Alan B
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| posted on 12/5/08 at 12:28 PM |
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Theory and practice
Simple question, where do you draw the line?
When do say ok that's enough theory, time to get my hands dirty?
I ask the question based on the long and interesting thread on CoG. Even as a degreed and practicing mechanical design engineer I am always finding
more stuff that I didn't know or didn't know how to apply, so threads like that are very important to stretch our knowledge and make us
think...we wouldn't be human otherwise.
However, a part of me just wants to say "Guys, enough already...we aren't designing F1 cars here...lets just get out there and get
building.
Obviously at one extreme of no theory/research/knowledge we'll end up with a finished (maybe) unsafe, bad handling POS...at the other extreme
we'll end with perfection..eventually....on paper, but nothing ever built...classic analysis paralysis.
So where does everone stand on this? what are your views?
Personally I'd say I was around 80% leaning towards theory...with 20% of me saying lets get out and build...
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D Beddows
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| posted on 12/5/08 at 12:41 PM |
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Depends where your interest lies really doesn't it  TBH I'm the other way round to you in that I think quite a lot of the time people
should pay more attention to the 'simple' basics and stop disappearing up their own backsides analysing things that they probably wont
notice when they've built the car (and in actual fact probably wont be able to actually create to close enough tolerances to matter anyway) and
should just get out there and build it 
On the other hand as you say you do pick up some interesting stuff (as long as you have a good enough b*ll sh*t filter) and for some people the
designing is more fun than the building - so I don't have a problem with it. The only time it annoys me is when you gently point out that
someone may be trying to redesign the wheel to no discernible benefit but at considerable cost and they throw all their toys out of the pram
[Edited on 12/5/08 by D Beddows]
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Mr Whippy
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| posted on 12/5/08 at 12:52 PM |
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You can read all the books you like but nothing beats hands on experience
The best engineers I worked with were the ones who built cars etc, those who just quoted from a book I'd rather have them make the tea.
Fame is when your old car is plastered all over the internet
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kb58
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| posted on 12/5/08 at 01:19 PM |
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I define "good enough" as: Design it just well enough that you don't have to work on any part of it more than once. Of course it
took me ten years...
I see builds where parts of the car have to be cut off and redone because it wasn't thought through beforehand - it wasn't designed
well enough before diving in and welding stuff.
Someone once told me, "You're walking a fine line between doing it right and getting it done." That's about it.
Mid-engine Locost - http://www.midlana.com
And the book - http://www.lulu.com/shop/kurt-bilinski/midlana/paperback/product-21330662.html
Kimini - a tube-frame, carbon shell, Honda Prelude VTEC mid-engine Mini: http://www.kimini.com
And its book -
http://www.lulu.com/shop/kurt-bilinski/kimini-how-to-design-and-build-a-mid-engine-sports-car-from-scratch/paperback/product-4858803.html
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liam.mccaffrey
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| posted on 12/5/08 at 02:21 PM |
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I have been guilty in the past of spouting a lot of over analysis bullship. However in my defense i did it at a time when i had no build facilities.
Since I have started building proper though I have been much better.
Sometimes the theory is justified and sometimes its not.
For example personally I think that inboard front suspension, whilst it certainly has some advantages, is a bit bling bling and unecessary on a 7.
However I decided to use inboard front suspension to overcome 2 specific design problems.
I think that most people could spend less time theorising and more time building and have comparable quality/performing vehicles. Not to mention
quicker builds.
However for most this is a hobby and does it really matter how long it takes or how complex they make their cars?
Build Blog
Build Photo Album
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Fred W B
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| posted on 12/5/08 at 05:37 PM |
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Nice post Alan
I find that there are so many variables in some areas that you have to at some stage take a decision and eliminate at least some of them, otherwise as
you say nothing gets built.
I find that in general as the second whatever you make is always much better than the first, and all the cad in the world will never replace holding
the finished whatever in your hand, I prefer to dive in, make up a very rough example of the part I am considering, refine it till it works properly,
and then make the final part.
The other thing I find, with swotting from books and internet etc, that the concepts and techniques described become so much more real and
understandable once you have tried to do at least something practically.
in order words, don't sweat it if you don't fully understand at first, just try to do something with what you do know, and then go back to
the books etc. I find bits of text jump out of the page once you go back to them and you really see what the guy was on about then.
