Chassis design
Discussion
Does anybody know if you could produce a space frame chassis from 3d computer model files I have? I have had a concept car designed by a colleague and I need someone to design the spaceframe (I have someone to do the bodywork) and the suspension design - but design only and not the fabrication which I have covered. Does anyone know if this is possible and is there anyone out there tha haas done this and can impart some good advice???
I have drawn my Locost chassis on CAD. Take a look on my website: http://gtslocost.locostsites.co.uk/ in the CAD section to see what I have done.
Its not a difficult job, but it does take a long time to do.
There are also some good free CAD programs availabel these days so you could have a go at doing it yourself. Sketchup is the first that springs to mind.
Cheers,
David
Its not a difficult job, but it does take a long time to do.
There are also some good free CAD programs availabel these days so you could have a go at doing it yourself. Sketchup is the first that springs to mind.
Cheers,
David
Thought I would include a couple of pics of the idea - have a look and do you think it would be complex? I was thinking about a grp monocoque section with 2 main sections at the front and 2 at the rear??? Ideas appreciated
http://nigeria.decdemo.com/tmpPics/car1.jpg
http://nigeria.decdemo.com/tmpPics/car2.jpg
Excuse the Chanel branding, my fiance asked for it....
>> Edited by jkyle69 on Friday 2nd December 18:10
>> Edited by jkyle69 on Friday 2nd December 18:11
>> Edited by jkyle69 on Friday 2nd December 18:11
http://nigeria.decdemo.com/tmpPics/car1.jpg
http://nigeria.decdemo.com/tmpPics/car2.jpg
Excuse the Chanel branding, my fiance asked for it....
>> Edited by jkyle69 on Friday 2nd December 18:10
>> Edited by jkyle69 on Friday 2nd December 18:11
>> Edited by jkyle69 on Friday 2nd December 18:11
Spaceframe chasssis is not difficult. Monocoque takes a lot more knowledge and experience, both to design and to fabricate.
The tricky bit is not the chassis, though, it's the suspension design. Unless you are happy for the designer to make their own decisions for you, you will need to give them quite a lot of information on running gear (weight and CG location of the engine/gearbox combination makes a big difference, for example) and brake/suspension components (are you happy to go bespoke, or do you want to use proprietary hubs/uprights?).
I'd be happy to take the job on, but I'd want paying for it and it wouldn't come cheap...there is a lot of analysis involved if you want it doing properly.
Cymtriks will be along shortly to tell you that you want a ladder frame chassis made out of 30x60mm rectangular section mild steel tube, though, not one of those nasty, floppy spaceframe things!
The tricky bit is not the chassis, though, it's the suspension design. Unless you are happy for the designer to make their own decisions for you, you will need to give them quite a lot of information on running gear (weight and CG location of the engine/gearbox combination makes a big difference, for example) and brake/suspension components (are you happy to go bespoke, or do you want to use proprietary hubs/uprights?).
I'd be happy to take the job on, but I'd want paying for it and it wouldn't come cheap...there is a lot of analysis involved if you want it doing properly.
Cymtriks will be along shortly to tell you that you want a ladder frame chassis made out of 30x60mm rectangular section mild steel tube, though, not one of those nasty, floppy spaceframe things!
Hello Sam_68, I have no problem paying for the work - would be using all off the shelf components except for the driveshafts, upper and lower wishbones on the front and rear - springs and shocks will be made on spec by one of the major brands - all full adjustable. Off the shelf components - reversible steering rack, electrically driven power steering (not decided on who yet), Tarox 10 pot calipers front and rear, Ford 460 racing engine and more than likely either a Quaife transaxle or a modified 6 speed Audi transaxle with redesigned gears (stronger materials), 19 inch alloys front, 20 inch rear (I have all of the exact dimensions of the car but dont have them with me at the moment). Chassis will need to be rated up to 1500 bhp and 1000 lb/ft of torque.
