FSAE Chassis Design, Need Direction

[DaConfusion]

Hey our school is having problems starting an FSAE team, so we want to start designing already so we can start building once all legal issues are sorted at the university.

I am a mechanical engineer undergrad who is nearing the completion of thermodynamics II, solid mechanics, and material science. (Also a couple other classes but they are not pertinent to this discussion.)

I have completed statics, dynamics and all engineer physics courses.

So basically I have a basic understanding of rigid bodies.

I need to apply this to a program such as solidworks, proE, and or CATIA. I can get access to either of those. I just don't know where to start!

I have purchased a few automotive engineering books but they mostly apply to vehicles sold to the consumer not a FSAE tublar frame chassis vehicle.

Can someone please direct me in the right direction? We really need this team to help ourselves professionally in the future.

 

[DaConfusion]

Ok basically the help I am looking for is in specifically the chassis. I have yet to find some literature that doesn't focus mostly on suspension or passenger cars.

For example, how do I design a triangular structure frame with the midsection wider for more rigidity? Or the fact that the hoop up top provides a significant amount of support.

 

[brewnog]

A two-second search on Amazon yields 3 possibly useful books. I'm sure your university library has dozens more. Then, why not do some research into Colin Chapman's designs for a similar product, and even look to Formula Ford and previous iterations of Formula Student vehicles for inspiration.

http://www.amazon.com/s/ref=nb_ss_w...d-keywords=chassis+design&Go.x=8&Go.y=11&tag=

 

[DaConfusion]

I so far have purchased Chassis Design by Milliken, Chassis Engineering (adams), and Theory of ground vehicles (wong) from a 30 second search on amazon, but like I said, they focus on passenger style vehicles. And frankly, I don't know where to start.

None of the professors have time or care to help us students find a place to start. And us college kids don't have unlimited money or time to experiment by purchasing 100$ worth of books.

My engineering department doesn't focus on application (so far) which means I will have to take some CAD design classes in the technology engineering department whenever there is time.

I just need something (book or online) or someone to help me get started.

By reading through some of those books, it teaches the theory, but I just don't know how to start.

 

[brewnog]

Which bit of 'getting started' are you having trouble with?

Your chassis needs:
- Somewhere for the driver to sit in comfort and safety
- Somewhere to mount wheels; I'm sure you can think about suspension here too
- Somewhere to mount an engine and gearbox

It also needs some consideration as to how the above 3 entities will work together; routing of transmission, controls, and vehicle systems. I suppose you'll also want something which can support an aerodynamic/protective structure.

After you've laid down your requirements, go for some concept designs. Throw away the ones which won't work, and develop the ones which might using the engineering principles you've been taught at university, common sense, and the expertise of others. The books are for when you get stuck.

Take your preferred concept design, and start laying it out in ProE (or your software of choice). Think about how the chassis will be manufactured; chances are it'll be fabricated by hand, so the primary purpose of your CAD model is to work out sufficient dimensions to be able to make the thing. You would also likely use this model for any FEA work you may wish to do to evaluate/optimise your design; if not then I'm sure your solid mechanics classes will have given you at least a bit of insight into how to proceed.

Finally, (if you haven't done so already), don't lightly brush off my suggestions of researching Chapman or Formula Ford. They both addressed the same problems you will, but forty years ago.

 

[DaConfusion]

none of my classes have given me enough knowledge to apply the concepts of torsion on an system of hollow tubes, only your basic single beam set ups.

I need to know where to get the knowledge to understand why people choose a triangular frame, the reason why it is the shape that it is for maximum torsional rigidity. Its hard to go from one single tube into a network of tubes designed for maximum rigidity when i have 0 experience.

I should get exposure to FEA next semester. I prob will use CATIA to design the vehicle.

I guess it just am overwhelmed by the task of designing a car since the only things we are learning are on basic objects like a single beam. I understand the concepts are the same but its still hard to grasp.

I will look into your suggestions of Formula Ford and Chapman designs.

 

[DaConfusion]

I know the car needs a place for a person to sit in and four wheels...As well as a requirement for an aerodynamic body.

But the thing is once i know those requirements, where to next? For suspensions, i am used to playing with regular passenger vehicles that use the mcphearson (sp check) suspension, that require strut towers. Obviously a formula chassis will not. I also have looked at an SAE paper concerning winston cup chassis, that seems still different from formula chassis.

The winston cup car papers are what are recommended reading from SAE, which makes no sense.

