What is your car like to Drive??

[John McCarthy]

I've had a bit of a look through the archives and not found anything that really discusses this topic, so here goes:

To All FSAE-ers, What does your car drive like? Does it go like hell? Does it turn hard through all 3 phases? Do your eyeballs pop out under brakes? Do you have to rev the puss out of it to get moving? Does it hate anything but nice smooth Asphalt? Does it spin Easily if you aren't careful? How does it compare to FSAE Cars you have built previously? Are you qualified to make comment or have some other racing/driving experience to compare it to?

We're only really playing with our first year car now (some 2 months after getting back from the competition) and It's hard to know how well we've done. None of us had driven before the Saturday at FSAE-A, so the times we put down aren't a reliable guide...

The floor is open. Any Takers?

[Joel Miller]

I know our 2002 car had shocking understeer, until we started driving it on the smoothest tarmac available. It came good and had tremendously sweet handling characteristics. All our cars are pretty stable with excellent steady state cornering characteristics, although our 01 car did tend to be a bit twitchy at times, leading to corner exit spins - probably more a function of a peaky torque curve (not recommended).

One thing though, is that it is critical to get a good suspension tune. From setting to setting, you can be driving an entirely different vehicle.

[Travis R]

The majority of our cars are pretty easy to drive quickly. And are very predicable at the limit. In fact they are pretty easy to drive beyond the limit. With the proper throttle and steering inputs they can be driven sideways around a sweeper.
They are not terribly upset by bumps, assuming they aren't so big as to bottom out the suspension.
Starting out is tricky for new drivers, but only because they aren't used the clutch, not for a lack of torque.
Braking performance is dependant on tires. Yes, the eye-ball-popping is possible if you are on good tires and they are up to temp. We just corded a set of old tires in cool weather last week... and braking performace was dismal.
The cars will spin, but only if you are doing something wrong. http://fsae.com/groupee_common/emoticons/icon_smile.gif If your cars spin on anything but smooth asphalt, then you probably need to re-evaluate your setup. Maybe your shock are too stiff, or your ride rate or roll stiffness is too high in the rear. It's hard to say. Like I said before, our cars are pretty easy to drive and predictable.
Good luck

[Kevin Hayward]

Thought I might put up a couple of notes to follow up on Joel's post.

He was right about the horrible understeer of the '02 car but not the solution. We had made a few steering geometry changes to the front end of the vehicle that didn't really work. When it ran in OZ for the '02 comp we were wearing the fronts really quickly. We had just switched from the Goodyear R095 compound to the R065 compound and anyone who knows the tyre will be aware of how sensitive to wear they can be.

Coupled with front shocks set too stiff in rebound we had a car that would start out okay for a while and then progressively get worse. That year while we had the 3rd quickest Autocross time and while we came second in Endurance our quickest lap in the Enduro was behind about 7-8 teams.

During this tune we did not have linear pots on the car but I am almost certain it was progressively jacking around such that the understeer was not apparent until a couple of laps had passed. Given that with a lot of our later training the drivers do a few warm-up laps before pushing hard the car seemed to be understeering a bit. Interestingly nothing indicating high inside tyre temps was being shown by the tyre pyrometer ... dynamic tyre temps are the way to go.

We were able to make few changes to the car about the time we got a new test area that Joel was talking about.

...

We learnt a lot of important lessons while testing the vehicle:

1) That tuning of the suspension is probably more important than the original design parameters.

2) Tuning suspension without DAQ is a painful process. Questions that are very easy to answer with the right sensor become much more time intensive.

3) It is difficult for inexperienced drivers to give valuable feedback for problems causing a gradual change in the balance of the car.

...

Basically we learnt that do do well in FSAE you need:

1) Good Drivers
2) A lot of testing
3) A well designed car

Unfortunately for us engineers I also think it is in that order.

Also John:

'01 and '02 have always required earlier application of the brakes to make a corner. '03 and '04 the brakes are fantastic. Good brakes have really allowed us to push a lot harder without taking more risks. May have something to do with twin brakes and a rearward weight bias ... but then again they do add a few hundred grams to the car so they would really slow us down around a corner.

Kev

UWA Motorsport

[PatClarke]

Hi All,
Don't forget the immortal words of the late Mr. Smith. "If your race car is not easier to drive than your road car, you have done something wrong"
Pat

[Joel Miller]

Thanks Kev. Someone told me that no changes were made, bar the Venue, but I find your version entirely more believable. Good job on the suspension tune.

