2015 Formula Student Germany

[ausracing]

Is coverage of all events on for this year of endurance only?
Can't wait.

Any thoughts on who has a chance of beating super GFR?
After Michigan it looked like it could be done!
Rennteam looked strong at FSUK, 3rd with no skidpad /accel and rain.

[JulianH]

Ryan, I agree with you. GFR does not look as "unbeatable" as in the 2-3 years before. This time it's not "DNF or Victory".

Rennteam was really strong at ZF Race Camp and in the UK. They tested a lot and only had bad luck Saturday morning in the UK. If they are good in the Statics again (Cost finals, Top 6 Design...), they should be able to give GFR a tough fight.
At one point, those 4 cylinder machines should be able to run Sub 4's in Accel. I mean, look at Wroclaw with 220kg+ and a 3,8 in the UK, the Wing is not too bad if you run it completely open. If Stuttgart is able to pull 4-5 tenths on GFR in Accel, then they should be in good shape.

Karlsruhe, Munich and Graz should also be in the mix.


But I guess the electric competition is going to be as awesome as last year. Delft, Stuttgart, Zurich and maybe Karlsruhe should be able to have a winning car on their hands. It probably will come down to "who makes the least mistakes" again...
Should be incredible!

[mech5496]

I would add NTNU in the list of the e-class contenders..

[JulianH]

I would add NTNU in the list of the e-class contenders..


I would add them as well (like TUFast Elektro!) but they both will sadly not participate...

[Swiftus]

Hehe. I appreciate all of the work the FSG organizers put in to making FSG such a great event. They have all of the companies as sponsors and they decorate the track with giant murals and informative posters. It really is a great event. But I think one of the graphic designers worked for too long when they made this poster.

http://i.imgur.com/3x16i9j.png
(http://i.imgur.com/3x16i9j.png)

[JulianH]

Hehe. I appreciate all of the work the FSG organizers put in to making FSG such a great event. They have all of the companies as sponsors and they decorate the track with giant murals and informative posters. It really is a great event. But I think one of the graphic designers worked for too long when they made this poster.

http://i.imgur.com/3x16i9j.png
(http://i.imgur.com/3x16i9j.png)

Well at least, they did not write "Oregan State University" ;)

[mech5496]

Oopsie! :P

Technical inspection status

http://www.formulastudent.de/fse/2015/technical-inspection-status/

[BeunMan]

And for completeness also the FSC TIS: http://www.formulastudent.de/fsc/2015/tis/
And the first episode of FSGTV: https://www.youtube.com/watch?v=p3ffJ9pRyYQ

[Swiftus]

And the FSE TIS: http://www.formulastudent.de/fse/2015/tis/

[BeunMan]

And the first results are in:

FSE:
Design Finals: Karlsruhe, Stuttgart and Delft
Cost: http://www.formulastudent.de/fse/2015/results/?user_fsgevents_pi1%5Bpdf%5D=63
Business: http://www.formulastudent.de/fse/2015/results/?user_fsgevents_pi1%5Bpdf%5D=62

And for skidpad: http://tk.formulastudent.de/fsg/display/indexN.php

[BeunMan]

Livestream: http://formulastudent.tv/

And for those not in Germany, you can use youtube: https://www.youtube.com/watch?v=lNWBTZdD9EI and thus chromecast ;)

[Pennyman]

Caught a glimpse of that Delft skidpad run on the livestream. Unreal.

[BeunMan]

Acceleration is on! (finally, after 1:30h of no cars ...). Still very quiet at 10:21, 2:39h left to go.

[BeunMan]

Zurich did 3x 3.30 and 1x 3.35. That car was so incredibly fast :x almost no wheel spin at the start! Also consistency.

[JT A.]

Seems like lots of teams are getting DNF's for scraping the track in AutoX

[mech5496]

Well, way more than expected! Was it a real issue, or overly strict judges?

[BeunMan]

Well, way more than expected! Was it a real issue, or overly strict judges?
Insufficient ride height.

[MegaDeath]

If that is actually the case, and officials were DNF'ing cars for hitting the track. THANK YOU!!!!!!!!!

The first time I went to FSG in 2011 they made a very bold statement during the drivers meeting for endurance that if your car hit the track in the same spot more than once, they would DQ you for the event. Hearing that, we raised our ride height a significant amount to be sure that we would not have to worry about it. We took the sacrifice in performance to increase our chances of finishing. Then endurance rolled around and there were many fast cars who were dragging under-trays all over the track and no penalties were issued.

So in 2012 there were a few teams that stood up in the drivers meeting after they made the same statement about DQ'ing cars who drag the track and asked if the rule would actually be enforced because it was not the previous year. The officials said that "Yes we let it go last year, but we will enforce it this year". So once again we raised the car up to be sure we didnt drag the track. Lo and behold, endurance rolls around and there were top teams dragging all over the track (GFR and Michigan Ann Arbor were the two biggest offenders) and once again, no action was taken against them.

2013 rolls around and once again they make the statement that "If the car drags on the track, you'll get DQ'ed" so we finally called their bluff and left the car low and let the under-tray drag over the bumps. And once again, no action was taken against any of the teams who dragged the race track.

I'm not sure what was done last year because I wasn't there. But I'm assuming it was probably the same thing that had happened the 3 previous years. If that's the case then it took 4 years for them to actually enforce this rule.

In my opinion, if the officials take time to blatantly spell out in the drivers meeting that "If you drag the car on the race track, you will be DQ'ed" Then that's what they should do!!!

That's the rule, the teams were made aware of it. If they didn't follow the rule, then they should get the penalty that they were told they would get!!

[BeunMan]

As far as I know (wasn't at the driver briefing this morning due to setting up acceleration timing) they told them a DNF was issued for everyone scraping the floor except for one place (the bump-trench-bump) but if you set your car up for the other bumps, it won't scrape the floor there either. That way the get the chance to increase their ride height an do at least one run. Due to the finish being moved, the drivers didn't have to take the last bump full throttle/brake on top, so it should have been safer anyway but the rule was maintained.

About rules: The last few days we saw some (in my opinion a lot) of drivers being late in the briefing or leaving before it was over. Until now no penalties have been applied but they will: see http://www.formulastudent.de/fsg/pr/news/details/article/no-more-additional-debriefing-without-penalties/ where debriefing is leaving before the briefing is over.

Another weird thing was the unclear end time of events in the past: The time is now shown on the website in news messages if changed during the event as well as on a board at the entrance of the event (e.g. the autoX was extended by 7 minutes because both fire trucks had to go to the testing area but one came back quickly after it all seemed ok). The exception is when the starting/end time is changed way before and shown at the briefing.

[JT A.]

I thought i remembered hearing somewhere that the FSG autocross course is always the same layout, or was it the endurance course? Or both maybe?

[MegaDeath]

I thought i remembered hearing somewhere that the FSG autocross course is always the same layout, or was it the endurance course? Or both maybe?

It's both.

They changed in 2012 when they expanded out onto the the actual race track from the infield.

But since then they have been very similar, just slight alterations to one or two corners over time.

[BeunMan]

The course is the same as last years, only the start/finish have been adjusted for safety reasons.

