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The Jr. Dragster tires are meant to be used burn-out free because they are attached to Briggs and Stratton engines that have trouble doing a burn-out in the first place and they come in a 8.5" wide model. I don't think they would have a problem finishing endurance, honestly.
The 8.5" wides are 8" wheels if anyone decides they need to go even smaller.
Alex and I have had serious conversations about Jr. Dragster tires but never had the funds to buy a set to test.
I have never really prioritized the acceleration event – rather I always assumed that one point earned in acceleration was worth half of two points earned in Cost. Or maybe that one point in acceleration was worth ten times as much as a tenth of a point in skid pad. Once I had satisfied myself that one point was in fact equal to a point, and that our overall score would not be adjusted because acceleration points have greater awesomeness than presentation points, I just put them all together into an overall event sim to see what concept worked out best over the whole event.
Some quick observations having skimmed through the above fairly quickly:
The reward for the Accel Event is in points. Points then sum to an overall score, which determines the overall event winner. The times above are interesting – but I didn’t notice anyone taking the next step to convert them to points. It is then you begin to see whether the changes required to bring about these times are feasible.
I would love to see a 300hp FSAE car. I would love to see how fast it was along straights. How much faster it would be around corners. How fast it would be under braking. How cheap it would be to run. How cheap it would be to build. How little fuel it would use. I would love to meet the powertrain leader and the traction control programmer. I would love to give the two of them a teacup, and call the teacup “grip limit”, and fill it to within 5mm of a line drawn just below the rim. At the sound of an academic wringing his hands and quietly sobbing the word “sub-optimal” I’d set them the challenge of filling the cup to the line using nothing but:
a metropolitan firetruck driven by banjo wielding bogans wearing Chev v8 t-shirts, and
a small bailing bucket with a traction control brochure in it.
I’d offer the two of them $50 to finish filling the cup to the line, and in plain view but without telling them I’d debit their credit card $25 for every litre of water that was wasted, and every minute spent on the task. Upon completion of the task, I’d get them to write a cost benefit analysis on cost benefit analyses until someone cried the word “futility”.
It is a constant amusement to me to see the way that the first reaction to Z’s input is one of antagonism - more often than not to identify some detail that is wrong, or difficult, or uncomfortable, or unfashionable, or just plain different – ridicule it – and then dismiss it. It is almost a sport. Z pokes his head up – and the masses quickly rally to shoot him down. Irrespective of his message.
Quick lads, better shut him up. How can we all agree on what it takes to be novel and creative while this guy keeps throwing up different ideas…
Now I do not agree with everything he says. But I enjoy hearing it. He challenges me. I learn from the challenge. I look for aspects that I might refute, and I look for gems that might help me.
Z and I chatted about acceleration event at Oz comp last year. He mentioned the concept of the 100% rear axle load acceleration vehicle. That was enough for me. I took the idea home. I wrote a simulation. I found that raising a c of g 30cm gave the same gain as 15 extra kW for the vehicle spec I analysed. I started thinking of ways to design a device that could jack up 30cm through reversible brackets, etc. I didn’t think of FSAE car, I thought of “self propelled jacking seat”. I had an original thought. I had fun.
It seems that others prefer to pick the eyes out of z’s words, in order to dismiss them and shield themself from a different way of thinking. I personally see that as exerting yourself in order to stand still. Seems a bit pointless really. Probably get you a good middle management job in Australian manufacturing, though…
Our society only celebrates critical analysis of what is wrong. Creativity often comes from recognizing and toying with what is good. The former is confining and narrows down the solution space. The latter is generative and expands it.
Z is the only guy here who takes the time to draw diagrams. Bloody good ones. Do any of his detractors bother to expend as much effort?
Should we dismiss his ideas just because he is not “one of us”? Does dismissing the different make us more creative thinkers?
Z is not here to teach detail. When he screams BROWN GO KART, he couldn’t give a ship about BROWN. Or GO. Or KART. The message is THINK OUTSIDE THE SQUARE. LOOK FOR INSPIRATION ANYWHERE. BE ORIGINAL. DON’T FOLLOW THE CROWD. The response? Duh….why brown????
Z is the guy here to stand up and make a call on the emporer’s new clothes. If you want to reject all he says without looking into his intent, then you are the one at the risk of smugly shouting in your underpants.
Geoff, you still keep amazing me with your posts! 10000% agreed with you!
thanks Harry! Hope you are doing well, mate
p.s. how to win FSAE
1. learn rules
2. build car to suit
how to win ten times:
Repeat above ten times
Geoff, sorry that I spewed times not points, but since the discussion was about massively improving acceleration times and EVs vs ICVs we can see the results from the UK.
Fastest Electric car: 75 points (3.439s)
Fastest IC car: 38.39 points (4.147s)
I would say in anyone's language or point sim that 36.61 points is quite a lot!! It is more than the difference between the highest performing IC car and EV car in the comp (around 19 points). In fact that points difference covers the top 5 cars in the field. It was the only event in which the EV cars showed a big points advantage (efficiency also gave a 20 point advantage). In this case the IC car is slower what we normally see as the fastest (closer to 3.9s to 4.0s). That would have still been a deficit of around 25 points.
