Over Engineering

[Wolffarmer]

Back in the 80's I tore apart a 15 foot 1955 Shasta. You would be surprised how it was built. The frame (which I made into a motorcycle hauler and still have ) is two 3 inch channel irons 4 foot apart, Bent together to make the tongue, No cross members at all except for one just behind the hitch for the propane. Just the leaf spring axle. The floor was cantilevered out from that on 2x4 laid flat over fiber board and about 1/2 plywood on top and it seems the floor went further back from the end of the channel. That is all that held the frame together. Side walls was made of little sticks with aluminum stapled to the outside and 1/8 ply ( or maybe even less ) stapled together.

And thinking back on it, I can not remember how the floor/cabin was held on to the frame as there are no holes in the channel iron or any tabs welded on. must have been clamped somehow

Randy

[Yota Bill]

good story about an engineer:

several years ago, I was an auto tech at a large dealership (I'll avoid naming brands, because everyone has their preference, and I get tired of those "discussions"), and a luxury car came in that would lose all radio volume when the car was put in reverse...the radio did not shut off, just lost all audio output, and only in reverse, but consistantly in reverse...one of the salesmen, thinking this was a new safety feature, tried finding some more info on it to no avail. He ended up calling the manufacturer to ask about this "new safety feature", to which they replied that they dont offer that feature, it must be a failure of some sort...

Thats when I was told to fix the "new safety feature" that was actually a problem.

Stumped me and every other tech (approx 30 techs, total) for almost a week before I called the manufacture, and talked to an engineer that worked on the audio system in that particular model. His answer: "Thats not possible" - click -

yes, he actually hung up on me

I did find the problem, by sheer dumb luck really, and verified the failed part by putting it on another similar car, which then had the same problem. I went over the schematics again, and could not come up with any way that part could cause the radios audio output to shut off when the car was put in reverse, or even effect the radio in any way, but it did it on 2 different vehicles.

I mailed that part ot the engineer I talked to, who had hung up on me. I never did get a response back.

[2bits]

As previously stated, from my construction point of reference, once I have a stout frame, I have the luxury of a little less worry about flex in the cabin, and less worry about water infiltration & subsequent water damage (are you guys getting the point that I'm worried about waterproofing issues?).

Well we certainly don't want to go engineer bashing, EVERY profession has it's cross section of jokes and funny stories. Just a thought to maybe head this off at the pass just to be on the safe side

Noting the quote above I would take a long look at the other home built models and take from the real world experience of others who are much less qualified/schooled/whatever like me and is the flex to leak ratio that high? It doesn't appear to be from the threads that I have seen. I am not questioning your logic, but only your concern, experience in the field with all of us as guinea pigs to examine, I think you have a pretty good cross section of what is and isn't a problem. In my humble opinion:

A: Water proofing definitely IS a HUGE concern. (Just ask me )
B: Flex really isn't the reason for leakages. So what is? That should be the quest.... What IS causing the leakage issues?

I hope that helps.

Now if you have any plans for an off road tear, I would over engineer the crap out of it!

[Goldwing]

IMHO over-engineering is waste of time and resources. You need enough plus a good safety factor for human cargo. Anymore adds weight, requiring a larger engine (more weight) more fuel (even more fuel required to move itself around) and thus a larger engine....and a still larger stiffer (heaver) vehicle to withstand it all.

Think Honda Civic, not Mac truck.

[2bits]

IMHO over-engineering is waste of time and resources. You need enough plus a good safety factor for human cargo. Anymore adds weight, requiring a larger engine (more weight) more fuel (even more fuel required to move itself around) and thus a larger engine....and a still larger stiffer (heaver) vehicle to withstand it all.

Think Honda Civic, not Mac truck.

I think this original idea was that if saving time and resources were not really a concern because he had a 3/4 ton truck and not a Honda Civic so it was not as much of a concern. I think alot of us think like you do though because we do own smaller vehicles and are trying to see how efficient we can be, myself includes. Either choice is a good one as long as it fits that person's particular scenario.

[Judeyramone]

Strengthen the chassis = less twisting & flexing as it drives down the road, and less glue joints fail in the wooden cabin sitting atop it? That's my logic, anyway. Strong foundation on a stationary house is one thing, but once it starts moving down the road?

Regardless, this thread has already caused me to rethink (and lighten) my mental chassis plans. Although, as mentioned above, it will probably still be over built to some degree, just for the convenience of using materials readily available locally.

[jimqpublic]

This thread has one (at least) problem:
Definition of the term "Over Engineering".