[Michael Royce]

Interesting comments and discussion about the "scrapping" DQ'ing/not DQ'ing.

We used to have this argument a number of years ago and the scrutineers always got criticized one way or another. We were damned if we did and damned if we did not! So for 2008 we changed the rules to require a 1 inch static ground clearance with the driver aboard. This was something that could be measured easily, no arguments, because either the car met or it did not. And Steve Fox even made some "hockey pucks on sticks" that made checking very easy. No more problems for the scrutineers and teams knew where they were. Then for some reason, the Rules Committee decided it did not like the "1 inch static ground clearance requirement" and the rule was dropped for 2011 and they went back to the "old" (present) rule.

Is it time for a change back?

Michael Royce.

PS. We still have the "1 inch static ground clearance" rule for Formula Hybrid!

[mech5496]

IMO it should be changed back, as it is an easy, objective way to measure it. P.S. To my experience, more than 1" is required to avoid scraping...

[JurrienK]

Final five almost on track, according to my calculations, KIT and Delft are almost equal on points. Both need to drive 74.8 average to beat AMZ (90% sure about that), which is the best team that has already finished.

[JulianH]

Congratulations to Delft. Impressive performance all week-end, without any mistakes, always placing on the top of the rankings.

The Dekra Award seems to be striking again:
2011: Zurich wins Dekra - Overall Delft P1, Zurich P2
2012: Zurich wins Dekra - Overall Delft P1, Zurich P2
2013: Zurich wins Dekra - Overall Delft P1, Zurich P2
2014: Zurich does not win Dekra - Overall Zurich P1
2015: Zurich wins Dekra - Overall Delft P1, Zurich P2

[JT A.]

Interesting comments and discussion about the "scrapping" DQ'ing/not DQ'ing.

We used to have this argument a number of years ago and the scrutineers always got criticized one way or another. We were damned if we did and damned if we did not! So for 2008 we changed the rules to require a 1 inch static ground clearance with the driver aboard. This was something that could be measured easily, no arguments, because either the car met or it did not. And Steve Fox even made some "hockey pucks on sticks" that made checking very easy. No more problems for the scrutineers and teams knew where they were. Then for some reason, the Rules Committee decided it did not like the "1 inch static ground clearance requirement" and the rule was dropped for 2011 and they went back to the "old" (present) rule.

Is it time for a change back?

Michael Royce.

PS. We still have the "1 inch static ground clearance" rule for Formula Hybrid!

In my opinion, more design freedom is always better. A 1" ride height rule doesn't guarantee the car won't scrape the track anyways, depending on spring rates and aero. So from what I've gathered from talking to various people, nobody has a problem with DQ'ing cars that scrape, as long as you enforce the rule when you say you're going to, and enforce it the same for everyone.

[Z]

As usual, EXCELLENT COVERAGE of everything by FSG. :)

Unfortunately, the digital fairies didn't let me watch Enduro live here (too slow updates/bandwidth...?). :(

But a quick check of results posted so far shows that in Enduro Combustion there were ~44/71 DNFs = 62%!!! (Edit, and 69% DNFs in Electric class!)

Does anyone know if some/many of these were DQs because of the "scraping" rule, or were they all genuine DNFs?

And if all genuine DNFs, then can someone give a brief summary of the failures?

Z

[Z]

Also, big congratulations to GFR (aka "The Team of Many Names")!

For those of you who still doubt that a 50 hp single can do well in these competitions, consider that second placed Stuttgart was 43 points behind GFR, and third placed Graz was 183 points back! Both these Teams have very high horsepower cars (Graz = 90+ hp from their website, not sure about Stuttgart).

Oh..., but just checked GFR's website, and ... they actually claim 51 hp! :)
~o0o~

Julian,

35 point penalty??? That, and better tyres for the Wet-Pad might have made the difference?

Z

[mech5496]

Wetpad did made a difference for sure.. With regards to DNF's, at least for the part I watched, they were almost all DNF's and not DQs. On the top of my head, the only DQ I remember was the one from KIT e-car for dripping coolant.

[JulianH]

Also, big congratulations to GFR (aka "The Team of Many Names")!

For those of you who still doubt that a 50 hp single can do well in these competitions, consider that second placed Stuttgart was 43 points behind GFR, and third placed Graz was 183 points back! Both these Teams have very high horsepower cars (Graz = 90+ hp from their website, not sure about Stuttgart).

Oh..., but just checked GFR's website, and ... they actually claim 51 hp! :)
~o0o~

Julian,

35 point penalty??? That, and better tyres for the Wet-Pad might have made the difference?

Z

Yes, WetPad and the penalty made the difference.
If you saw the Delft car on the WetPad, it's insane. Like there is no water. I guess every half-decent team would win with those tires. Impressive what they managed to design!

The penalties got a lot of teams this year. There is an online-tool for ESF. I actually don't know how it exactly works but they told me, you get like dozens of mails of failed documents (it's not one document but for every(!) electrical part of the car, LV and HV) and they missed deadlines.
It's no excuse whatsoever (just make yourself an Excel list when which part has to be re-uploaded...) but as the list shows, it got a lot of teams. Actually Delft had the same 35points penalty but it got removed, I don't know why...

But at least you can be proud of the Zurich team for their Acceleration time. 3,300 ; 3,352 ; 3,303 ; 3,300 -> That's quite good ;)


Harry, there were a couple of DQs in re-scrutineering: KIT Combustion had a restrictor that was too big, Munich was too loud in noise (probably would have been third overall), Zwickau got DQ as well (something electrical).

As far as I know, there were no scrapping DQs in Endurance (although Rennteam Stuttgart "denounced" GFR on a Facebook post that they would be scrapping a lot, not very sportsmanlike...).

The DQs in AutoX killed the event. Yes, I know it's within the rules. But it made watching AutoX really bad. You did never know if you can cheer for a good time because half of them got DQ'd.
The guys on the track listened veeeery carefully at some cars and did not care about others (talked with another guy).
Additionally you cannot challenge a ruling. Who has proof? Who decides?
And the worst part: Some drivers got told after the first run that they got a DQ and could decide if they go out and change the car or do another run. And some guys got not told! That's outrageous!
I think we need another rule there. It's very very frustrating.
Hopefully they do something about it...

[BeunMan]

Yes, WetPad and the penalty made the difference.
If you saw the Delft car on the WetPad, it's insane. Like there is no water. I guess every half-decent team would win with those tires. Impressive what they managed to design!

The penalties got a lot of teams this year. There is an online-tool for ESF. I actually don't know how it exactly works but they told me, you get like dozens of mails of failed documents (it's not one document but for every(!) electrical part of the car, LV and HV) and they missed deadlines.
It's no excuse whatsoever (just make yourself an Excel list when which part has to be re-uploaded...) but as the list shows, it got a lot of teams. Actually Delft had the same 35points penalty but it got removed, I don't know why...

...

They succesfully appealed, they did al the documents on time so a penalty would be wierd.

[mech5496]

Julian, it made watching the AutoX really frustrating indeed; that's why I am for the "old" ground clearance rule, it was really easy to check, albeit (as already mentioned) depending on the setup, you could definitely scrape...