 

[brewnog]

But the thing is once i know those requirements, where to next? For suspensions, i am used to playing with regular passenger vehicles that use the mcphearson (sp check) suspension, that require strut towers. Obviously a formula chassis will not. I also have looked at an SAE paper concerning winston cup chassis, that seems still different from formula chassis.

The winston cup car papers are what are recommended reading from SAE, which makes no sense.

There's very little chance you're going to independently invent a new design which is better than anything already being produced. The best path to success is to analyse existing designs of similar products, identify strengths and weaknesses, and capitalise on those to your advantage. Is your engineering degree teaching you to analyse, criticize and optimise; or just to ask someone else every time you encounter a challenge?

If it were me, in my garage, with my tools, I'd go for a steel spaceframe with independent double wishbone suspension all round, possibly with in-board coil over shocks. However, it's not; and if race car chassis design was as simple as getting opinions from a forum then there'd be little point of Formula Student.

What I'm trying to say is that this forum is an excellent place to ask directed, specific questions during your design and build (i.e. 'how do I calculate whether this halfshaft will live'?), and we look forward to helping you out on such queries.

 

[DaConfusion]

I am not asking you to design my car for me, its just hard to start with 0 help. Most universities have professors that have automotive experience or time to help. We are having problems obtaining that help. Our university is ABET certified so I believe it meets a minimum for quality.

You can't just design a bridge without ever seeing how a bridge frame actually looks like, and that's where the problem is.

I just need help finding literature that helps me get started. But thanks anyways.

 

[DaConfusion]

In case other people are looking for similar help, here is a link I found with a listing of more pertinent books:
http://fsae.com/eve/forums?a=tpc&s=763607348&f=125607348&m=1956095883&r=7156045093#7156045093

 

[Bram]

Basically I think you’re of to a bad start. You say you have trouble starting up a team, which tells me you basically don’t have a team yet.
Going into chassis design immediately skips a lot of more important steps in the design.

You want to start with setting up a project plan, investigating the FSAE rules, do a couple of brainstorm sessions with the team about which sub-systems you require and how you will divide the workload. Then make a preliminary planning of when you will start developing those subsystems.
Then start making decisions about the most important subsystems: engine, tyres. These two will give you your starting points.
Design the suspension, drivetrain, safety systems, driver positions etc.
These are all far more important than a chassis; the chassis is just a framework on which you connect your subsystems. It’s basic dimensions are set by the suspension geometry, the engine, other mounting points and the FSAE rules about safety etc.

When designing your suspension you will probably learn enough to eventually design your chassis. Things like how rigid it must be will al be set when you design your suspension since it basically is a part of the suspension sub-system.
Start your chassis design when you have all major subsystems positioned in mid air in your CAD program and start connecting the dots, build up different solutions and test them in FEA and through a iterative process of adjusting positions of the subsystems and your chassis tubes you will come to a chassis that’s (close to) what you want.

Also a good advise is to watch some photo’s from other FSAE teams to find out how they do it. I can tell you they all look just like each other

 

[DaConfusion]

sounds good.

I have purchased Race Car Vehicle Dynamics by the Milliken brothers. They developed an entire curriculum, workbook and software to go with it. Since my school doesn't offer a class in automotive engineering (all our profs are involved with oil and wind turbine research), I will follow the lessons so I can be nearly on the same page as some of the students competing.

Bram, you are sort of right, we actually had a SAE car designed and built while we were with the technology majors. The technology department ended up having a change of heart and made it a non engineering project. So all the engineers from that team are trying to start a new one but we are being hindered by legal issues.

We want to redesign the car so it is ours, and I was never there when they started that car, so that's why i am having problems getting started. But everything you said makes sense and is consistent with what the students on FSAE.com are saying.

You have a point, most of those cars do look very similar to each other.

 

[Bram]

Most of the dimensions of the chassis are set by the rules: front roll-hoop, rear roll-hoop, X% percentile person that needs to fit and crash structure for example.
You can start by sketching these in your 3d program and start with those. You can also make a prediction about where the suspension mounts will come, these are very important in your design since these are the points where the major forces act on the chassis. You can start with making concepts for these points so you can transfer these loads the best way you can. The design judges will also look very closely at this.

Good luck :P

 

[Rickertsen2]

Come on people, he isn't asking you to design a car for him. He is merely looking for a place to start to ask the right questions so that he can learn on his own.

