Monocoques vs. Spaceframe

[MikeWaggoner at UW]

I don't understand why so many teams still go with steel spaceframes. It's not much harder to design a monocoque, and the monocoques are a lot specifically stiffer/stronger.

Western Washington University FSAE
dot.etec.wwu.edu/fsae

[MikeWaggoner at UW]

I don't understand why so many teams still go with steel spaceframes. It's not much harder to design a monocoque, and the monocoques are a lot specifically stiffer/stronger.

Western Washington University FSAE
dot.etec.wwu.edu/fsae

[Richard Lewis]

Well its pretty straightforwards for us anyway.

1) We don't have a composites lab here.
2) We don't have the money to spend on CF. Our frame cost us under $200 canadian last year.
3) We can build our frame in 2 days. (not ideal, but we've done it)
4) We can repair our frame, or modify it very easily and inexpensively.
5) Cost analysis.
6) ...made for the weekend autocrosser. Who is much more likely to have MIG welder in their garage than an autoclave to make mods or repairs.

Don't get me wrong, I think composite tubs are great, and I'd love to have that option. But without all the fancy equipment and the big budget, its no where near as easy and a mild steel (or chromemoly) space frame.

-------------------------
UVIC Formula SAE Team

http://www.engr.uvic.ca/~fsae

[Charlie]

I agree with those reasons, cost, repairability, etc. Also, it has been pretty well proven that a steel space frame can be made lightweight, and stiff enough for the suspension loads.

I see it as a similar arguement as turbo vs. NA. A turbo is ideal, you can get more torque in the unrestricted area, and maximize the air you can get through the restrictor overall. Comparing peak powers NA is close, but the area under the curve the turbo will be better (properly designed).

So every team should go turbo right? Not really, if you have a system that doesn't meet it's potential (because of lack of time & resources to perfect it) it often isn't any better than a optimized system of lesser quality.

If you go monocoque great, but you better be prepared to tread new territory and do it right the first time, or risk teams with the 'inferior' space frame pass you by.

I'd love to build a car with a monocoque, turbo, and wings. But not if it's slow! And definitely not if it never makes competition, or is unfinished and makes us look bad. I know we've got a ways to go before Auburn can achieve that level.

-Charlie Ping
Auburn University FSAE 1999-present

[MikeWaggoner at UW]

There's an image of complexity around monocoques that I don't think they deserve. Aluminum monocoques provide much of the benefit of composite tubs, but have the ease of buildability of steel tubeframes. It's simple to have bent sections at the corner and rivet two panels to the bent section (you keep doing this until you get box sections etc.). You can see this on old can-am monocoques and airplanes, it's relatively simple to do.
The main problem with monocoques is actually planning. Adding suspension and steering brackets etc. as an afterthought is difficult because you have stress concentrations on weak panels.
We're doing a carbon monocoque again this year for SAE, but I'm building an autocross racer of my own using these practices and am satisfied with the results (so far). A mass produced car that uses similar practices (although they extrude large aluminum sections instead of riveting) is the lotus Elise, and it has demonstrated extremely light weight and performance in a far more competitive field than FSAE is.
I will admit that changes and repairs are a little tougher to make to an aluminum monocoque (a little cutting an riveting), but the materials aren't very expensive ($150 in aluminum, $15 of rivets, an air-hammer gun $25-100). Also for mass production the panels could be cut out on a CNC router ($4,000), resulting in a very precise chassis that can be mass produced.

Western Washington University FSAE
dot.etec.wwu.edu/fsae

[Jeffrey Pace]

Look at the teams that are consistently in the top 10. Only a very small percentage use carbon fiber monocoques. Obviously a carbon fiber monocoque chassis, when designed and constructed properly, will have a superior stiffness to weight ratio when compared to a spaceframe. However, given the limited budgets, facilities, and experience most teams have, spaceframes will continue to dominate the competition.

[Lyn Labahn UW-Madison]

For two years now University of Wisconsin has ran a aluminum monocoque and chromoly steel spaceframe hybrid. We are very pleased with the results and we are using this design again for the 2003 car. I agree that most teams could probably do an aluminum monocoque if they planned right, but you better have a damn good idea what you are getting into and be ready to make a few mistakes along the way. Why don't we run a carbon tub? We do not have the resources to produce a tub that is up to our quality standards. Not to mention it is difficult to repair, and is extremely costly!

2002/2003 Team Leader

[sticks]

In general, I must agree with Waggoner, the monocoque is the way to a structurally superior car, whether it be a carefully planned aluminium skin or a properly layed out carbon tub. Naturally, the stiffer material will mean improved gains, given the assumption of proper associated strength and design. However, even given the FIA's contentions, it goes without saying that a composite tub will be more difficult to repair and modify. Modification can be a hinderance, but with the exception of first year schools, most teams have the knowledge and access to empirical data from past cars in which to base suspension and powertrain considerations. Also, as Ohio state proved this past year, a failure doesn't necessarily mean damage to the tub (I believe it was nylon blocks that were added to the underside of the tub, which proved significant upon the loss of a wheel in testing). Of course, this is a competition wherein the objective is a vehicle under $25,000 for the typical weekend autocrosser. But I believe it is far more important to learn or at least experiment with that which is not readily available in terms of the proven and reliable.
Carbon is in fact expensive, and it does take a significant amount of time to make proper bucks, molds, fixtures and such, and then to vacuum bag, autoclave (optional to extents) release and prep. I'm learning this entirely to quickly. But contrary to what I seemed to be observing in a few cases at competition, carbon is not the ideal material for all, or in fact, many applications. To schools without composites labs and autoclaves, these are relatively minor set-backs. But to those who insist and truly believe in the power of the spaceframe, obviously they have significant merit. Excuses, however, should not be the engineering background behind a design decision.

[vinHonda]

Stiffer perhaps. Repair issues again....and to win FSAE, it's all about on track performance and explaining your design. Tub cars are great when you're in the professional business and throwing tonnes of $$$ at the projects.

For FSAE, I agree w/ hybrid. How heavy are other teams? I thought our car was pretty light in 02.

University of Toronto Formula SAE Racing Team
www.fsae.utoronto.ca

[Nigel Lavers]

We all know that a superior frame would result if it were a properly design monocoque rather than a space frame, but the real issue here is being able to manage the design and construction of various vehicle systems within the time constraints created by annual competitions and bi-annual final exams!

I'm sure that once a well managed team builds a mononocoque leaving themselves with 2 months of testing time they'll out-race the space frames any day of the week.

But, because a simple space frame can essentially be built in under 2 weeks then I bet that the decision made by most teams [img]/infopop/emoticons/icon_wink.gif[/img] will be to test the car for an extra 3 weeks rather than make it %50 stiffer and %10 lighter.

At least that's the way I see it...