60 inch wheelbase...

[rjwoods77]

We have finalized our frame and came to a shocking conclusion. By running a 60 inch wheelbase we have no overhang past the rearward and forward edges of the front and rear tires except for a crash attenuator that sticks out about 6 inches from the front edge of the front tire. Anyone else got something like this or near it. And th driver has a ton of room lengthwise.

[rjwoods77]

We have finalized our frame and came to a shocking conclusion. By running a 60 inch wheelbase we have no overhang past the rearward and forward edges of the front and rear tires except for a crash attenuator that sticks out about 6 inches from the front edge of the front tire. Anyone else got something like this or near it. And th driver has a ton of room lengthwise.

[Matt Gignac]

So am I right to assume that the engine is besides the driver? And probably a single?

And going for something really really light?

[rjwoods77]

Nope. Engine is right behind me. Aiming for 300lbs car. Most likely end up 325-350 but we have a hundred pound girl driver on the team who races sprint cars so I think that will push the weight bias furthur our way.

[Charlie]

CG? Weight split?

[rjwoods77]

gunna be between 50/50 and 40/60 depending on a couple equipment choices

[Travis Garrison]

...and the engine is a ____?

Travis Garrison
UW FSAE

[Angry Joe]

I for one would like to see a CAD model of this thing. Is the driver in the fetal position?

[rjwoods77]

X-Y plane is the side view. The delta x from the vertical plane defined by the shoulder blades to the front edge of the drivers heel is 53 inches

[Lyn Labahn UW-Madison]

I am having a really hard time believing that could be right. We had a 60.5 inch wheelbase last year, and there was definately some overhang on the front! Please post a CAD snapshot or something to clarify..

[rjwoods77]

I think people have been ragging on me real hard for " just cause you dont think it can happen doesn't mean it can't be done". Stick yourself to the same monkey see, monkey do formula that most people use then you will have problems like this. Engineering is suppose to be creative within tight confines of resources. You'll see it when we show up.

[jack]

yeah, but the thing is, we have all designed >>and built<< fsae cars before, and this just doesn't sound right. besides, what reaction did you expect from this post?

does this sound like a segway to anyone else?? http://fsae.com/groupee_common/emoticons/icon_eek.gif

[rjwoods77]

Just wondering if anyone else had done it or something near it. RMIT said they did it in 60.25 inches on their website. I just wanted to know who else did it. I didnt expect any reaction. I just asked a simple question and the "no you cant do that" shit started rolling in.

[Eddie Martin]

Well Rob you obviously posted to get a reaction and also to tell the world about the car, so you shouldn't be that shocked when it gets a reaction. http://fsae.com/groupee_common/emoticons/icon_smile.gif

From what you describe you are using a single cylinder engine. With the driver position you have described you either have the motor transverse and your sprockets are close together with the diff centre line behind the rear wheel centre line or the motor is mounted longitudinal with a shaft going back to the diff.
The weight distributions you are probably looking at maybe down to a torsen vs. spool decision.

Have a look at the Tokyo-Denki car that was in the states in 2003. It was blue with white stickers. It was 1525mm wheelbase with no over hangs, their driver was quite upright which looked like it hurt their c.g.

[rotor]

Rob

Our 2004 car has a wheelbase 5mm above the minimum, with 150mm negative rear overhang.. and 150mm front overhang.
This is with a single again and a mighty tall driver (hi geoff)
I think with a little creative thinking and some small COG sacrifices it could be done, after building a couple of cars that it is!

As we coming to the US i look forward to seeing it next may rob.

Mark Hester
RMIT Chief Engineer 04

[Kevin Hayward]

Rob,

I don't think you got any comments along the "no you can't do that" line. Merely you had a few questions as to how you did it. Most of the people who replied are well aware of the ways to shorten a car. Some of which are not adopted for other reasons such as COG height and longitudinal location.

However if you have managed to build a car with good low driver seating, reasonable F:R weight split and adequate driver leg room with no overhangs and a low weight then I too am interested to find out how.