If Z is right and an IC car can equal these times it is a worthy exercise to investigate the claims. From a rules perspective if you want to run EVs against ICs and Z is wrong then the rules absolutely need to change. Handing a 35-55 points advantage (efficiency & accel) to the EV cars with no apparent detrimental event (except cost event appears to be a 10-15 point loss) is not something you can overcome by fiddling the concept. Remembering that an IC brown go-kart can be met with an EV brown go-kart. There is no weight penalty for the top EV cars in powertrain anymore.
Does that satisfy your points requirement Geoff?
Sorry that I used results rather than a simulation, but the calcs performed earlier back up these sorts of times, and hence points.
Kev
Kev, I'd respond promptly but as you know the internet here in Cockatoo is delivered by horse, and deliveries stop whenever it starts raini.. damn
Hi Kev,
The point I was making was that a fair analysis would cover the whole breadth of the competition. I.e. the two options should be analyzed across all events, cost, energy used, etc. For each of these factors, relative points allocations should be compared.
I'm sure there is not much new to you there kev.
Cheers
Geoff
I will try to avoid a two person conversation happening ... especially one between to self-acknowledged gasbags.
What I am not sure is blatantly obvious is how well a small handful of EV teams have exploited rules that favour EV performance over IC cars. They should be commended for it, and not have their toys taken away. Z is spot on in saying that there is a lot more to look at in the IC cars, but I think way off base in any assumption that would claim parity between EV and IC in the current ruleset.
Once there is a powertrain performance advantage (power, efficiency, handling) with no noticeable detriment (with cost as the exception) then the solution is clear. It is definitely not an option for all because there is a very large monetary cost associated with the high level EV powertrains.
I am a big supporter of all teams running points analysis over the full comp. However with some issues there is a clear technical winner. High grip vs low grip tyres for instance, no need to run the points sim on that one. It just so happens that for competitions between EV and IC cars there is a clear winner in the powertrain department. A well executed IC team will not be able to beat a well executed EV team. The points just aren't there. I would also add that people need to chuck the crazy into their points sims even if they don't think it will happen. No one expected the high powered EVs to weigh what they do now, and have enough energy to do the endurance at full tilt. Has everyone considered what an IC car could do if it was 120kg with aero? What would happen if a team had custom made slicks capable of sustained mechanical grip of 2.5g?
My take is that if your concept is within 10 (maybe 20 points) then you can call it about equal and in with a chance. Anymore and you carry a deficit that is unlikely to be overcome in a large competition (i.e. ~100 teams) The reason for doing the overall comp points analysis is not to show that all concepts have an equal opportunity, it is to try and find if there is a clear winner (or an alternative strategy that differs from the leaders, but close enough to give you a chance). Or to plot out the best value in terms of points per dollar or points per hour. In that equation the IC cars still come out on top.
I do worry that without careful consideration of where the competition is heading that we will lose something special. Now having been involved with a team building a custom engine I have seen first hand how difficult it is to build a better engine than what you can buy off the shelf. Any team can access (for $2-5k) an engine good enough to build a comp winning IC car around. Build a simple vehicle around that out of fibreglass, glue and balsa, a couple of steel suspension members and you can have an innovative high performance vehicle. With the right skills a team can legitimately build a top level IC car for $20k. ECU's most recent car with carbon folded tub, carbon wings, plenty of spare wheels and tyres, and a custom engine cost around $40-50k. Monash's probably a lot less for more performance. The higher spends on these cars don't translate well to improved performance. Mainly because the nearly all components can be built by students at a very high quality, and there aren't too many of them.
For the EV programs these amounts of money do not even start to pay the bills.
Just don't run them against each other. The points sims validate this ... but don't trust me ... do the calcs, and please post the results if they say something different.
I'm sure there is not much new to you there Geoff.
Kev
I REST MY CASE.
=============
Firstly, thanks Geoff for the supportive words.
I gave the "points argument" for faster Acceleration at the top of page 6 (and some more words later regarding E-Car-bias in Fuel Efficiency). The ~50 points that are on offer from doing Acceleration properly, and the self-evident fact that better straight-line acceleration out of slow speed corners (ie. NO fish-tailing!) also means more points in AutoX and Enduro, are my main reasons for pushing this point.
(And to repeat "my point", it is that Teams (other than Maryland+) should, for the first time in 30 years, start thinking about weight-distribution and tyre sizes, given FSAE's particular power levels and track layouts. The answer is only "50:50 with equal-sized tyres" when you have a sub-~30kW engine.)
But I have all but given up trying to help anyone from the "University" system.
LONG MAY THE DENTALLY-VENTILATED LIVE, for they are the only hope humanity has left...
~~~o0o~~~
PROOF POSITIVE OF MY PREVIOUS POST - The fastest Acceleration time at the just run FSG was ET = 3.36 seconds with Vmax = 115 kph = ~32 m/s (this taken off the web, so I shouldn't trust it, but anyway...).
This was a 4WD E-Car, but note that,
* It has LESS POWER than the maximum available to a C-Car (and as noted many times, MAX POWER IS NOT VERY IMPORTANT!!!)
* It uses the SAME TYRES as those available to ALL other FSAE cars (NOT magical "super-sticky" drag racing hoops). So same Mu, and same Fx/Fz.
* It set the time on the SAME TRACK as that used by all the other FSAE cars (NOT a specially prepared dragstrip).
