space frame help

[philipcurtis100]

im thinking of doing a space frame mini
wanna make it as light as possible
i was thinking alluminium any advice of
what size type of box to go for would be appreciated

 

[onenastyviper]

Hi, this is my first post (so treat me gently please!)
Aluminium may be light and strong but fatigue life is important (if I recall correctly)
Roll cage material may be very suitable and is steel. Look at cold drawn seamless tubing, T45 number might mean something to someone here...

I hope I have suggested a valid alternative...

 

[Dangle_kt]

you need a tig set and argon for alu. plus what has been mentioned.

cold drawn tube looks spot on, but is hard to weld, especially in position. your best with mild steel box, unless your pretty practised imo.

 

[adi]

t45 all the way

 

[Bobtail4x4]

dont use Box,

its not as suitable as tube for all sorts of reasons,

when did you last see a box rollcage?

 

[philipcurtis100]

im thinking box because its going to be for the floor
im going to put tube for the roll cage
im going to be doing this at work they have a very good tig
and can weld ok so im still wanting to do this in alli if poss
for weight reasons any suggestions on alluminium i should use
its gotta handle 200bhp

 

[oz.]

Before you go off making your own stuff have a look at one of my online friends company. http://www.force-racing.co.uk/front-suspension/ He is a very successful mini modifier and you can purchase a complete front end from him including suspension and all the danglies. He will also make some custom engine mounts for you if you specify them.

You mention 200bhp so i'm assuming it's going to be a motorbike engine as they are small, reliable and usually have a fairly high power output if you get something like a busa. Going from that I'd say you're putting it in the back? And making it rear wheel drive possibly? If so simply incorporate the engine mounts into the roll cage.

I suggest you go for a steel spaceframe, you say you want it to be light so you want to use aluminium. A few things to consider - alu may be lighter but it is much more likely to crack rather than bend as it is more brittle than steel. To get alu as strong as a steel spaceframe you're going to need to put more material into it meaning the weight will be pretty much the same either way.

Tube is less likely to bend than box - thats why it is used in roll cages.

 

[hotrodder]

Forget aluminium. Aluminium is around a third the density of steel but it's also around a third as stiff and (for the weldable alloys) at best around half the strength of something like T45 alloy steel. For example 7020-T6 (aka 7005) has a UTS or around 350MPa compared to T45 with a UTS of around 700 - 900 MPa. It gets worse when you look at yield strength and elongation.

Welding WILL soften aluminium (anneal/partially anneal the HAZ) further weaking it. 7020 makes a better 'recovery' from welding than the other high strength alloys (6xxx series) but is even less formable than them, use a bendable alloy/temper and you'll be lucky to see a quarter the strength of T45. Smaller things like bike frames are heat treated but something the size of a car...

Remember the Renault spider? Welded aluminium space frame, kinda similar in philosphy to the Lotus elise, similar size but weighed a good 200kg more. Lotus made far better use of aluminium (complex extrusions for stiffness like motorbikes) and glued it to avoid the welding problems but they still used a steel subframe for the rear end- too much going on in that area, aluminium kept cracking. Forget aluminium

 

[rosco454]

I would also say T45 tubing for a spaceframe,although not as light as aluminium its still a pretty lightweight material.

Carl at force racing (link posted by oz) always gives good advice so it may be worth a chat with him to go over your options.

 

[TheJoker]

I'm no expert, but I have a very keen interest in this sort of stuff.

There's no race car out there with an aluminium space frame. If it's a space frame, say up to late 60's, early 70's Formula 1 car, it's steel. Thin walled high quality steel.

If it's aluminium it's aluminium sheet (often sandwich construction too), folded and welded. Think between spaceframe and carbon fibre Formula 1 cars.

This picture shows an Alu F1 "body" and the carbon fibre body.

It's a bit pointless doing a alu-sheet car as you'll also need a "normal" bodywork on the outside.

Henceforth, for us mortals that can't sculpture a whole bodyshell out of carbonfibre/kevlar; high quality steel tube is still the best bang for-the buck. Another option is chrome moly, but whilst being stiff, it's also prone to breaking.

Good luck with your project!

 

[Dangle_kt]

dont use Box,

its not as suitable as tube for all sorts of reasons,

when did you last see a box rollcage?

I have never seen a roll cage made from box

I have seen plenty of box section used to fabricate chassis though

now which is he making?

If the guy is a good welder he wouldn't have asked the question about alu, so it shows he is a novice - personally I'd say he has a better chance of safely welding box than the complex curves of tube - after all it needs to be safe.

