Trojans take on engineering

[artie on edge]

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....

[fabr]

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.

[SPEC]

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
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...

[Engineer]

 


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. 

[dre]

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. 

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?

[Ozpilot]

Someone needs to start arguing Trojans side though, as there is to much common sense prevailing here.

 

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 ...

[artie on edge]

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...  :-\

[Yummi]

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." 

[fabr]

yep

[Engineer]

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

[fabr]

Wag + safety factor ............  Build   then   Test= engineered.

[SPEC]

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
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 :-[

[Engineer]

Poor sand mouse........... 

[SPEC]

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 :-[

[Boostinjdm]

I felt  like shit :-[

Pussy