Another RX7 in the mix

He has some stuff wrong, that's understandable, it's his first draft and he's posting here for advice and he's getting it. He's not building the cage yet.

John you wrote "What is the MAIN POINT I am trying to accomplish?"

I think you are misisng his main point. As I understand it his main point is to pass a course and get his credits. To do so he's decided to build a cage, which he has to design using some fancy computer SW, or it wouldn't be a 2012 course. Passing RA or NASA tech, is secondary (but his goal regardless).

So it doesn't matter that the fancy CAD desing offers nothing over a pencil sketch, or simply referring to FIA , it's a requirment of his course.

At least that's my take.

-Martin.

Evan,
You can use an inverted V in the back, don't forget somewhere you have to attach the shoulder harness. Focusing on the rear hatch as an escape route should be way down on your list.

Look at the FIA drawings for door bars...none of them show your uphill the wrong way configuration. You basically have one sill bar protecting the occupants body. You'll have a hard time convincing me to logbook that configuration....

Gene McCullough
RA western tech supervisor.

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john vanlandingham

But I could do it with the physical parts.

In the cage realm, every step taken away from the car towards a keyboard is a step away from having a cage in the car..

I spent all yesterday with daylight out in my car with tape measure and masking tape. After the sun went down and I could no longer see the numbers on my tape measure or work in the car, I started the CAD work.
As stated, I can't draw things up by hand very well at all, and so I use CATIA for my "chalkboard" which allows me to make sense of and edit my ideas.
I'm not trying to pose as some hot shot computer jockey. This is just part of the process that works for me.

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john vanlandingham

The CAR, real physical thing, is the CENTRAL thing, not opinions , not anything. The RULES come next, the cage must satisfy the rules but it must FIT WITHIn the CAR. And leave some sort of tiny cramped, annoying and ultimately limited space for the poor bastids who will be crammed in there.

That is true. Thank you for reminding me of it.

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john vanlandingham


Evan, Your signature posits a seriously erroneous idea with relevance to this first basic step of the cage---which we see has veered away from the point of the cage and reality...
Your siggy:
My life as an engineering student, stated by my friend Joe:

Quote

"We were brainwashed in elementary school to think that making assumptions makes an ass of you and me, and that's crap.
As engineers, we make assumptions, check them, and if we're right then we're geniuses"

You and Joe were not brainwashed. Your friend Joe was not smarter than those who obviously did not manage to teach him well enough..they may not have been smarter, but they had experience, an often good substitute for intelligence.
A usually good substitute.

Cutesy homilies aside, assumptions are the root of most blunders.
Assumptions in small details, assumption about the main purpose of doing things, about our own abilities, everything.......

The part that is particularly flat wrong is "we make assumptions, check them and if we're right...."

No that's what lifetime students with unlimited funds and who never need to get anything done do...

Engineering is not about "making assumptions"...

I have to go work on some actual physical things made of steel and bronze, but this subject is one you should explore ---with an open mind and with a broader question "What is the MAIN POINT I am trying to accomplish?" in mind.
Exploring this one fundamental error could be the most important thing you do at college.

Woah John, did that hit a nerve for you? And by the sounds of your response, has further solidified an opinion of me being some dumbass kid who doesn't know what he's doing... Which actually is partly true.
I'm getting a pretty good idea of how to go through the engineering process to design a part. Comparatively, I'm still much more of a novice when it comes to fabrication. I'm aware of this, and I have so much respect for you and others who have years of skill and experience with this. I don't think I'm better than you or smarter than you or my teachers.
This brings me to my MAIN POINT that I'm trying to accomplish with this -- I want to have a roll cage in my Mazda RX7 and start turning it into a rally car. But even moreso, I want to gain experience and skill in fabrication. I want to learn how to build a roll cage. In essence, I want to learn how to be more like you.

As for addressing the whole deal on assumptions, when you start analyzing elements closely enough, it is impossible to incorporate all variables and structures that are affecting the element. There are just too many of them. This makes assumption much more of a requirement than you might know.
For example, you are not going to inspect the grain structure of the steel tube under a microscope along the entire length before adding it to your cage. You might take a sample of it to an MTS to test that it meets all the strength requirements you seek, but probably you'll just end up assuming the manufacturer knew their shit and made it correctly.
Another example can be camshaft lobe design. There are 6 or 7 sequential derivatives in design that all have an effect on performance, but with current technology, it is impossible to analyze and design past "pop". The most important factors are velocity, acceleration, and jerk. Beyond that, the derivatives become much more esoteric, and so we assume that they will fall into place and the whole thing will work out.
I posted my signature for humor. But it should probably be put in parallel with another quote:
"The more I learn, the more I realize I don't know and have so much more to learn." -by Claude Rouelle from Optimum G

---

"The more I learn, the more I realize I don't know and have so much more to learn." - Claude Rouelle, Optimum G lecture June, 2011



Edited 1 time(s). Last edit at 01/27/2012 01:32PM by MeCalledEvan.

