DTSFab.com (Desert, Trail and Sand)
UTV's Off Road ( RZR, YXZ, Mini Buggy, Carts,etc.) => UTV Toy Showcase => Topic started by: trojan on April 28, 2009, 12:36:31 AM
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Doug, when you say "designed", what design criteria did you use?
How did you determine what loads are in play and their magnitudes?
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OK I redesigned them off of crudly built Arms. The geometry was changed as well to what they supplied me as overall dimentions. The shop Im refering to does everything old school and fits alot of stuff like Yoshi does. They dont use CAD and turned to me to have the laser work cut. I dont have solid works or andysthing to perform any type of analayis on the part. Its probably just over built. They have never destroyed one. Ill post up some videos of this truck getting in wrecks and the Arms survived. Its quite impressive!
Look up on You tube. Johnny Greaves and Corr Racing, These are the guys. I also do work for about a half dozen other teams. Scott Douglas, Scott Taylor, and Jeff Kincade just to name a few.
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Name dropper! ;D ;D ;D 8)
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If you are not aware of the loads and forces involved, you drew them up, not "redesigned" them. That's cool in itself, but it's not the same thing. If you don't get what I mean, Eng (or any engineer) will be able to explain the difference better than me ;)
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What does it matter?
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Trojan is talking about the kind of "design" that they do on airplanes, where every ounce is counted, and every part stress analyzed. Most engineering work that I have seen doesn't go that far into the details. I worked at Great Plains, who manufacture's agriculture equipment. They never "designed" anything according to Trojan's definition. However they started with an idea, and ended up with complete grain drills, so somewhere along the way some design happened. The next step was to
abuse test the equipment to verify that the guesses that they made on material sizing were adequate. If something failed, then possibly they would start investigating stress levels. I think the truth is depending on quantity to be produced or the application (aircraft) etc, spending the time to analyze every part is a bit overkill.
Of course a main structural beam, or frame member that has basic forces on it can be calculated for sizing, but would you do it to every gusset? What is interesting to me is that every engineer that graduates from college is trained to analyze stress, crunch numbers, use formulas, but I never saw a class that addressed how to formulate an idea, how to come up with a design, how to develop a concept. All they teach is how to critique the ideas that have been generated. Anyone can be trained to analyize the stress in a tube, but the creativity to start with a concept, and turn it into a design, and parts is much more impressive IMO, yet overlooked as anything special.
You have to cut Trojan some slack, he looks at the whole world working in harmony, and see's no design present. I guess he assumes that GOD didn't stress analyze the wood in a tree trunk before he made it grow. Thank goodness it worked out by chance! ::)
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If you are not aware of the loads and forces involved, you drew them up, not "redesigned" them. That's cool in itself, but it's not the same thing. If you don't get what I mean, Eng (or any engineer) will be able to explain the difference better than me ;)
Did that help clarify? :D
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Grow that tree in the ABSCENCE of wind and you'll soon see how it adapts and how your premise is misguided to the point of being ignorant and presumptuous :-*
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Same goes for house building. We analyze (yeah sure we do) main structural elements to meet the needs of the structure as a whole. LOL!!! That's is NOT how the real world does it. The real world just puts a 5-600% safety factor into it to cover your ass.
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Grow that tree in the ABSCENCE of wind and you'll soon see how it adapts and how your premise is misguided to the point of being ignorant and presumptuous :-*
I'm sorry but what is wind? A gentle breeze or a tornado? I haven't seen too many trees engineered to withstand a tornado. Same thing applies to engineering anything. Without known info you CAN'T engineer a thing.WIthout building it FIRST you have NO idea what the failure point is so therefore you CAN'T engineer it. IMO engineering anything is nothing more than voodoo science that becomes REAL once tested. BTW ,just because something is engineered does not mean it will work.
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According to Grim, engineers nowdays are taught to copy and modify rather than design... *shrug*
Fab, to come up with a value of 5-600 you first need to KNOW what 100 is ;) guessing what 100 is leaves you "drawing it up" not designing it :P
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I'm sorry but what is wind? A gentle breeze or a tornado? I haven't seen too many trees engineered to withstand a tornado. Same thing applies to engineering anything. Without known info you CAN'T engineer a thing.WIthout building it FIRST you have NO idea what the failure point is so therefore you CAN'T engineer it. IMO engineering anything is nothing more than voodoo science that becomes REAL once tested. BTW ,just because something is engineered does not mean it will work.
Any wind, breeze or otherwise. Try it and you'll know what I KNOW. While your at it get your head around the calculations it takes to actually design at the level I'm referring and then you wont think it so irrelevant... coz it's not. just because you don't understand it or don't have the capacity to understand it, but have the ability to speak, does not make your explanation or the excuses for not understanding it valid sorry.
