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Thread: Two simple rules to improve results.

  1. #91
    Quote Originally Posted by Z View Post
    MCoach,

    Some specs on these would also be good.

    Better yet, bring one to Lincoln!

    Z
    They are very popular with the top level national racers when they have a spare moment to do so.
    They are also very popular with drivers trying to advance into sprint cars as they handle very similarly.


    Specs:
    Mass: Minimum kart and driver weight is 450lbs (204kg) total (with fuel).
    Track width: adjustable from about 38-46" (965 - 1168mm), depends on kart manufacturer
    Wheelbase: adjustable from 41-43" (1041 - 1092mm)
    Rear Gear : 13-15 tooth drive gear, 23 - 75 tooth driven axle gear
    Engine: Open class, 550cc 2 or 4 stroke engine (both have same displacement), typically make 85-100hp (63 - 75kW) at the crank. Peak rev is typically 8-12k rpm.
    Tires: different for each corner and variable from slick or treaded and 11x5-6 to 12x9-6 (diameter x width - wheel diameter)
    Brakes: One rear brake on the rear axle and one left front wheel. The right front does not use a brake.
    Frame: standard oval racing offset chassis with a cage made from 3/4" x 0.083" tubing. The cage is sprung from the kart via 4 valve / die springs at each corner.
    CG:I'd estimate the CG is 55% left side weight, and about 12-18" (457mm) high due to the wing height, driver height, and upright driver seating position.

    Aero:
    CLA and CD are hard to quantify but there is also attention to CLS that is needed.
    Most people are familiar with coefficient of lift and coefficient of drag, but many are not familiar with coefficient of side force or literally Fy from aero forces which this generates a lot of.

    Either way, it is a single element giant wing with asymmetrical end plates. Throw some numbers in simulation.

    The wing is adjustable in angle of attack via a push-pull cable from the driver and is directly mounted to the cage. This in effect means that the chassis is unsprung mass, but the wing and roll cage is sprung mass.
    Interestingly changing these springs change how the karts fundamentally handle.

    Cost:
    The top-of-the-line open kart chassis is available for about $4500 without motor. Race built motors tend to run $1-5000 depending on the quality and reputation.
    Used, these karts can be found for $2-8000 with motor.
    Last edited by MCoach; 06-10-2017 at 06:54 PM.
    Kettering University Vehicle Dynamics
    Formula SAE 2010 - 2015
    Clean Snowmobile Powertrain 2012 - 2015

    Boogityland 2015 - Present

  2. #92
    Z,

    Quick stats on the kart, in English units because that's what my tape measure uses.

    1) With driver, 150# front, 222# rear, 60% rear. Without driver 182#.
    2) Front overall width 45 1/4", rear overall width 51 1/2", wheelbase 41", c.g. height estimated at 6". Measurement of CG height difficult due to small value and unwillingness to get dumped on my head on my garage floor.
    3) 12.5 cubic inch displacement, clutch engagement at 3300 RPM, 8 horsepower (crank on pessimistic dynamometer at Briggs and Stratton) at 5500 RPM, redline 6100 rpm.
    4) Single reduction by chain drive, 15t driving sprocket concentric with crankshaft, 59t driven sprocket concentric with rear axle. 34" rear tire circumference WHEN STATIONARY.
    5) With downforce-generating bumpers and sidepods removed, I lose about 15# and am about 0.5% slower than without. CdA is about 5 square feet, estimated from speeds at a different track.
    Charles Kaneb
    Magna International
    FSAE Lincoln Design Judge - Frame/Body/Link judging area. Not a professional vehicle dynamicist.

  3. #93
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    MCoach, Charles,

    Thanks for the specs.

    I would really like to see students simulating the above cars, on typical Autocross tracks, to compare laptimes with the super-uber-mini-F1-style cars of their dreams.

    Then, of course, the students should also factor in Cost, build-time, and reliability, to see which is the more sensible direction to go ... assuming they WANT TO WIN!

    Hmmm..., thinking, thinking... idea!!!
    ~o0o~

    Claude,

    How would you feel about hosting a "Virtual FS World Championship"?

    Teams would logon to your website and use OptimumLap to design a car, which then sets a laptime on a given Autocross track. Only one entry allowed per registered FS/FSAE Team.

