Chassis: Overkill?? not enough?
Discussion
hello again yall. been knocking together this design for me chassis (just the front end to complete) and beginning to think it may be a bit ott, mostly compared to seven type chassis but ive heard storys of them bending on the track?!? it is starting to look very similar to the gtr chassis (dont worry i havent copied, just using the same design principles) but according to my calculations will be much lighter, based on 1" 12g steel tube (round) the material so far comes in at 57kg not including brackets and welds (and the front) thats if ive got the weight per meter right (1.212kg) so since the gtr chassis wieghs 130kg ish (according to a previous post on this site) the bits i havent included so far cant possibly amount to 73kg or can it? its confusing me and i need peace of mind 
am missing some thing or am i a genius??
comments, advice greatfully accepted.
more pics available if you want, please excuse the triangular roll bars, i havent totally figured out cad yed
>>> Edited by suparuss on Tuesday 22 April 19:51
am missing some thing or am i a genius?? comments, advice greatfully accepted.
more pics available if you want, please excuse the triangular roll bars, i havent totally figured out cad yed
>>> Edited by suparuss on Tuesday 22 April 19:51
Okay, not enough triangulation at the front, no crumple zone or anything much at all ahead of the occupants feet, too 'open' an engine bay (removable triangulation or brace needed IMHO), not enough triangulation across the frame. The front end needs major work, eg where is the suspension going to mount ? The most positive element is the side impact and rollover protection, the back end just needs tweaking,but the front is a fair way off in that:
Not enough triangulation at the front, no crumple zone or anything much at all ahead of the occupants feet, too 'open' an engine bay (removable triangulation or brace needed IMHO), not enough triangulation across the frame. The front end needs major work, eg where is the suspension going to mount ?
I think you're not too far off in the centre and rear section, but you need to think a bit more about tying them together laterally.
Sorry if this is a bit negative, it took a year to sort the design of the seven we used to have, but it was worth it in the end
Not enough triangulation at the front, no crumple zone or anything much at all ahead of the occupants feet, too 'open' an engine bay (removable triangulation or brace needed IMHO), not enough triangulation across the frame. The front end needs major work, eg where is the suspension going to mount ?
I think you're not too far off in the centre and rear section, but you need to think a bit more about tying them together laterally.
Sorry if this is a bit negative, it took a year to sort the design of the seven we used to have, but it was worth it in the end
cheers jaydee, i cant really do much with the front until i can measure a sierra windscreen, you got one layin around? 
or whatever screen i decide to use, same with the engine bay brace, but yeah it definately needs one since the shock will be mounted horizontaly above of the upper wishbone mountings pointing towards the front of the car, so those forces need to be transmited through to the center bulkhead. not bad for 2 weeks work anyway! anyone else got any views?
Cheers again.
or whatever screen i decide to use, same with the engine bay brace, but yeah it definately needs one since the shock will be mounted horizontaly above of the upper wishbone mountings pointing towards the front of the car, so those forces need to be transmited through to the center bulkhead. not bad for 2 weeks work anyway! anyone else got any views? Cheers again.
I would agree pretty much with jaydee...however I would add that your material choice is odd....most 1" tube used is usually 16g or less....for that kind of weight per foot you could probably go for 1.5" x 16g and get a much more efficient use of material (way stiffer) Have a look on www.locostbuilders.co.uk in the mid-engine section...many of us are building mid-engined stuff there.
HTH
Alan B
www.desicodesign.com/meerkat/
HTH
Alan B
www.desicodesign.com/meerkat/
have you considered asking Chassis for advice?
he is something of a pass-master at this kind of thing, having built a RWD, RWSteer mid-ferrari-engined fiat punto. from scratch.
without any education.
although i heard he read 'Ben has a Ball, a Big Red Ball' cover to cover in 45 minutes once. Look him up.
he is something of a pass-master at this kind of thing, having built a RWD, RWSteer mid-ferrari-engined fiat punto. from scratch.
without any education.
although i heard he read 'Ben has a Ball, a Big Red Ball' cover to cover in 45 minutes once. Look him up.