Hope this helps?
Any opinion on the pictures by the way?
Hope this helps?
Any opinion on the pictures by the way?
You really want the suspension design tied down before the chassis so you have control over mounting points and load paths.
In theory you should be able to transfer your 3D images to a CAD program to establish dimensions and locations. I suppose it depends on what you have designed them in.
HTH
In theory you should be able to transfer your 3D images to a CAD program to establish dimensions and locations. I suppose it depends on what you have designed them in.
HTH
The pictures look good; main concern if you are intending a spaceframe is that the sills don't look deep enough to get the sort of structural stiffness I'd be looking for with a big V8. Also, have you done any work on the packaging? It looks quite a short wheelbase with the cockpit set well forward, so with wheels that size I'd guess the front wheelwells will be quite intrusive.
Do you have installation measurements/drawings for the engine, and have you considered how you are going to cool something that powerful? Remember how long if has taken Volkswagen to sort the cooling problems on the Veyron; it's (relatively) easy to build a 1000 horsepower engine, but getting rid of the heat it generates is a lot more tricky!
Are you intending rear wheel drive only? Again...transmitting that sort of horsepower and torque to the road is easier said than done!
Do you have installation measurements/drawings for the engine, and have you considered how you are going to cool something that powerful? Remember how long if has taken Volkswagen to sort the cooling problems on the Veyron; it's (relatively) easy to build a 1000 horsepower engine, but getting rid of the heat it generates is a lot more tricky!
Are you intending rear wheel drive only? Again...transmitting that sort of horsepower and torque to the road is easier said than done!
Jkyle69,
It is easy once the principles are understood but if you're new to structures this won't be the case. Most kit car spaceframes are fairly inefficient for this very reason. I'd advise anyone new to bounce their ideas around a few forums. Some good points might be raised for free! Have a read of kitcaranalysis (Google for it). I wrote it after fielding questions just like yours.
Spot on. You will need a rough idea of where things will need to fit to get a concept design going. To get this to a finished stage will require you, or someone else, to specify the suspension exactly.
Sam_68,
do you do the calcs by hand as in "Costin & Phipps"? Or do you use some FEA package? Curious!
Jkyle69,
I do structural analysis for a living btw. I have a bank of small models of some of the more popular kit cars. One of these might be similar to what you have in mind! If this is the case then I'd do a small amount of analysis for free.
Must resist.... must resist.... must resist...
For the benefit of Jkyle69 this is a much erm, debated, issue. Just to let you know my thoughts here they are.
30x60mm is way too small. But 100x50 with a 2mm wall made into a simple X braced frame with front and rear spreaders just like a hot rod Duce chassis, that would be a bit stiffer than the cheaper seven clones, as in the Locost derivatives, and a bit lighter aswell. The real issue here is that the spaceframes in question are not very good, which allows the ladder frame to sneek ahead. Listening to all the hype over spaceframes you'd never think this could ever be true though.
Designed to the same standards I reckon a spaceframe car will be around 5 to 10 percent lighter than a ladder frame equiped one for the same chassis stiffness. The ladder frame would be simpler, cheaper, probably easier to work on and allow getting in and out to be easier as well. For a race car or a very fast light weight road car there is no option, maximum stiffness for minimum weight is critical so the spaceframe wins. But back off a bit and the ladder frame starts to look like a sound choice.
One last point. Take a look at Jay Esters ultimav12.ca site. Judging by the power output you mentioned he might not be a million miles from what you want.
Sam_68 said:
Spaceframe chasssis is not difficult. Monocoque takes a lot more knowledge and experience, both to design and to fabricate.
It is easy once the principles are understood but if you're new to structures this won't be the case. Most kit car spaceframes are fairly inefficient for this very reason. I'd advise anyone new to bounce their ideas around a few forums. Some good points might be raised for free! Have a read of kitcaranalysis (Google for it). I wrote it after fielding questions just like yours.
