yeah right where we wanted it. Cool. But what they can never figure out is the load a by-pass shock will take. We do most everything in G FORCE.. Well how meny G's does a by-pass shock see? Any one??? Any one??? Who knows...?? Thats just one veriable in a huge slew... Mother nature... Polar moment....Scrub??? WHat effects does scrub have in the dirt?? Figure that one out..... Plus the other thing we have going for us(off-road trucks now-a-days) is HUGE amounts of wheel travel... So how much does caster and camber matter when your pushing 20+ inches of wheel travel in the dirt... The problem most engineers come across when working with off-road trucks in OVER ENGINEERING... Thinking like its a road car... Its not... Lots of the came priciples apply but its not the same... So basically I build the thing send the weight and piviots to the engeneers and they come back with...YEAH IT SHOULD WORK!! What is the Right way to build an off-road truck or car??? You tell me??? Is there a RIGHT WAY??? Is there the RIGHT WAY to build a-arms?? Or there is? Well what about all the wrong ones out there that win races??? TO MENY VERIABLES.....To be totally honest most of the fab guys out there are not to cad freindly.. We are just learning ourselves... We have been playing with the cad for a couple of years... But we still like to use the old methods of desighning a truck... String....Chalk..... Floor...... I know of 4 trophy trucks that were built from complete computer drawings the rest started with a flat concrete floor and a pile of tube... Not to say that one is better then the other... I just know that sometimes what looks great on paper looks like ca ca in the real world. But we are really getting into the whole cad thing... Having a good time.... Learing more and more everyday... Its alot easier to copmlete piviot points with a cad thats for sure.... But I learned how to build these things on the floor.. Its hard to teach and old dog new tricks.

NEVER LIFT!!!!!

[vwguy]

as an autocad user i thinks its gocd for some things to sketch out but im just starting to design 4 links etc and to me like kreg said its seems easier to do it all by head, experience, and concrete. but most its TRIAL AND ERROR

[FABRICATOR]

Bob,
We all use CAD+R, and that stands for Cactus And Dust, and we must never forget Rocks. CAD as you may know it, is good in our sport for checking geometry, strength of parts, some ratios and spring rates, chassis design (most of it) and that's about it. No CAD program at any price will figure in all the variables, which the dezert is full of. Even if you had the greatest CAD program, you would have to "know" what safety factor to throw in at each step of the way. Otherwise your computer would design an Army tank. CAD is very useful in the design of each part, but only if you know ultimate loads, cycles, and the old problem of abuse. There is no doubt copious use of CAD could improve nearly any off-road race car. The most sophisticated programs might collectively be able to somewhat design a car for the rough, but how rough and at what speed? I don't think even NASA is there yet. Unfortunately, there are few if any Off-road race cars that are at a level where this is would make enough difference. Most off-road cars are loaded with parts, brackets, and mounts, that are mismatched as far as ultimate strength goes, and that's where CAD would help the most. It's sort of like putting an off-road race car through wind tunnel testing (and this has been done). Does it help? Yes. Does it win races? No. Most other forms of racing and also aircraft are made to do one thing and not be abused to any great extent. Ask yourself how an IRL car would be different if it were designed to survive anything short of hitting the wall at a steep angle. By the time CAD is truly a major force in this sport, all the cars will be virtually the same. We don't even know if they (the fastest) will be 2 or 4 wheel drive! That's what makes it so interesting and elusive. Craig is right about using chalk on the concrete. We also use pieces of welding rod, string, carpenters levels, tape measures and most of all the eyeball. So far, for the most part, it's all been a matter of improving what has already been done and borrowing ideas from wherever we may see them.

[Greg]

Kreg, has anyone that you know of taken the time to run real time tests on shocks? Like to use an accelerometer and presure monitors (on both ends of the shock) and gathered data? I have access to equipment like this. I have not run tests yet but even when i do i wont be shure what to do with the data. If someone has or could come up with basline parameters then this info could be used to set up other vehicles with much less trial and error.

Greg

[Bob_Sheaves]

Hi Greg,

This is a very common thing to do in the automotive industry-both on a
"shock dyno" and on development vehicles. As Kreg stated, it inputs are
what must be know for the data to have value for development of vehicle
specific valving.

FYI- these parameters are some of the most highly guarded secrets among
the automotive manufacturers.

Best regards,

Bob Sheaves

[jeff]

Greg-

I can't remember the team names but... About six or seven years ago I remember seeing some teams that were testing shocks in the manner you describe... I remember watching some pretty interesting footage of all the gizmos and gadgets that they had hooked to the shocks. They ran a few vehicles, both street and off-road through their paces - in some cases they had an Indy car hitting a "bump" at 200mph - the off-road guys had footage of a Dakar type rally vehicle nailing a whoop at 100mph... the instruments recorded just about every damn parameter you could think of. All sorts of interesting stuff came out of it... ESPECIALLY THE EXTRA SLOW MOTION footage - it's amazing to watch springs do weird things. There was good footage of certain winds in the spring actually collapsing under extremely fast compression - to the point where the coil would no longer absorb energy - it just locked there before your eyes. It's cool to hear about it - but to see it was amazing. I can't remember which shops I was at - one was off-road and the other was a Indy type roundy round chassis analysis lab. I'll put a post-it on the dash of my truck to remind me to try and remember the names.

Oh yeah - on the CAD discussion... history has proven that even the best designs fail when poorly constructed. I know that's not the point of this thread - but if the fabricator screws up or the materials aren't up to spec - all the CAD in the world won't save you.

[Dylan]

A note about "CAD"
people think CAD is much more powerfull than it is. Programs such as autocad simply draw lines, one step above pencil and paper. Solid modleing (solid works, catia) works like a lathe and a mill in real life but with no chips on the floor and quick easy changes. These programs with the added FEA package are very usefull and will simulate testing like bending and braking parts, but in the wrong hands will give totaly worthless results " garbage in garbage out". I would like to take a look at at DADS software from what i've heard its very usefull. you can also do dynamic analisis on math software like " mat lab or Maple" but you need to know a lot about dynamics to use it. I got maple for $100 but i havent used it lately.

I use a solidworks sketch and excel to figure out caster, camber, scrub, scub radius, roll center,anti squat, dive, motion ratio, ect. but I could do it all with paper and pencil too, "and have done it with chalk and string on the shop floor at 2:00AM when need be". As for strength of parts its good to do some rough calc's on vulnerable parts then multiply by 2 just to be safe because you never know how big a rock your going to hit.

My questions:
I can calculate pitch moment, anti squat, ect.... but what do you want for these values? If DADS can tell me that then PLEASE send me a copy. (I've got my own guesses)

how well does FEA simulate a tube's impact with a rock?
what about the second impact when the tube is already dented in??
with a lot of work you could do that on FEA but it would be a lot more fun and understandable for the dezert-people to just go try it.