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According to Grim, engineers nowdays are taught to copy and modify rather than design... *shrug*
Fab, to come up with a value of 5-600 you first need to KNOW what 100 is ;) guessing what 100 is leaves you "drawing it up" not designing it :P
Not in MY world.Lumber has been extensively tested to know nominal values that are used to do the engineering.It is still spec'd at 5-6 times it's design needs.So YES they do know what 5-600% of 1 is.
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Not in MY world.Lumber has been extensively tested to know nominal values that are used to do the engineering.It is still spec'd at 5-6 times it's design needs.So YES they do know what 5-600% of 1 is.
Exactly, now argue how you're not being contraire ::)
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Any wind, breeze or otherwise. Try it and you'll know what I KNOW. While your at it get your head around the calculations it takes to actually design at the level I'm referring and then you wont think it so irrelevant... coz it's not. just because you don't understand it or don't have the capacity to understand it, but have the ability to speak, does not make your explanation or the excuses for not understanding it valid sorry.
Oratory does not make you right. Nor does attempting to ridicule a person. There is no need for that. IF you have something of value to add to this please do so. Insults are BS here sir.
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Exactly, now argue how you're not being contraire ::)
WTH are you talking about now .
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Oratory does not make you right. Nor does attempting to ridicule a person. There is no need for that. IF you have something of value to add to this please do so. Insults are BS here sir.
IMO engineering anything is nothing more than voodoo science that becomes REAL once tested.
Then I appologise for your misunderstanding of my attempt to be frank. No insult intended.
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Perhaps if you substitute "don't want to understand it" for "don't have the capacity to understand it" you will get my intent.
:-*
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Wow! Now things are starting to get interesting. I think that it would be rather difficult to analyze every load and load path that most parts on our rigs would actually see in a true off road condition. So many things are happening to the suspension components at the same time. Anything can be bent or broken when you drive these cars like I do. I have a buddy that goes to the dunes with me on a regular basis that I truly believe can break anything.
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I have a buddy that goes to the dunes with me on a regular basis that I truly believe can break anything.
I have friends like that too !! Unfortunately I'm usually the fixer ::)
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Yeah, its weird how many friends a guy with his own fab shop has. If I got paid to fix every thing that I have fixed I would be and efen millionare. Good thing I have friends like fastcorvairs. He actually returns favors.
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Your at the right site TOO.
I think we prolly got the best group of guys on the web here for helping eachother out ;D
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Even trojan is a big plus!
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I see and agree with alot of points on this thread. But to stand corrected. Yes I drew them up. An A-arm I cant say was my concept. Just like a trailing Arm. How it was put together and where the bends need to be for the simple puzzle fit fabrication was what I was to do.
I dont get paid from these guys as they help me out ALOT! They have a full shop at my disposal (within reason) and donate alot of goodies to my personal builds. The Crew Chief is responsibe for setting me up with the FOX dealership. Sometimes its all who you know. Soon I hope to meet Jermey McGrath as he is the driver for the Pro 2 truck for this race team.
OK cxxtinue
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I classify myself as a OzarkAmerican Engineer. I did go a year and six weeks to engineering school. I build things from my head. I or my friends test them. If they break, I build them stronger the next time. If they don't break, if requested, I build them lighter. I once built a wheely bar for a quad that weighed 2lbs. I just knew it would bend, but it didn't. Dunbsh$t luck I guess. Now I can run ideas by this board and get opinions. I don't expect as many failures. Thanks guys. Tim
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I classify myself as a OzarkAmerican Engineer. I did go a year and six weeks to engineering school. I build things from my head. I or my friends test them. If they break, I build them stronger the next time. If they don't break, if requested, I build them lighter. I once built a wheely bar for a quad that weighed 2lbs. I just knew it would bend, but it didn't. Dunbsh$t luck I guess. Now I can run ideas by this board and get opinions. I don't expect as many failures. Thanks guys. Tim
And THAT my friend is where ALL engineering begins. 8) 8) Good to see we Ozarks(hillbillies) engineers understand that. ;D
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Don't forget the JACK PINE SAVAGES...
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Don't forget the JACK PINE SAVAGES...
It this for real?
"So what is a jackpine savage?
Jackpine savages eat venison and like it, often have dirty fingernails even if they are millionaires and like the unpredictable. John Wayne was a jackpine savage. Bill Clinton and Prince are not. Willie Nelson is a savage, Tom Cruise is not.
Being a JPS has nothing to do with net worth, college degrees, breeding or religion, but most JPSs are spiritual. I guess that goes with being passionate.
