The ever popular diet

[MrSwa]

My team went to comp this past year out west. We took our first real car. We had an idea of what to expect, but one thing that caught us off guard was the weight of other cars. I'm not asking for you to give up your team's bread and butter for weight loss, but what are some areas that you can typically lose pounds. We are in the process of designing our 08 car and trying very hard to lose weight. Any major area we should look into? I'm not sure if anyone will respond to this seeing as it's a pretty competitive field, but any general ideas would be greatly appreciated.

Just for background purposes, our car weight was 533lb without driver. We are eliminating the dry-sump system (yes we have weighed this decision, and do not take it lightly) and are going over every other system we have. Once again any ideas would be greatly appreciated.

[Anday]

Every little bit counts. Every fraction of an ounce adds up.
Last year we set a weight savings percentage goal and met it. Every part/system on the car had to be XX% lighter than the one on the previous years car.
Setting and meeting goals, and a near obsession with weight-savings is how you can stick to that diet. (All while retaining the reliability to keep the car together)

[fade]

lets see... chassis, powertrain, electrical system, body and any thing else related to those systems. I dont see how you can take your design and make it as light as a number listed on the forum without some type of analysis. Whats stopping you from making it lighter without this information?

[Matt Gignac]

Assuming you're set on a wheel size and engine size...

Take a look at the weights of all your sub-systems, and try to identify where you can save some weight. Do a little benchmarking to see where you need improving, and where you're doing ok. Very easily (except maybe on the pocketbook), you can save a bunch of weight by identifying off-the-shelf components that will save you weight (especially wheels, engines, dampers, and stuff you wouldnt think about like batteries).

From there, assign a weight savings budget for every sub-system, and work towards that. You'll find it easier to meet a goal when it is very clearly defined.

Also note you can save a lot of weight by clever packaging: using brackets for many purposes, arranging your suspension mounts to exploit existing tubing or monocoque planes.

Then look at the rules for minimum wall thicknesses: try to minimize the length of tubes with a minimum wall thickness.

Then the devil is in the details: properly sizing components and such. I doubt most of your gain will come here though.

Matt Gignac
McGill Racing Team

[drivetrainUW-Platt]

Find a small, short Asian female driver and design the car around her....make sure shes good looking too for the rest of us.

[flavorPacket]

size your fasteners properly. Even the best teams out there use stuff that's WAY too big (I'm talking 5/16" rod ends on pushrods!). I have never seen a FSAE suspension that wasn't overbuilt (including mine). PSU is probably the closest to doing it right IMO.

[Joy Pathak]

Put alot of speed holes.

[Biggy72]

[QUOTE]Originally posted by flavorPacket:
I have never seen a FSAE suspension that wasn't overbuilt (including mine). [QUOTE]

Found one.... http://www.youtube.com/watch?v=XJL4-wGPjCo

[cmeissen]

If you post pictures of your car we would probably be able to give better suggestions. But from my experience I would first focus on drivetrain and suspension since rotating and unsprung weight is most important. Then just pay attention to all of the small details on the car. Insignificant things quickly add up to a lot of weight. For example we used 1/4in fasteners on almost everything on are car just because we had a lot of them. We dropped a significant amount of weight by using rivets and tiny fasteners on many items.

[Kurt Bilinski]

I absolutely agree about incorporating the right mindset regarding weight. During my build, one guy said I was going overboard, "It's only a pound." Yeah, that's exactly how people end up fat, too. Every single ounce matters! Also, if you have 24 suspension bolts, and each one is "only" two ounces overweight, that's three pounds over! Also, trim your bolts so they have the minimum thread out past the nut. Any longer and it's throwing performance way for no reason except laziness.

And agreed about getting an Asian girl driver - of course I like Asian women!

[adrial]

What is the wheelbase and track of your car?
Obviously...a smaller car weighs less.

Knowledge of loads via acceleromters or strain gages will allow you to build a lighter car.

How thick a material did you use for the gas tank? What about the headers? Intake? Are you using an all aluminum differential housing? What diameter and wall thickness for the a-arms? Tie rods? How much did you machine out your sprocket? Are you using tripods? Integral tripod housing on the rear hub? Gun drilled axles? Can any of your bearings be downsized?

The list goes on...

Don't build a light car to win design, build a light car to win endurance because thats what its all about.