I am aware of those DQ's, but I believe these were not marked as DNF's, might be wrong though! ;)

[Michael Royce]

The intent of the ground clearance rule is spelled out in the comment in T6.2, namely it is intended to minimize ground effects with sliding skirts and to minimize track damage to pristine surfaces like Ford's Romeo VDF where we ran the Michigan FSAE for 3 years. Picking out cars that are intent on circumventing the ground effects part is relatively easy as it ties in with the design. But calling the scrapping was, and apparently still is, problematical.

The current rule relies on a transient condition and is based on call-ins from the corner workers/marshals which can be very subjective (some might even say "biased".). Do you call-in a front wing end plate or a side pod touching the track briefly or not? Or do you look for it scrapping for 1 or 2 seconds? JT's comment that the "1 inch static ground clearance" rule will not prevent all scrapping, but it did cut it down a great deal on the subjectivity. With the old (current) rule, we scrutineers either got an earful from a certain member of the SAE staff about being too tough on teams (we were not being "customer friendly"), or we were criticized by some teams for not being tough enough! We could not win! That criticism went away with the "1 inch static" rule.

Michael Royce,
FSAE Rules Committee 1995-2009,
Chairman 2000-9.
And other "stuff".

[theTTshark]

Or you could just have no rule about ground clearance or touching. If somebody wants to drag their wings or chassis on the ground, they'll punish themselves enough by messing up their car and when they choke off their underbody flow. I understand why the rule exists when we were at Michigan and the track was freshly repaved before the first NASCAR race there in 2011, but after that the Cup guys are more then willing to drag anything on the ground before or after crashing. At Hockenheim all the open wheel series are touching the ground constantly and besides that all the bumpy sections are in the parking lot section of the courses. Lincoln Air Park definitely doesn't care. I don't know enough about the other events to talk about them. I know it will never happen, but it seems like a rule that could be gotten rid of entirely.

But if a rule has to exist, the 1" ground height clearance is the lesser of evils I think. Whenever a human/multiple humans have a chance to make a judgement call they will screw up at least occasionally if not more often.

[Z]

But at least you can be proud of the Zurich team for their Acceleration time. 3,300 ... -> That's quite good ;)

Julian,

Yes, it is impressive.

Now, where did I see exactly that time of 3.300 seconds for Acceleration before? And why do I have a feeling that Combustion Teams could also do such times ... at least if the students spent more time talking to their friendly Toothless Hillbillies at the local dragstrip? Hmmm....??? ;) :)

Well, for next year's RWD-C-car students, I have found some guidelines on how to match, or even beat, Zurich in Acceleration - ACCELERATION - INTO THE LOW 3s (http://www.fsae.com/forums/showthread.php?11784-2015-FSAE-Rules&p=120498&viewfull=1#post120498), and more discussion on Acceleration Launch V-T Graph (http://www.fsae.com/forums/showthread.php?11784-2015-FSAE-Rules&p=120571&viewfull=1#post120571). Also, here are some thoughts on "Why More R%" (http://www.fsae.com/forums/showthread.php?11906-2014-FSAE-Australasia&p=122428&viewfull=1#post122428) not only gives you faster Acceleration times, but also greatly improves your performance in AutoX and Enduro (and more discussion throughout those threads).

Julian, out of curiosity, would it be possible for you to post a Velocity-Time graph of ETH/AMZ's recent 3.300 second Acceleration runs, so we can compare it with the above V-T graph I drew last year?
~o0o~

Small pedantic point (because I had to look it up).

Scrap - n. 1. small piece of something larger, a fragment. ... ~vb. scrapping ... 6. to discard as useless. [C14: from Old Norse "skrap"; see SCRAPE]
...
Scrape - vb. 1. to move a rough or sharp object across a surface, esp. to smooth or clean. ... ~n. 11. the act of scraping...

So ... I think that the current Rules require the cars to be DQ'd for "scraping", after which the Team might think about "scrapping" them.

Z

(PS. Fully in agreement with TTshark. In fact, put more bumps on the track, and let the well-suspended cars separate themselves from the bad-suspension cars (which either have low ground clearance and get ripped to pieces, or must be set-up with high-clearance/hi-CG and are thus slower...).)

[BeunMan]

Since you are talking about V/T; For those interested, the speed at FSG Acceleration was measured over the last 5 meters.

[Z]

The FSG-TV-Livestream site was the only one where I could find speeds at the end of the Acceleration runs. Assuming those were reasonably accurate, here are some comments on the performances.

Car#..Team.............Speed...E.Time
==========================
E33...ETH-Zurich..112......3.30 - 1st - because fastest (smallest) time.
E13...Munchen.......103......3.56 - 2nd - must have had very good launch because only needed slowish top speed.
E15...Delft..............122......3.58 - 3rd - clearly a poor launch because had highest final speed (of all cars), but slower ET than Munchen.
...
C15...Graz..............106......3.90 - 1st C-car - similar top speed to above, but clearly TOO MUCH WHEELSPIN at startline!
...
C9....Esslingen.......112.......4.21 - ~Mid-field - same top speed as Zurich, but must have spent FOREVER at the startline!!!

Conclusions.
===========
1. The V-T graph I drew a year ago has very similar top speed (top-edge of graph) and ET (right-edge of graph) to Zurich's numbers above, and since "area inside the graph" is also the same (ie. = 75 metres), it follows that Zurich's "rate of acceleration" throughout the run (ie. the slope of left-edge of graph) must also be very similar. So things like the tyre-road-grip, max-power-expended, etc., are also remarkably similar.

2. To match or beat Zurich's Acceleration times the RWD Combustion-cars need MORE R%!!! Fortunately, this will also make them faster in AutoX and Enduro.

Z

[Thijs]

1. The V-T graph I drew a year ago has very similar top speed (top-edge of graph) and ET (right-edge of graph) to Zurich's numbers above, and since "area inside the graph" is also the same (ie. = 75 metres), it follows that Zurich's "rate of acceleration" throughout the run (ie. the slope of left-edge of graph) must also be very similar. So things like the tyre-road-grip, max-power-expended, etc., are also remarkably similar.
Z

We've had discussions about this when you first posted the graph you mentioned. I still think you're off on some of the most important numbers, and I think that an identical end time of 3.3s does not necessarily imply 'remarkably similar' rates of acceleration throughout the run. There's many different speed curves that will lead to identical finishing times over 75m. By saying that your particular curve must be pretty close, you're implying that your assumption of 2.5g off the line is also right (a key assumption in your thesis of how to get to sub 3.0s acceleration runs for RWD cars). And it's not. I'm not saying it's not possible in principle (although I also doubt that), I'm saying that's very likely not how Zurich did it.
It's much more likely they started at below 1.5g, and, thanks to downforce, hit about 1,75g just as they hit their power limit at around 17 or 18m/s.

I think you're also not taking into account that cars are allowed to start 0.3m before the start line. This makes a massive difference (the car crosses the start line already going almost 3m/s). I'm pretty sure it took Zurich about 3.49 seconds to cover the actual first 75 meters (so from where the car was staged to 74.7m into the measured run). That's another reason why I'm pretty sure those two speed graphs will look quite a bit more different than you seem to think.