    The tricky bit is that each car is also assessed by a secret formula that gives it a score for "Cost/Build-time/Reliability", with lower score = better. This discourages the Teams from choosing minimum mass + maximum power +++, etc. Typically, a 100 hp engine is much more costly (and raises minimum selectable mass), than a 10 hp engine. Uber-aero-numbers have longer development time than middle-of-road numbers, so are more "costly" because less testing time, and so on. But exact details of the formula are not given, reflecting the fact that even professionals struggle to predict exact costs and finish times when "pushing-the-envelope".

    Then, at the end of the year, or end of a given "competition period", the secret "Cost" score is added to each entry's laptime in seconds, and lowest total score is crowned "OptimumG's Virtual FS World Champion"!!!

    The Cost-formula is now revealed, to show students how stupidly expensive they were in their design decisions. The next year (or next comp-period) the track is changed, setting a different "problem" to be solved, and the "Cost" formula is tweaked to reflect those different conditions.

    This idea may need thinking through? Maybe..., build it, test it, improve, repeat?
    ~o0o~

    MCoach,

    BTW, yes, those aero-sideforces certainly are useful. I see some big opportunities here that no team has yet exploited.

    (Big hint: Flat-plates are nowhere near as good as cambered-aerofoils. And vertical cambered-aerofoils that can switch camber from left to right-side, as needed, are ancient prior-art.)

    Z

  4. #94
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    Erik - such a virtual FSAE thing already exists: VI-Grade Virtual Formula

  5. #95
    Here's an outline for the "OptimumLap Virtual FS Champion 2018"
    Suspension - Whatever's light. It's not modeled anyway so it just needs to connect the tires to the chassis and have them somewhat straight and vertical. All aluminium A-arms since it only needs to do one lap.
    Chassis - Rules minimal spaceframe, mild steel
    Engine - 80kw and flat torque from 2000-10000rpm, because I said so. Weighs 30kg.
    Aero - Literally drives upside-down at 20km/h

    You get the point.. without extensive validation (how? who?) this would be unfeasible. Who's going to check that the CAD density for steel isn't half what it should be.

    One way you could make it work is to provide formulas for each part e.g. Engine is 0.75 kg/hp. You can buy a 1kg weight decrease for $1000
    Of course once you settle on an acceptable set of numbers teams will cry out "Our engine is 20% lighter and 20% more powerful and we bought it for $1000 off Ebay".
    Chances are something like this would be won by a simple script to search all possible configurations for the fastest/cheapest car - might take a week to compute but expect a couple of teams with the same setup

    Maybe this still has value in showing there's more than one way to win, but it would require a lot of work to make an evenly balanced competition.

  6. #96
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    Tim W,

    Looks like I'm six months late.

    Nevertheless, that VI comp seems similar to what I had in mind. Except it seems to be E-car only (I just had a quick look?), and it misses the important "Cost" component/discouragement (see below).

    (And what happened to Adelaide? You came dead last!)
    ~o0o~

    Tim P,

    Read my paragraph beginning with "The tricky bit ...", and continuing with "This discourages the Teams from choosing minimum mass + maximum power +++ ...reflecting the fact that even professionals struggle to predict exact costs and finish times when "pushing-the-envelope"...".

    The SECRET Cost formula I suggested is aimed directly at Teams who start the year dreaming of,
    Engine - 80kw and flat torque from 2000-10000rpm, because I said so. Weighs 30kg.
    Aero - Literally drives upside-down at 20km/h
    ... with these Teams invariably ending the year with a non-running car that scores zero dynamic points (ie. the core theme of this thread).

    So, to do well in the Virtual contest, Teams have to be REALISTIC (perhaps even conservative) in their choice of mass, horsepower, aero, etc, lest their unexpected, but exorbitant, Cost-overruns cripple them.

    Z
    Last edited by Z; 06-14-2017 at 05:46 AM. Reason: Added "SECRET" in case Tim P misses it again!

  7. #97
    Z,

    How do you propose setting up this magic formula?
    Historical data? - doubt it would be any use as I'd judge the skills of the team more important than their car concept.
    A table of parts with costs and probabilities of failure? Still assumes that each team is essentially the same.

    FSAE is more execution-dependent than design-dependent in my opinion. Take all the aero-13" wheel-cbr600 teams and plot their results. And all the Emrax-spaceframe-no aero teams. And probably the AMK 4wd, practically-drives-itself teams. I doubt you can find a winning concept, at least in AUS.

    There are plenty of simple cars that fail as well as complicated ones. I doubt there's a real correlation in Australia.