1. Does it mean putting an obsessive amount of effort into engineering calculations, design alternatives, failure point modeling, or other obsessive design analysis instead of just building? (Usually trying to eliminate all potential failures which would make it heavier and stronger- but consistently)

-OR-

2. Does it mean building with stronger/stiffer/heavier materials?

It seems much of the discussion is related to option 2, but I think that's the opposite of "over engineering". It's under engineering to just go up a size to be sure everything is plenty strong.

The easy way to get a failure is to use stronger/stiffer/heavier materials along with fastening systems not up to the task. Or using 3500 pound springs and 80 psi truck tires under a 900 pound trailer. I would define that as under engineering.

An example of "under engineering" was when I replaced the stock 19 mm hollow anti-roll bar on my car with a solid 25 mm model. Then one of the mounting brackets failed so I replaced the frame brackets with stronger, stiffer models. Then one of the brackets on my suspension ripped off and I realized that the original engineers had designed a whole suspension system and only an idiot would arbitrarily "beef up" a single component.

(edited to make myself look smarter than I really am)

[bobhenry]

Or using 3500 pound springs and 80 psi truck tires under a 900 pound trailer. I would define that as under engineering.

(Quoted from above)

To me it would be over engineered but I an starting to see the problem with this thread

you see under engineered as a poorly thought out process.

and other see it as not enough meat in the product itsself.

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conversely over engineered would be ?

covering all aspects of the loads transfered completely thru all part and pieces that are involved with the transfer and taking them to the minimum members and connection design that will work.

OR US who see it as throwing a ton of material at a problem because we don't have an engineering degree but also don't want it to self destruct in use.

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

What do they call the process where planned obsolecense is factored in where it just works for a while , breaks and you go buy another?

[Larwyn]

To me over engineering most often results in an under built product. Over built is usually the result of little or no actual engineering, which is not always a bad thing.

[Cliffmeister2000]

To me over engineering most often results in an under built product. Over built is usually the result of little or no actual engineering, which is not always a bad thing.

Over built! That's the right description for most of our trailers.

[Judeyramone]

using 3500 pound springs and 80 psi truck tires under a 900 pound trailer....

Using my own definition (no, not the one about driving the train), engineering is finding the simplest effective solution to a problem, and the example above is under engineered - Not enough thought has gone into it. For examples of over engineering see Rube Goldberg.

[Engineer Guy]

Re: the comment above [paraphrased] to 'over-Engineer the guano out of an Offroad Camper':

http://wyoming.craigslist.org/rvs/2047323177.html

We bought a wonderful King Bed made of Walnut. A hideous 'box' underneath held up the center. I got rid of it for a clear span solution. I glued and screwed, from the inside, 2" x 2"s on both sides. I notched and hung 1" x 6"s across that sat on the 2 bys and stabilized them at the edges. The 1" x 6" bottoms are center-stabilized by a single 1" x 4" screwed on running lengthwise Head -> Feet. I put on 1/4" Ply as the platform to hold a dense Foam Mattress. Screws through the Ply into the 1" x 6"s made it act like half a Stress Skin Wall. It was my 'Airplane Wing' solution. And, I got the clear span look I wanted.

Like TJI Joists that sag on the Delivery Truck, but hold up long-span House Floors when installed vertically, Ma Nature offers solutions like a Bird's Wing that we can emulate.

Beautiful Chassis there Thomas...

[2bits]

"Over Engineering" to me means over thinking when you're already come to the solution. Sort of like "splitting hairs".

That definition does not fit this thread in all, or even most cases. I think it is a VERY good point that we all see the differences in the way the terminology can be used and to contribute to their own particular bent along ones own definition, and over engineering on purpose changes the scene entirely!

Sooo what a conundrum... This is what I do at work. I scroll all the way back to the original post and this will usually provide the answer.. to wit Forrest says:

"So what in your opinion is something that most builders over engineer?"

In this light, the original question is that since he is an engineer, he does not want to over think things that are needless and over build things to a degree that is unnecessary.

As you can see Forrest, threads can deviate in many different ways from the original question, and may need a little gentle prodding to redirect back, but at the same time these deviations can be quite entertaining and can sometimes provide answers to questions you never even thought to ask and makes you consider things would have never come to mind otherwise. (Like over engineering on purpose for a specific reason, such as off roading etc) This has happened on many occasions with me, and is why I love this board so much.

If you cannot tell I get all sappy after a couple of beers

[Goldwing]

Just enough and no more.

[2bits]

Just enough and no more.

DAY YUM... you gotta love that...