* Its ET and Vmax are remarkably similar to that of Team Toothless's in my last post, so its V-T graph should be very similar to curve B.
So, to anyone who has a skerrick of understanding of the simplest 1-D Mechanics (ie. as spelt-out in my last post), A SIMILAR TIME IS POSSIBLE FROM A RWD C-CAR! (In fact, see below to see why RWD can be faster.)
~~~o0o~~~
But, in the SAME competition, on the SAME track, with the SAME weather conditions, ALL the C-Cars had the SAME SLOW TIMES that they have been getting for the last 30 years!
Here, from some earlier posts, are paraphrased the LAME EXCUSES for this PERENNIAL UNDERACHIEVEMENT.
* "A 200 kg total mass is IMPOSSIBLE because the driver MUST weigh at least 70 kg." - Just really, really stupid!
* "A lightweight car with a reasonably powerful engine is IMPOSSIBLE... because NO ONE HAS DONE IT YET." - So, you best go back to living in caves.
* "It is IMPOSSIBLE to go faster, because if the times keep dropping we'll suddenly be at 0.0 seconds..., which is IMPOSSIBLE" - Groaaannnn... How about just taking a few percent off the times each year (which you can do FOREVER!!!)?
* "It is IMPOSSIBLE to go faster..., err ... unless we spin the tyres impossibly fast..." - Jonny, a lot of the 4.5+ second teams where doing just that.
* "It is IMPOSSIBLE to go around a corner with a Junior-Dragster tyre. Just IMPOSSIBLE! And even if you could, they'd wear-out INSTANTLY!" - So, you may as well QUIT RIGHT NOW. Go home to Mummy... Or spend 2 x $150 (RRP on link) and have some fun.
(For the record, I DO NOT think any sort of special tyres are needed for a RWD C-Car to get into the low 3s. But, sadly, I do know of a team of PERENNIAL LOSERS who are planning to spend ~$8,000 on totally inappropriate tyres this year, simply because their $chool gives them a huge wad of cash each year. I say "sadly", because it is my tax dollars they are pissing away!)
~~~o0o~~~
The above are just some examples of the FSAE world's STUPIDITY and LAZINESS. To some degree you can pass the blame for that onto the Education System, for it is they who have fostered your belief that "Going faster is IMPOSSIBLE, just IMPOSSIBLE... But if we keep optimising our ridiculously ornate rockers, then WE DAMN WELL DESERVE OUR GOLD STARS!".
But you CANNOT BLAME OTHERS FOR YOUR COMPLETE LACK OF WILL TO WIN. All of the knowledge of how to do well in FSAE, both generally and in Acceleration specifically, has been spelled out on this Forum for years. Yet, year after year after year, you all seem oh-so happy to just STAND STILL, DO NOTHING, and GO NOWHERE.
I pity your children...
Z
(PS. I don't know why I bother, but one more time.
* To get really fast Acceleration times, THE CAR'S CG MUST LIFT as it comes "out of the hole"!
* This puts MORE THAN 100% of the car's weight on the driving wheels (so faster than 4WD with constant CG height).
* This "launch" lasts a split-second, and covers ~2 metres.
* Measure that 2 m time, and get it right.)
Kevin,
(Almost) ALL the current C-Cars handicap themselves by using off-the-shelf powertrains (ie. "gearboxes", usually from motorbikes). Bad idea because;Quote:
Z is spot on in saying that there is a lot more to look at in the IC cars, but I think way off base in any assumption that would claim parity between EV and IC in the current ruleset.
1. These totally mess up the overall mass distribution of the cars. It is hard to get much more than 50%R, and gives too high a Yaw inertia.
2. These gearboxes, typically with rather weak clutches, are not very good at converting the constant and high level of power available from the IC engines (which is on par with E-cars), into the most appropriate torque at the wheels. Especially so at the lower speeds. (Note that for the E-cars, this "power-to-torque-gearing" is really just a software problem (PWM?), albeit reliant on expensive electrical hardware.)
But the typical FSAE aversion to solving these problems really boils down to LAZINESS. There is NOTHING NEW to be "invented", and the cost of using the "right answer" is NOT high.
I remember a long thread (possibly several threads) covering these issues back in 2005. There was huge negativity back then, just as there is now. Very, very few Teams have tried to solve these problems. Usually they are very small Teams, typically with only one highly motivated member. After some limited success, the new team members decide it is MUCH EASIER to simply jump back into the middle of the FSAE flock. "Hey, sooo much easier, and we still get our Gold Stars!"
Your Team is one of the very few who are now addressing this problem. PLEASE KEEP DOING WHAT YOU ARE DOING. Burn it into ECU's DNA.
IMO the path to E-Car-like drivetrain performance is only a few steps away. I hope you come to Oz-14, so we can talk about stuff. Like tractor IVTs, or the typical drag-car drivetrain, which at the lower power levels use mildly modified auto-boxes (hint, hint..., very simple FSAE system, suitable for your engine... :)).
~o0o~
IMO the only pro-E-Car BIAS in the current Rules is that they pretend that energy supplied from coal-fired steam-engines, that then suffers countless transmission and conversion losses, is somehow GREENER than a fuel you can grow in your own back paddock (= ethanol). I also like propane...