Before you even begin to think about design, i think you need to find a way to get the school involved and find a source of funding. Without these two things you are doomed from the start. You are going to need a place to work and a sizable chunk of cash. Faculty support is pretty important in pushing through the school bureaucracy.
read: http://students.sae.org/competitions/managingprojects.pdf
if you havn't already. If possible, i would try to attend at least one fsae competition to see what things are all about and to take pictures of other cars and ask lots of questions. I would highly recommend the to win books by Carrol Smith.

As far as chassis goes, a BASIC outline might go as follows:
1.)Figure out where you want the wheels and what wheels & tires you will be running
2.)Design your suspension geometry. This is almost certainly going to be some form of a double A-arm SLA suspension with a push or pull rod leading to a bellcrank and coilover shocks. Examples of things to consider here are roll centers, camber curves etc.
3.)With the suspension geometry out of the way you should have the locations of the pick up points where the suspension meets the frame. Assuming a steel spaceframe this gives you the the locations of your front and rear box. Alot of the other tube sizes are specified in the rules. Play connect the dots. Figure out where to put the driver motor and everything else to achieve the weight distribution you are looking for. If you can teach yourself enough of an FEA program to simulate the frame that would be helpful. I promise you nobody is doing torsional rigidity of an entire frame by hand. Since this will be your first car your objective will be to show up with a car that passes tech inspection. It is very unlikely that you will be competitive with your first car. Competitive teams have reached that status through years of design iterations. It will be better to overbuild something that under build it. Your first car is probably going to be heavy. It is a big achievement just to show up with a first design and doing to will probably teach you more than you will learn in all your engineering classes combined.

The FSAE community being is not always forthcoming with help. Everybody has secrets to protect and many have sticks up their ass. Good Luck and don't be discouraged. Read all that you can. Buy the carrol smith books. They are far less technical than Millikan and easier for a beginner. Remember you are not re-inventing the wheel yet. Study what other have done. Also, take care of the organizational issues first. At least get yourself an interested faculty advisor.

 

[Cyrus]

My school has a FSAE team. I will tell you this, they have around $25-30k in funding, and years of experience competing. So, you REALLY need to find someone that knows what they are doing. Our FSAE team has a professor who got his PhD in automotive design and does ARMY testing on vehicles for a living and racing on the weekends as a hobby. You really need to get everything squared away before you go to the race track against people from around the world.

 

[Danger]

DaConfusion, wlecome to PF.
These guys really know what they're talkng about; don't disregard them. I am, however, going to put in my 2 cents as an amateur. It's worth checking into Powerblock. That's the 'Spike' TV website, and Lou Santiago from 'Muscle Car' knows frames inside out. If he hasn't already covered what you need to know, I'm sure that he would provide a basic overview if you ask. I've seen him build some incredible stuff from scratch, just by following the various sanctioning bodies' rules. It's always safe, straight, legal, and set up for maximum performance.

 

[DaConfusion]

Wow sorry for not checking on this post, I thought it had died.

I really appreciate all the help you guys have posted. I am currently on my winter break and have been browsing the FSAE forums a lot.

I have also gone ahead and purchased the Carroll Smith books as on top the Milliken RCVD and Chassis Design books.
The Milliken books are more for graduate readers but I am working through them.

I have an internship coming up this year but I will see if I can find a way to attend an FSAE competition in the summer.

I also am doing a few tutorials for CATIA. (Currently I am set on using that software to do our 2009 car)

In regards to the post about the people we will be up against:
By looking at the FSAE forums, I realize there are numerous schools that have been doing this for YEARS. I understand that it is not practical to set a goal to compete with them. I believe the judges actually take into account "rookie year" cars and judge them accordingly. We aren’t trying to beat them, just get this started so the other students can improve our design for the years to come. (Trying to be practical and realistic)

I am still working on university support, so far no faculty members in the ME department want to help. Most of our faculty members are involved with anything but automotive.

My plan is to go to the dean of engineering for support instead; I am hoping maybe a civil engineering or industrial engineering professor will be interested. (Worst case scenario, the dean can appoint a faculty advisor if I can present the team as a benefit to our school) The FSAE (2008) rules state that a faculty advisor is required, but since they are not allowed to contribute to the design or construction in any way (only general theory), I think I can legally have even an English professor be our advisor lol.

 

[brewnog]

I'm shocked and a bit disappointed to hear that your university don't want to offer support; Formula Student experience is one of the best things you can put on your CV after a good engineering degree to get a job. I think your plan of pestering other people around the university is a good one.