I saw one explanation of jackpine savage that likened it to being stupid. I don't think so, unless stupid means being dumb like a fox."
:o
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Jack pine savage to the Bone here,
I came
I saw
I conquered....
Not sure wich nationality was the 1st to be called JPS but I'm sure it was us scandinavians, Logging through the brutal winters up here...Alot of the timber can't be gotten to during warm months...have to wait till the swamps freeze so can haul the logs out over the frozen lakes and swamps...
I guess I was proud to be a savage...still am... I miss the lifestyle of being a Jackpine savage...
I've since been housebroken...and Tamed...er aaah Mamed :-[
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Am I right in assuming this thread started somwhere else and was broken out?
Either way I am a qualified mechanical engineer, spent 5 years at university doing stress/strain analysis, FEA, CFD, statics, maths etc. My job now is designing agricultural equipment. I use Autodesk inventor as my design/drafting software.
I have never had a proper load to build anything around, it is all based on making it bigger/heavier than it need to be to make sure it never breaks. On no part we build could I tell you a safety factor. I still designed it though, through a mix of experience, common sense, talking to users and breaking a few things I have a fair idea how big is big enough. I designed the geomerty to make sure the linkages don't foul, etc, etc.
Doug it interests me that you say these guys don't analyse their parts at all. I have often wondered about that because everyone in offroading seems to equate bigger with better. Look on RDC, the guys there put up a picture of a trailing arm and if it is chunky with nice welds most guys say how great it looks. Is weight not a factor here...a lighter car will be quicker, more fuel efficient, etc ,etc but that doesn't seem to enter the equation.
I have been trying to design a buggy in my spare time, at the moment I am worknig through the suspension geometry, but the thing I am struggling with is I have no idea what loads to use to verify the strenghth of parts. I am planning on making it as light as I possibly can as the class it will run in are limited to 1600cc motors so power is not limitless. How am I going to make it light and make sure it is strong enough...not really sure. May end up building a heavier prototype car that will be hard to break, then setting up some strain guages and go from there. Either that or go on some basic road load assumptions and accept some (a lot) of breakages. Not sure that answers this thread at all, but as a trained engineer I thought I would put my hand up.
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Is weight not a factor here...a lighter car will be quicker, more fuel efficient, etc ,etc but that doesn't seem to enter the equation.
This is the crux of the (original) debate, Most folk dont go to the trouble to 'design' an item, they simply overbuild it, (as has been stated on here on more than one occasion, me included) this I think is Trojan poijnt... good post....
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I think we all agree on that dre. Engineering begins,in the days before strain gauges and such, with building it/breaking it/making it better OR build it/make it lighter till it breaks. Either way we "engineer" it till it works as we wish it to.
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Thats a good point...
I too have been engineer schooled...But common sense, with a wild hair(knowing how I drive stuff) Plus having some idea of the weight, leverage, compression put on components...AND WHAT I THINK THE LIFE EXPECTANCY should be... drive me to the way I build parts...If I was building a 1 show oval track car, main hoops and door bar heavy guage...The rest of the components as light and thin gA. as possible, A car that's going to be woods pounded...Meaning a long walk back to the truck...It's all built as not to break period...I hate that walk back to the truck...Shit falling off at the track just adds to the excitement of more stuff to go around ;D
My point is...I think what your goin to do to the car should be the most important aspect of the engineering that you do...Unfortunately, cost and safety should be in a tie for the title of most important as well...
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ff:
Nice post Dre.
Someone needs to start arguing Trojans side though, as there is to much common sense prevailing here.
Like you Dre, I am working on a design, and I am trying to be very weight conscious on it. It disappoints me that the shock makers give no info for guidance.
If we have a two seater (1,200 lbs) with two people in it (1500 lbs total). And it comes down front first, and all of the weight hits on the front. First off all of the load will not be absorbed by the shocks on this landing but quite a bit will go into the suspension mounts. But gestimating that the load went into the shocks it would be 750 per side. Now if we land from 10 ft high and soak up the hit in 20" of travel how may G's are we seeing in decelerating the fall? 4? What does it spike to if the bottom of the shock is hit? 6? 8? If we have 750lbs and design for 5 G's then you have 3750lbs, and if the shock has a 2:1 ratio then it is 7,500 lbs at the shock eye.
All of that is no more than guesses, and I am not sure how you would figure it for the real off-road world. As Dre pointed out, strain gauges on an existing known design would be the best option.
Should probably start a new thread, but on sheetmetal arms, I was planning to go .062" on the top and .074-.120 on the bottom, possibly jumping size from around the shock mount to the end of the arm.