Discussion, anyone...? :)
Z
Too much time in a dragstrip? :P Drag racers really know their game when it comes into (usually 4-link) suspension geometry and "anti's", without using nothing more than paper and pencil. In fact, some of them could ballpack your rear suspension setup based on the available grip (slippery or super sticky track) and available power. Plus all of them seem to realize that the "launch phase" and Fz on tires is a highly dynamic phenomenon, an that you could (and in fact do have) more than 100% of car's weight on the rears, just because of that. You could find examples of people running really exreme values of antisquat, albeit I have heard from people that very powerful cars tend to start spinning their tires after the initial launch phase, because the Fz drops after a few milliseconds... Oh, and there is nothing forbidding having "special" suspesion pickups for the acceleration event only... ;)Quote:
Originally Posted by Z
EDIT: By the looks of it, ECU was doing something right in the launch phase of accel. at FSUK
I like that! And as said, the M/Ts I have linked come in a FSAE-friendly size...Quote:
Originally Posted by Z
Z,
I should be at Oz 2014. The team has plans for moving away from the current style of clutch. A clutch is really only important getting going and there are much better ways of doing that than a multi-plate wet clutch. The clutch was probably the hardest thing to work around in the whole custom engine deal, and the first engine subsystem in line for a change in the next design. Next gen wont be around for another couple of years for the team though.
I was surprised to find out how what is done with clutches in drag racing and how much they are the first port of call for tuning the early stages of the run. I had incorrectly written off drag racing when I was younger, only to realise as the amateurs go the local guys at the drag strip are practicing better vehicle dynamics and data analysis than the guys at the circuit. It is almost impossible to find someone with a decent drag car that doesn't go through data, and almost impossible to find a similar circuit racer that does.
I am still not sure that you could keep enough load on the rears long enough to generate the sustained g's in the early launch phase, but I know what you are proposing teams exploit. The M/Ts might have a low enough torsional stiffness to make better use of the spike in unsprung vertical load. When I was a student we were running the older Goodyears that were very torsionally stiff and even tuning springs and dampers to try and improve the temporary vertical load (with reasonable CoG lifting) we could only get about a tenth. Additionally you could only go so low with the tyre pressures before you were running on very stiff sidewalls that screwed things up. The 10" LCO's would probably be a lot better.
The other issue we dealt with is that a lot of the dampers available had high inherent damping even without the valves. The first versions of the kinetics cars would have been able to run reasonably well around a track without the adjustable valves in at all. Later versions pulled out a lot of the damping due to path restrictions. The MTB shocks were garbage and hard to get in the range we would have needed to improve the launch. I have tested the current crop of Ohlins twin barrel dampers with one of my classes. They suffer from similar inherent damping to the early Kinetics cylinders we made at UWA. Not really a problem for track work and the adjustability is great, but they limit what you can do in the acceleration. Frankly I think they are not the best choice for dampers. The ECU guys switched to Penske non-adjustabe (but rebuildable) single barrel dampers. They weight exactly the same, and you can buy 2 for less than the price of one Ohlins. A much better unit to be working with to make the most out of Accel.
By the way for the teams that haven't done back to back testing of different style dampers, please do. Pull a couple apart and get an idea of what is happening to that oil squirting through little holes. If you don't have a damper dyno then build one. We built one in 2003/2004 and the required parts, control systems and DAQ, are much cheaper today. There is almost no reason for any decent FSAE team not to have one.
Most of the point sims I have seen in use don't have the fidelity to model the acceleration event properly, and should be used with caution when making tuning decisions on the basis of the results. The code I was running for my Thesis (focused on evolutionary optimisation algorithms) used a vehicle dynamics model designed for fast computation. As per most models of this type it was quasi-static. One area this lacks considerable accuracy is in launch zones, where transient behaviour dominates. We did some work with a much more accurate transient model of the acceleration event, but I would need to try and find the code for that, and change a few assumptions. Casting my memory back though I still don't see think magnitude of transient rear load you would need for 0.4 seconds of 2.5g accel being possible (in an FSAE event). It would be great if someone currently running a decent transient sim could post some numbers to confirm or deny this. Also out of curiosity how many teams are running good search algorithms on the solution space for their points sims? I would love to hear about any improvements on that front. Most of the approaches I hear about are 1 variable at a time style searches, or incredibly coarse searches with only a couple of variables each time. How are teams going about determining whether they are close to the global optimum, rather than local optima for their given sims?
On the face of it I would think that some of the newer cars would be in a better place to be tuned for the accel event than the older UWA cars. Weights, tyre construction, and basic design (i.e. wheelbase, available dampers, weight distribution, and even power) have gone in the right direction when compared to the mid 2000s. It is a little surprising that the times haven't dropped a tenth or two from back then.
I think you are right in that there is a lot of time that can be had by designing a car that can be tuned for accel (while still working well for the other events). I just disagree on the magnitude of the improvement possible. But I am proved wrong on a daily basis.
Kev
Kevin,
really a pity we did not catch a word or two in FSUK, I am pretty sure it would be massively interesting! Any plans to get back to Europe soon? Anyway, back to topic!