Thijs

[BeunMan]

So, like the runs already suggested: You need a really good launch control to get sub 3.5 as most cars are first traction and then power limited (up till their max speed, assuming they reached it and for all electrics this is the same).

[Z]

Thijs,

I repost my Launch-V-T graph below to better explain this.

My main point is that Zurich's Acceleration runs must have been much closer to my curve-B (= Team Toothless :)) than to curves C, or C' (= Team Testosterone).

So all the excuses that several generations of students have been making, namely that low 3 second times are impossible without special dragster tyres, specially stickyed-up dragstrips, and super-mega-powerful turbo-engines, are nonsense. (I remember many such "It's impossible!!!" excuses when I insisted that low-3's were feasible back in 2005.)

https://lh5.googleusercontent.com/-hwj2i2rl3-I/U9MEUYJs9HI/AAAAAAAAAQw/mklPsKXMcEM/s800/LaunchVTGraph.jpg

Based on the 0.3 metre jump start you mention (= "infinite" acceleration at T=0), I would say that Zurich's V-T curve starts off above the left-side of my curve-B, and probably stays above it for the first ~half-second (ie. the first 5 to 10 metres). Zurich's curve will then track reasonably close to curve-B up to about T = 1.5 seconds, then dip below it to T = 2.5 seconds, then above it again for its slightly faster top speed.

Put simply, Zurich's curve will be a rounded-off version (plus DAQ noise) of my curve, which was drawn as a number of straightline segments to simplify things. Importantly, any "area" that is under Zurich's curve but is "outside" my curve-B MUST be matched by an equal area being lost inside my curve-B. This is because the total area under each curve must equal the total run length of 75 metres. (This assumes FSG's Acceleration track was truly 75 metres long. There have been athletic events chasing World Records that have, ahem..., favourably adjusted their track lengths... But I doubt FSG would do that? :)).

Anyway, most important message is that any good RWD-car, E or C, should be able to do similar low 3 second times. Or better. No magical super-sticky dragster tyres are needed.

So from now on, any Acceleration time of 4 seconds or more = LOSER!

NO MORE EXCUSES!!! :)

Z

[Thijs]

Z,

I still feel you're brushing over the differences in the graph I posted below a little easily.
Of course this is an estimate, I'm not part of the Zürich team, but I've been with the Delft team long enough to know how electric 4WD 80kW cars move about.

We are of course in agreement that low 3's are possible, so yay :) I'm still not sure how you would do that with a combustion car though. Zürich showed what you can do on this surface with almost perfect controls (just the right tiny amount of wheelspin).
Delft showed that even with a car with slightly better specs (bit less weight, bit higher top speed), you can lose 3 tenths if your controllers don't work well (their wheels spun quite a bit more).
How would a C-car ever match the smooth torque delivery of individually controlled electric motors?
With higher R%, I'm sure they can get a bit closer to 1.5g at the start, rather than 1g where most of them are now, but try to accelerate at 2.5g, and they'll still end up like every car in this pretty awesome video (that unfortunately doesn't show the Zurich getaway...):
https://www.youtube.com/watch?v=fVrC565ynzQ

Anyway, let's see if anyone at FSA can go below 3.3!

Thijs

[JulianH]

I asked this year's team about the data. Apparently it is on a USB-Drive somewhere ;)
As soon as I get it, I will post it here to hopefully end the discussion about curves :)

Cheers

[Thijs]

hmmm curves

would be nice Julian

[BeunMan]

Question from someone not knowing a lot about 'mechanics': What are the power losses in friction, heat buildup and wheel slip and what is the actual transfer (%?) to the ground (resulting in forward momentum)?

Also, air resistance and tire friction are significant at higher speeds, do they matter in any way (even without wings) to the end result?

[tromoly]

Thinking out loud, others elsewhere in the forum have said that an acceptable Mu for simple tire calcs is about 1.5, if that's the case then by using F = Mu * W and F = m * a (with a couple g_c thrown in for unit conversion) would mean that even with 100% of vehicle weight on the driving tires the maximum acceleration would be 1.5G, neglecting any additional aero download onto the tires of course.

Side note, about this time last year an acceleration discussion started in an event thread and there was talk of spinning it off to its own thread but never happened, anyone else think a dedicated acceleration thread should be created?

[JulianH]

Hey guys,

I just got the data from Zurich. It's their fourth Acceleration Run at FSG.

They crossed the starting line roughly 0.22s after the real start (with a speed of ~11kph) and crossed the finishline after 3.52s with a topspeed of 111kph (the FSG speed trap seems to be quite accurate!).

Have fun discussing it ;)

Cheers
Julian

[Thijs]

Thanks Julian,

I had expected the car to pick up the acceleration rate a bit, making use of wings, as it approached its power limit. The fact that the car still got to 3.3s without doing that probably means I overestimated drivetrain losses.
It still looks very close to my estimate though. I predicted crossing the starting line at 'almost 3m/s', or 10.8km/h (it's apparently 10.66km/h in real life) and crossing the finish line at 3.49s.
The acceleration rate looks almost constant up to about 66km/h and averages 1.42g, which is what my graph started out at, and which supports my main point that 2.5g off the line is not how Zürich got to 3.3s.

Either way: impressive stuff from the guys from Switzerland!

Thijs

[Z]

Julian,

Thanks for your above post with data. Haven't had time to look at it closely now, but I guess it confirms what I have written below. Will comment again later.

The following is a rant I wrote earlier today, just before my "credit expired" so I couldn't post it, and I had to go and do other stuff...
~o0o~

Thijs,

Firstly, you have many, many years of hard grumpiness training ahead of you before you can rightly call yourself a "Grumpy Old Fart". I suggest running naked through the blackberry bushes every morning for the next, ooh..., several decades, just to properly develop your grumpiness skills... :)

Back to Acceleration Event.


... By saying that your particular curve must be pretty close [to Zurich's], you're implying that your assumption of 2.5g off the line is also right (a key assumption in your thesis of how to get to sub 3.0s acceleration runs for RWD cars). And it's not. I'm not saying it's not possible in principle (although I also doubt that), ...

Actually, my key assumptions are given in the boxes at the right of my "Launch V-T" sketch (above), together with the assumption that the distance covered is 75 metres, indicated by the equal 75 m area under all curves in the sketch. The initial 2.5 G acceleration is somewhat incidental to the story (more below).

More importantly, my key AIM of that sketch was to show the usefulness of Velocity-Time curves for understanding these things.

The most important point here is that the AREA under the curve MUST ALWAYS be the constant 75 metres. On the other hand, the shape of the curve, and hence the car's Velocity at any given Time, can vary quite a bit, but ONLY as long as the "area" constraint is met. And momentary Accelerations (= slope of curve) are the most fickle, and can vary hugely without having a great impact on the final result. To see this, imagine a lot of "noise" on the curve, which can give huge variations in Acceleration, but only smaller variations in Velocity, and perhaps NO variation in Area under the curve (= Distance).