But please do not be so arrogant to think that other people are simply "monkey see monkey do" engineers. Either show us a screen grab, give us some info, or quit bragging about a car you will not say anything about.

Kev

[Charlie]

Well put Kevin.

I'm not sure what you are after here either Rob. Yes plenty have built a car with a 60 in wheelbase before. I don't understand why you are concerned with overhangs, I can't see how they affect a cars performance. Yes lighter is good, but if you are stuffing the driver in and up to accomplish a slightly shorter frame, you are raising your CG at the expense of a few pounds.

How are you you balancing this compromise? How did you decide how to compromise between total weight and CG? Or is CG something only monkey-see monkey-do engineers look at? http://fsae.com/groupee_common/emoticons/icon_rolleyes.gif

[The guru of guru's]

Whats so good about having a single engine beside the driver?

So where do they give engineering degrees to monkeys?

[rjwoods77]

Thank you rotor. That was all I was asking for. See, it wasn't that hard people.

[BryanH]

Charlie, low polar moment, concentrating mass about the cog, is the holy grail of race vehicle design. High polar moment is good when designing arrows

[Lyn Labahn UW-Madison]

It wasn't meant to be an attack by any means, but from my personal experience designing and building a 60.5 inch wheelbase car, it was difficult, as others have mentioned, to balance all of the other factors. For example, is your driver in a comfortable position? My intuition tells me your driver compartment may to too short and the wheel will be too close to the driver. Is it easy to work on your engine while it is in the vehicle? Is the engine easily removable? Does your rear end accomodate a variety of sprocket sizes? Is your exhaust header close to roasting your driver? Etc. etc.

There are a lot of things that as a first year team you may not think of till after the car has been built. Most of the people here are willing to help, but you have to be willing to give out more than rudimentary information, as saying goes, if your input is shit, what do you expect your output to be? Something like a sketch of the layout, or basic dimensions of your compartments would go a long way in recieving some benefitial feedback that could save you days of frustration in the spring. I feel like I am beating a dead horse here, you can let this thread die if you wish, or if you want some feedback, I (and others it appears) would be more than willing to contribute.

[Angry Joe]

Our 61-inch wheelbase car was not easy to do. There was quite a bit of front overhang and from the driver's standpoint it could have done with more.

It was not perfect, but it was not a monkey-see, monkey-do formula (although some of the design sessions would have been more productive if we had tried flinging our poop at each other)

[rjwoods77]

I stated the distance from shoulders to heels as an x distance. That tells you how much longitudal space the driver has. Thats enough space. I was just wondering if anyone else did it. Didn't really ask for an opinion on anything.

[rjwoods77]

Angry Joe,
I dig your guys car. It's what the comp was intended for us to produce. Cheap, light, and effective(long as nothing breaks. sure that wont happen to you guys again.). There is one thing that RMIT did to show everyone out there more than anything. To show that if car is designed right, that the big 4 cylinders are a waste of space, time, money and complexity. University of Buffalo (us) ran a turboed KTM one year. The guys who built it screwed up on the application of it but the car showed huge promise. If you look at it, it is very similar to RMIT. They did this in 97 i think. Another year of develpment and the subtraction of stupid errors would have made that thing fly. Was nice and light,simple and no frills. Any time I talk to anyone on my team about it they avoid the conversation. Its like the black sheep around here. Instead of working with it, bowing to the pressure of "everyone competetive is using...." they went the wrong direction and went with a 4 cylinder. Monkey see and monkey done it.
I was stuck onto the 4 banger way of doing things till I saw what RMIT did. If they can do then we can do. That is if we do our homework....

[Drum]

Here you go Rob, the packaging layout for the new car

http://www.fsae.rmit.edu.au/hostedpics/packaging.jpg

Now monkey do....