    From 2016 Aus scores. Teams that score higher in Cost tend to finish more dynamic events. However, R^2 = 0.23, and I'd wager that can be explained by cost penalties and cost task. Remove Western Sydney Uni, and the R^2 goes down to 0.18
    cost.jpg

    I think the lesson is that teams need to select a concept which is achievable with their budget, organisational skills and engineering skills. I'm sure Delft and AMZ etc could build great brown go karts, but i doubt they'd be more reliable, and definitely wouldn't score more points.
    If you know you can pull off an ambitious concept, do it. If you don't - don't. That's what I think teams are lacking.
    For example a certain team that designed half an EV, toured a 2015 car and built a 2016 car, another which built a (purple) EV and an IC, and one that built a (red) IC with wings and a fancy gearbox. All of them didn't do as well as they wanted to.

  8. #98
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    Tim W,

    I have looked a bit more at the VI-Grade comp, but it is taking me ages to download some of the stuff. So ... can you fill in some of the details?

    The VF2017 Rules/Regs seem straightforward enough, only 4 pages!

    The idea of competing in Accel, Skidpad, and Autocross events is also good, because it makes it harder to "optimise" a single vehicle design.

    I also agree very much with the inclusion of a FUEL EFFICIENCY score (essentially a "Cost" on OTT designs), because it again makes it harder to find an "optimum". Just chasing maximum horsepower or biggest wings becomes counterproductive.

    Question: I noticed that there are "cone penalties", so is this a "Driver-In-the-Loop" simulation? Something like the video games (GTA?)?

    If so, then great, because that is the type of VD sim that I am now developing (slowly, in spare time). But my general proposal for a Virtual FS comp could also use the more conventional "computer drives the car" simulator.

    I would also be interested to hear any other interesting details of how this went.

    Anyone from Adelaide care to comment?
    ~o0o~

    Tim P,

    I sense much confusion in you.

    It would help if you listen to (or read) what others have to say, and then CONSIDER such, before blurting out comments like "...doubt it would be any use...".

    But you did get this bit right.
    I think the lesson is that teams need to select a concept which is achievable with their budget, organisational skills and engineering skills.
    Which is the theme of this thread.

    Selecting "the right concept" is also the reason for doing good simulations, in that it is pointless aiming for an exotic, super-spec, car, when the sims show that a much simpler and quicker-to-build car, is very nearly as fast. And it uses less fuel, so it wins on points anyway!

    Z

  9. #99

    Briggs Kart vs E-AWD

    Dear Z,

    I took the numbers of the Briggs Kart and did a Optimum Lap sim. I assumed a pretty flat torque curve with a maximum of 11 Nm. Coefficient of friction longitudinal was 1,5, lateral was 1,6. I estimated the downforce at 0,3 mē ClA.

    The competitor was an average European Top10, all-wheel-drive, carbon everything, full aerodynamic package car with this specs:
    car with driver: 265 kg
    driven type: AWD
    Engine: AMK DT5
    CdA: 1,5 mē
    ClA: 3 mē
    tire radius: 0,225 m
    longitudinal coefficent of friction: 1,4
    lateral coefficent of friction: 1,5
    torque peak: 112 Nm
    peak power: 80 KW
    Final drive: 13

    I did a simulation of all FSG Dynamic Events, except that the Wet Pad was a Dry Pad.

    Results:

    Briggs Kart:
    Skid Pad : 4,5s
    Acceleration: 9,8s
    Autocross: 87,5s
    Endurance: 104,5s/lap

    E-AWD:
    Skid Pad: 4,8s
    Acceleration: 3,4s
    Autocross: 69,9
    Endurance: 75,3s/lap

    The lower CoG and track width were unregarded, because of point mass calculation. Both would surely play in favor for the kart. For a event points calculation i assumed the Kart setting the top time in Skid pad. The other top times were estimated with Delft-ish times. Efficiency was not considered.

    In total the dynamic points for the Kart are: 108/575 (because for everything except skid pad it received only the points for completing)
    The E-AWD dynamic points are: 493/575

    Just looking at those numbers and looking at the speed plots I see, that the disadvantage in traction and weight of the E-AWD is almost completely compensated by downforce. So what makes the difference between those two is the amount of power the E-AWD is putting out. But interpret it for yourself. Speed-distance plot AutoX.jpg
    I don't think a Kart could be somewhere near competitive. I agree that the simplicity and radical reduction on necessary parts only is something many students can learn from Karts when they have super fancy electrically adjustable titanium blade ARB's in mind. But a Kart itself would be nothing which could win anything (let alone all the modifications which had to be done to make it rules compliant).