This usefulness of V-T curves, and the perhaps misleading nature of Acceleration-Time curves, can be seen in the A-T curve you posted (and thanks for that). To get useful information out of the A-T curve you must integrate it once to get Velocity, then integrate again for the Distance covered. I can see that your two A-T curves, red and blue, have the same area under them, so they suggest (misleadingly *) the same final Velocity (= 30 m/s). But trying to "see" the Distance covered at any time with an unaided eye is much harder, perhaps impossible.

(*) Worst problem is that a "flying start" appears in a A-T curve as an infinitely high Acceleration at the left of the curve, that lasts for dT = zero seconds. But that "zero-width spike" has FINITE AREA under it! See below for an example of how the integral of Infinite-Acceleration x Zero-Time = Finite-Velocity. Or look-up "Dirac Delta function". There are many examples like this in Mechanics, so beware.

Bottom line here, A-T curves can bounce around all over the place, but these large variations can make very little actual difference to the car's Velocity or Distance on track.

As for the "2.5 G off the line" (or more!), well, that is not my opinion, it is a much repeated historical fact. Please re-read what I wrote about launch techniques (specifically about pro-lift, and unsteady aero-downforce...), which was the most important point of my previous posts... (more on this below).


... I think you're also not taking into account that cars are allowed to start 0.3m before the start line. This makes a massive difference (the car crosses the start line already going almost 3m/s)...

Yes, it does make a big difference. It makes it much easier to get a low time!

If my sketch's curve-B had that 0.3 metre "flying start", then it would need ONLY ~1.5 G initial acceleration up until it was 60 kW power limited (ie. at T = ~1+ sec), and yet its final ET would be LESS than 3.3 seconds. This because its initial "acceleration" at the start of the timed section would be "infinite", but only for zero dT (ie. at T = 0 the curve rises vertically to an initial velocity of V = 3 m/s, after which it slopes up-to-right at a much more gentle 15 m/s per second).
~o0o~


... I'm still not sure how you would do [low-3s] with a combustion car though...
Zürich showed ... perfect controls (just the right tiny amount of wheelspin).
Delft showed ... you can lose 3 tenths if your controllers don't work well (their wheels spun quite a bit more).
How would a C-car ever match the smooth torque delivery of individually controlled electric motors?
... they'll still end up like every car in this pretty awesome video ...
https://www.youtube.com/watch?v=fVrC565ynzQ

Tristan also suggests that "You need a really good launch control to get sub 3.5...

And Tromoly also suggests that "... an acceptable Mu for simple tire calcs is about 1.5, if that's the case then ... the maximum [startline] acceleration would be 1.5G... "

Now, Thijs, thank you for that YouTube link, ... because it shows how PATHETICALLY PISS-POOR ALL FS-Teams' cars are! (See, that's how you do Grumpy! :))

All your cars look like the V8-utes (ie. with ~30%R) that young Australian country-boys have fun with on a muddy paddock after the local B&S Ball. (Cultural note: B&S Balls are a rite-of-passage for rural Australian youth, with the B&S standing for Bachelor & Spinster, ... or maybe Beer & Sex, followed by circle-work with the utes...)

All your FS-cars most obviously have ~NO GRIP, because they show ~NO FORWARD PROGRESS!!! Geez, one car even shows large amounts of rear-wheel floppy toe-wobble as its feeble Fx forces kick in (see at 1:08)! Mutter, grumble... :(

So, ... get yourselves down to the local dragstrip and learn how to do this properly. The Toothless Hillbillies there are really very friendly. and they will help you. They will tell you to STOP WASTING YOUR TIME talking about "controlling" what you currently DO NOT HAVE.

FIRST OF ALL YOU NEED THE "MECHANICAL GRUNT" to get your cars moving quickly, and only much later will you have to worry about "controlling" it.

So, first make sure that ALL OF THE CAR'S Fz IS ON THE DRIVING WHEELS (ie. NOT your current "dynamic-R%" = ~60%!).

It is easy to see when you have this, because the front of your car MUST JUMP UP OFF THE GROUND when "coming out of the hole".

Your rear-tyres' sidewalls MUST wrinkle as the car's rearward-weight-transfer, plus the PRO-LIFT, plus the unsteady-aero, pushes the driven rear-wheels DOWN INTO THE GROUND.

In short, your cars should LEAP across the start-line, like a startled antelope...

And during the extensive Launch-testing you should be doing, you should have numerous drivetrain, suspension, etc., FAILURES due to the awesome forces involved.

And then, after you have strengthened all those weaknesses, maybe more than ~35% of you can also finish Enduro?


Anyway, let's see if anyone at FSA can go below 3.3!

Yes!!! Oh-so easy, and FUN! :)

Z

[JulianH]

Thijs, since we got a 4WD, the wings are always in minimum drag position and do not produce a massive amount of downforce.
I saw that Delft started the run with a closed DRS and opened it up after roughly one second. We tried that last year and the effect was not really there. (But you risk that your DRS is not working correctly ;)).

Back in 2012 with the 2WD car, we drove with a closed rear wing which gave us the mentioned effect. Since you now need the grip on the front axle, a closed rear wing hurts more than it helps.

[Thijs]

Z,

I'm not going to get to everything in your previous post, we've already covered a lot of it in previous posts.
I will say that when I said 'I also doubt that [that is possible]', I meant the 2.5g launch, not necessarily the super fast acceleration times. Given the right surface, who knows, although those last 3 tenths will be hard won (and my bet is still on 4WD electrics).
I'll also say, if it wasn't obvious from context, that the blue A-T curve I posted corresponds to a run of exactly 3.30s. (the red one that's taken from your V-T diagram actually takes a car from 0.3m to 75.3m in 3.15s, so it's not completely apples to apples, the final speeds were very close though, 31 vs 30m/s, taken from Zürichs run and your graph respectively).
I do think that A-T diagrams are interesting, as they say a lot more about what forces act on the car at any given time, and you can differentiate much clearer between the theoretical runs you and I proposed.
V-T diagrams tend to look pretty similar pretty quickly.

We're in agreement on most of the mechanics, and the usefulness of various tools.
However, one of the most effective Toothless Hillbilly tricks (dramatically increasing mu by putting glue on the track, https://www.youtube.com/watch?v=1VMb0fmalqo, who needs Fz if you have that) is unfortunately not transferable to FSAE.
I think that means we won't see 2.5g launches, no matter how much dynamic-R% you manage. Electric 4WD's already put 100% of their Fz on the driven wheels. Transferring a larger portion of that to the rear axle shouldn't all of a sudden get you from 1.5g to 2.5g, especially if you take tire load sensitivity into account. I don't we're going to agree on how much of that remaining 1g can be bridged by the dynamic effects of pitch inertia on cars lifting their front wheels.

I'll be on the lookout for blackberry bushes, thanks for your encouraging words on that topic.

Thijs


edit: I just found these strange Brits:
http://www.fwddragseries.co.uk/index.php
http://www.fwddragtimes.co.uk/
https://www.youtube.com/watch?v=kFTZVDbT2hU&feature=youtu.be
They have lots of fun doing drag runs in their 1100hp FWD cars, averaging 1,7+g over the first 20 meters, suggesting to me that raw mechanical grip has as much to do with why dragsters accelerate faster than FSAE cars, as does how you load your driven axle.