[rjwoods77]

I posted a pic of the human and frame. The centerline distance from the main roll hoop to the centerline front roll hoop is 34 inches. The centerline distance from the main roll hoop to the centerline front bulkhead is 52 inches. 18 inch tires with 10 inch rims. 95th percentile man in car. model is the "dude-2" that i found here on this board. The guy is 6'2 and 230 lbs.

[ethanL007]

Throw a helmet on your 6'2" dude and check you 2" clearance from hoop to hoop. Also lots of stuff needs to be crammed into the front of your car. Master cylinder placement needs to be aft of the front bulkhead. My biggest concern is the placement of the rack and tie rods, which seem to occupy the same space as the drivers legs. Just a few things to check out.

[Kevin Hayward]

Halfast,

I will not try to dispute that low polar moment of inertia is important in race car design. However I think it is important to look at vehicle yaw response. A driver, however good, will have a lag between vehicle disturbances and the ability to make a corrective input. Furthermore these corretive inputs may under or overshoot the requirements requiring further inputs. If the response time of the vehicle is very low in comparison then control of the vehicle may be lost or a vehicle oscillation may be induced.

The yaw response of the vehicle is affected by the polar moment of inertia in yaw. There will be a point at which the polar moment of inertia is too low for the driver to respond adequately. Whether this is able to be achieved in a FSAE car is another question. But given that very low moments of inertia are achievable in these cars I think Charlie's concerns are valid.

Kev

[rjwoods77]

If you saw the front view you will see there is enough room. Notice the judges broomstick. The rack is mounted just off that lower rail in a rear steer configuration much like RMIT. The master cylinders are going either under the feet of the guy(the reason his feet are elevated) or they will be mounted vertically in the front bulkhead plane(sprint car trick). There isn anything else in the front footbay. Also looking into the possablilty of pullrod with longitudal mount dampners that would be placed under the calves. False floor deal. Cool thing we found is that we dont have to have an adjuastable pedal box. In mockup we found that the shorter the driver, the straighter the legs get to naturally compensate for distance change. Also we found that the shorter drivers preferred a more straightleg setup while the taller drivers liked the inclined legs. Just a feel thing we worked out. Still working some stuff out but nothing too terrible. I am doing another pic. Check that out.

[rjwoods77]

look in the buffalo formula thing again

[Denny Trimble]

Kevin,
I agree that the bare minimum polar moment of inertia is not necessarily what we want. But what I don't understand, maybe because I'm not a kart guy, is how the 250cc roadrace karts go so damn fast. Doesn't one hold the lap record at Laguna Seca?

[Kevin Hayward]

Denny,

The response to yaw disturbances is also highly controlled by tyres. I have found a couple of sources that speak wonders of Kart tyres ... but haven't really had any firsthand experience working with karts.

However there is also an issue of response times of drivers. Driver ability has been linked to fast, trained responses. This reduces the reaction times required.

If I could hazard a guess I would say that us humans driving the same kart around Laguna Seca would have a lot more trouble.

But it still raises the questions for FSAE vehicles. Can we even get polar moment of inertia below a practical minimum? Can we effectively make our drivers better?

My previous post was more of an attempt to suggest there may be a little more to the problem than low PMOI = racecars, high PMOI = arrows http://fsae.com/groupee_common/emoticons/icon_smile.gif

Kev

[BryanH]

Kev, I have found that vehicle stability is mostly a funtion of front end geometry. Don't agree with your polar theory, A high polar moment vehicle needs a highly experienced driver to explore its limits (eg porsche 911).
I have personal exp. racing a 600kg/270hp offroad car. I could powerslide it around tight corners but with that engine hanging out past the rear tyres it was almost impossible to slide around fast sweepers, my head was telling me to keep it straight. I tried overriding my head and ended up looking back at where i'd come from. A very low polar moment vehicle such as a kart can be kept on the chosen path with very small corrections by the driver so that even though it is being driven on the ragged edge it appears from the outside to be driven very straight.(straight is fast)

Karting is the purest form of motorsport, you learn a bit about chassis/tyre dynamics playing with them for 3/4 of your life. Kev it's never too late to start.

btw in a recent TV doco Shumi was shown to have the same reaction time as most other 30 year olds, it's just that he knows what to do next....... before it's actually happened.