Sam_68 said:
The tricky bit is not the chassis, though, it's the suspension design. Unless you are happy for the designer to make their own decisions for you, you will need to give them quite a lot of information on running gear (weight and CG location of the engine/gearbox combination makes a big difference, for example) and brake/suspension components (are you happy to go bespoke, or do you want to use proprietary hubs/uprights?).
Spot on. You will need a rough idea of where things will need to fit to get a concept design going. To get this to a finished stage will require you, or someone else, to specify the suspension exactly.
Sam_68 said:
I'd be happy to take the job on, but I'd want paying for it and it wouldn't come cheap...there is a lot of analysis involved if you want it doing properly.
Sam_68,
do you do the calcs by hand as in "Costin & Phipps"? Or do you use some FEA package? Curious!
Jkyle69,
I do structural analysis for a living btw. I have a bank of small models of some of the more popular kit cars. One of these might be similar to what you have in mind! If this is the case then I'd do a small amount of analysis for free.
Sam_68 said:
Cymtriks will be along shortly to tell you that you want a ladder frame chassis made out of 30x60mm rectangular section mild steel tube, though, not one of those nasty, floppy spaceframe things!
Must resist.... must resist.... must resist...
For the benefit of Jkyle69 this is a much erm, debated, issue. Just to let you know my thoughts here they are.
30x60mm is way too small. But 100x50 with a 2mm wall made into a simple X braced frame with front and rear spreaders just like a hot rod Duce chassis, that would be a bit stiffer than the cheaper seven clones, as in the Locost derivatives, and a bit lighter aswell. The real issue here is that the spaceframes in question are not very good, which allows the ladder frame to sneek ahead. Listening to all the hype over spaceframes you'd never think this could ever be true though.
Designed to the same standards I reckon a spaceframe car will be around 5 to 10 percent lighter than a ladder frame equiped one for the same chassis stiffness. The ladder frame would be simpler, cheaper, probably easier to work on and allow getting in and out to be easier as well. For a race car or a very fast light weight road car there is no option, maximum stiffness for minimum weight is critical so the spaceframe wins. But back off a bit and the ladder frame starts to look like a sound choice.
One last point. Take a look at Jay Esters ultimav12.ca site. Judging by the power output you mentioned he might not be a million miles from what you want.
I would like to keep the design as it is as I am happy with the final design. I am also happy to have custom wishbones machined, springs and shocks made to fit the design so that is not a problem to me. What I need to know is what would be required to move forward from here? Would it be possible to have a chassis designer to take the 3d models and then design a space frame chassis and suspension and then had FEA analysis done to ensure that the chassis does not twist under load?
I am quite specific on the power train I want to use in this case and have engineers to bulid these components etc but it seems to be a bit of a black art to get the chassis and suspension designed - fabrication is covered and I am happy with the idea of using a space frame over a ladder chassis. What I need to be able to do is to be able to take the design to a rolling chassis.
I am quite specific on the power train I want to use in this case and have engineers to bulid these components etc but it seems to be a bit of a black art to get the chassis and suspension designed - fabrication is covered and I am happy with the idea of using a space frame over a ladder chassis. What I need to be able to do is to be able to take the design to a rolling chassis.
cymtriks said:
Sam_68,
do you do the calcs by hand as in "Costin & Phipps"? Or do you use some FEA package? Curious!
FWIIW, odds and sods I do by hand, as per Costin & Phipps, for my own amusement. Full analysis I don't do myself...I keep tame structural engineers for the mundane jobs!
They use FEA or frame analysis software, though - I don't think anyone would go to the trouble of a full set of calcs by hand these days, would they?