 

[philipcurtis100]

people at work tell me to use tube
i still wanna use alli if poss mabe im being stubarn
i weld quite a bit at work and thats where i will construct it
its a car engine front mounted rear wheel drive or poss 2 mororbike engines
thanks
phil

 

[TheJoker]

i still wanna use alli if poss mabe im being stubarn

Go for it then. Sometimes listening to people means you're limited to the convention.

 

[philipcurtis100]

alluminium: doesnt rust, looks better, lighter
steel: cheaper, stronger?,

i will price up so if i went for alluminium would
3" od x 10swg wall Aluminium Tube
metric:
76.2mm x 3.2mm
or
what size steel
would that size aluminium be ok
thanks phil

 

[MajorPayne]

I'm no expert, but I'm sure I read 4mm would be good to use.

I could be very wrong, never built one myself or even thought about it. Just I'm sure I've read around in another post they said 4mm.

Was also thinking, why not use Ti alloy? If you really want summit light and strong, I'd say 2.5"~3" with 3~4mm. Also you could weld it on a DC model.

anyway I'm interesed in what others say about this subject

 

[pedrobedro]

By the time you have made an aluminium chassis as strong as a steel one it will probably weigh just as much. The drawback then is that aluminium has a finite lifespan due to flexing and work hardening whereas even ordinary mild steel is rated much higher. Add the higher cost of the material and the dearer gas and wire or AC/DC tig you will need and it soon becomes prohibitive. I just looked at your guesswork for the aluminium tube and if those are the measurements you will have no room for the engine after you build the chassis. Have a look at Z cars mini for an idea of what you want but don't look at their prices or you'll fall through the floor. Most kit car manufacturers (Westfield, MK, MNR and MAC 1#) use 1" or 25mm rhs which is resistance welded square tube or a combination of square and round (Caterham) Go ahead and prove them all wrong by all means but look at the easier route if you want to actually finish your project.

 

[oz.]

You're ideas are good and were not saying you're stupid or anything BUT the idea really isn't practical. I know of someone on the PSOOC forum who wants to do something difficult "because it hasn't been done before" but it's pointless.

Use this to your advantage that you have been advised by more experienced on things. I'm learning similar things everyday when a daft idea pops into my head and i mention it to a friend.

Something I want to do is to make a twin engined mini, but different to most others make it 4wd engine in the front, engine in the back. Safer than putting so much power through the back wheels

 

[hotrodder]

alluminium: doesnt rust, looks better, lighter
steel: cheaper, stronger?,

i will price up so if i went for alluminium would
3" od x 10swg wall Aluminium Tube
metric:
76.2mm x 3.2mm
or
what size steel
would that size aluminium be ok
thanks phil

It is soooo much more complicated than that. Copy the 'typical' steel tube chassis but use larger diameter tube with a thicker wall and the likely result is going to either be

1. no lighter, probably heavier than an alloy steel tube chassis
2. not stiff enough (although this is a design issue more than a material one)
3. develop fatigue cracks very quickly (or just break)
4. all of the above


Aluminium has VERY different properties to steel, totally different animal. The big car manufacturers are making good use of Al (and other lightweight materials) these days but they have many millions for R&D resulting in one off extrusions, castings and special joining techniques to overcome aluminiums shortcomings for this sort of application

Have a look here. Note the cross section of the tube and spherical bearing housing details in this article, quite a bit more going on than for a typical steel wishbone. Many/most of the extrusions used are not available to the likes of you or i, especially for sensible money, as the manufacturer owns the extrusion dies

The aluminium single seater tubs shown earlier... AFAIK all were riveted or bonded and riveted and had a (short) finite life. From memory any welded bits were substructures that bolted to 'hard points' in the tub- suspension pick ups etc. Pretty sure i've read a book/article covering the re-riveting of tubs to get another season or two out of 'em after they 'loosened up'

 

[MrFluffy]

I suggest you visit http://www.locostbuilders.co.uk and have a browse round their sections.

Then go and read http://locost7.info/files/chassis/kitcaranalysis_V2.doc

Also :-
http://www.kimini.com/

And if you havent forgot the idea of using ally tube for a spaceframe by the time youve read all that lot and read all the posts here, then I wish you luck, because your going to need it (and shares in dye penetrant suppliers...)

 

[adi]

people at work tell me to use tube
i still wanna use alli if poss mabe im being stubarn

oh oh !! , someone is gonna end up hurt
rather you than me mate