[BryanH]

One thing that Mark did at RMIT in 04 was to give team members a close up look at state of the art Euro karts, as they are a near perfect example of minimalist,effective and at the same time very robust design. Very "enlightening" if you have never seen one. Next stop is finding a bunch of current model Formula Fords (at a race meeting) and seriously crawling all over them. Very attractive/fast talking team members will come in handy to avoid size 10 boot in butt.
A light & reliable fsae car requires a common mindset by all team members and it is a mindset few people grow up with, it needs to be aquired.

[Composites Guy]

Find a 100lb freshman girl... train her to drive!

I can't even talk my school's team into entertaining that idea!

Barring that... the easiest way to lose weight is go to 10" wheels. That adds a bit of packaging complexity, but the weight savings are worth it. We have somewhere in the neighborhood of 20 pounds of unsprung weight (total) per front corner counting wheel, tire, hardware, caliper, rotor, bearing, spindle, center-locking nut, upright, half of a-arms and push-rod and brake line. Rear brakes are inboard making things a bit lighter.

After that change is made major weight savings can be had by switching engines, and learning to use carbon fiber everywhere. I agree with BryanH... make sure you look at the technology on a shifter cart.

[Wesley]

You have a lot of weight you can lose even with 13" wheels.

I know without our aero we were in the neighborhood of 430 pounds with a spaceframe, 4-cyl, and no titanium (except for bellcranks)

Design, design, design! Trim materials, perform FEA's, and try to make parts as light as possible - that's all part of the design process. Try substituting parts you can make for off-the-shelf components that are sized for much bigger vehicles.

I think the cars that are built like go-carts violate the intent of the rules, which is to build a car for SCCA style AUTOCROSS events for the average racer.

Thats the motto we've always followed, and though the competitions present tighter courses than we design for, we'll take that so we can do well at other events.

[flavorPacket]

Wesley, I agree with you. 10" wheels add a lot of difficulty to things with little benefit. I would not recommend them to a new team, and tire size is most likely not the greatest barrier to a team's weight goal.

[Peter]

Originally posted by Wesley:
I think the cars that are built like go-carts violate the intent of the rules, which is to build a car for SCCA style AUTOCROSS events for the average racer.


Where is there mention of SCCA in the rules? If a go-cart like car is a teams chosen solution to an engineering problem defined in the rules and compliant with the rules, what is wrong with that?

Also the weight savings are found in the conceptual layout of the car. Minimal size of the car, integration of structural parts. If there is a rule for a minimum use ithttp://fsae.com/groupee_common/emoticons/icon_smile.gif Optimizing parts, bolt sizes etc is needed to achieve your weight goal, but the diet really starts at the concept and peoples mindset.

Peter
Delft FSUK04, FSG06

[benjo]

Originally posted by Peter:
<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by Wesley:
I think the cars that are built like go-carts violate the intent of the rules, which is to build a car for SCCA style AUTOCROSS events for the average racer.


Where is there mention of SCCA in the rules? If a go-cart like car is a teams chosen solution to an engineering problem defined in the rules and compliant with the rules, what is wrong with that?

Also the weight savings are found in the conceptual layout of the car. Minimal size of the car, integration of structural parts. If there is a rule for a minimum use ithttp://fsae.com/groupee_common/emoticons/icon_smile.gif Optimizing parts, bolt sizes etc is needed to achieve your weight goal, but the diet really starts at the concept and peoples mindset.

Peter
Delft FSUK04, FSG06 </div></BLOCKQUOTE>

Page 77, 2nd last paragraph. Specifically mentions SCCA, it's in regard to the presentation event.

Although I do agree about the smaller cars being a valid solution, I think it's good to see a variety of cars such as small light singles and big powerful turbo fours.

[Peter]

OK, thanx for pointing that out! As I am out of FSAE for a while I did not know that.

Peter
Delft FSUK04, FSG06

[Wesley]

There's nothing wrong with building a go-kart-esque vehicle, and it can be done with as much engineering flair and talent as any other.

But I just feel (personally) that smaller isn't always better for racecars. If it were I'd ride a street luge with vectored jet thrust.

Variety is, however, the spice of life.

I do agree with Peter in that the overall weight lies in the conception of the car at the beginning - you can trim pounds here and there, but losing a lot of weight starts from the ground up.