Having said which, I only use mathematical analysis to refine the design. First stage, as Frik says, is to establish the suspension geometry. The chassis is just there to join the dots, and you can't do that efficiently until you know the exact position and magnitude of the dots. After that, I draw up 2D and 3D models, then make a balsa model. Only after considerable refinement of the drawings and balsa model by 'gut feel' would I progress to mathematical analysis. For something simple like a Seven or a hillclimb single seater, I wouldn't even bother with the calculations...given the inherent inaccuracy of FEA/frame analysis compared to real-world, measured stiffness, by the time you've finished fannying around with numbers you might as well just build and test a chassis straight from the balsa model, anyway.
I have to admit that I don't consider the chassis frame (or tub) itself to be the most interesting, challenging or important part ot the puzzle - it's just there to link up the useful components whilst providing adequate stiffness and crash protection for minumum practical weight and cost.
cymtriks said:
Must resist.... must resist.... must resist...
You can't seriously think that a ladder frame would be viable for something with a potential torque output of 1000 lb.ft!?
To be honest, if these figures are anything like realistic, I'd have very serious concerns that even a properly designed spaceframe, or two wheel drive for that matter, is up to the job.
Regrettably, jkyle69, if you really are envisaging those sort of power/torque fugures, I guess I'd better withdraw my offer of chassis design...you're talking about a very serious motorcar (bearing in mind that the McLaren F1 was a mere 627 bhp & 479 lb.ft). If you can give me the necessary data/drawings (including aerodynamic data, with that sort of speed potential - you'll be needing significant and balanced downforce, which will effect the suspension calcs), I'll happily come up with a suspension design, but I think you really need to look at a composite monocoque tub, the design of which would be better entrusted to a specialist (try Lola or David Gould, for a start).
Edited to add... in terms of running gear, I'd be inclined to approach Quaiffe and see if they think the driveline from their GT car can be uprated to deal with that sort of torque. My guess is that it can't (though it would come a lot closer than a modified Audi transaxle), but it's the nearest you will get to an off-the-shelf solution for a mid-engined car of this type. Perhaps if you fit an engine management system capable of limiting torque in the lower gears?
>> Edited by Sam_68 on Saturday 3rd December 09:24
I was going to use the full Motec 800 system to allow a more complete engine management system which should allow better control. Do you think it is impossible to design a spaceframe for this kind of power or would it be a better option for a carbon fibre monocoque with front and rear space frame sections?
A spaceframe wouldn't be impossible, but I think you've got to accept that with that sort of power level you would need to start with the chassis and design the bodyshell to fit over it, rather than the other way round as you have done so far - as I mentioned earlier, you will need pretty substantial sill stuctures to give adequate stiffness, which would dominate the design of the cockpit area and doors.
I'd be more inclined to go with a composite monocoque, or perhaps a 'deep beam'/tub type structure similar to the Elise's (difficult as a one-off or very limited production run if you do it in alloy, but yo0u could do an analogous structure in composites quite easily).
If it's nt a silly question, though, why do you need that much power...McLaren, Lamborghini, Ferrari et al are all happy with roughly half as much for their hypercars, and it's generally accepted that the Veyron can't actually deliver anything like its full complement of horses to the tarmac under most conditions - it is managed down by clever electronics. Even Peter Wheeler at his most power crazed eventually admitted that the 800 horsepower TVR Speed 12 was too much for road use!
I'd be more inclined to go with a composite monocoque, or perhaps a 'deep beam'/tub type structure similar to the Elise's (difficult as a one-off or very limited production run if you do it in alloy, but yo0u could do an analogous structure in composites quite easily).
If it's nt a silly question, though, why do you need that much power...McLaren, Lamborghini, Ferrari et al are all happy with roughly half as much for their hypercars, and it's generally accepted that the Veyron can't actually deliver anything like its full complement of horses to the tarmac under most conditions - it is managed down by clever electronics. Even Peter Wheeler at his most power crazed eventually admitted that the 800 horsepower TVR Speed 12 was too much for road use!