[Kevin Hayward]

Thijs,

It is entirely possible to have a vertical force on the rear tyre that substantially exceeds 100% of the vehicles weight without aerodynamics. Unfortunately if we model a vehicle as a point mass, and exclude certain suspension setups then you are incorrectly lead to believing that a vehicles acceleration must be no greater than the mu of the tyre times gravity.

This is not true. Part of the peril of not appropriately searching the solution space.

The only real argument against Z is the likelihood that this transient state can be maintained for a useful amount of time.

Also the glue on the track at a drag car allows something above 4g. I would expect that drag cars on our surfaces (retuned) could pull 2.5g without the glue. I would also note that our combustion cars have a very underutilised system that is crucial for drag car tuning. A system that once well understood could make sure power delivery is beautifully smooth and no worse than than EV traction control.

Kev

[Thijs]

Kevin,

I understand the physics, and Z has talked about this at some length as well. The magnitude of the effect you talk about is however itself still also dependent on mu. On an ice floor, there will hardly be any load transfer, let alone lifting front wheels, and you won't really get to use pitch inertia to your advantage (or only for a very short time, if you put the CoG very high/just in front of the rear axle). It's much easier to make use of on a drag strip that has ridiculous mu to begin with.
But yes, my main criticism is that with these tiny, short-wheelbased cars, I doubt that this state can be maintained for a long enough period of time, like you yourself indicate might be an issue.

I'm sure those massive, soft (and pre-burned-out!) drag tires are good for something, so I too have no doubt that an actual drag racer could come a lot closer to 2.5g on an FSAE track than an FSAE car.

Thijs

[mech5496]

Thijs,

It is entirely possible to have a vertical force on the rear tyre that substantially exceeds 100% of the vehicles weight without aerodynamics. Unfortunately if we model a vehicle as a point mass, and exclude certain suspension setups then you are incorrectly lead to believing that a vehicles acceleration must be no greater than the mu of the tyre times gravity.

This is not true. Part of the peril of not appropriately searching the solution space.

The only real argument against Z is the likelihood that this transient state can be maintained for a useful amount of time.

Also the glue on the track at a drag car allows something above 4g. I would expect that drag cars on our surfaces (retuned) could pull 2.5g without the glue. I would also note that our combustion cars have a very underutilised system that is crucial for drag car tuning. A system that once well understood could make sure power delivery is beautifully smooth and no worse than than EV traction control.

Kev

+1 on your notes about getting more than 100% weight on the rear tires and the simulations... Regarding your last sentence, are we to expect something really unique (for FSAE) regarding, ehm "clutching devices"? :)

[BeunMan]

Even I am now convinced you can go faster than 3.30 (maybe place the light beam 5 cm short ;), wasn't the case at FSG though. It had been remeasured at days start).


So ... FSA ... Zurich ... please decide this once and for all?

[RenM]

Now, Thijs, thank you for that YouTube link, ... because it shows how PATHETICALLY PISS-POOR ALL FS-Teams' cars are! (See, that's how you do Grumpy! :))

Z

Don't be ridiculous. Those starts are chosen for the Video, because they look more spectacular then a perfect start and this video does by no mean show an average of the FS starter field.




So, first make sure that ALL OF THE CAR'S Fz IS ON THE DRIVING WHEELS
Z

Yeah nice idea, but for a rwd car not what you want if the car has to run other dynamic events in similar spec.

[tromoly]

It is entirely possible to have a vertical force on the rear tyre that substantially exceeds 100% of the vehicles weight without aerodynamics. Unfortunately if we model a vehicle as a point mass, and exclude certain suspension setups then you are incorrectly lead to believing that a vehicles acceleration must be no greater than the mu of the tyre times gravity.

Forgive my silly question, I'm having a hard time wrapping my head around how anti-squat works on a car with a-arms, can engine torque in an a-arm car actually compress the suspension (neglecting weight transfer, of course)?

On a solid axle 3-, 4- or 5-link car the links can be positioned so when the pinion tries to climb the ring gear and the axle housing tries to rotate, the links cause the tires to be shoved into the ground, increasing vertical load. The part about an a-arm car that's tripping me up is the engine torque trying to rotate the differential is captured by the chassis, and the resulting torque at the wheels is delivered in a way that it can neither compress the suspension nor force the tires into the track surface.

Any thoughts would be helpful, this could be an interesting discussion.

[Z]

[Ominous rumbling...] ... Where to begin this rant... Stupid students? Stupid Officials (and Grumpy Old Farts)? STUPID MODERN WORLD!!!?

Hmmm... let's start with...
~o0o~

Julian,

http://www.fsae.com/forums/attachment.php?attachmentid=708&d=1439025242

Thank you for your V-T graph (above) of Zurich's recent 3.300 second FSG-Acceleration run.

I printed out your graph and started to apply some old-school analysis to it. This started with me making the following ASSUMPTIONS.
1. The accuracy of the data is of similar order to the thickness of the lines used to depict the data.
2. The horizontal axis (Time [s]) and vertical axis (Speed [kph]) both vary "linearly".
3. A Swiss "kilometre" is one thousand metres long.
4. A Swiss "hour" has 3,600 seconds in it.
5. Zurich's measured Acceleration run was from the Starting Line at T = 0.220 seconds to a time 3.300 seconds later, namely T = 3.520 s, and presumably in a reasonably straight line.

From above, I deduced that a Speed on your graph of 36 kph should also equal 10 metres/second, and so on. I also deduced that the "area under" the Speed curve, between a vertical line at the Start Time = 0.220 s and another vertical line at the presumed Finish Time = 3.520 s (and, of course, above the horizontal axis), should equal the Distance travelled during the Acceleration run, because Distance = Speed x Time.

So I graphically measured that area, and found it to be ... [dramatic drum roll] ...
...
LESS THAN 72 METRES!!!

(In fact, I have a reasonably accurate 71.6 metres.)

I decided to make another cup of coffee and move on...
~o0o~

Thijs,

Very briefly, the ~1.7 G accelerations of Front-WD drag cars, together with the well known 4+ G accelerations of Rear-WD drag cars on the same sticky tracks, CONFIRMS everything I have been saying. But no point me presenting the calculations here (does anyone read them?), although you might try doing them...

Also, "pitch inertia" is NOT IMPORTANT for good launches (as I explained last year). When I say that RWD-cars should lift their noses off the ground, that is just to indicate that all weight is indeed transferred to the rear-wheels. For really good launches, the tail of RWD-cars should also lift upwards, preferably even higher than the nose!
~o0o~

RenM,

I am quite sure that video was made to show just how "awesomely fast" all the FS cars are. And that very same thinking is why 30 year's worth of students have been designing and building their cars to do exactly that same thing. Namely, spend ages spinning their rear-wheels, ... while going NOWHERE fast. (And did you see the wheel-wobble at 1:08!!!?)


