Acceleration(droping the clutch)

[Blake]

we are having quite the nice little discussion as we are debating on weather it is needed to "drop the clutch" to do well in the acceleration event, or as im concerned if its a good idea. Today we DESTROYED the sprocket connection dropping the clutch at 6000-8000 rpm i said there is no need to do this and another member swears a bunch of teams do this no problem without destroying there stuff. Am i right is this just ridiculous, i mean its not a drag car, or is he correct is his abusiveness of my drive train.

Blake
lsu fsae

[Blake]

we are having quite the nice little discussion as we are debating on weather it is needed to "drop the clutch" to do well in the acceleration event, or as im concerned if its a good idea. Today we DESTROYED the sprocket connection dropping the clutch at 6000-8000 rpm i said there is no need to do this and another member swears a bunch of teams do this no problem without destroying there stuff. Am i right is this just ridiculous, i mean its not a drag car, or is he correct is his abusiveness of my drive train.

Blake
lsu fsae

[Wright D]

I would always want to lose traction before parts brake no matter what any type of car it is. You never know who might get into the driver seat, and dump the clutch.

[SpdRcr]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by Wright D:
I would always want to lose traction before parts brake no matter what any type of car it is. You never know who might get into the driver seat, and dump the clutch. </div></BLOCKQUOTE>


??? I don't understand what you are trying to say

[Nick McNaughton]

It's got to be able to do it. A clutch drop into wheelspin is nowhere near as harsh as an all-hooked-up powerslide over bumps. Either way, the part's not good enough.

[Wright D]

Sorry, I changed thoughts mid sentence, so my words got all jumbled up. What I was going to say was... oh; just read the post above, he said it way better then I did. http://fsae.com/groupee_common/emoticons/icon_wink.gif

[Micko..]

We run a pneumatic clutch, for launches (i.e. acceleration runs) we have it on the fastest release. This is basically a snap release, letting launch (around the 6-8k mark) and traction control do the rest.

You should be designing your driveline to withstand these shock loads, the first couple of launches are no worries, it is once you have done 15 or so in a row and the tyres are stinking hot, that's when you get the really big torque spikes. We had to raise the launch rpm considerably with hot tyres.

I have seen some of UQ's drive shafts that looked like spiral spaghetti after a big day of acceleration testing (but they were gun drilled and pretty soft).

So in conclusion, design your parts to hack it and drop the clutch. If your not sure do a couple of launches and then crack test driveline parts.

cheers
Miko

[Blake]

sounds good, do you think thats it should be able to take 6-8 thousand or say even 12-13 thousand, also i wondering if my bolts were grade 8. Does anyone know if machine bolts(black Allen head) are grade8 because i couldnt find them in specific grade 8 but the guys at our shop told me they were just as strong

[drivetrainUW-Platt]

I thougth that some teams actually start the acceleration event in 2nd gear so that they dont spin the tires half way down the track?

[Mike Cook]

I always lunch in second and basically use the clutch to modulate wheel spin. While this is happening I slowly increase rpm and basically, by the time the clutch is fully released i'm at red line in second and I shift.

[Micko..]

Most black socket head cap screws are grade 12.9 do a google (or better yet engineering handbook) on 12.9 shcs and see what you get.

we run launches at that rpm because if we launch any higher than that it is just all wheel spin. I would suggest (hope) that dropping the clutch at 12-13krpm in 1st gear will just spin the wheels, which will result in less torque load going through the driveline because the tyres are not producing as their maximum amount of grip.

Miko

[Erich Ohlde]

We also use pneumatic clutch/shifting. One of our team members is a big drag racer and we dropped the rears to about 6 psi and did a clutch drop at about 10k, blazingly fast times, didn't damage the car. Although we are using the quaife, which has 6 AN6 bolts holding the sprocket to the diff housing

[Bill Kunst]

I agree with both sides. Unless you have traction control, dropping the clutch may not be the fastest. Wheelspin does not equate to going faster, but there is a degree of slip angle that will allow the fastest accel. Can most people yield these slip angles? NO, hence traction control, but if you don't have it, slipping the clutch in second might be faster than dropping in first.