Do you think it would be possible to make a composite monocoque rather than a spaceframe and use 2 smaller spaceframe sections front and rear and would I then be able to keep the design? I guess this would also allow for a different variation if was able to have alternative possibilities at the rear spaceframe so I could in theory have different engines. Is it easier to create a monocoque from the 3d models rather than creating a spaceframe? The amount of power is likely to have a max output of 800 bhp but with the Motec system you will be able to really tweak it as you like and control torque and power in different gears and allow alternatives for track days and racing.
Does anyone have any experience of monocoque design and what about the analysis difference involved to ensure that is is safe etc????
Does anyone have any experience of monocoque design and what about the analysis difference involved to ensure that is is safe etc????
Sounds like your doing much the same as what I am in the process of doing..... With that kind of spec, yours is going to be an awsome machine.
I paid a specialist to do the geometry design and make the wishbone's, I also paid him to fabricate the suspension possitions so I knew they were right and have pretty much done the rest myself based off of his advice. He does provide a full design and build service but I just couldn't afford that.
Your use of parts is much the same idea as mine (different choices though), I'm using a less powerful engine than you plan (twin turbo BMW V12) but I have got an M800 Motec unit to run it. I also purchased unmachined Prosport uprights and have machined them to use uprated Porsche 996 bearings and new hubs. This has opened the door for a huge range of alloys available to fit my car.
I have a set of Tar-rox 6pots but have decided to use Brembo 6pots which have a larger pad size (fitting the Tarrox units to my caterfield). rears will be 4pots brembos as fitted to the front of an F40 I beleive!
The rack is a bespoke item made for me by Titon.
I very much doubt that you will find your transaxle choice will cope with 1000ftlb especially if it has good traction. The quaife heavy duty box is guarenteed to 500ftlb and the audi is a real unknown at that level, although I've heard it can be modded to take over 500.
However I do know of someone who is developing a box that will take the power you want and is quite compact, but you'd need to design it into the chasis at the start as it'd never fit mine due to its planned width.
Andy
I paid a specialist to do the geometry design and make the wishbone's, I also paid him to fabricate the suspension possitions so I knew they were right and have pretty much done the rest myself based off of his advice. He does provide a full design and build service but I just couldn't afford that.
Your use of parts is much the same idea as mine (different choices though), I'm using a less powerful engine than you plan (twin turbo BMW V12) but I have got an M800 Motec unit to run it. I also purchased unmachined Prosport uprights and have machined them to use uprated Porsche 996 bearings and new hubs. This has opened the door for a huge range of alloys available to fit my car.
I have a set of Tar-rox 6pots but have decided to use Brembo 6pots which have a larger pad size (fitting the Tarrox units to my caterfield). rears will be 4pots brembos as fitted to the front of an F40 I beleive!
The rack is a bespoke item made for me by Titon.
I very much doubt that you will find your transaxle choice will cope with 1000ftlb especially if it has good traction. The quaife heavy duty box is guarenteed to 500ftlb and the audi is a real unknown at that level, although I've heard it can be modded to take over 500.
However I do know of someone who is developing a box that will take the power you want and is quite compact, but you'd need to design it into the chasis at the start as it'd never fit mine due to its planned width.
Andy
looking at your body design, I'd also say that packaging is going to be THE critical thing. In order for someone to design a chassis inside that body, they will need to know the dimensions and possition of every component to prevent you running into a show stopper further down the build.
As a guide take dimensions from similar supercars and see if your car is smaller, if you are its unlikelly your going to succeed without serious compramise or financial investment.
You also need to decide what kind of car you want, one that very good looking but is cramped with offset pedals etc making it unpleasent to drive....
I started with my requirements and allowed other areas to be compromised, for instance, I've added another 10kgs to my chassis as a direct result of me inisting my driving possition remained unchanged from my clean sheet design.
As a guide take dimensions from similar supercars and see if your car is smaller, if you are its unlikelly your going to succeed without serious compramise or financial investment.
You also need to decide what kind of car you want, one that very good looking but is cramped with offset pedals etc making it unpleasent to drive....
