How many shifts during Acceleration event?

[murpia]

Just a quick survey, how many shifts does your car need during the 75m Acceleration event?

Also, do many teams start off in 2nd?

Thanks, Ian

[murpia]

Just a quick survey, how many shifts does your car need during the 75m Acceleration event?

Also, do many teams start off in 2nd?

Thanks, Ian

[Dan G]

None.

http://fsae.com/groupee_common/emoticons/icon_cool.gif

[Marshall Grice]

3, from second.

[Erich Ohlde]

We are doing some testing right now with gearing. Currently we launch in 1st and top out second about 5 feet from the finish. times are around 4.3s. with burned up 8inch rears on a somewhat sandy asphault lot

[Agent4573]

we start in 1st and shift to second and third

[murpia]

Thanks guys,

Interesting, as I was looking at some of the FStudent team design specs on gear ratios and they implied teams would need to reach 5th or 6th gear by the end of acceleration (~120kph). 2nd gear looked only good for ~70kph.

Anyone care to comment on this terminal speed?

In case any FStudent teams are worried about confidentiality a) I have the specs because I am a design judge and b) I will not publish any team-specific data or identify teams. I'm just trying to get a clearer idea of appropriate performance envelopes with a little simulation.

Ian

[raska]

Start in 1st, was shifting into 3rd between the 2nd last interval of cones in Detroit. Speeds weren't all that great though, ~4.2s I think, but we didn't have a very good setup for acceleration in terms of anything, no two step, too much tire pressure, etc. I couldn't give you the speeds off the top of my head, but 6th would string out to 170kph at 10,000 rpm I think.

[BeaverGuy]

I'm not sure if the Formula Student design spec sheet is the same as FSAE but on the specs It asks for vehicle speed at the max power point which should be before the shift point and well before the revlimiter. Asking for revlimit speeds may be more helpful on the spec sheet.

[murpia]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by BeaverGuy:
I'm not sure if the Formula Student design spec sheet is the same as FSAE but on the specs It asks for vehicle speed at the max power point which should be before the shift point and well before the revlimiter. Asking for revlimit speeds may be more helpful on the spec sheet. </div></BLOCKQUOTE>
Agreed, the specs aren't very clearly defined. In fact it's only by inference that a peak power or torque figure is asked for...

Let's re-phrase the question: What speed, revs and in what gear did you pass the 75m mark at?

Thnaks, Ian

[Charlie]

If I understand you correctly you are saying a team's spec sheet implies they will shift 4-5 times in the accel event? It's a nice idea, but it only works if you lose no acceleration over the shift.

[Agent4573]

when we set up an accel event in our test area at school last time, we were lucky enough to have the campus police around, so we asked them to clock us throug the trap. I forget the exact distance we went, i think it was around 80 yards(73 meters) and we crossed the trap in just over 4 seconds at an average of just over 60 mph(96.5 kph). This was done starting in second gear and crossing the line at around 10 grand in 3rd. Hope that info helps.

[murpia]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by Charlie:
If I understand you correctly you are saying a team's spec sheet implies they will shift 4-5 times in the accel event? It's a nice idea, but it only works if you lose no acceleration over the shift. </div></BLOCKQUOTE>

Exactly my point - I've created a spreadsheet simulation, I put in data from some spec sheets and I get 4 or 5 shifts. So, to correlate the simulation parameters I need some real data. 75m speed & gear, plus elapsed time.

