Hi there, before I start my build I'm modelling my entire car in my favourite CAD software, SketchUp, and I thought I'd just pass my roll bar concept by you good folk and see what you think of it. It’s not final at the moment but it is of the style that I would rather like.



Biggerer



Biggerer

So, what do you think?

I know many people don't even fit them but the stays supporting the hoops look too narrow a diameter if drawn to scale. Nice software though.
Incidentally does anyone know how high the roll bar needs to be for a 6' 2 driver cos I'm trying to get one from a Westfield that is 330mm I think.

yeah they are a little, but as I say its not final.

I like it!! Very modern and stylish

Paul

thanks bro, I'll licence the design for you at a reasonable price!

Looks similar to the design I had in mind for our next build

Phil

Very nice looking, I would have had that design on my indy if it had been available.


Well there may be an opertunity to have a few made rather than a one off.... I can recomend a place in Woking that can roll and bend which is what that looks like it will need.

I don't know if you will find someone who can do that tight bend on the one side, or is it a welded elbow?

Cheers

Fred WB

well, I has hoping it could be a single piece rather then a welded elbow. I'll have to do some research. Thanks for the comments so far

Pete

Yes, find out what radius bends you can get done, and work from that, rather than the other way round.

While a lot of places say they can bend tube, not many can put a nice mandrill bend into a pipe with a sufficent wall thickness to make a roll bar

Cheers

Fred WB

Do you want a honest answer ?
A chocolate teapot would be more effective and look better.

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A chocolate teapot would be more effective and look better.

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I like the look of it in that picture but as non-triangulated 'squares' you're asking for them to be significantly less effective than they could be. In a high-velocity impact (which is when you want the roll-bar!) they'll tend to fold/break at the upper corners.

I do like the 'look' though!

Cheers,
James

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Originally posted by britishtrident
Do you want a honest answer ?
A chocolate teapot would be more effective and look better.

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Well bt, Donkervoort seam to think it looks better than a chocolate teapot, as it was their J25 that gave me the idea.

Thanks James, I'll see what I can do with the design; maybe modify it so there is more strength in the corners. Think I'll run it through some stress analysis simulations so what it comes up with.

Cheers
Pete

The main shape is good. Instead of running the support all the way to the bottom of the rear frame, run them to the top corners of the rear frame. And bulk them up - they prevent the main hoops from folding over backwards and what's there is nearly useless.

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Originally posted by kb58
Instead of running the support all the way to the bottom of the rear frame, run them to the top corners of the rear frame.

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Yes. I'm making the assumption there'll be a corner tube down to the bottom, and the whole thing covered with a sheet and riveted. If the corners are to be radiused that won't be strong enough though.

Another way is run them straight back and down to the same tube instead of the corner, then run tubes down the back, connecting the upper and lower rails.

Regardless, you have to rivet a sheet on the area to get enough strength... and even then I worry about it buckeling. Anyhow, it's better then running a tube directly all the way to the bottom rail - it'll buckle with very little force.

[Edited on 10/18/05 by kb58]

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Originally posted by Mad Dave

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A chocolate teapot would be more effective and look better.

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I think thats a little harsh

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Originally posted by paul v6

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Originally posted by britishtrident
Do you want a honest answer ?
A chocolate teapot would be more effective and look better.

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Have you ever said anything positive on this forum??

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Great bit of CAD work there Commander!

I'm not going to be saying anything constructive about the roll bar but I must say it certainly looks slick!

What are the pros of SketchUp compared to other CAD software? I like the ability to add a light source and the resultant shadows. It looks much tastier on the eye...

Chris.

Well if you want to be constructive how about some advice rather than just slating it...........??

I'm just a software engineer, not a mechanical engineer and my experience in this area isn't as great as that of you folk. The book doesn't go into much detail about roll bars hence asking for advice from people I hoped could help me out.