If someone would volunteer the weight of their lower front arm, it would make it much easier to decide how much steel to throw at it. ;D
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ff:
Nice post Dre.
Someone needs to start arguing Trojans side though, as there is to much common sense prevailing here.
Like you Dre, I am working on a design, and I am trying to be very weight conscious on it. It disappoints me that the shock makers give no info for guidance.
If we have a two seater (1,200 lbs) with two people in it (1500 lbs total). And it comes down front first, and all of the weight hits on the front. First off all of the load will not be absorbed by the shocks on this landing but quite a bit will go into the suspension mounts. But gestimating that the load went into the shocks it would be 750 per side. Now if we land from 10 ft high and soak up the hit in 20" of travel how may G's are we seeing in decelerating the fall? 4? What does it spike to if the bottom of the shock is hit? 6? 8? If we have 750lbs and design for 5 G's then you have 3750lbs, and if the shock has a 2:1 ratio then it is 7,500 lbs at the shock eye.
All of that is no more than guesses, and I am not sure how you would figure it for the real off-road world. As Dre pointed out, strain gauges on an existing known design would be the best option.
Should probably start a new thread, but on sheetmetal arms, I was planning to go .062" on the top and .074-.120 on the bottom, possibly jumping size from around the shock mount to the end of the arm.
If someone would volunteer the weight of their lower front arm, it would make it much easier to decide how much steel to throw at it. ;D
Now...what happens if you don't jump level and it comes down one wheel first? Might try to lay out some calculations on all this, a lot of assumptions will have to be made either way. Is coming down off a jump the worst case, or is it hitting a steep whoop at speed? Or something else?
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ff:
Someone needs to start arguing Trojans side though, as there is to much common sense prevailing here.
;D
I agree with the common sense approach. But I'm up for a challenge - I'll have a go.
So I take the theoretical approach and look at what Trojan said.
"If you are not aware of the loads and forces involved, you drew them up, not "redesigned" them."
So we look at what "Design" means.
Oxford English Dictionary says:
Design, v:
1.To point out by distinctive sign, mark, or token; to indicate.
2. To point out by name or by descriptive phrase; in Law, to specify (a person) by title, profession, trade, etc.; to designate, name, style. Sometimes with double obj. (direct and complemental).
3. Of names, signs, etc.: To signify, stand for.
4. To appoint to office, function, or position; to designate, nominate.
5. To appoint or assign (something to a person); to make over, bestow, grant, give.
6. To set apart in thought for the use or advantage of some one; to intend to bestow or give.
7. To appoint, destine, devote (a thing or person) to a fate or purpose.
8. To form a plan or scheme of; to conceive and arrange in the mind; to originate mentally, plan out, contrive.
9. To purpose, intend, mean.
10. To purpose or intend (a thing) to be or do (something); to mean (a thing) to serve some purpose or fulfil some plan.
11. To have purposes or intentions (of a specified kind).
12. To have in view, contemplate.
13. To intend to go or start; to be bound for (a place).
14. To make a sketch of (an object or scene); to sketch, draw.
15. To plan and execute (a structure, work of art, etc.); to fashion with artistic skill or decorative device; to furnish or adorn with a design.
16. a. To trace the outline of a figure or form; to put a graphic representation on paper, canvas, etc.; to draw, sketch. b. To form or fashion a work of art; in a narrower sense, to form decorative figures, devise artistic patterns."
First, I didn't know what design meant till just now.
Secondly, I can't read Doug's mind (to work out what he meant by design) and I am having trouble reading Trojan's mind as well, but, in context, 8, 10, 11 and 12 seem to be the closest definitions and it is clear from the fact that drawings resulted that 14 and 15 and possibly 16 (b could be a matter of taste) are involved.
So ...
Somebody else had better start arguing Trojan's case - a total lack of common sense isn't working either ...
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Now...what happens if you don't jump level and it comes down one wheel first? Might try to lay out some calculations on all this, a lot of assumptions will have to be made either way. Is coming down off a jump the worst case, or is it hitting a steep whoop at speed? Or something else?
If you are going to really design an item you will also need to 'design' the point at it becomes sacrficial, perhaps even down to 'how' it can be sacrificed.
For mine I certainly want the arms to fail long before the chassis is damaged.
More so I would rather the heim joints failed long before the arm was damaged.
Where do you stop? Yoshi advocates leaving a good amount of heim thread out of the arm to allow a weak link. Personally I dont have an opinion on this issue , yet, but the idea has merit, a heim is easier to carry and replace than an arm.