Yeah nice idea, but for a rwd car not what you want if the car has to run other dynamic events in similar spec.

As I have explained endlessly now, an FS car only needs about 60%R (or maybe 66%R if it has extremely low CG), PLUS some simple set-up adjustments, to do really fast Acceleration times. The modern-era Bowlby DeltaWing runs ~72%R as standard, and is as fast as most other contemporary racecars that have twice the horsepower. Many ~1970-80s F1, F5000, etc., cars ran ~70%R, firstly because that was allowed back then, and secondly because it made them MUCH FASTER than the ~60%R cars! (Note that most modern Formulae very tightly constrain tyre sizes, thus preventing high R% and good acceleration, because that keeps the top speeds down.)

You kids should stop making excuses for being so slow...
~o0o~

Tromoly,

Again, I explained this all in the similar discussion last year, and many other places. Look up "longitudinal n-lines" and "jacking".

Specifically, raise the wishbone-to-chassis front attachment points, and/or lower the rear ones, so that in side-view the wishbones pivot about an axis (on chassis) that slopes up-to-front. A lot! Start the car with very low ride-height, and then during launch let the wheels go a long way into droop (ie. so car lifts a lot). (Julian, you might advise AMZ to do this on all four wheels, but especially so on the rears.)

It is also well worth fitting a large area undertray, preferably with front-splitter and side-skirts mounted to the uprights so they are always close to the ground, but with the majority of the undertray fixed to chassis so it rises up with it. Any sudden upward movement of the undertray will cause a large "suction" below it, for large "unsteady" aero-downforce. (It is the "dPhi/dt" term, which most of your Colourful Flow Diagrams DO NOT calculate!)
~o0o~

I wonder if any young person will EVER do anything interesting... :(

Z

[mech5496]

Forgive my silly question, I'm having a hard time wrapping my head around how anti-squat works on a car with a-arms, can engine torque in an a-arm car actually compress the suspension (neglecting weight transfer, of course)?

On a solid axle 3-, 4- or 5-link car the links can be positioned so when the pinion tries to climb the ring gear and the axle housing tries to rotate, the links cause the tires to be shoved into the ground, increasing vertical load. The part about an a-arm car that's tripping me up is the engine torque trying to rotate the differential is captured by the chassis, and the resulting torque at the wheels is delivered in a way that it can neither compress the suspension nor force the tires into the track surface.

Any thoughts would be helpful, this could be an interesting discussion.

Z gave a deeper analysis of this in the past, I'll be brief...think how anti-dive works and now think this backwards on the rear of the car. It is all about reaction of tire force and n-lines.



It is also well worth fitting a large area undertray, preferably with front-splitter and side-skirts mounted to the uprights so they are always close to the ground, but with the majority of the undertray fixed to chassis so it rises up with it. Any sudden upward movement of the undertray will cause a large "suction" below it, for large "unsteady" aero-downforce. (It is the "dPhi/dt" term, which most of your Colourful Flow Diagrams DO NOT calculate!)
Z

I wonder how this would work under braking or in any other dynamic event except acceleration...

[Stef de Jong]

After an absence of some years I went to this forum to read up on some FSG comments.

To my uttermost delight I find here exactly the same conversation as there has been for many years with the same Z trolling about, and the same people, yes that's you Thijs & Julian, wasting their time to argue with him :). I wonder where Bemo is at, normally he also would be contributing...

I also wonder where Z would be in life if he would dedicate his energy on actually doing this instead of talking about it; there is a guiness book of world records you know... With the (E-)acceleration times getting increasingly difficult to beat (or so we think), surely your expertise in this field would be highly valued. I cannot imagine how busy you must be in enlightning racing teams all over the world, your phone must be red-hot.

I think the only thing we really get out of this discussion in the longterm will be the actual proof that the Godwin principle does not apply for ALL internet discussions ;)

---
Stef de Jong
Delft

[Thijs]

Z,

You're right about the graph. Here's an overlay of the 3.30s V-T diagram that goes with the A-T diagram I posted earlier, and the graph Julian posted.

http://www.fsae.com/forums/attachment.php?attachmentid=711&d=1439197214

Not sure what to make of that, maybe it was simply a different run than one of those fast ones at FSG, maybe one of the relevant sensors is off (although I doubt it, because the end speed looks about right).
I do know that FSG takes the length of their acceleration track (and how cars are staged) very seriously.


I'm about done with this back and forth now. Like last time, we just end up with a bunch of people who are frustrated because they feel the other dismisses their point of view without really understanding it.

See you next year ;)

Thijs

[RenM]

I am quite sure that video was made to show just how "awesomely fast" all the FS cars are. And that very same thinking is why 30 year's worth of students have been designing and building their cars to do exactly that same thing. Namely, spend ages spinning their rear-wheels, ... while going NOWHERE fast. (And did you see the wheel-wobble at 1:08!!!?)
Z

Well, i know the guy who does the videos rather well ;) and the videos are only chosen for being spectacular and not fast. Mild to no wheel spin is faster but very boring to watch. Thats also the reason why there are almost no electric cars in the video, because they have working traction control. Making a perfect start with a combustion car with the right amount of wheel spin is way more difficult to achieve then just say oh yeah i need that amount of wheel spin.
Knowing the theory and realizing it are two different things.

[mech5496]

In that case, tell the guy that did the videos that they are great! :P Seriously now, I have been showing the teaser video all over work today, fantastic work!

[Z]

Harry,

My undertray would have rear flaps (and small side vortex tunnels) that would give large downforce whenever the car is moving. So plenty of DF when braking at the end of straights, and through the corners.

But the problem with Acceleration event is that you want the maximum grip at the very start, and unfortunately that is when there is no "dynamic" (ie. already moving) aero flow. So the solution is to use the very large aero forces that are available from "start-up" flows.

For the aero students, the "Phi" I mentioned before is "Velocity Potential" and the dPhi/dt term can be found under "unsteady Bernoulli equation", or similar...
~o0o~

Stef,

As I keep pointing out at great length, every Toothless Hillbilly, in every corner of the known Universe, already knows how to do this Acceleration thing. And they have known it, and been doing it, for at least half a century. So they hardly need my help.

But the really sad thing about the failed education system is that it is making the students so stupid that they are incapable of recognising their own stupidity. The "slowness" of FSAE cars was blindingly obvious to me the first time I saw them run, a dozen odd years ago. Interestingly, I did NOT see the Acceleration event that year, but the cars' complete lack of forward thrust was patently obvious in AutoX and Enduro. Car after car just sat there at the exits of the slower corners, their rear-wheels furiously spinning ... and going nowhere fast. Nothing has changed since...

Of course, the last 30 years worth of Design Judges are also complicit in this stupidity. But the big problem is that, despite all the Interweb++ resources available, the, ahem, "Engineering" students make NO attempt to analyse this problem theoretically. And worse yet, they are so lazy-stupid that they do not even bother looking at the "prior art". Namely, seeing what the THs do now, or what previous generations of unrestricted Formula cars did (ie. before tight constraints were put on tyre sizes and R%).

Yep, a Gold-Star every day since kindergarten means the students now think that whatever solution they come up with, no matter how slow, = "I am a genius!"