[Denny Trimble]

Halfast,
I think you're confusing center of gravity location (Porsche 911, most rear-engine offroad buggies have 60-80% rear weight) with polar moment of inertia.

A car with higher PMI will require more input / disturbance to change its yaw angle. This means slower transient response, which is good in high-speed turns, but bad in low-speed turns. You can still have a car with a large PMI that oversteers, but it will take its time to spin on you.

Ultimately, driver skill has to go up as PMI goes down, the "control system" (driver) has to work faster than the "output" (car) responds, or you have instability.

It's a great feeling as a driver when you go from driving reactively, to driving proactively. All of a sudden it just gets easy...

[Angry Joe]

I don't think any of us need to worry about having too small a polar moment of inertia. If you ever get that far then show your car to NASA and then go work for them.

The single cylinder engine is definitely a nice package, but not without its drawbacks. For starters the car had better be super light or you just won't have the powerto weight to compare to the big four cylinder motors...

[Paul V.]

Hey Rob,
I posted our design. We have a 53.3 inch wheelbase and only a little overhang. look under UAH FSAE.


http://fsae.com/groupee_common/emoticons/icon_biggrin.gif
Paul

[Kevin Hayward]

Halfast,

I am not intelligent enough to come up with my own ideas. The idea of Polar moment of Inertia and its affects on response is in Milliken & Milliken (chapter 6 I think). There is also a good quote from RaceCar Engineering and Mechanics by Paul Van Valkenburgh:

"With the modern mid-engine race car, it is possible that the polar moment of inertia may be less than optimum and some increase might be desirable to reduce response time demands on the driver."

It is quite clear that these comments do not refer to a 911 style vehicle, which has a whole different set of problems.

...

As for the comments about driver response times. If the driver nows what to do next, say the required input in 0.1s, then that will effectively reduce the reaction time for that action. I was not suggesting that good drivers were fundamentally genetically different to the rest of us. Rather that by knowing what is needed the initiation of a control input could happen earlier. Either way I think its a case of semantics and we probably agree on the final consequences for the car.

Kev

[Big Bird]

<BLOCKQUOTE class="ip-ubbcode-quote"><font size="-1">quote:</font><HR>Originally posted by Angry Joe:

The single cylinder engine is definitely a nice package, but not without its drawbacks. For starters the car had better be super light or you just won't have the powerto weight to compare to the big four cylinder motors... <HR></BLOCKQUOTE>

I'd argue that AJ. Super light?? Our little porker weighed in at 200kg at FStudent, (70kg more than Delft) but was still the fastest car there. The reason we won was that we didn't try to achieve too much in one year, and concentrated on getting the thing running reliably. It didn't have the most or the least of anything, but it was sorted and the drivers knew it.

Personally I couldn't give a flying fish for having a speccy power-to-weight ratio, and I think that might be the stumbling block for others that have tried singles so far. There is so much more to be had from having a car that runs exactly when and how you want it to.

We were able to play our weather strategy exactly how we wanted to in the UK, because we had a car and a team that were ready. We completed all our Saturday events by 10:30am, well before the lunchtime rain came. So while everyone else was stressing about when the track would dry out, or about still trying to pass through scrutineering, Rotor and I were over at the caravan chatting up the Race Control girls. A few teams said they would have given us a better run if they hadn't been caught out by the rain - but the plain fact was that they were, and that was no-one else's fault but their own.

The more you sweat over those last few kilos, those last few weeks of refining the design, or that last inch or two of wheelbase, the less time you have to build the car and get the damn thing running right. We were astounded by the number of teams at FS that still hadn't finished their cars two weeks before the event, but were still supremely confident that they were going to blow everyone into the weeds. Some of them told us we had no chance with a car so heavy and with so little power.