Yeah a really hard hit on a sharp edged bump (or largish rock) is the pits (I Know, cost me several Bilstein shocks). Any sort of 'normal' jump should be well within the parameters of a suspension system, even a one wheel landing.
So, design away, but make sure you protect your intellectual copyright it in some way... demons on the loose around here... :-\
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This conversation suggests that "design" is a final process; but the word itself has many connotations. Therefore it would seem that any phase of "design" from a cocktail napkin drawing to a full blown crash test with stress loads would qualify as "design."
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yep
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Thanks Ozpilot! I think you put this one to rest.
To your question Dre, I think the worst case senario would be if the shock bottoms. Woop or jump, when it goes solid, the force has to spike IMO. That is the downward force on the shock. I don't know how you would design for something else to fail in that scenario. Now a Witch's eye or a square edge impacting straight on, is going to be altogether different, with its loads going more into rod ends and frame mounts.
Another thought, if it comes down one wheel first, then the loads will also be going into frame mounts, not straight down on the shock. There was a video of a car on the front page that landed right on the nose. Also jet's pictures. I don't think that the shocks did much in either case.
Wag + safety factor ............ Build then Test
WAG=Wild ass guess
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Wag + safety factor ............ Build then Test= engineered.
;D ;D
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Thanks Ozpilot! I think you put this one to rest.
To your question Dre, I think the worst case senario would be if the shock bottoms. Woop or jump, when it goes solid, the force has to spike IMO. That is the downward force on the shock. I don't know how you would design for something else to fail in that scenario. Now a Witch's eye or a square edge impacting straight on, is going to be altogether different, with its loads going more into rod ends and frame mounts.
Another thought, if it comes down one wheel first, then the loads will also be going into frame mounts, not straight down on the shock. There was a video of a car on the front page that landed right on the nose. Also jet's pictures. I don't think that the shocks did much in either case.
Wag + safety factor ............ Build then Test
WAG=Wild ass guess
You said witches eye ;D
I parked my ass in one of those...took 3 hours ,a Rhino with a winch...and a poor sand mouse's death to get the buggy iout :P :-[
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Poor sand mouse........... :'(
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Ya,
I felt really bad for him :'(
Poor little fooker was in his burrow minding his own business when WHAM a big fookin paddle came through the roof...scooped him up out of his easy chair and tossed him 20 feet into his back yard...
I felt like shit :-[
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I felt like shit :-[
Pussy ;D
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;D
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OK, after being beaten over the head with a dictionary (thanks Oz) I'll rephrase:
Draughtsman vs Engineer.
it seems a lot of draughtsmen call themselves engineers....
And like I said, the fact that Doug drew it up for them is cool in itself.
Newtonian Physics.
F = ma
P = mv
S = ut + 1/2at^2
http://en.wikipedia.org/wiki/Vector_sum#Vector_addition_and_subtraction
http://en.wikipedia.org/wiki/Strength_of_materials (http://en.wikipedia.org/wiki/Strength_of_materials)
http://en.wikipedia.org/wiki/Trigonometry (http://en.wikipedia.org/wiki/Trigonometry)
http://en.wikipedia.org/wiki/Structural_analysis (http://en.wikipedia.org/wiki/Structural_analysis)
etc......
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You mean Draftsman vs. Engineer?
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Let's take trojan to task here. Use as an example a front lower a-arm with no rake. Seems pretty simple and I'm sure that many of us have built them (notice I didn't say design or engineer them). Starting at the frame , detail for us where you would start with engineering them. Lets assume they are 20 inches long. Shock mounts to a arm 15" from frame pivots. ASsume the arms are symetrical and the mounts are spaced 12" apart.Car will weigh 1200#'s with a 60/40 weight distribution.Car front track is 72". Objective is to allow the arm to survive a 10mph impact to the outer heim from any direction with an immovable object/tree. What else is needed? ANyway,trojan ,engineer it.
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Let's take trojan to task here. Use as an example a front lower a-arm with no rake. Seems pretty simple and I'm sure that many of us have built them (notice I didn't say design or engineer them). Starting at the frame , detail for us where you would start with engineering them. Lets assume they are 20 inches long. Shock mounts to a arm 15" from frame pivots. ASsume the arms are symetrical and the mounts are spaced 12" apart.Car will weigh 1200#'s with a 60/40 weight distribution.Car front track is 72". Objective is to allow the arm to survive a 10mph impact to the outer heim from any direction with an immovable object/tree. What else is needed? ANyway,trojan ,engineer it.
I say build it outta 25 mm (oops sorry 1") solid bar, try it and see if it bends. If it doesnt, up the size by 200 percent to allow a safety factor...