This might sound really stupid but as you've got a CAD-generated model of it, go to your local model shop and get some lengths of 3mm or maybe even 5mm square section balsa wood and a tube of balsa glue. Make a 10th or even 5th scale model of it (you don't have to worry about the balsa bits being solid instead of hollow and you don't have to worry about cutting the correct angles on the ends of the sticks - the glue can fill big gaps!) When you've finished (and it should only take a few hours) grab it by the front spring mountings and the rear spring mountings and twist it gently. You'll get a very good idea of which bits are useful and which bits are dead weight INSTANTLY. Honestly, it's one of the best tools this side of an expensive finite element analysis programme and you'll be amazed how much twist you get! You can try adding and removing "tubes" until you get something you're happy with.
Other than that, I agree with the general comments from the other posters. There are too many "holes" in it at present so it's likely to be pretty floppy (unless you intend panelling it with sheet material - in which case that would do the same job as the diagonals in flat bays. In general, you should aim to have no bays anywhere in the chassis that have more than 3 sides. This is relatively easy to do until you start putting people and engines in!
Other than that, I agree with the general comments from the other posters. There are too many "holes" in it at present so it's likely to be pretty floppy (unless you intend panelling it with sheet material - in which case that would do the same job as the diagonals in flat bays. In general, you should aim to have no bays anywhere in the chassis that have more than 3 sides. This is relatively easy to do until you start putting people and engines in!
meerkat: thanks for actually answering my question, or at least parts of it. 16g tube brings the current weight down to 43kg, which brings me back to why its way lighter than the gtr chassis?!?! ill check out that site.
cheers.
mikeylad: please take me seriously, id like to think i know a little more about cars than chassis, thanks anyway though.
avocet: my axpensive finite stess analasys program came this morning, in the form of nastran 4d, ill let you know how it comes along!
cheers.
mikeylad: please take me seriously, id like to think i know a little more about cars than chassis, thanks anyway though.
avocet: my axpensive finite stess analasys program came this morning, in the form of nastran 4d, ill let you know how it comes along!
When I built and designed my chassis for my car ( a lamborghini replica) I followed as much of the orginial as possible. I made changes where necessary for different front suspension and engine placement.
Instead of using the balsa wood for a chassis mock-up I used solid copper wire. I used about 1.2mm copper wire and soldered it together in the exact shape of the chassis I needed. Then came the good bit. The twisting and bending loads. You can tell soooo much from such a simple thing. I found many places where tubes would not have been necessary and just the simple placement of others really strengthened the chassis. You can also test front end crumple zones by either making up just a front end or as I did by placing the chassis rear against a hard non-moveable surface. Then using very strong rubber bands (lots of them), I catapulted a brick against the chassis!!!!! This was done from the front and with the chassis against a non moving surface, I was able to see how the front AND rear crumple zones worked. The copper wire was easy to straigten out for re-tests. Similar things were done for side impact.
I have photos of my chassis but dont know how to put them on here for your viewing pleasure !! But needless to say there is nothing like testing in the flesh.
Just a quick note though, I also made up one of the Ultima/Kitdeal chassis. I found that generally it performed like a wet lettuce leaf. A few extra tubes in the right places made a tremendous difference to the torsional strength of that chassis. - all is not as it seems ........
Instead of using the balsa wood for a chassis mock-up I used solid copper wire. I used about 1.2mm copper wire and soldered it together in the exact shape of the chassis I needed. Then came the good bit. The twisting and bending loads. You can tell soooo much from such a simple thing. I found many places where tubes would not have been necessary and just the simple placement of others really strengthened the chassis. You can also test front end crumple zones by either making up just a front end or as I did by placing the chassis rear against a hard non-moveable surface. Then using very strong rubber bands (lots of them), I catapulted a brick against the chassis!!!!! This was done from the front and with the chassis against a non moving surface, I was able to see how the front AND rear crumple zones worked. The copper wire was easy to straigten out for re-tests. Similar things were done for side impact.
I have photos of my chassis but dont know how to put them on here for your viewing pleasure !! But needless to say there is nothing like testing in the flesh.
Just a quick note though, I also made up one of the Ultima/Kitdeal chassis. I found that generally it performed like a wet lettuce leaf. A few extra tubes in the right places made a tremendous difference to the torsional strength of that chassis. - all is not as it seems ........
suparuss said: which brings me back to why its way lighter than the gtr chassis?!?! ill check out that site.
