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WesBrooks

101 Vehicle Dynamics Read?

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I may have asked this before a while back excuse the repetition if so! My background is mechanical engineering to a degree level, along with general aquired information from the following 17 years of life in engineering related industrys and of course floating around these forums!

I'm looking for a read on vehicle dynamics that is a general introduction that would allow you to go forward and start to play with ground up homebuild vehicle design that's backed up by a little more than seat of the pants instinct and heresay. ...or more accurately allow you to take heresay and nuggets of experience from others and try to start understanding the mechanics of what they have observed.

A recent post talking about getting engineers advice on a spacer on the axle made me realise I understand all of the basic potential failure mechanisms such a fatigue, shear, tensile load, etc., but coming up with reasonable estimates for loading to design to is a vast gap in my knowledge. Take even a very prescribed case such as driving into a curb a 20mph with 285 75 r16 tyres. Where to draw the line on what is a failure level event?

Don't get me wrong, I'm not nieve enough to think one book (or website) will make me an expert. Navigating options on online book sellers is difficult because there are many options. I will have a look for recommended reading lists from motorsport engineering courses but welcome suggestions.

My ultimate aim is once I have finished my current project to move onto a ground up design of a independent suspension electric off roader. I'm not trying to do something that is ground breaking, but would like some confidence it is safe and grounded on fundemental best design practices! Over engineering is fine, but it adds mass which counters the objectives of the initial desire to engage in over engineering!

 

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Posted (edited)

I guess most of these questions are traditionally answered by live data collection on increasingly complex tests.

In a way what I'm attempting to do is more challenging than what vehicle manufacturers do. With that in mind I guess I will have to adopt over engineering on safety factors merely because I have less confidence in the expected loading the components will experience in use.

That said I assume you get my point about over engineering not being the answer to all my problems!

 

 

 

Edited by WesBrooks

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Could be worth having a read of this:

http://www.legislation.gov.uk/eudr/2007/46/contents
 

It’s similar to the Machinery Directive but relates to motor vehicles and components. I haven’t read it all yet but I’m expecting it will state the required safety factors etc for automotive use or at least give a guide.

Then there will be an EN Standard somewhere that supports the legal requirements and will usually go into greater technical detail.

Apologies if it’s stating what you probably already know 😊

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Working ok here....

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24 minutes ago, western said:

Big66 the link does not work. 

Don’t forget the J for Joe😉😉

 

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Posted (edited)

Certainly a vast quantity of information there. Is that what is normally reffered to as the construction and use of motor vehicles (or something similar!) regulations?

I've dived into the latter occasionally when trying to understand obsurities in the IVA test regulations. If the current regulations percist, then I will be building to pass an IVA if intended for road use, but you're right I should have a passing knowledge of the regulations that is built on, and there maybe a few gems in there!

Edited by WesBrooks

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48 minutes ago, WesBrooks said:

Certainly a vast quantity of information there. Is that what is normally reffered to as the construction and use of motor vehicles (or something similar!) regulations?

I've dived into the latter occasionally when trying to understand obsurities in the IVA test regulations. If the current regulations percist, then I will be building to pass an IVA if intended for road use, but you're right I should have a passing knowledge of the regulations that is built on, and there maybe a few gems in there!

No Con & Use is subordinate legislation under the Road Traffic Act. The legislation I linked to earlier is more of a design requirement but there will be related guidance and best industry practice to support it. The directive will, for example, state a required safety factor for a component but not necessarily tell you how to achieve that. For that you need to go to the relevant standard that will give you things like calculations etc.

Designers and manufacturers need to demonstrate compliance with such legislation and standards in order to obtain type approval or CE certification.

 

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3 hours ago, Bowie69 said:

Working ok here....

strange, works ok on my laptop, but won't on my phone.

 

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I think the first / main thing you'll want to narrow down is what you're trying to get out of it? Are you doing it for the engineering aspects or are you wanting to build to vehicle to use?

Since you have your head screwed on correctly (or at least appear to) I think if you're trying to achieve the latter then you may be best off looking at "equivalent" builds that are proven. An extreme example but for example for building an off-road vehicle then you could use Ultra4 / Trophy Truck as a basis, i.e. if it survives that abuse then it's likely to survive the abuse you'd give it. But then you can apply your sensible hat and determine that a 4" chromoly reinforced trailing arm is likely to be overkill for a vehicle that doesn't exceed 10mph so perhaps better off looking at, say, a Defender as a basis for sizing components.

If you're doing it more for the engineering aspects then from my brief knowledge of what goes on in equipment design it's mostly down to experience, rigorous testing and to a certain extent simulation these days. It may be worth seeing whether you can have a chat with people involved in this kind of stuff, @discomikey springs to mind and @RedLineMike (although the latter I suspect is build it as strong as possible because we're gonna break it at some point!). You could take a punt and phone up Caterham or Ricardo and see whether anyone's interested in a friendly chat.

I've got a friend in Spain who works / used to work for Análisis y Simulación in Vitoria Gasteiz who loves nothing better than to sit down number crunching in Excel designing bikes. We built some data loggers and strain gauges built into the hubs of Formula 3000 cars so that they could record what was going on around circuits. Slightly scarily the logger could tell you how much your little finger was deflecting this solid block of aluminium. Got another friend who works for Ilmore Engineering who I suspect might be able to pass on some useful information about whether there's anything to read up on.

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Thanks for the great comments and suggestions so far.

Far point on lack of objective. My thoughts are very early stage feasibility at the moment. I'd spotted an open source design of a 200kW motor controller that started cogs whirring!

Lightweight side of things as far as possible. If things proove feasible I'd like something that is green lane capable so low speed. Unless something incredible happens with storage over the next decade trying to do much more will just end up requiring a crazy weight of batterys. As it is I'm expecting 500-800kg will be batteries, most likely salvaged from something like a leaf. Room for 4, with reasonable luggage space. In a nutshell a rugged, basic, vehicle just juiced by volts rather than IC.

The vehicle dynamics side of things is mainly trying to come up with targets for the interplay of roll centres, centre of gravity, anti squat, etc and how these should move around with suspension motion. I appreciate it is mainly designing for something adjustable rather than trying to hit a specific target, but knowing what range to target is the art!

 

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There's the big grey book "Race car vehicle dynamics" but it's spendy and may not fit what you want in an off-roader;

https://www.sae.org/publications/books/content/r-146/

Plus Carroll Smith's "...to win" series (Tune To Win, Engineer To Win, Screw To Win...), again aimed at racing but does at least show you a lot of what you didn't know you didn't know.

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I'd recommend 'Chassis Engineering' by Herb Adams Chassis Engineering as a good introduction. It is aimed at racing and as it's American it tends to have a focus on oval tracks but it has a good range of information on general vehicle dynamics and chassis design. It doesn't particularly cover offroad use but all the basics are there.

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For general vehicle design info (generally a 'how it's done' for modern and electronic systems rather than a first principles dynamics approach) I'd recommend the Bosch Automotive Handbook: 

https://www.amazon.co.uk/Automotive-Handbook-Robert-Bosch-GmbH/dp/1119530814/ref=sr_1_1?dchild=1&keywords=bosch+automotive&qid=1592901267&sr=8-1

10th edition is the latest, it's a bit spendy - you might find an earlier edition at a better price if you don't need the latest on aftertreatment OBD control etc.

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If you, ahem, go beyond the 1st page of Google into the less trodden web you can find a lot of these books to download for free as a PDF.

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