And you, Stef, are supporting them!
~o0o~

Thijs,

No graph visible in your post (as I write this)???

Further to my old-school analysis of Julian's graph, when I printed it out there was about 30 mm vertical for 10 m/s. The blue V-T curve itself was well under 1 mm thick (ie. implying tolerence <+/- ~0.1 m/s). So putting some straight pen-lines about 1 mm ABOVE the blue curve adds about 0.3 m/s to all velocities. Over the 3.3 second run that adds about 1 metre to the Distance.

Bottom line, the area under this easily measured pen-line (which add ~1 metre distance to the blue curve) is well under 73 metres.

Julian???
~o0o~

RenM,


Mild to no wheel spin is faster but very boring to watch....
Making a perfect start with a combustion car with the right amount of wheel spin is way more difficult to achieve ...

With almost all current RWD FS-cars having static R% of 45-55%, you have...
furiously fast rear-wheelspin = pathetically slow acceleration,
mild, or "perfect" amount of rear-wheelspin = pathetically slow acceleration,
small rear-wheelspin = pathetically slow acceleration...

The magnitude difference of the above three "pathetically slow"s is of order +/- 10 %. Maybe +/-20% at most. Check the numbers on the TTC Forum.

The magnitude increase in acceleration possible by going from the current wrong R% (and the wrong kinematics+) to a good R% and set-up is of order 100%! Do the calcs!
~o0o~

In summary, for now...

As is almost always the case here (why!?), it is interesting that the students' first approach to solving this problem of "pathetically slow" is to look for small-picture, complicated, fiddly little solutions, such as "Launch/Traction Control". Not just RenM above, but several other posts on previous pages went straight to the "We need to control it better" option. I am surprised that no one has yet cried "Oh, but we really need DBW/ETC...".

The point is, it is POINTLESS TRYING TO CONTROL WHAT YOU DO NOT HAVE!!!

All RWD FS-cars (E or C) need MORE VERTICAL LOAD on their rear-tyres. That means MORE R%!

(And I gave the numbers for this, specifically the typical FS-car's Mass, Power, and Velocity, in my earlier link to "Why More R%". I ask anyone who disagrees with those numbers to please either post their theoretical analysis, or point to some empirical evidence that contradicts my numbers.)

A good big-picture approach to FS-car design should start with the big-picture numbers. Things like overall size, including length, width, wheelbase, total mass, etc. Very soon after that you should decide on a good R%, because it is a VERY IMPORTANT NUMBER.

Your current R%s are ALL WRONG, and you have only got them by BLINDLY COPYING previous year's cars.

Please start doing some Engineering...

Z

[tromoly]

Z and Harry,

My apologies, I misused "anti-squat" in my previous post, the words I lacked should have said I'm having trouble understanding how torque-induced jacking forces are possible on an a-arm car. With the differential housing mounted to the chassis it can't rotate in the way a solid axle can, and the only other place where the halfshafts ride is in the uprights, but the torque really just passes through to the hubs/wheels and doesn't create a moment at the upright.

A mental test I've been thinking of is if the wheels of an a-arm car were locked so they couldn't move (like an external fixture, not like locking the brake calipers) and a torque was applied to the differential in a perfect moment (i.e. not a "force applied to a distance" like a torque wrench), would the chassis rise, fall, or stay the same?

Hopefully that's clear as mud, rewrote this four times over the last hour trying to word it in a way that makes sense.

[Thijs]

Thijs,

No graph visible in your post (as I write this)???

I tried to properly embed the image, but apparently I'm now the only person that can see it (it's still there on my screen..)

Hopefully this works:

[Mitchell]

Your current R%s are ALL WRONG, and you have only got them by BLINDLY COPYING previous year's cars.

Please start doing some Engineering...

Z

It's worth mentioning, getting anything over 50% with most of the engines known to fsae is not a particularly easy task. To do it with a motorbike engine it needs a stacked gearbox and very efficient (especially in the longitudinal axis) driveline packaging. I can see why many teams stick to what they know wrt engines. This puts them in a place where instead of choosing a R% at a concept level they just find it easier to try and justifying what they have ended up with.

Z, you will get some enjoyment out of our accel time this year.

Accel times in general are pretty disappointing across the IC cars. Our 2012 car weighed in at 270kg, ~60% front (yes, front) weight and only had 65hp. Managed a 3rd place. There were many cars at that years comp that should have made us look like we were standing still.

[Z]

Thijs,

Thanks, graph is now visible. It is as I thought -> slightly under-area...

And the Swiss used to have such a reputation for precision!? :)
~o0o~

Mitchell,

I am looking forward to seeing your car this December. All round I think it is a good concept. Simple, straightforward, and built early. I hope you are (or will soon be) getting lots of testing in.

Worth noting that more R% = much bigger forward acceleration FORCES = much greater driveline loads (mainly of "shock" type) = need for generally beefier components back there. Some "springy" components can help absorb the shock loads, such as rubber-doughnut CVs, small diameter, solid driveshafts (rather than, say, large diameter, hollow carbon tubes), chain-drive (possibly with "cush-drive" sprocket) rather than fully gear-drive, etc.

Z

[Dylan Edmiston]

The point is, it is POINTLESS TRYING TO CONTROL WHAT YOU DO NOT HAVE!!!
And what do FSAE combustion cars lack which makes it difficult to control?

It should be very easy to understand why so many teams spin their rear wheels. Is it the best thing to do? No, but it is simple and effective I've got our car (UF) to ~3.9s and there was definitely more to be gained on a powertrain standpoint due to a design error with the new intake and lack of time to do proper ignition tuning. I'd imagine with fixing the issues we had and enough time tuning the setup and LC the car could achieve a ~3.7-3.8. And that would still be spinning the tires a lot through 1st gear.

So I am in favor of spinning the wheels a lot because it is easy to control (but what are we controlling that we don't have much of!?!??!) and simple to adjust. I think there is a better option, but it is more complicated.

This discussion would be better suited for an accel specific thread and I'd gladly get involved in the discussion (but I have more important things to take care of at the moment before I spend too much time talking about this).

[P^squared]

And what do FSAE combustion cars lack which makes it difficult to control?

Forward Acceleration capacity at the rear tyres.
The launches won't get any quicker no matter how much BHP the engine produces.

[Dylan Edmiston]

Forward Acceleration capacity at the rear tyres.
The launches won't get any quicker no matter how much BHP the engine produces.
This will be more apparent with high revving engines, but think about the torque curve and why it may be a good idea to spin the wheels so much (for a simple RPM limiting LC system).

[MCoach]

I found the Z "MORE REAR %!!!!" car.

https://youtu.be/DWhilacxpvg


It is a clear front runner off the line.

[JulianH]

Thijs, Z, et al.,

I asked again. This run was in fact the "real" run at FSG.

One thing that could be "unprecise":
The 30cm mark could be a bit more to the right and therefore a larger area under the curve (if it's not from 0,22s to 3,52s but rather from 0,28s to 3,58s or something).
The Sensor is not that accurate at really low speeds.

I would not think that FSG runs Accels that are too short ;)