Err, because you need to add quite a number of struts to the design to get the torsional rigidity up, I would guestimate that you've only got about half of the total chassis components you'll need then add welds, powder coating, brackets that's going to take it closer to the Ultima's weight. The ultima is also stressed for a huge and (relatively) heavy V8 with 500+ lbsft of torque, you may not need that level of strength.
I agree that 1.5" 16g is a better choice. It's also a lot easier to bend. There are also different steel grades to consider.
It would be worth trying Avocet's approach before launching into FEA as you can do the broad design more easily looking at a physical model, then tweak it with Nastran.
Once you're actually building how much fab are you thinking of doing ? For curved components I suggest building them up with cheap easily formed tube (eg exhaust pipe) and then having a local fabricator form the CDS (or whatever) as their bends will less stress and wall deformation than yours (unless you've access to a hydraulic mandrel bender)
I wouldnt sacrifice safety in strength for a few pounds of weight. Take the weight off somewhere else if you are that worried about it. Dont bend pipes either. A bent tube in a spaceframe chassis is as good as an ashtray on a motorbike.
Engine torque is not such a problem in a mid-mounted vehicle because the torque reaction is only from the engine mounts to the rear axle line, perhaps only about 30 inches in most cases. A front engined vehicle has to resist torque over virtually the whole length of the car from the front engine mounts to the rear axle, therefore the chassis will have to be inherently stiffer to compensate for engine AND suspension torque - which will increase weight.
Engine torque is not such a problem in a mid-mounted vehicle because the torque reaction is only from the engine mounts to the rear axle line, perhaps only about 30 inches in most cases. A front engined vehicle has to resist torque over virtually the whole length of the car from the front engine mounts to the rear axle, therefore the chassis will have to be inherently stiffer to compensate for engine AND suspension torque - which will increase weight.
lawrence1 said: I wouldnt sacrifice safety in strength for a few pounds of weight. Take the weight off somewhere else if you are that worried about it. Dont bend pipes either. A bent tube in a spaceframe chassis is as good as an ashtray on a motorbike.
I suspect that the triangular roll bars might be being replaced with something a little more curvacious
Providing tubing has sufficient inherent stiffness there is no problem with using a bent round section tube where necessary-obviously linear paths are preferable, but areas like the scuttle surround tend to result in compromises. Using larger c/s thinner wall tube to reduce weight will not result in a net reduction in strength if the design is well thought out and will increase stiffness ditto. 
No kidding at 300km/h I'd want to be in something I hadn't welded ! What have you got then ? Do you have a build site ?
A lesson was learnt by us (1 engineer (him), 1 person with a good idea what happens to people in accidents
(me) ) as regards strength when the propshaft decided to exit the car via the transmission tunnel 
The steel in that area was hurredly replaced with something a bit more meaty.
A lesson was learnt by us (1 engineer (him), 1 person with a good idea what happens to people in accidents
(me) ) as regards strength when the propshaft decided to exit the car via the transmission tunnel The steel in that area was hurredly replaced with something a bit more meaty.
Oh no !!! Not the old "Prop shaft out the tunnel trick". A guy I worked with had that, and it came off at the gearbox end and flipped the car - sadly killed the passenger, and took off the drivers arm and leg ...
I welded my own chassis. Thin wall tube is easy to weld with a MIG, but I done my suspension stuff with TIG.
Ive just got to get my site up and running. Sooo many pikkies and even a website design course and I still havent got round to posting something.
I have a 350 Chev in my car coupled to a Renault 21 Turbo box. The 3.44 diff and a 0.76 5th gear gives me that top end. But mother nature sees to it I cant go any faster - but at that speed, I'm already 3 times the national speed limit anyway !
I welded my own chassis. Thin wall tube is easy to weld with a MIG, but I done my suspension stuff with TIG.
Ive just got to get my site up and running. Sooo many pikkies and even a website design course and I still havent got round to posting something.