Everything has to be designed from the minimalist perspective - what can I get away with safely and not compromise integrity for weight?

Tanks can finish endurance. Balsa A-Arms can't.

[Composites Guy]

Wesley, I beg to differ. Balsa a-arms can finish endurance! I prefer to use PVC foam though ;-)

[BStoney]

How much does your electrical system weigh without DAQ? If it is not less than 10 or so lbs with ECU and relay/fuse box and even battery...then you're probably haven't engineered it and it's just moderately pieced together. I see all too often teams with wires everywhere and using the wrong wire for the application/wrong components. (And yes, I've been there too...)

Use the Keep It Simple Stupid philosophy on most stuff, and you should be able to keep weight down. Also, set goals for each of your sub-systems for overall weight of that system and make sure you stick to them, and do what's necessary to meet them.

[VinceL]

Quote:

"Barring that... the easiest way to lose weight is go to 10" wheels. "

Remember that the reason for loosing weight in the first place is to maximize the value a=F/m. Going to 10" wheels reduces m, but also reduces F (take a look at the TTC data). So the performance gain from losing the weight will be far less than 1:1. Obviously 10" wheel cars can go fast (RMIT, ETS, Delft). What I'm saying is that I think you need to have a pretty light car to begin with to make 10" wheels work well. Just simply getting your car and switching to 10" wheels might not be the best idea. But then again I haven't done any sims of that scenario, so maybe you know better than me. http://fsae.com/groupee_common/emoticons/icon_smile.gif

[murpia]

A lot of the above advice advocates a 'bottom up' approach to weight loss, going round all your car components and trying to save a gram of two with refinement. I often hear this kind of thing from Formula Student teams when I ask them about their design targets, typically something like 'last years car was too heavy so we told all the subsystem designers to save 10% of weight'. I also often hear 'we set a design target of 200kg but actually it weighs XXXkg' (insert embarassing amount, typically 10->20% over).

I'm here to tell you that's the wrong approach. Imagine if Boeing or Airbus offered to produce a new aircraft simply by slashing 10% off all the bits - would anyone buy it? No. No-one would know for sure how it would perform, or if it would even fly... What customers want is product performance, defined at the start of the design process then carried through by analysis to the detail stage and then by component, subsystem and system testing back up to verification of the entire product. This is often referred to as the 'System Engineering V'. It's not the only approach, but it's a good one.

Don't think that saying 'as light as possible, as stiff as possible and as low a CG as possible' when asked about design targets gets you off the hook. Firstly, I think that's worse than unambitious numbers, because it promotes incoherent design and doesn't drive the detailed designers hard enough. Secondly, more importantly, those factors trade off against each other and you need to make a decision as to where you stand. And finally, those aren't product performance targets, they are actually the first stage of analysis.

Following this kind of discipline reaps all kinds of benefits: done properly you'll know up front your weight, parts count, cost, CG and inertia values and you shouldn't have any embarrasing structural failures. Most importantly you'll have an excellent foundation in engineering skills for the real world, which is the point of the competition after all.

Regards,
Ian Murphy
FSUK Design Judge Team Leader

[Kurt Bilinski]

Murpia, I agree to some degree that it's not as simple as saying, "Make it 10% lighter than last year's car." However, just because it's a top-down approach doesn't guarantee success either.

What bugs me is where this ambitious weight loss value comes from - it's an emotional target that isn't based on engineering. Yes, we all need targets, but engineering should drive it, not someone's emotions. A clean-sheet design team leader deciding that since other cars are around 400lbs, his is going to be 360lbs, is bad news. Why *that* number*? Where did it come from? He then makes sure that every component is forced toward that weight target, which is fine from a Project Management standpoint, but where's the engineering? That is, is it practical, reasonable, and affordable to knock off XX% of a car's weight and set that as a goal? You are right that ALL the project's subsystems must work together, but there are limits. If the suspension engineer says he's already using the lightest (affordable) wheels, what would you have him do? If the roll-hoop is already of minimum size, where's this presumed XX% reduction coming from? Subsystems that cannot meet this arbitrary emotional goal will transfer their share of the required weight loss to some other hapless subsystem. I agree that the factors trade off against each other, but often to the detriment of the last guy in the door. Imagine being the last subsystem guy to get to work, discovering that because others couldn't achieve their goal, your required weight reduction is now 60%...