Pete

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Originally posted by Winston Todge
What are the pros of SketchUp compared to other CAD software? I like the ability to add a light source and the resultant shadows. It looks much tastier on the eye...

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As a mechanical/design engineer I agree its not braced well enough, but quite a few I've seen look less affective. It does look classy though and If your going to spend hundreds of hours and thousands of pounds on a car I want it to look as well as it goes!!

Paul

The shape does look pleasing IMHO, but it's not a practical shape.
Making bends that tight is impossible even with NC benders. As a rule of thumb, the minimum achieveable radius is 3.5 times the tube's OD.
The only way you could make those hoops is by cutting and shutting straight lengths of tube and donuts.
AFAIK, that's how some of the flash looking alloy glam bars are constructed for the back of utes/pickups. The welds are sanded down and buffed up so they're virtually invisible.
That method of constructing a roll bar is something I wouldn't like to stake my life on though.
Composite roll bars are banned in many classes of motorsport.

And of all the people to listen to, I'd go with whatever Rorty says (99% of the time - the 1% is when I need convincing).

Pat...

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Originally posted by Avoneer
And of all the people to listen to, I'd go with whatever Rorty says (99% of the time - the 1% is when I need convincing).

Pat...

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Having designed and had my own roll bar made recently for my GT project with rolls and bends, I'd say that those hoops are going to be impossible to make from one length.
Doesn't mean its not worth asking first though.

As for srength, I'd consider what type of car you are building... the heavier the car the more bracing you need to add.

However I also think a cut and shut roll bar would be a bad idea (regardless of weight)

my advice, for what it's worth, is a mixture of the above.

1) yep it looks nice

2) it will be heavier than a "normal" bar

3) you can't make it in one piece per "hoop"

4) don't even consider butt welding pieces of tube together to make it

5) the roll bar, though important, is still connected to the chassis under it, which on most sevens is pathetically under engineered for the task of roll bar support.

placing the inner ends of the hoops into the "middle" of a tube as per the drawing makes this even worse, i.e. the chassis will just crumple even if the bars hold up on top of it!

PS, at least yours has rear diagonal bracing, just looked at the Donkervoort one!!! Ha Ha Ha now that really is a chocolate teapot!!! Go upside down in that and the bars will just be like a mousetrap over your neck!

my two pence worth

1. the bends may be possible we bend 2 x od of tube depends on distance between bends

2. the rear brace is better going to the bottom chassis rail as per your original drawing

3. would go slightly larger on the od tube for the rear stay

4. quite like the shape ( something different )

hope this helps

best regards

marc

We'll be seeing them on the Vort X next

Pat...

So, with roll-bar sorted, now lets consider the side impact protection.

[Edited on 20-10-05 by Hellfire]

heh heh!!

folding pelvis?

I'm more concerned about rear-impact protection (ooer!).

There's not much between the petrol tank and the outside world, and not much between me and the petrol in the tank, if a following car smashes into it - even a minor impact.

Anyone fancy fitting a bumper?

David

nah, not really cos the chassis that it would be attached to would still fold up and burst the tank anyway!.

Shame - all I need now is a few hundred Pounds for a racing-style fuel cell...

DJ

that's the one!!

just make sure you don't get rear-ended!

Thanks for all the comments guys, you've definitely cleared up a lot of things for me, I have a new idea forming at the moment that I may share with you later if it pans out, but for now Hellfire, David J and NS Dev, maybe you lot should be building one of these if your concerns are side and rear impact protection!!

What about machining roll bars/hoops from billet aluminium??

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Originally posted by NS Dev

5) the roll bar, though important, is still connected to the chassis under it, which on most sevens is pathetically under engineered for the task of roll bar support.

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I have an RAC approved bar on mine and will be sticking with the illusion of safety that it gives, unless I go road rallying in it, in which case I guess I will really have to fit a full cage!

That lady in your Avatar.....There`s no need to suffer PMT now with the new drugs available..
Alex