Seriosuly Trojan, this challenge is beneath you mate..Id ignore it.... if I wasnt such a smartarse ....
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Everyone in the real world knows that science and engineering are done in metric ::)
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It's not a challenge.It is asking for an explanation of the process that wouild be involved.Trojan posted up a bunch of stuff that is relevant and I assume he knows how to use it or it is irrelevant. The point is that there is no exact science in engineering anything.That is why 10 engineers will come up with 15 different"correct" answers to the same question.IMO my "challenge" makes that perfectly clear.TOO MANY variables to be able to engineer it in the first place. Engineer has it right IMO with WAG.
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I can take it if I'm wrong.
If it was "Wild ass guesses" analysis software couldn't do it's job?
It's not easy, that's my point.
Simply, so you get to ignore things like friction and gravity, hell include them it's your dime, you would define everything required and convert from your "medi-evil" system to metric ;D
Then:
A dash of: http://en.wikipedia.org/wiki/Polar_moment_of_inertia
A sprinkling of: http://en.wikipedia.org/wiki/Area_moment_of_inertia
A scoop of: http://en.wikipedia.org/wiki/Section_modulus
A pinch of: http://en.wikipedia.org/wiki/Elastic_modulus
A touch of: http://en.wikipedia.org/wiki/Yield_(engineering)
Then find yourself a table of yeild strengths for the material you want to use and apply what you've got to to that. eg: http://www.davesport.com/cgi-bin/davesport/specs.html
Munch!
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Heheheheheeee,I know that and yet it still requires a lot of hunches and best guesses. That's my point. I'm not saying it CAN'T be done just that it will alll be based on WAG.
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nah no WAG. in your example, hitting the immovable object dead on will transfer the most energy, and will cause the buggy to rotate about an axis. knowing the total mass and length of the "lever" and the speed, we can calculate the force applied. Calculating the overall yield strength required of the triangle is matched to the triangulated yield strength of the arm constructed of the minimum sized available tube.... giving the answer you asked for.... essentially like Finite Element Analysis software does.... or are you saying FEA software just guesses wildly?
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OK, after being beaten over the head with a dictionary (thanks Oz)
Sorry Trojan, I was biting my tounge till the "invitation" turned up - I just figure "design" means stacks of things and I thought Doug's use of that word was fair. To use an example, I said on this board recently something about "designing" my al trailer. When I "designed" the trailer I carried out calculations with data being specific corner weights of the buggies and material weights etc in formulas to work out the loading involved and resulting moments to position the axle but the rest of the design (material sizes etc) was from experience - so when I say "design" it doesn't always mean calculations.
BTW, I have a long standing gripe about draftsmen calling themselves engineers. Draftsmen have valuable skills (mainly in using software these days from what I know). However, if you can't sign off then you're not an engineer (in my book) so I understand the point you were making.
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Mate, don't be sorry! I'm glad to be shown where I'm mistaken, misled or wrong, even though the latter never happens ;D
And I'd like to think I'm man enough to take it on the chin ;)
Now, being merely contraire (hi Fab) on the other hand, is down right annoying :P
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Yes,(trojan) being contrary just for the fun of it is annoying. ;D ;D ;D ;D Now tell mewhere I'm wrong in what I said about engineering being the RESULT of trial and error and then engineering slowly came into being with the lessons learned from that very trial and error.Secondly where am I wrong in thinking that much of what is "engineered" is just a Wild Ass Guess at best that can be demonstrated with math tobe correct but based upon that very WAG.
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:t
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Aw,c'mon,mate! You know I'm right! ;D
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Here's an example of what I'm referring to:
http://icutebluezone.orconhosting.net.nz/Jaime-FEM-presentation.pdf (http://icutebluezone.orconhosting.net.nz/Jaime-FEM-presentation.pdf)
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The problems with FEM analysis is that forces and angles still have to be assumed. You pick a direction and a force and a input function and the software plot's your results. Sure it will show you where the stress concentrations are but only for that particular angle of inpact. In order to properly "design" an a-arm this way would take thousands of hours running simulations from all angles with varying loads. The sum of all these results would have to be reviewed to determine the proper tradeoff's.
Building a set of arms and driving the car until it they break provides the same information as the program it just takes more work. Lesson's learned during years of experience and testing will always be more valuable than a few weeks simulation with a computer.
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My point exactly. And welcome BTW Islander!
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Thanks, been lurking for awhile. Currently got a pair of ST3's with some of Ricks touches in progress. More of a winter project though summer's for golfin.
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Well ,keep us updated if youu wish!
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My point exactly. And welcome BTW Islander!
BULLSHIT (again) your point was that it's all WILD ASS GUESSES, which it is not. I take Islander's point and in fact it was considered in my opinion.