I guess my point is, I agree with you to a point, but once the subsystem engineers are all saying, "I can't reduce weight affordably and safely, and meet the requirement", you're done. Having the Project Engineer saying the car's going to be lighter is not good engineering - unless he knows where the weight's going to come from *before* making it a requirement. Yes, I know people need goals to work towards, but not knowing ahead of time what's achievable means that most of the time, the goal won't be met. It's not a failure; all it indicates is that the design is as good as it can get without changing the entire approach.

Personally, I think round-table discussions before the new design starts, bouncing ideas off one another - that's the only right way. This way, everyone's on board, knows why things are changing (not arbitrarly), knows the target, and is working hard to achieve it.

To me, weight loss is a consequence of good design, not a goal unto itself.

[Mike Cook]

533lb is not all that bad. Our first car was 620, our second was 530, third was 520, and forth was 466.

A few things to consider:
A lighter car will be faster (F=MA) but to a lot of teams, there are more important things than taking off 20 more lbs (consider the endurance finish rate). In my experience, it took a lot of analysis and time to go from 530 to 466. Compromises must be made and it isn't easy. The biggest thing a team can focus on is reliability, and that is certainly at odds with lowering weight. It is not a good idea to say we need to be 40lbs less weight, but rather, we are going to reduce the weight of parts we did analysis on, and our weight will be what it's going to be.

All that said, some suggestions:

1) If have no good justification for making your car larger than 60" WB, don't. A smaller car will be less weight.

2) Use appropriate size bolts.

3) Use a lightweight wheel, (6-7lb for a 13")

4) Don't over build your frame. 1"x028 exists. Our first frame was somewhere like 90lb, our most recent frame was about 55lb.

5) Size your wires correctly for the current they're carrying.

6) Fuel tanks can be made pretty light. .04" aluminum sheet. (You could go thinner, but I won't)

7) Seats can be made less than 5 lb.

8) Thin walled exhaust tubing and intake tubing.

9) Appropriate sized brake rotors.

10) Produce a clean car. Clean cars weigh less. In my experience, rushed cars always weigh 10-15lbs more than they should because people just throw shit on there to git r done.

11) Low weight body. There shouldn't be anything on the car that doesn't need to be there.

etc.etc.etc.
Make small steps each year. The teams that win are low weight, but they DONT win entirely because they have a lower weight. Rather, there low weight is an consequence of good engineering.

[MrSwa]

Reading all of this is giving me a ton of ideas. Keep it coming. Our frame weighs about 55lbs this year, so we're looking to really buckle down on the other subsystems. I feel a lot of computer time coming.... Oh well. There is a lot of weight we can lose. Now to prove it.

[flavorPacket]

the way we think about it is:

If Renault F1 teamed up with McLaren, Ferrari, and Audi Sport, and they built a FSAE car with the same resources and materials as us, how much would that car weigh?

We thought about it for a while, came up with a number, and that's our goal. It'll probably take us 2-3 years to get there, but there are ALWAYS places to take weight out.

[Bill_Murray]

Got to agree with mike (above) but wanted to add one thing:

When you a are searching for weight in parts that have hopefully already been correctly sized for the expected loads (right?), you can't usually cut xx% weight with the same concept. If you are going to cut the weight it requires a system design change. A change in the way parts or systems of parts carry their loads (direct load paths).

Mike's suggestions will take you from 520 to ~460. Then you will need to look at things on a systems level as Murpia is talking about and understand the interactions of these systems to get to 400 or less. This is where good team management comes in. Read some of the other posts on managment.

[murpia]

Originally posted by kb58:
What bugs me is where this ambitious weight loss value comes from - it's an emotional target that isn't based on engineering. Yes, we all need targets, but engineering should drive it, not someone's emotions...
To me, weight loss is a consequence of good design, not a goal unto itself.
Maybe I wasn't clear enough, but I'm not advocating a weight target I'm advocating a set of perfomance targets for the completed design.

How much it costs and how long it takes to complete the project will depend on how aggressive the performance targets are. However, you will find that once you analyse the engineering principles you need to follow to achieve your performance, the total mass is a very important factor, if not the most important. This is due to a) physics, b) the competition rules.