Z,
Would you mind running your numbers again using a 50:50 weight distribution and 681 pounds / ~310kg? I'm curious what it would come out to, these numbers are mostly from this year's University of Kansas car, which runs a 4cyl engine and full aero package.
https://fbcdn-sphotos-g-a.akamaihd.n...80730692_n.jpg
I'm also curious on the numbers because I'm writing my own acceleration code and would like to compare numbers with what your simulation gives. On a similar note, could you possibly share what numbers and assumptions were used for your initial simulations, I would be grateful to use those for comparison as well.
Thinking on your weight transfer comments, I ran some numbers last night and found that a 441 pound car with 60% static rear weight on a 60-inch wheelbase accelerating at 1.5g only needs a CG height of 16-inches to get 100% rear weight transfer, that's pretty remarkable as it's far lower than I would have thought. I ran the same numbers under braking (with a tire Mu of 1.5) just to see what would happen and it gave a front weight transfer of 80% at peak load, that's pretty remarkable.
Now, I don't have enough of a grasp on cornering performance to run numbers in cornering, so anything hereafter is just speculating. If the CG is causing such massive weight transfer front-to-back, wouldn't that have a dramatic effect on cornering performance as well? This is what's tripping me up, something is telling me the lateral weight transfer would be an issue.
A 16" CG height seems excessively high in a FSAE car. Maybe if you had a way to change your suspension to get the "gasser" style suspension for accel, possibly with some accel ballast to help with weight transfer.
Maybe it was just the points analyses that I always ran, but acceleration always seemed to be one of the easier places to not worry about a few tenths of trade off due to the weighting relative to every other event. If you dropped a few tenths there you could pick up in cost and efficiency (then again that is just the justification for not running a 4 cylinder, right?)
Harry,
"Plus all [drag racers] realize that the "launch phase" and Fz on tires is a highly dynamic phenomenon, and that you could (and in fact do have) more than 100% of car's weight on the rears, [...but...] the Fz drops after a few milliseconds...
Oh, and there is nothing forbidding having "special" suspesion pickups for the acceleration event only..."
Yes and Yes. More below...
~~~~~o0o~~~~~
Kevin,
"The team has plans for moving away from the current style of clutch. A clutch is really only important getting going and there are much better ways of doing that than a multi-plate wet clutch..."
Yes. And especially so the smallish motorcycle clutches that are designed for the lesser duty of getting a light-ish bike going.
Given that an IC engine does not work well at low revs (~or AT ALL), the choice at launch is to, 1 - slip the clutch, or 2 - slip the tyres. The Top Fuel dragsters have only one gear, and they slip their BIG multi-plate sintered-iron clutches for most of the run. (Interestingly, electronic control is banned, so they have to use a carefully set-up pneumatic-mechanical system.)
So, once again the standard FSAE approach of using an off-the-shelf motorcycle engine is a handicap, because fitting a bigger, better, clutch can be a major hassle. I reckon better is to start with an engine-sans-gearbox (there are lots of options), and then build your own custom (but simple!) drivetrain, probably integrated with the diff. A bit like you are doing!
"... I still don't see magnitude of transient rear load you would need for 0.4 seconds of 2.5g accel being possible (in an FSAE event). It would be great if someone currently running a decent transient sim could post some numbers to confirm or deny this."
I would definitely be doing "transient sims" for all the Dynamic Event analyses. (Very briefly, ~10 ms time-stepping, "F = P-dot" each step, and DRIVER-IN-THE-LOOP! So run it like a video-game.)
But above is NOT necessary to "confirm or deny" this particular case. See next...
~~~~~o0o~~~~~
Troy,
"Z ... I'm writing my own acceleration code and would like to compare numbers with what your simulation gives..."
Ahh..., Old-School vs New-School... :)
The SUM-TOTAL of my "simulation code" is ...
... the graph I drew. NOTHING MORE! I repost it here so that the next lot of words make more sense.
Stuttgart's #26 E-car did FSG Acceleration (of presumably 75 metres?) in 3.36 seconds, with a final speed (?) of 115 kph = ~32 m/s.
The car apparently weighed ~166 kg (on FSG website, though ~178kg on Team page?). With lightweight driver the total mass should have been not too much over 200 kg. (Given assumed computerised-everything-control, I reckon they could have signed-up a 10 kg macaque from the Biology lab to do the driving.). Team page says 4 x 25 kW motors, and given that high-G acceleration will put 70-80% of weight on rear-wheels (so fronts NOT capable of much Fx), a Pmax = 60 kW, while GRIP-LIMITED, is also pretty close.
So, comparing Team Toothless's curve B below (ie. the cross-hatched area) with a guessed-at V-T curve for Stuttgart.
1. The area under the two curves MUST be the SAME at 75 metres (assuming nothing funny at FSG?).
2. Stuttgart has a very small extra ET = 3.36s (cf. TT=3.30s) so their "75m area" extends very slighly to the RIGHT of curve B.
3. Stuttgart has a very small extra Vmax = 32m/s (cf. TT=30m/s, and I assume Stuttgart did NOT go faster in mid-run, and then hit the brakes just before the finish line!), so their "75m area" extends slightly ABOVE curve B.