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The problems with FEM analysis is that forces and angles still have to be assumed. You pick a direction and a force and a input function and the software plot's your results. Sure it will show you where the stress concentrations are but only for that particular angle of inpact. In order to properly "design" an a-arm this way would take thousands of hours running simulations from all angles with varying loads. The sum of all these results would have to be reviewed to determine the proper tradeoff's.
Building a set of arms and driving the car until it they break provides the same information as the program it just takes more work. Lesson's learned during years of experience and testing will always be more valuable than a few weeks simulation with a computer.
Years of testing vs weeks of simulation are no where near comparable especially if you delude yourself as to what testing is (like some manufacturers) and call it a few laps in the car park outside the shed.
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The problems with FEM analysis is that forces and angles still have to be assumed. You pick a direction and a force and a input function and the software plot's your results. Sure it will show you where the stress concentrations are but only for that particular angle of inpact. In order to properly "design" an a-arm this way would take thousands of hours running simulations from all angles with varying loads. The sum of all these results would have to be reviewed to determine the proper tradeoff's.
Building a set of arms and driving the car until it they break provides the same information as the program it just takes more work. Lesson's learned during years of experience and testing will always be more valuable than a few weeks simulation with a computer.
So,trojan,you disagree with this? All engineering has to be based on real world results. Real world results are what the engineering math is based upon. Engineering as shown in that statement IS based on WAG in one way or another.Assume(WAG) the wrong thing ,and you must assume some things, and the engineering goes out the window.But again ,trojan has shown me the path to trojan enlightenment for me to see the only true opinion that counts. Of course my opinion is once again BS since it is not in line with his opinion. mm: bb:
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I'm not saying that FEM doesn't have it's place. If you are trying to shave pounds off a design to increase fuel economy or reduce manufacturing costs per piece. Sure finite element is a great and useful tool.
Most of the stuff on this site will never reach mass production in the true sence of the word and therefore the design doesn't require cost optimization.
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Again I agree. You have experience with FEM?
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We dealt with it a bit in school, I am a mechanical engineer in the aerospace industry and believe that all designs come with different criteria. Aviation FEM is crucial to the final design of the aircraft. Recreational buggy building, make it strong. Break it, then make it stronger.
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Again ,agreed.
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this thread came out of a professional build to differenciate between "engineered" and "drawn up".
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BULLSHIT (again) your point was that it's all WILD ASS GUESSES, which it is not. I take Islander's point and in fact it was considered in my opinion.
My point was that all engineering began with a WAG. Without those initial WAG there was no where to start engineering from in the first place. Call BULLSHIT all you wish trojan.
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this thread came out of a professional build to differenciate between "engineered" and "drawn up".
Doug never stated he "engineered" these arms he designed them. Where we are disagreeing is on what constitutes a designed set. There is no black or white here its not Designed or Drawn Up. There are levels of design all across the board. As far as that goes, two different designs will have different design constraints. Tensile stresses will be considered for one design, buckling for another, weight for one design cost for another.
I do understand that you are considering this as all or nothing. It's engineered or it's not. I'm just stating my opinion that design and engineering are not the same thing, design is the concept generation, inital fabrication and testing. Engineering comes into play for optimizion of the design or preparing for production.
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As someone who has had 4.5 years of mechanical engineering classes, the salary and job title of engineer, it's now my turn to throw in a couple of cents worth.
Break down of engineers:
75% Crappy engineers - Lack real world experience. They get stuck in manufacturing engineering positions, or in crappy economies like the present, are likely laid off for long periods of time. I call these engineers problem makers instead of problem solvers.
20% Okay engineers - good with calculators, always hear them saying things like "Well it looks good on the computer screen" or "It works on the computer"
4% Great engineers - These are the true problem solvers of the engineering world. They have lots of real world experience. These people usually have many patents and they tell the okay engineers and the crappy engineers what to do. These are the guys who use there brains instead of their computers. These guys will never be out of a job for long periods of time.
0.75% Professional engineers - These guys are insured and bonded. They put their life and livelihood on the line every time they put their wet stamp on an engineering drawing. (These guys are also known as Crazy engineers)
0.25% Smart engineers - These engineers really are brilliant. They take some great engineers concept and modify it just enough as to not get into copy right infringement lawsuits and make millions.
ff:
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New guy here. First some background information.
I have been an engineer for 20 years and got my PE license 15 years ago. I designed underground mining equiptment for 13 years, primarly front end loaders. We did many calculations, FEA and strain gage testing. Here's my take for what it's worth.