I'd gladly trade off a few hp, or a spectacular power to weight ratio for a happy and confident team and a reliable car.

Cheers all

[rjwoods77]

Exactly. We are coming to the table weighing 300-350 lbs and about 30-40 hp at the wheels. I am not the least bit concerned right now about power. We get what we get and we are concentrating on handling,reliability, simplicity and low cost. We will get more power next year. We are looking into this real lightweight(approx. 7 lbs) 3 lobe roots blower based on a 3" diameter rotor that has been used to huge effect on a drag motorcycle by the local engine builder nut. Very low power loss to operate and all sorts of benefits. But that is for next year when we have time to worry about such things as supercharging, superlite this and that. Just gotta fend off teamates from masterbating with carbon fiber. http://fsae.com/groupee_common/emoticons/icon_biggrin.gif

[BryanH]

Denny, the 911 was the only high PMI vehicle I could think of in 15sec. Pre '90 cars are 40/60. GT3 is closer to 43/57. In real world the 911 tends to oversteer in transient and will spin if not powered through the turn. 300kg of lead mounted ahead of the front bar would close the gap btwn the steer axis and the cog.
An easy experiment to feel the effect of changing PMI only would entail loading 4 big guys in front seat and another 4 up against the rear door of a 1 ton van and taking it for a thrash on your fav. road, then get all 8 to huddle behind seat and thrash back home.

Looking at skid pad times, the spread is very small and also does not seem to be a predictor of on track performance. Seems to me that transient response is a major factor in actual track performance.
Increase PMI to gain high speed stability? why not add a little castor?
V-Angles is very left field.
If anyone could do it, it wouldn't be worth doing.

[Cement Legs]

I agree with a lot of the replies here, nobody is attacking your idea they are just trying to wrap their collective heads around what you have proposed. It's not a negative thing to have people question your ideas, its actually something that should be used to build up your ideas with the experience of others. Every engineer will try ideas based on theory and not fact to explore the results; benefits and faults. Every engineer will also use proven ideas and facts to facilitate getting more of an expected result.

What it all comes down to in my mind, nice presentation or not, is how the car does in the dynamic events. I'm not a paper pusher per say but I get by with what I know. I think what you guys are doing sounds cool, and I hope that some of the feedback here helps you make it work the best that it can. Good luck in Detroit.

Cheers
Dave

ps Cornell has won the event like 50% of the time over the last 15-20 yrs and if my memory serves me right, last year they used a 68" wheelbase!http://fsae.com/groupee_common/emoticons/icon_smile.gif So when it seems like people are comming down hard on you guys I think they are simply questioning the benefits.

pss the Dolpins really suck this year http://fsae.com/groupee_common/emoticons/icon_frown.gif

[Angry Joe]

Big Bird,

Most of the problems leading to lack of testing with our '04 car had to do with the new powerplant. Aside from the usual new-engine headaches, I'm sure you know figuring out a thumper throws in some more. The rest of the car was built around making as simple a vehicle as possible. Ironically it was the 'simple' swingarm that caused some problems in the end http://fsae.com/groupee_common/emoticons/icon_frown.gif

[Barnard1425]

Since Rob won't offer up any pictures of his all-conquering, 320-pound, single cylinder, turbocharged, 60-inch, no overhang, low PMOI machine, I've taken it upon myself to obtain a spy photograph of the vehicle:

http://www.letsmow.com/gallery/leonhardtsmower.jpg

Okay, so I'm being a smartass. Just a joke, really.

On the other hand, I have a hard time understanding anybody who uses the phrases "turboed KTM" and "simple and no frills" in the same sentence. It seems to me that the 600cc fours are about the simplest engine packages you can get. Beyond a simple intake and exhaust (and fuel mapping), they're damn near stock.

[rjwoods77]

I used the ktm as an example of an overall system reduction. It was very RMIT like in nature. We arent using that motor though.It has more than one cylinder and less than 12. http://fsae.com/groupee_common/emoticons/icon_smile.gif