Ian

[murpia]

Anyone care to share data on the time lost during an average shift?
(Duration of torque interuption for a manual shift)

Thanks, Ian

[Schumi_Jr]

There's an SAE paper written on this very topic - 2004-01-3554. It's quite good but the author seems a little sketchy http://fsae.com/groupee_common/emoticons/icon_wink.gif

[jonno]

The time lost on shifts is factored to the spread of your gears: our 2004 car was a cbr600 geared to over 130mph in top. In a forced clutchless shift, there is a visible point where the drivers head nods forward as the acceleration yields for a second, then it is pushed back as the next gear fully engages.
Our 2005 car has a horizontally mounted wr450 single attached to a honda quad limited slip diff, however the gearing of the setup means that at the rev limit, the top speeds are approximately as follows...
1st.... 20mph
2nd.... 30mph
3rd.... 40mph
4th.... 50mph
5th.... 60mph
because each gear is so close, the car pops into each gear on clutchless shifts with no real visible "nod" of the driver. From a basic accelerometer plot it was pretty linear with marginal dips. Teams at the italian comp questioned how we were shifting so smoothly, we had nothing special, no powershift mechanism, just a hand operated lever.
Anyway in answer to the question, i belive we did low 5's (maybe a 5.1s) this is nothing special, but we had in the region of 30bhp in a car of around 200kg. The gearing is so close with reasonable torque low down that we pull away in 1st and 2nd with no real difference in times. We pretty much hit 4th either way on the 75m line, pushing roughly 50mph at that point.

I don't see why many teams have cars geared up to 130mph, that speed is never seen anywhere in FSAE. In any other form of racing, the gearing is always optimised to the circuit to get maximum performance (as an aside but related following the japanese gp, kimi complained that his car was topping out in 7th, such is the precision employed in f1 matching gears to circuits). Sorry it's not actual data to support your study ian, but it's theories that appear to work for us at least. The guys are driver training this weekend in the car, so hopefully i'll be able to get some definate numbers for you...

[Charlie]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by Schumi_Jr:
There's an SAE paper written on this very topic - 2004-01-3554. It's quite good but the author seems a little sketchy http://fsae.com/groupee_common/emoticons/icon_wink.gif </div></BLOCKQUOTE>

Yea but who wants to pay for a paper? (http://www.cpmaverick.com/Misc/2004-01-3554.pdf)

[kwancho]

Great paper! Thanks!

[murpia]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by jonno:
Sorry it's not actual data to support your study ian, but it's theories that appear to work for us at least. The guys are driver training this weekend in the car, so hopefully i'll be able to get some definate numbers for you... </div></BLOCKQUOTE>

If you are going to be at Silverstone this weekend, I may see you there.

Plugging your mass, hp & gear numbers etc. into my spreadsheet yields 5.0s elapsed time to 75m for a launch Mu of 1.0. I am happy with that as a correlation...

Thanks for the info, Ian

[jonno]

Sorry Ian, I may not be there as I have now "retired" the new team will be there and am sure will give you any advice you need (they're testing tomorrow too as a final shakedown, I'll ask them to do a few trial accel runs)

[Marshall Grice]

just thought i'd add this (http://www.csupomona.edu/%7Efsae/video/MOV00584.MPG) to the conversation.

[Welfares]

We've been using 1st 2nd 3rd, 13-52 final drive on a 99 r6, last 8 comp runs have been under 4 seconds.

[Michael Palaszynski]

1 shift launching in first while bouncing off the rev limiter for the last 15 feet or so...

3.976 at west

god i love that sweet summer sun...

[Tommo]

1 shift worked pretty well

[MTTec]

We in Chalmers are using one shift in the acceleration event. Start in 2nd and hit the rev. limiter some meters behind the finish line. 2006 car finished 2nd in FSAE West with a slightly different gear ratio.

[Iloper]

The Chalmers 2006 car uses 3 gears, we start on second or 3rd (http://www.youtube.com/watch?v=gLYHaQfOAlc) and finnish on 5th at 109 kpm. The movie is from baltic open 06, we use no shiftcut or anything.

At West 2007 we used shift cut, set to 0,045 sec i think. it went quite well, 3,925 sec. I think we started on second gear.

The Helsinki team used four or five gears in 06 i think, quite interesting since this theoreticaly is the correct way to go if you have a peaky powercurve.

[kwancho]

Out of curiosity, what does your final drive look like? You'd have to get some serious reduction to have gear speeds that look like that.