Designing a part is the process of deveeloping a concept and taking it through to final drawings. In my case this is all done on a computer using Solidworks.
Engineering is the analysis part of the process. This can be calculations, FEA or testing. You can be a designer without the education but not an engineer. The product I currently work on is pure design, no engineering required.
If you took a existing a-arm and reconfigured it in some way, (hopefully improving it), that would be "redesigned". If you modeled the original design in cad and then did some stress analysis to help determine the weak points and then came up with an improved desgn, that's "engineered".
Just because it's engineered doesn't mean it won't still break under some load condition. The art in the engineering is determining the load inputs when working with such a complicated system as an off road vehicle. That's where experience and testing come in.
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I think it's the diff between design and engineer. People were doing design work long before math. Someone designed the spear. Then redesigned over and over. Then someone got smart and enginered one. The engenered ones are found in the olympics. The designed ones are leaned against a hut door somewhere waiting on the hunting party. In my openion if you got some sence and are a thinker you can design things all day. That design may take years to work right. Thats where the enginering comes into play.
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It is pretty naive to think that you need to FEA a buggy for it to be called designing. It's very naive to think that you
can replicate all the conditions that an off road car will experience. IMO, if you can't design a simple space frame
without FEA and only using all the info that is already available on this subject that is out there than you are not that
good of a engineer in the first place or you are seriously lacking in hands on experience. The design aspect in our cars
comes into play with the suspension for the most part. Making it perform and handle exactly as desired and
understanding how you want it to perform. Not in running FEA on stuff which inevitably you will be using estimated
values for. NO ONE person or manufacturer will ever FEA an entire car to the point of it not needing testing. If
running FEA on a couple load paths with some BS numbers that you guessed on helps you justify an engineering degree,
than more power to ya I suppose.
I'll take real world testing anyday of the week in THIS application.
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It's still all based on a WAG ultimately. The WAG(wild ass guess) is what everything comes from. IMO,not worth much I know, FEA and all the other stuff can be used most effectively by showing that something CANNOT do whatever more so than showing that it WILL do anything. Am I wrong and how so if I am?
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The Wright brother's built a small wind tunnel to test models of wing and propeller designs. I believe modern aircraft propellers have an efficiency level only 5% better than theirs. It was primarily trial and error. I would consider them engineers though which I'll get into later. They would have started with WAG. The first propeller was probably slanted boards. Their drag testing on wings revealed that the the air foil shape caused less drag. They applied experience from one thing to another and made the prop air foil shaped as well. Still trial and error though. In determining which angle of attack provided the best thrust for the power input, I would guess that they did not just keep tweaking it 1 degree at a time and tested every possible permutation of length, angle, etc. I would imagine they went about it in a methodical approach such as a 10 degree change until they pasted the optimal point then either did made or made an educated guess as to a good starting point halfway between the previous two best points. Making calculations to determine the next step based on previous real world results is where I would call them engineers. Next they probably kept a table of optimal prop angle for various RPMs. Since the outer end of the prop has a higher speed than the inside, they made the inside of the prop have a steeper angle than the outside. There is no way they simply fell into the rate of increase of angle. They had to have determined optimal angle for a given speed then calculated the angle over the length of the blade.
Using computer software to model how a part performs is still trial and error. An educated guess was made at what is needed. It does not matter if tensile strengths were looked up, etc. That just adds to the educated part of the educated guess. If it were possible to build a part solely off calculations then there would be no need even for modeling how a part performs. You would know the results before the models were even run. If the part fails in the model, the weak points get beefed up and the model run again. It is just to save time over building a prototype for destructive testing. Either way, someone could simply build it beefier and try again. They could also measure what it took to break then calculate how much thicker the material needs to be to prevent the failure. I think it is more about the methodology and thought process than the tools used. Either test may still not represent how it is stressed in real use.
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Propellors? A genuinely fascinating subject: http://en.wikipedia.org/wiki/Propeller for starters...
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Fab, I'm honestly trying to rationalise where you're coming from, do you equate WAG with estimate?
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yup
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OK ;D
I'm not going to pick about defintions of words....
I get you now, see I do try :-X
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That's fine. I TRY to understand Strine! To me an estimate is a WAG. A good one perhaps but still a WAG.
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That's fine. I TRY to understand Strine!
Ok now let's move on to politics ;D
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Only this time we'll bash on all Oz has wrong with it instead. ;) ;D
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Whats wrong with Australia?
Other than that wanker Trojan living here, I mean!
;D ;D ;D
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Toilets flush backwards. ???
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DAMMIT Yumster you beat me to it ;D
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Toilets flush backwards. ???
CRAP! ... uh... oh sorry.... bad terminology...... :-[