Sorry not a very considered response, I'm going through this at the moment with laying up fiberglass - is it possible to get a styrene
hangover?
Cheers
Fred W B
[Edited on 12/5/08 by Fred W B]
You can do it quickly. You can do it cheap. You can do it right. – Pick any two.
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Alan B
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| posted on 12/5/08 at 05:55 PM |
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quote:
Originally posted by Fred W B
Nice post Alan
I find that there are so many variables in some areas that you have to at some stage take a decision and eliminate at least some of them, otherwise as
you say nothing gets built.
I find that in general as the second whatever you make is always much better than the first, and all the cad in the world will never replace holding
the finished whatever in your hand, I prefer to dive in, make up a very rough example of the part I am considering, refine it till it works properly,
and then make the final part.
The other thing I find, with swotting from books and internet etc, that the concepts and techniques described become so much more real and
understandable once you have tried to do at least something practically.
in order words, don't sweat it if you don't fully understand at first, just try to do something with what you do know, and then go back to
the books etc. I find bits of text jump out of the page once you go back to them and you really see what the guy was on about then.
Sorry not a very considered response, I'm going through this at the moment with laying up fiberglass - is it possible to get a styrene
hangover?
Cheers
Fred W B
[Edited on 12/5/08 by Fred W B]
Thanks Fred and good post back too...made a lot of sense....looking for the balance..
Yes you can get Styrene hangover...ask me how I know?...LOL
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Triton
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| posted on 12/5/08 at 06:08 PM |
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Sorry not a very considered response, I'm going through this at the moment with laying up fiberglass - is it possible to get a styrene hangover?
Oh yes mate and a banging headache so wear a mask to cut out the fumes especially on a warm day as boy does it hum....
Good thread by the way..
Mark
My Daughter has taken over production of the damn fine Triton race seats and her contact email is emmatrs@live.co.uk.
www.tritonraceseats.com
www.hairyhedgehog.com
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Fred W B
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| posted on 12/5/08 at 06:50 PM |
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quote:
Oh yes mate and a banging headache so wear a mask to cut out the fumes especially on a warm day as boy does it hum....
and in SA every day is warm......
Sorry Alan, we are drifting.
You know how when you have a good couple of pints on a night out, and when you have a slash the next morning you just smell beer........On sunday
morning I swear I could smell styrene in the bathroom
Cheers
Fred W B
You can do it quickly. You can do it cheap. You can do it right. – Pick any two.
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andyd
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| posted on 12/5/08 at 09:42 PM |
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Thought I'd add my inexperienced 2c in...
I'm currently designing purely in CAD mainly because I'm not well placed to actually fabricate anything... garage full of crap... no spare
cash to buy parts etc.
What I'd like to be confident of though is seeing the thing through to the end. As I'm far more comfortable with a PC than a welder,
I'm of the opinion that if I can "solve" as much as possible in a CAD model then I'll personally be happier that I'll be
able to build the end result.
I admit though that at some point I will want to be able to step back and admire something physical. On that note I have asked a mate of mine to CNC
some parts from plastic that I've designed just so I can "feel them".
Andy
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rpmagazine
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| posted on 13/5/08 at 04:05 AM |
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Too often when we ask a reflective question such as this we get many answers of 'the line is here and if you don't agree then you are
wrong!' and more often than not such answers simply reflects the personal bias and abilities of the individual making the comment.
Where 'the line' is will of course be dependant on the individual: what their values are and what they are trying to achieve - which is of
course what the whole 'hobby' car building exercise is about for most of us.
The theories are of course just tools for us to use in attempting to understand what is going on in vehicles. they all have their flaws and their
applications, use what you will, after all the majority of them have been in the public domain for a very long time!
If you are building a car for a sunday drive then it could be a relatively simple exercise, if you are building a car for advanced performance or
competition then it could well be a much more exhaustive exercise as far as application of theory, the engineering involved and also the skills
required to make the vehicle with sufficient accuracy.
Just as with everything there is no 'best fit' that will cover everything.