4. The above two differences (2 and 3) means that Stuttgart can have slightly less area at the LEFT side of curve B. So a slightly less steep "launch acceleration", but ONLY SLIGHTLY LESS!
https://lh5.googleusercontent.com/-h...nchVTGraph.jpg
So, whichever way you draw Stuttgart's V-T curve, it still has to have a QUITE STEEP launch acceleration so that it can fit its "75m area" within the upper Vmax boundary, and the right-side ET boundary. In round numbers, I guess "quite steep" is ~2 G-ish, if not more. Any less than initial 1.5 G at the left-edge, and the "75m area" is pushed outside the top or right-edges...
And, MOST IMPORTANTLY, Stuttgart's tyres are the SAME tyres, on the SAME surface, as available to ANY OTHER RWD C-CAR TEAM.
Now Stuttgart's front tyres might have been doing maybe 30% of the work during launch (probably less). So take a purely RWD car (E or C), put less rubber on the front, more rubber on the rear, set it up for ~100% weight on the rears at "launch" (say, by giving it ~60%R-static, as noted below), and you have the SAME situation as Stuttgart's, at least as far as tyre-Mu, Fx/Fz, etc., are concerned.
So, bottom line, a RWD C-Car can have the SAME numbers during the most important GRIP-LIMITED phase near the start-line, and NO reason to believe the RWD car (with right sort of driveline) should be any slower.
~o0o~
I've waffled on a bit much, so briefly ...
"I ran some numbers last night and found that a 441 pound car with 60% static rear weight on a 60-inch wheelbase accelerating at 1.5g only needs a CG height of 16-inches to get 100% rear weight transfer..."
The MASS of the car makes NO difference. The "Gs" account for that, and always give the same % weight transfer...
"If the [16" high] CG is causing such massive weight transfer front-to-back, wouldn't that have a dramatic effect on cornering performance as well?"
NO, no, no. Not if you SET-UP the car to suit the different Events.
So for SP, AutoX, and Enduro I would definitely set-up the car with LOWEST POSSIBLE CG, and whatever else is required for good performance there.
But for Acceleration (remember = 75 points!) you could set-up the car with 4" of ground clearance. The Rules say you must have AT LEAST +/-1"of suspension travel, so 1" bump and 5" droop should be OK. (I don't have Rules here just now, but IIRC "shims, spacers..." and other adjustments are allowed.) So getting a 12" CGH up to 16", JUST FOR Acceleration, should not be hard. And not really necessary... (see below).
Or, easier, you can have a special "booster seat" for the driver that has a very thick squab. Given that most seat-backs slope backwards at about 45 degrees, I reckon you could easily move the driver up 4" and back 4". But check Rules on this...
More importantly, with CGH = 12" (0.3 m) and 60%R on a 60" WB (ie. ~0.6 m + 0.9 m = ~1.5 m) means 2 G gives you 100% on the rear. With same CGH, 2.5 G has you "popping a wheelie". However, you become power-limited a bit after 2 metres (see graph), so the Gs drop off and the nose comes down. Also any front-wing aero should start to act by this stage, pushing the nose back down.
So aim for as-low-as-possible CG for "normal running", and with 60%R you only have to bump it up to 0.25 m to 0.3 m for the Acceleration event.
~o0o~
The other big set-up change, hinted at by Harry, is the "rear-anti-squat", perhaps better called "pro-lift" here. Move the rear-suspension's front-pickup points (ie. near MRH) upwards. Quite a lot, say 4+". Now a forward Fx force at the rear-axles pushes the car's CG upward (through the up-to-front sloping n-lines), and by action-reaction, the rear-tyres get forced down onto the road. So more than 100% of car weight is possible on the rear-tyres.
But this increase is only brief, because it only lasts while the car's CG is accelerating upward. So best to start with the CG quite low, so that the pro-lift can last for as long as possible. And you have to find the right balance. Too much pro-lift and you get a nanosecond of great launch, but then the car jumps TOO high, grip is lost, wheels spin..., slow ET. Not enough "wheelie" or "pro-lift" = slow launch, and Team Toothless is laughing at you (although you have beaten most other FSAE teams).
I would suggest that the best way to find this right "balance" is with lots of real testing. Not much space is required, perhaps only 50 metres of straight road, because you are mainly trying to get that first 2 metres right. Well, that and then keeping the power on for the next 10 metres as well (see graph).
If you have all the fancy DAQ stuff, as Kevin says all the THs have (they're as cunning as sewer rats! :)), then you might try plotting the data as a V-T graph, as above. Just keep trying to push the initial part of the curve leftward.
Personally, I reckon a day spent practicing launches would be great fun... :)
Z
Aah, joy oh joy. Some intelligent conversation, and some engagement with Z rather than just ridicule. Nice work on the diagrams too, Z.
Was just signing in to say that you don't need to have a CofG at 16" above the ground for all events - but I see Z has addressed that. No mind.
Part of me is wondering how many teams sweat over the Presentation Event as much as they do over Acceleration???
Cheers all,
Geoff
Geoff,
I'm not sure any of this discussion is implying the accel event is more important than others, just an interesting discussion of the dynamics of launch. Given that just about everything here can be done without sacrificing points anywhere else I say it is valid.
Keep your presentation plugging for the people wearing pocket protectors :)
Right now we are talking about ETs on the 3/64 mile.