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MRWmotorsports
He has some stuff wrong, that's understandable, it's his first draft and he's posting here for advice and he's getting it. He's not building the cage yet.

John you wrote "What is the MAIN POINT I am trying to accomplish?"

I think you are misisng his main point. As I understand it his main point is to pass a course and get his credits. To do so he's decided to build a cage, which he has to design using some fancy computer SW, or it wouldn't be a 2012 course. Passing RA or NASA tech, is secondary (but his goal regardless).

So it doesn't matter that the fancy CAD desing offers nothing over a pencil sketch, or simply referring to FIA , it's a requirment of his course.

At least that's my take.

-Martin.

Martin:
That pretty much nails it as far as schoolwork and credit goes.

The reason I chose to do this in the first place though was to learn how to design a cage to FIA/RA specifications, and to become a better fabricator. I don't like just designing things, I like to get my hands dirty as well and want to be better at it.

Thanks for pitching in.

---

"The more I learn, the more I realize I don't know and have so much more to learn." - Claude Rouelle, Optimum G lecture June, 2011

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heymagic
Evan,
You can use an inverted V in the back, don't forget somewhere you have to attach the shoulder harness. Focusing on the rear hatch as an escape route should be way down on your list.

Look at the FIA drawings for door bars...none of them show your uphill the wrong way configuration. You basically have one sill bar protecting the occupants body. You'll have a hard time convincing me to logbook that configuration....

Gene McCullough
RA western tech supervisor.

Gene,
Escape is way down there, but it is still on that list. Hopefully I'll never need it, but the option should still be there.
I realize I still need a harness bar. Before I put one in though, I need to get seats. I don't want to put the harness bar in, and then have it be wrong after I install racing seats. Thanks for double checking!

I'll reevaluate that bar. JVL raised a good point that a cage needs to work with the car, be within the rules, protect the passenger, and then can work with ergonomics. I can learn to turn left without banging my elbow on a anti-intrusion bar. I can't undo a crushed pelvis or worse, if it is a flawed design that fails upon impact.

---

"The more I learn, the more I realize I don't know and have so much more to learn." - Claude Rouelle, Optimum G lecture June, 2011

Atta boy, we'll get you thru it.

I've had to turn down logbooks on more than one car with a 'creative' roll cage. That results in a cutout and do over. Expensive... so I try everything to guide this along from a tech standpoint to a successful conclusion. My CAD comments weren't meant to be disrespectful of your schooling or abilities, just wanting to make sure we have a happy camper when the welding is done.

Quote
heymagic
Atta boy, we'll get you thru it.

I've had to turn down logbooks on more than one car with a 'creative' roll cage. That results in a cutout and do over. Expensive... so I try everything to guide this along from a tech standpoint to a successful conclusion. My CAD comments weren't meant to be disrespectful of your schooling or abilities, just wanting to make sure we have a happy camper when the welding is done.

Thanks Gene! I appreciate that. I didn't really feel like you were being disrespectful of me, more just not accustomed to the design process I'm using.

I agree. I want all of my cutouts and revisions to be virtual. If we can make it so my cage will pass without revision after I finish, I would love that.

---

"The more I learn, the more I realize I don't know and have so much more to learn." - Claude Rouelle, Optimum G lecture June, 2011

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MRWmotorsports
He has some stuff wrong, that's understandable, it's his first draft and he's posting here for advice and he's getting it. He's not building the cage yet.

John you wrote "What is the MAIN POINT I am trying to accomplish?"

I think you are misisng his main point. As I understand it his main point is to pass a course and get his credits. To do so he's decided to build a cage, which he has to design using some fancy computer SW, or it wouldn't be a 2012 course. Passing RA or NASA tech, is secondary (but his goal regardless).

So it doesn't matter that the fancy CAD desing offers nothing over a pencil sketch, or simply referring to FIA , it's a requirment of his course.

At least that's my take.

-Martin.