The same venue thesbian also said that a fast car will not be a "nice" car to drive. Pat, I like the idea of a race car being easier to drive than my Bluebird, but did Mr. Smith mean that if our car is not "nice", then we have done something wrong? Or was he talking about ergonomics, rather than handling?

[Kevin Hayward]

Joel,

I have had the chance to take my daily driver around the same track as '02 when it was not handling so good. It was an absolute pig in comparison.

I had hopped out of '02 disappointed with the amount of understeer and then found out how bad things could get.

This is from a car that is great to drive around on the streets.

A FSAE car will always be a bit harsher than a road car because of things like lower deg/g roll gradients, higher natural frequencies and spherical bearings. However they should be much more direct, controllable and balanced than your road car.

Basically much "easier" to drive at the limit.

Kev

[nathan s]

Our '02 car is really hard to steer because the scrub radius is huge. The pivot axis is on the inner edge of the wheel. We did an analysis on it and found out the loads needed to steer. It turned out that our lightest driver needed about 40 ft-lbs of torque and the heaviest needed close to 65 or 70 ft-lbs. That explaines why we were flexing the steering wheel in the turns.

[Sam Zimmerman]

2001 - Lots of power, fun to drive, lots of oversteer, rookie of the year car, better than sex.

2003 - Little power, easy to drive, no understeer, fastest car built here to date.

2004 - Lots of power, lots of understeer, sex is better than driving a car that won't turn.

[Frank]

2004 - most straight line speed at FSAE-A and FS, it gives me wood

[John McCarthy]

Probably a little too much info Frank.

Any chance of a drive???

[Frank]

certainly,

we have a small fixit to do

some pillock at the motorshow picked up the front of the car by a wishbone http://fsae.com/groupee_common/emoticons/icon_frown.gif

[Marshall Grice]

i've driven a couple fsae cars

our 2000 car was very heavy and drove just like you would expect. lots of intertia, not incredibly responsive. measureable understeer although not excessive. the car really needed an agressive technique(aka throw it around) to get fast times out of it.

2003 car was LOOSE. It weighed about 60lbs less then the 2000 car. very stiff springs. rear RC was about 2" higher then the front. Had issues with stability under braking, well everywhere really. The old driving techniques no longer applied. aggressive driving was rewarded with multiple spins per lap. It didn't like bumps either.

2004: suspension geometry was very similar to the 03 car. after a year of reaading and rereading RCVD we came up with a much better better balance. Still can't get rid of the stability issues, which tends to make it kind of difficult to drive. Rookie drivers still get rewarded with spins. Steady hands(and feet) can turn out some pretty fast lap times.

[Joel Miller]

Originally posted by Kevin Hayward:
A FSAE car will always be a bit harsher than a road car because of things like lower deg/g roll gradients, higher natural frequencies and spherical bearings. However they should be much more direct, controllable and balanced than your road car.

Basically much "easier" to drive at the limit.

Sorry, wrote a reply ages ago, but it obviously didn't go through. And I obviously don't check the forums often enough.

I don't think "nice" was to suggest a cushy soft suspension. When communicated to me, "fast cars aren't nice" implied that a car tuned to be optimally fast will necessarily be responsive, yet nervous and unforgiving, thus making it difficult to drive. Just wondering whether this is correct and if it stacks with Carroll's suggestion that the race car should be easier to drive. At first glance, the two seemed to contradict.

But if it is all about holding a car on the limit, I can dig that. After all, road cars have vague controls and don't communicate that well.

[Joel Miller]

Originally posted by Marshall Grice:
Still can't get rid of the stability issues, which tends to make it kind of difficult to drive. Rookie drivers still get rewarded with spins.
Marshall, all the aero teams I've talked to claim that the addition of wings made their vehicle very stable and difficult (even "impossible") to spin. Is it possible your CP location is leading to instability? Is the instability related to speed? Or is it purely a suspension issue?
Thanks.

[Matthew Robinson]

Very very fast

[Lyn Labahn UW-Madison]

http://www.stardestroyer.net/Empire/Tech/Propulsion/Hyperspace2.jpg

[Marshall Grice]

Joel:

with our wings on the car is very stable. silly me, i was describing the car with out the wings on. We do the majority of our suspension tuning sans wings to ensure a good mechanical setup. the wings will cover a lot of problems, stability being a big one. You turn our huge endplates into the wind and it straightens the car our like a dart. In addition our CP is rearward biased which adds a certain amount of high speed understeer. Only once have i spun the car at speed with wings on and i was just being stupid at that point.

So i guess to answer your questions, yes it is only unstable at low speeds. and yes it is purely a suspension issue.