Maybe we should take it to another topic, and start another one on the 55m oval :)
Kev
Yo Kev,
The thread is actually about the 2015 rules ;) My comment was just drawing attention to the fact that there are some things that we are very keen on arguing (dynamic events) and some that we sort of forget about.
Anyways, I'm actually really interested in the dynamics of launch, this is turning out to be a damn good thread. Aside from my feeble interjections, of course!
Oh, and if you are putting down Presentation Event presenters - I did it like 6 times for RMIT...
As you were...
At the design review held at FSG the past week, Pat Clarke and Owen Carless confirmed some of the 'rumors' about the new rules for 2015. I'll sum up from what I heard, but in details I might be wrong.
Aero rules:
The rules for the aerodynamic devices such as wings and diffusers will be tightened again. According to the 2 chief judges, a few years ago the aero rules were loosened so that more teams would venture into aerodynamics. This was done because the rules commitee was of the opinion that too little research into aerodynamics was done. They now feel that the time is there to tighten the rules again and make it a bit harder to create a beneficial aero setup. In what shape or form these rules are was not discussed.
4WD electric rules:
There will be a drop in power for 4WD electric cars. How much was not specified and is not known yet.
Design Scoresheet rules:
Pat Clarke and Owen Carless made the 'announcement' that FSG (maybe FSAE? not sure) was looking into evolving the design scoresheet to better reflect current rules and regulations, especially considering the electric vehicles.
I'm only paraphrasing here, so I might have one or two exact details wrong. It would be nice if either Pat Clarke or Owen Carless would comment on this :)
THs (on the contrary of common belief) have also benn using internet a lot these days, so lots of info is available if you look into the right places.
Pro-lift forcing an "action/reaction" increase of Fz is a highly dynamic matter because of rotational dynamics (car wants to "pop a wheelie" and has a significant rotational inertia around that axis that works FOR you). Moreover, THs usually opt for 100% anti-dive (or close to that value), because exceeding it by far (having too much pro-lift) might plant the tires very hard in the first few milliseconts but eventually the nose gets back down and tires begin to slip, especially in very powerful drag cars. This is much dependant on track conditions, whether is slippery or not, and available power, so most drag cars are highly adjustable in terms of anti-lift. Moreover, in the matter of nose lift and coming down, front springs and especially dampers play a significant role as well. I would suggest to anyone interested to search the web for a Mr. called Bill Shope...Quote:
Originally Posted by Z
I guess you had to do something if you couldn't fit in the car!Quote:
Originally Posted by Big Bird
Then again the RMIT guys probably wheeled you into the presentation with you halfway into a rant, then wheeled you out when you were a little bit past halfway through a rant. The judges would have been both astonished and bewildered. Must have been worth a few points.
If we are on the marketing presentation, how would you propose that you maximise the early launch phase of powerpoint to ensure you finish with the most number of words conducted during the event? And does the ridiculously high centre of gravity you possess enable you to exceed over 100% weighty words per sentence?
Kev
What do you mean I couldn't fit in the car? I did skid pad and presentation in 2003. Unfortunately I got the two confused. For my presentation I found myself talking in circles a couple of times, so I turned it around and went in a different direction. I then went off course, meandered around in circles a couple more times, to find that I had actually gone nowhere and I was exactly back where I started. It was all over in just over twenty seconds.
My fastest skid pad time was ten minutes, which was followed by three minutes of questions.
As for launching the presentation, I never found squatting at the back end to be all that helpful. You have to understand, we were running a smaller, lighter presentation than you guys - fewer words, much less weight to them, but less chance of choking when under full power. And I remember our presentation sounded a bit flatter than yours too - but then a single presenter always sounds flatter than four inline...
Quote:
"If the [16" high] CG is causing such massive weight transfer front-to-back, wouldn't that have a dramatic effect on cornering performance as well?"
NO, no, no. Not if you SET-UP the car to suit the different Events.
So for SP, AutoX, and Enduro I would definitely set-up the car with LOWEST POSSIBLE CG, and whatever else is required for good performance there.
But for Acceleration (remember = 75 points!) you could set-up the car with 4" of ground clearance. The Rules say you must have AT LEAST +/-1"of suspension travel, so 1" bump and 5" droop should be OK. (I don't have Rules here just now, but IIRC "shims, spacers..." and other adjustments are allowed.) So getting a 12" CGH up to 16", JUST FOR Acceleration, should not be hard. And not really necessary... (see below).
Or, easier, you can have a special "booster seat" for the driver that has a very thick squab. Given that most seat-backs slope backwards at about 45 degrees, I reckon you could easily move the driver up 4" and back 4". But check Rules on this...
More importantly, with CGH = 12" (0.3 m) and 60%R on a 60" WB (ie. ~0.6 m + 0.9 m = ~1.5 m) means 2 G gives you 100% on the rear. With same CGH, 2.5 G has you "popping a wheelie". However, you become power-limited a bit after 2 metres (see graph), so the Gs drop off and the nose comes down. Also any front-wing aero should start to act by this stage, pushing the nose back down.
So aim for as-low-as-possible CG for "normal running", and with 60%R you only have to bump it up to 0.25 m to 0.3 m for the Acceleration event.
~o0o~
Z
T1.2.3 The vehicle must maintain all required specifications, e.g. ride height, suspension travel, braking
capacity (pad material/composition), sound level and wing location throughout the competition.