[Edited on 13/5/08 by rpmagazine]
www.racemagazine.com.au
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Doug68
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| posted on 13/5/08 at 12:18 PM |
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This is an interesting question and gets close to what I do for a living which is involved with the sale of 3D CAE systems for the Engineering and
Design of things like, petrochemical refineries, power stations, ships etc.
When you look at something like a Chemical Plant it is a huge Design task and essentially each one is unique in its physical design.
This makes them very different to something like production car or washing machine where the design is done once and a million copies are made, so it
needs to be right the first time or its going to get very expensive very quickly with each cock up. I think this is very analogous to what what’s
undertaken in designing and building your own car.
Using a decent 3D design system will find virtually all of these mistakes if done properly and typically to fix a problem in the field will cost 100’s
of times more there than a dedicated effort to find and resolve issues in the 3D model before construction begins.
What you use or how you do your 3D model is not really the point, in CAD, Balsa or anything else is fine providing it’s done with some level of
rigour.
Going through the Engineering & Design phase of my project I’ve tried to implement these same principles essentially as I don’t have the time or
the money to repeatedly screw up in “real life”. I recently spent a week of evenings doing the pedal box support only to find it was crap and had to
cut it all out again, that probably consumed $10 worth of metal but it was 2 weeks on the job instead of one. I really hate that and the reason it
happened is due to me not doing a mock up of the pedals in the 1:1 MDF model I had at one point to make sure that I would fit in the thing (I didn’t
BTW and had to make the whole thing 8” wider (another lesson))
It’s one thing though when talking about Design which is essentially making sure all the bits fit together in a constructible way, wheels can bounce
& turn without interfering with the chassis or bodywork (and a million +1 other things) as opposed to Engineering which is the analysis the car in
all the different ways we can imagine such chassis stressing, suspension dynamics, aerodynamics and so on.
I think with the Engineering at some point you have to call enough is enough and just get on with it, essentially IMHO there is no such thing as the
perfect solution any of these problems and the hardest part of any of these questions is choosing appropriate goals to aim for in the first place.
It’s easy to get carried away with the idea that one design virtue overrides all others and then screw the whole deal up as a result.
[Edited on 13/5/08 by Doug68]
Doug. 1TG
Sports Car Builders WA
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rpmagazine
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| posted on 13/5/08 at 12:41 PM |
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good points. I agree on the worth of a mockup, it has reduced waste and stopped me designing seriously flawed aspects of my car. If I had tried it is
steel it would have been expensive.
www.racemagazine.com.au
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Gakes
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| posted on 14/5/08 at 06:27 AM |
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Great post! I too get stuck in the theory of things...All the time! but, no knowledge can be generated without a direction based on some information
that u stumbled on sumtime. Mockups are the key to test ur ideas. In industrial design we are are encouraged to make a model of our project to see
"reality flaws" that 3D models and theory can't always resolve. so make a mockup, like i'm doing at the moment, and
it'll help more then any other source of info
 
Description
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Syd Bridge
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| posted on 14/5/08 at 09:14 AM |
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Hi Alan,
You pose a good and relevant question.
The limits on theory are fairly obvious. If anyone involved in this thread had worked in a design office doing roadcars or racecars, then they would
know where the limits are exactly.
Polar Moments and Roll Centres don't come anywhere near the discussion.
For roadcars, packaging and cost are prime. This is where a lot of FEA comes in, because the lighter a part can be, then the cheaper it is to make and
install. Then fitting it all in to give maximum cabin space is paramount.
Road cars are designed primarily with costs a major concern, then speed and ease of assembly are next. No great concern is given to ease of
maintenance, as we all come to find out.
Racecars are as I have put previously. Keep it all as light as possible(FEA again), as low as possible, and as central as possible. Any physics and
maths is done after the fact, to compare with previous design work.
As is shown in another thread on here, some knowledge of springs and wheel rates, and basic mechanics and physics, is essential. That little rear
engined thing doesn't need 700lb springs in a million years, if it truly has a 1:1 ratio on the pushrod suspension. My suspicion is that there
is a flaw in the maths, and that is where some proper knowledge of an area of relevant and applied theory is necessary.
Coffee is gone, back to work.
Cheers,
Syd.
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