I have a 350 Chev in my car coupled to a Renault 21 Turbo box. The 3.44 diff and a 0.76 5th gear gives me that top end. But mother nature sees to it I cant go any faster - but at that speed, I'm already 3 times the national speed limit anyway !
No sorry. Flogged it a fair while ago I'm afraid.
Luckily our propshaft exploded midway (nowhere near a weld, never quite got to the bottom of it) but it still demolished the area the passenger would have been in had there been one We beefed up the area extensively (including plating it out in steel) and would have considered Spectra or Kevlar retention straps had we done more racing.
Luckily our propshaft exploded midway (nowhere near a weld, never quite got to the bottom of it) but it still demolished the area the passenger would have been in had there been one
We beefed up the area extensively (including plating it out in steel) and would have considered Spectra or Kevlar retention straps had we done more racing.Sorry to come into this discussion at a relatively late phase but I thought I would chuck a few comments in:
1. There seems very little torsional stiffness, apart from the roll cage, which will have little effect on the stiffness front to rear.
2. Side protection doesn't look very good, unless it was a glancing blow, but a full side load would just fold in the sides.
3. If you are having inboard suspension, which you mention, the cross bracing is non existent on the front end which will cause the whole effect of folding in.
4. Why so much bracing under the drivers/passengers seat? A reasonable gauge ally sheet would work and probably be lighter? (Or of course a composite sandwich plate)
5. From a weight point of view, you have not taken into account any suspension mounting brackets, steering column mounts, steering rack mounts, pedal box location, etc. The weight will go up significantly.
6. Have you thought about what steering set up you would use? (ie rack/column) bear in mind the steering column length in relation to the length of front end, the intermediate shaft will need to be taken into account as angles of universal joints are essential for smooth steering torque through the wheel is essential.
7. With a mid mounted engine, make sure you get the engine/gearbox as low as possible or you will end up with Elise style handling, ie jacking of the rear end. The geometry is essential to stop this.
8. Last question, is this a University project, or something you intend to build and drive?
Sorry for all the comments, at least you are doing something I never did. Always wanted to design my own car!
Cheers and good luck,
Mark
1. There seems very little torsional stiffness, apart from the roll cage, which will have little effect on the stiffness front to rear.
2. Side protection doesn't look very good, unless it was a glancing blow, but a full side load would just fold in the sides.
3. If you are having inboard suspension, which you mention, the cross bracing is non existent on the front end which will cause the whole effect of folding in.
4. Why so much bracing under the drivers/passengers seat? A reasonable gauge ally sheet would work and probably be lighter? (Or of course a composite sandwich plate)
5. From a weight point of view, you have not taken into account any suspension mounting brackets, steering column mounts, steering rack mounts, pedal box location, etc. The weight will go up significantly.
6. Have you thought about what steering set up you would use? (ie rack/column) bear in mind the steering column length in relation to the length of front end, the intermediate shaft will need to be taken into account as angles of universal joints are essential for smooth steering torque through the wheel is essential.
7. With a mid mounted engine, make sure you get the engine/gearbox as low as possible or you will end up with Elise style handling, ie jacking of the rear end. The geometry is essential to stop this.
8. Last question, is this a University project, or something you intend to build and drive?
Sorry for all the comments, at least you are doing something I never did. Always wanted to design my own car!
Cheers and good luck,
Mark
thats ok mikeylad, that guy was hillarious, love the way everyone strung him along so much. hope he didnt waste too much money tho
i wasnt sure just plate would be enough, most cars ive seen have got pretty much the same as ive done, but thinking about it i could replace those members with some thing much more usefull (and triangular). and the sva manual reckons that would be ok.
appreciate the help!
Cheers,
Russ.
Mark B said:
4. Why so much bracing under the drivers/passengers seat? A reasonable gauge ally sheet would work and probably be lighter? (Or of course a composite sandwich plate)
i wasnt sure just plate would be enough, most cars ive seen have got pretty much the same as ive done, but thinking about it i could replace those members with some thing much more usefull (and triangular). and the sva manual reckons that would be ok.
im doing this mostly as a hobby with a view to a possible buisness opportunity later on. its still very early days yet though, and lots of work to do.
8. Last question, is this a University project, or something you intend to build and drive?
appreciate the help!
Cheers,
Russ.
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