    Also adressing the other points you stated:

    Cost: A lot of the parts we use came in through sponsoring, In our experience, it is pretty hard to find a sponsor which purely gives you money. It is way easier to get materials, parts or machining time for free, than cash. So the best materials/parts we can get for free will make their way into the car. If there is somebody that will make us titanium bolts, I don’t see any argument why we should not say thank you and take them. They do the same job and safe almost a kg on the car even though they would be ridiculously expensive if bought. On our teams savings account they cost zero.

    In case there are two or more possibilities to choose from, for example a cheap and heavy cardan joint and an expensive fancy motorsport joint or in a another example different qualitites of carbon fibres, where you would have to compensate the lower mechanical abilities with more material to pass the SES, I do a simple “return of investment” calculation. When technical features are comparable and it comes down to costs vs weight, I have a number what every saved gramm is worth to us. This number depends on our overall budget and varies from year to year, for example 1€/gramm. This would mean that if we could save 10 kg on our existing design through higher quality/lighter material, it would be worth 10.000€. This is not based on actual numbers, just to give an impression of the way of thinking.

    To be able to fund your car it is a game of give and take with your sponsor to keep them on board. When I think about what we can give them I have a list of 4 points:
    - Good results and a neat looking car, so they see their logo well represented
    - Impress them with the performance of our car on sponsor driving days, to activate the emotional side
    - Impress them with knowledge and state of the art technology so they might want to invest in you
    - Co-development of new technologies/materials/software they also benefit

    My point is, if you build a, like you call it, kind of mini-F1-style car you get access to sponsors who will help to make this possible for you. So this is not a cost question. If you have the option to use high-tech materials and electronics which give you a competitive edge you take it and say thank you. The weekend racer idea is dead. At least in Europe the majority of the teams is purely performance/innovations driven.

    I was just talking real money in the last three paragraphs, because I think the majority of FS people would agree that cost report money doesn’t mean anything. The number in your cost report doesn’t have anything to do with real costs and also has no parallelism to the real costs. But that’s a different story. FSG realized, that letting students calculate the costs of their vehicle in a report which takes 45 min to print and therefore is impossible to be thoroughly inspected by the judges is pure bollocks and only promotes fiddling the figures.

    Build-time: Having a top level aero kit doesn’t need to stretch your development time in my opinion. The top aero teams did not get there in one year. It is usually a “let’s take lasts years aero and increase downforce or efficiency closer to our target values” kinda approach. Like probably all teams, we have a design freeze. This marks the freeze of airfoils to be able to send the mold data to our manufacturing partners. While this happens, further optimizations of aero balance, AoA, gaps, vaines, plates and gurneys can be done without risking trouble in the overall time table.

    Reliability: I’m not quite sure how you judge the reliability potential of a concept, but a pure comparison of weight to power seems a bit too easy for me. In don’t have any statistics to back this up, but if I look at the DNF’s at events I would guess that it’s above 50% a CAD/manufacturing/assembly issue. So the initial concept was perfectly fine, it was just mistake of one person not doing their job properly, like bolts which weren’t properly fastened, stress raising edges, bad welding, wrong positioning of BOTS, aero positioning out of the designated areas, wrong power limits at e-cars, wrong engine mapping resulting in too much noise. Also for e-cars a lot of electrical issues were the cause for DNF’s, which don’t have anything to do with weight.
    Personally I would much rather try to keep the reliable and good performing parts from last season and only do detail work on them so you can shift focus on parts with bigger issues to really optimize reliability and performance. In think it’s often the missing work on the details like tolerances, friction, deflection and all the little small side effects nobody thought of, which can cause a good concept to not work as it should. For us this was often the case when we tried something completely new or to radically optimize systems which were already good.

    - Freddy
    Last edited by FrederikWe; 06-15-2017 at 03:35 PM.

  10. #100
    Freddy,
    Care to post your OptimumLap files?
    I'd be interested to add in a 2wd EV and aero IC car
    If you don't want to give up the track files we can use this one:
    Endurance FSAE-A 2015.zip
    Last edited by tim_pattinson; 06-15-2017 at 06:52 AM.

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