Someone's already thought of the super adjustable ride height. Sorry to burst your bubble.
I'm intrigued at the rest of the post though. Thanks.
Fair call MCoach. It is a long time since I've read the rules from front to back. You guys are much closer to the coalface than I these days.
However, my next step if I was confronted with such a rule /constraint would be to seek out definitions, and see if there is room for movement. Ride height must not change - so what is ride height? The distance between the lowest point on the main body and the ground? is it the whole floor plan of the car? Can we design a mechanism that leaves the lowest part of the floor at "ride height" level, and the rest of the car lifts upwards? Maybe an engine/drivetrain tray that can be adjusted up and down for different events.
What does "all required specifications" mean - has anyone asked that question?
The point is that there could be a whole range of interesting and alternative solutions floating around in the margins of our interpretations of the rules. I would point to the recent UWA cars which have a very interesting interpretation of "Suspension". Engineers are very adept at finding reasons to not be different. If the mindset changes from "that's not possible" to "lets see if it is", then things can become very very interesting.
The only real required specification in the rule regarding Ride Height, CoG etc. is passing the tilt table.Quote:
Originally Posted by MCoach
I think the more interesting question would be how many teams actually change anything on their car during competition, and why they don't.
I see very few changes being made in between events. The top teams tweak a bit, the middle teams catch up on sleep, and the back-markers are still gluing together bits of carbon. I'd be very curious to see how extending the time for dynamic events would change this, as I know we were always caught between changing set-ups and prepping the car for endurance with our four-ish man team. Also not having dynamics a 30 minute walk from the paddock (at least at MIS and Fontana) would help.
P.S. I'm finding it increasingly amusing that the experienced alumni, has-beens, and old guys around here tend to agree more with Z than the still egotistically fragile young budding engineers he's trying to help.
"How dare you insult our theoretically perfect car! Last year GFR won with this same design so it will certainly work for us too!"
Having been there myself, I hope some listen. I wish I had.
At one point in FSUK, changing car setup between dynamic events was encouraged. That contradicts the 'T1.2.3 The vehicle must maintain all required specifications, e.g. ride height, suspension travel' statement.
Is this a rule inconsistency, or does FSUK cover it in the event rules not the FSAE tech rules?
Regards, Ian
Does that rule not simply mean that it must continue to meet all the rule requirements? In the case of setup surely maintaining the minimum +/- 1" of travel is all that's required, otherwise anything that's adjustable, and passed scrutineering as such can be adjusted. No?
Dunk is correct.
The rule does not prevent you from changing the ride height (would be horrible in Germany...) or something else. As long as you don't touch the ground and don't lock your suspension, you can do what ever you want with it.
There was not only a single but now multiple people who thought that changing your car set-up during competition was illegal?
My mind has officially been blown for the day.
The best thing to do would be to have pull/push rods for accel in order to bump up your CG. However, I do not think a part swap would be allowed without going back through tech. So the limitation we have on RH adjustment relates to the length of threads on the rod ends. A funny thing to note about this is that we are adjusting CG, a key thing with tilt testing. So it's possible that a team could make this adjustment and no longer pass tilt.
Good skidpad times are not quite possible without changing your setup after acceleration. Or try doing the acceleration with your skidpad setup and vice-versa and end high. (Yes I know Delft did it at fsuk this year... exceptions/rule).Quote:
Originally Posted by Alumni
Dylan, no a part swap would be 'illegal', that would require a rescrutineering and dsq for the previous dynamic events if I'm correct. otherwise you could rescrutineer haf your car after the accel/skidpad events. As long as the part isn't the same as the one which was scrutineerded.
You can obviously replace a broken part with a part with the same functionality.
But I'm diverting from the original theme of this topic: New rules. Lets wait untill 23rd? of August. Untill then just assume most of what has been said and keep your options open.
I think the rules are a bit too much.
Yes, Aero will still work, but for smaller teams, it will not justify spending time on it. I think the rule makers will get the exact opposite of what they wanted. Instead of "everybody has fairly good working big wings" (Delta between an awesome Monash/GFR/Munich package compared to a "quick and dirty" one is surprisingly small), it will happen that the good big teams will run with efficient, working wings and the smaller teams without them. Bigger delta in my humble opinion...
Looking forward to see the results, I know that the CAD workstations are running already... :)
This has been my opinion the whole time these rules have been talked about. And I can't think of a single series that has come up with these kind of rules before...Oh wait.Quote:
Originally Posted by JulianH
As we have continued to say in our feedback and in the surveys, this increased complexity in the rules benefits the teams with bigger resources and disadvantages smaller teams. I agree with what others have said that this will have the opposite effect of what the rules committee wants, which I would expect is a more even field. History has continuously shown (there are many examples) that tighter limits on the rules benefit bigger teams disproportionately because they have the resources to chase smaller gains in many areas, where smaller teams won't be able to "waste" resources to the same level.
I can confirm the CAD iterations are already running, watch out for 2015!
Yes. Just as I said.Quote:
Originally Posted by BeunMan
If we could do it, it'd be the best thing to do (for desired setup change). I was pointing out the limitation.
So there is no other way to lengthen a pushrod other than the rod ends at either end? Presuming you wanted more extension - you can't design something that could extend further??