Well Martin I didn't "miss it" , I asked wht he's thinking the main point is. I sorta hinted that there are appropriate uses of the tools he has, CAD is cool shit. Kevin Hawkinson and i did a whole series of measurements and plotting the Volvo 240 from B pillar back inside and out, then made models of the towers and the link boxes and shocks and the whole Topiletta axle, then he made 'em "work"...and we caught a potential problem with the links banging into the siade of the box in extreme of axle movement---something we're trying to do with long travel stuffs..
That let us mod the boxes BEFORE shearing and bending and welding the fuckers in and only THEN---or on some stage somewhere, finding the contact and bending sumpin..

THAT was a good use of CAD.
As was doing the Volvo front spindle and strut to do the hats and discs we wanted---we got 11.75 x 1.25 standard circle track buggers under several 15" wheels....
But the shell already exists, use appropriate tools.. And a tape measure and chalk or a Sharpie is the correct thing---FIRST.

---

John Vanlandingham
Sleezattle, WA, USA

Vive le Prole-le-ralliat

www.rallyrace.net/jvab
CALL +1 206 431-9696
Remember! Pacific Standard Time
is 3 hours behind Eastern Standard Time.

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john vanlandingham
But the shell already exists, use appropriate tools.. And a tape measure and chalk or a Sharpie is the correct thing---FIRST.

I thought a bunch of herbal medicine, late night, pencil and paper was the best thing first.

---

Grant Hughes

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heymagic
Atta boy, we'll get you thru it.

I've had to turn down logbooks on more than one car with a 'creative' roll cage. That results in a cutout and do over. Expensive... so I try everything to guide this along from a tech standpoint to a successful conclusion. My CAD comments weren't meant to be disrespectful of your schooling or abilities, just wanting to make sure we have a happy camper when the welding is done.

Evan, I ain't upset, we are talking PRIMARILY about "stuff"....I am trying to help you avoid a serious drawback that many guys develop in their educational process---a presumption that they are discovering "new' stuff...

And, from personal experience with well virtually 100% who I have known who go thru Westerns auto thing---a tendency never identify the "main point" and thus wander off, or expend time and money and resources on stuffs that yield infinitesimally gains in either performance---or knowledge...

We should yakk on the phone some so's youse knows the tone I's using...or come visit...

I think Martin was close "He's there for ..."

I made the huge mistake in the various times I went to college which was, in the words of the Provost at Evergreen in Olympia while we were having a beer at the tavern accross from my house "You're just fucking yourself, John, you're looking at this thing as an educational process!" Me: (sluuuurp) Yeah? what is it if'n it hain't a educational process?" (sluuuuuuuurp)
Provost: "Oh ferfuckssake you know it isn't! Its a socialization process!!!"

But I did have a LOT more fun than any other guy I knew down there

---

John Vanlandingham
Sleezattle, WA, USA

Vive le Prole-le-ralliat

www.rallyrace.net/jvab
CALL +1 206 431-9696
Remember! Pacific Standard Time
is 3 hours behind Eastern Standard Time.

John,

Alright, cool. Glad I misinterpreted. I thought you were taking a fat shit on me.
I'll give you a call this weekend, and try to make it down sometime in the next couple of weeks. I would like to talk with you and bounce ideas off you in person.
When is a good time to call?

---

"The more I learn, the more I realize I don't know and have so much more to learn." - Claude Rouelle, Optimum G lecture June, 2011

Dont call early mornings on holidays! Its the one time we will be brief on the phone!

---

First Rally: 2010 First RallyX: 2004 (a bunch)
Driver (0), Co-Driver (7)
Organizer (3), Volunteer (3)
Cars Built (2.5), Engines Blown (2) Cages Built (0) # of rotations (3.5)
Last Updated, Apr 9, 2023

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MeCalledEvan
...In essence, I want to learn how to be more like you...

I think I am going to get a plaque made up with that on it. :-)

---

"I, for one, welcome our Robot Overlords." - Philip J. Fry

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pdxphil42

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MeCalledEvan
...In essence, I want to learn how to be more like you...

I think I am going to get a plaque made up with that on it. :-)

---

Andrew Steere
Lyndeborough, NH
KB1PJY

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Gravity Fed
Dont call early mornings on holidays! Its the one time we will be brief on the phone!

Hahaha that's totally understandable.

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pdxphil42

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MeCalledEvan
...In essence, I want to learn how to be more like you...

I think I am going to get a plaque made up with that on it. :-)

Glad you appreciate it. I mean it. I can design a part all day long. I can work with carbon fiber or fiberglass and make a beautiful part. I can manual machine or CNC almost anything.
Welding and fabrication? It scares me still and I have no end of admiration and respect for those who are skilled at it.

---

"The more I learn, the more I realize I don't know and have so much more to learn." - Claude Rouelle, Optimum G lecture June, 2011