I started with my requirements and allowed other areas to be compromised, for instance, I've added another 10kgs to my chassis as a direct result of me inisting my driving possition remained unchanged from my clean sheet design.
The car is about the same length as a Saleen S7 and is about 43-44 inches in height. I have not made a decision on which way to go with the chassis - should I use a space frame design or a composite monocoque and use smaller space frame sections to the front and rear where I could alter the rear to fit different engines and potentially different transaxles? Is it easier to use a monocoque to remain faithful to the designs (I already have the interior designed and it has been done in a fairly clean and simple fashion and is symetrical to alloe left and right hand drive - so I think I have a level of flexibility inside the car for positioning).
If it's as long as a Saleen then the picture is deceptive and you've got a much better chance than I thought.... it only looked slightly larger than an elise.
Key areas will be width and driver possition.... my car has a relativelly short 2610mm wheelbase, but at around 2000mm its very wide, this helped me get a good driving position with a ridgid chasis without huge sills that make it hard to get in.
Key areas will be width and driver possition.... my car has a relativelly short 2610mm wheelbase, but at around 2000mm its very wide, this helped me get a good driving position with a ridgid chasis without huge sills that make it hard to get in.
The dimensions of the car are:
Height: 1050mm
Length: 4400mm
Width: 1990mm
Wheelbase: 2700mm
I think there will be enough space in the cockpit for a lot of flexibility but I guess it will depend on the length of the engine and transaxle. I had thought about having the car 4 wheel drive but I think it would be a lot easier in the first instance to stick with rear wheel drive and some control via the Motec M800 system over power and torque outputs.
Height: 1050mm
Length: 4400mm
Width: 1990mm
Wheelbase: 2700mm
I think there will be enough space in the cockpit for a lot of flexibility but I guess it will depend on the length of the engine and transaxle. I had thought about having the car 4 wheel drive but I think it would be a lot easier in the first instance to stick with rear wheel drive and some control via the Motec M800 system over power and torque outputs.
andgtt
Can you tell us any more about your project, it sounds very interesting!
Who did you approach to design the suspension? I noted that you said he offered a full build and design service, it sounds as if he has an interesting consultancy somewhere!
jkyle_69
1000ftlbs is a hell of a lot! You mention a Ford 460 in your e-mail, is this turbocharged, supercharged or nitrous? I can't see how you would get to your power requirement otherwise. Did you just get the car 3D model made for you or did you commision the styling aswell?
If either of you have any thoughts on self build and design then there are a lot of us (especially me!) who would like to know.
The most difficult part seems to be the bodywork which can be done by the following methods-
1)Aluminium shaped by hand
2)traditional buck (plaster or resin etc), take moulds, make fibre glass or other composite panels.
3)The DPcars route of using a CNC machined buch to jump over the labour intensive buck shaping stage.
I'd be interested on your thoughts on this issue.
>> Edited by cymtriks on Saturday 3rd December 21:43
Can you tell us any more about your project, it sounds very interesting!
Who did you approach to design the suspension? I noted that you said he offered a full build and design service, it sounds as if he has an interesting consultancy somewhere!
jkyle_69
1000ftlbs is a hell of a lot! You mention a Ford 460 in your e-mail, is this turbocharged, supercharged or nitrous? I can't see how you would get to your power requirement otherwise. Did you just get the car 3D model made for you or did you commision the styling aswell?
If either of you have any thoughts on self build and design then there are a lot of us (especially me!) who would like to know.
The most difficult part seems to be the bodywork which can be done by the following methods-
1)Aluminium shaped by hand
2)traditional buck (plaster or resin etc), take moulds, make fibre glass or other composite panels.
3)The DPcars route of using a CNC machined buch to jump over the labour intensive buck shaping stage.
I'd be interested on your thoughts on this issue.
>> Edited by cymtriks on Saturday 3rd December 21:43
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