Should parts break? All cars, all manufacturers (oem and aftermarket) will have parts fail under these conditions. Most racing components are not designed to withstand an undetermined amount of abuse. NASCAR cars will see a beding of the lower control arm throughout the Daytona 500. This is designed to be light as possible, and to last only one race. We sometimes wonder why the car gets faster and then breaks? Design the car (replacable)parts to withstand the abuse you will put into it throughout your season. If it doesn't last, you miss-calulated the abuse.

I, personally, wouldn't be dropping the clutch...just my thoughts.
Bill

[drivetrainUW-Platt]

So, assuming your drivetrain can handle the power, wouldn't using say rain tires give more traction for the acceleration event assuming slicks and rains are both cold?

[Bill Kunst]

Duwe,
Rains are softer, but they have less contact. Not only that, there are some rules governing the swapping of tires for events. But, yes, that rain compound would give better traction than the dry compound, but the tire may not.
Bill

[jdstuff]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by Blake:
sounds good, do you think thats it should be able to take 6-8 thousand or say even 12-13 thousand, also i wondering if my bolts were grade 8. Does anyone know if machine bolts(black Allen head) are grade8 because i couldnt find them in specific grade 8 but the guys at our shop told me they were just as strong </div></BLOCKQUOTE>

Just a word of advice, if you're looking into fasteners for any high stress/tolerance applications, look into AN and NAS fasteners. You won't find any McMaster special black oxide SHCS anywhere on our drivetrain.

Also, we do our acceleration launches around 8-8500rpm, and design our drivetrain parts to live for 1 competition and a good summer of testing. Anything above that is just icing on the cake....

Mike, if you happen to be running Goodyears, the R065's and the rains share the same compound. So the rains would definately be a disadvantage, as they are the same tire but with void.

[Jersey Tom]

There are rated black oxide SHCS fasteners on McMaster. Usually around 150ksi minimum tensile strength.

[absolutepressure]

Idk a lot about tires, but why is it the opposite for automotive tires as far as tread and grip. If you have brand new tires, they're going to grip much better than a set that's worn flat like a slick. It happened on my car. I didn't wait that long, but I can no longer squeak the tires like I used to. Same's true for cornering. Not that I'm complaining my car gets more grip (even more than trucks in the winter...man, my car is so good I can outperform trucks in the winter and summer) but why is that true?

[pengulns2001]

the only reason thats true for street tires is by the time there is no tread left you are past the tires tread depth meaning you no longer have the same compound you started with, its just like when the tire depth gage holes are gone on our slicks, they no longer perform the same but still have the same (or better) contact patch... street tires have tread because of the rain/dirt/snow you have probably noticed that the higher performance tire you buy (look at some toyo ts1's) the less tread there is

[VFR750R]

I think we did a lot of runs starting in third, some of us dropped the clutch, I slipped the clutch most of 3rd, on our slippery test road, we've even experimented successfully starting in 4th, but didn't stick to it due to the extra grip at comp.
I also seemed to be faster using my left foot 'PID', although the 'dump' was perhaps more repeatable.

[conekilr]

See Jayhawk_Electrical's Post...

Also, we have a way to 'slip' the clutch but it's definitely not optimal for acceleration, more for moving around the pits more comfortably. We find that just dropping the clutch around 8-10k rpm and controlling wheelspin a little until it hooks results in good acceleration. We've made countless launches like this on the '05 car and beat the shit out of it but nothing has given way yet (crosses fingers).

[Erich Ohlde]

except for that upright issue.....

[conekilr]

Haha, ya that made some fun noises at the autocross. Front bearing failures don't count. Plus I filed and sanded the upright so it's good as new right?

[Conor]

Does anybody have any tips for somebody driving in the acceleration event for the first time? Our team is essentially a first year team and none of our new parts have been tested and proven. It sucks, but that's life. I'm very confident in our components, but I don't want to take the chance of failing a differential bracket because launching at 10 grand would give me a better time. Play it safe or go balls to the wall?

[Bill Kunst]

Play it safe. Are first year we had the same problem. You can finish better than 90% of kthe field in all events by just finishing, or go balls out and not finish the event you are trying to "win".

[Marshall Grice]

you can go balls out after competition to validate your designs for the next car.