Regards, Ian

[Composites Guy]

KB58:

Weight loss is a goal that won't be achieved without a VERY focused intent from the outset. Low weight is a good ENGINEERING based goal.... there is no EMOTIONAL aspect to that decision. A lightweight car WILL be faster than a car with excess (baggage) weight on it. Systems on your car should be designed as a whole for low weight and simplicity. Then each part should be designed for low weight, given the constraints of neccessary strength and deflections. The fact that RMIT makes a darn good car at less than 340 lbs means it is possible...

A captain deciding to make a 360 lb car when others are making 400 lb cars should be saluted! Its a good goal, and an attainable one! Of course he must assess the abilities of himself and his teammates and make sure that everyone is onboard for some very hard work.

Affordability is NOT a determining factor for FSAE. If all you can afford is 15lb junkyard wheels something is wrong. You CAN, and SHOULD find more money. That money is out there and if your team spends 5000 hours designing and building parts and 5 hours getting money... something needs to change.

If it takes an extra $5000 to get you from 400 lbs to 360lbs then find the $5000. If your systems engineers can only 'safely' build a 400 lb car then find some new engineers.

[Chris Allbee]

"If your systems engineers can only 'safely' build a 400 lb car then find some new engineers."

I understand that you are using that as a comparison to the 360lb by spending $5000 thing...but WTF?! There are SO many other variables involved here. This IS a learning competition and if you fire your team every year because they fail to build a car that meets some lofty magical number it will be damned hard to every build the body of experience to reach that goal. Don't fire them, educate them.

Hell, we keep anyone with the drive and passion to put the long hours into this project. Are they all the world's best vehicle engineers? Not yet, but no one else has stepped up to take on the challenge so if you just get rid of them then you have to spend time finding someone to replace them. Thats time not spent working on your designs, building, or testing the car. and then when you find this engineer (already trained and competent in all facets of vehicle design and an expert with all the software packages required) at a university then ask them why the hell they quit F1 to come back to school.

And I suppose that reaching that 360lb weight will require using new methods and materials, so why you are out raising money, please find the time to learn those new methods and how to properly manufacture things with those new materials. This may surprise you, but not every school has good access to composites facilities or CNC machines among others things. So now you have to take MORE time to raise the money to out source or find sponsors.

At this point, the average sized FSAE team will have spent so much of its manpower on attaining funds and sourcing sponsors that the car is likely to be finished in a rush just before competition meaning the build quality will not be as great and there will have been very little time for testing and tuning. Guess what? If the car breaks or isn't tuned very well, then it won't do your awesome design all the credit it could.

You do mention that the team captain should look at the abilities of the people he has, but don't be so callous about suggesting that the captain should toss people aside so easily. Even if the captain has wonderful goals, if the team doesn't see eye-to-eye with him on that aspect then there will be problems. And if the captain decides to get rid of those that don't agree with him it won't be long before he is the only one left. That would REALLY make it hard to build that 360lb vehicle.

I believe that someone mentioned earlier in this thread that you should set a performance goal and then design your parts to the best of your knowledge, abilities, and resources. In this way you can be more certain of the structural limitations of the vehicle and you are more likely to finish the car on time. If it weigh 500lbs, then it weighs 500lbs. But with the test time you get and by finishing endurance, you will most likely place better than a car that didn't get much test time or finish endurance EVEN IF IT IS 360lbs.

However, your team should learn each year and retain and pass this knowledge down. As your knowledge of materials, analysis methods, vehicle dynamics, manufacturing processes, test methodologies, etc. increases then so does "the best of your abilities." If you continue to do the best you can then your car should get progressively faster and more efficient (and most likely lighter).

So before you decide that you are going to push for that 360lb car, then make sure you are currently capable of falling within the ballpark of that goal. Chances are that if your last car was 430lbs then a 360lb car might be too much of a leap to attain in one year. Hell, once you start approaching the 400lbs barrier it becomes a lot more expensive and time consuming to lose weight.

When it all comes down to it, the performance equation includes a lot more variables then weight. A 360lb car is not necessarily faster than a 400lb car.

[VFR750R]

.... A 360lb car is not necessarily faster than a 400lb car.

Good quote. Remembering that going fast is the ultimate goal, and that weight will sometimes be a compromise of many other things that make the car go fast, maximum potential points must be tallied. So, how many points is a 10 lb weight loss worth?

Considering i've seen a 225lb guy drive our car faster then 150lb guys...i'd say in the single digits...