OptimumLap – Vehicle Dynamics Simulation, Simplified.

[OptimumG]

Dear FSAE friends and fans,

In engineering projects in general and FSAE projects in particular, a common goal is improving performance. In most cases, improved performance can be achieved in many different ways. We'll then face the question – What's is the best and most efficient way to improve performance?

In the past, time and resource constraints can make it difficult to explore all different options. However, with modern computers, we are now able to model and predict the behavior of different systems via simulation – for example a race car. Simulation is a great method to explore different design solutions without having to build a single physical part. Analyzing simulation results gives us a better understanding of how our race car reacts to parameter changes and we can make decisions based on data (rather than gut feelings) – something Geoff outlines really well in this thread: http://fsae.com/eve/forums/a/t...25607348/m/217101453 (http://fsae.com/eve/forums/a/tpc/f/125607348/m/217101453)

Recently, we asked ourselves: How come so few FSAE teams use simulation to determine what their car should look like? To determine which areas of the car to focus on? We found that the level of complexity of most readily available simulation software were so high that it required a team days if not weeks to get a first result. A common misconception is that increased complexity leads to better, more useful results (Damian Harty demonstrates in his paper "Myth of Accuracy" that this is not case).

With OptimumLap we set out to simplify vehicle dynamic simulation – to the point where anyone can get reasonably accurate and very useful results within minutes. By reducing the vehicle to its most fundamental components, we define a car with only 10 parameters. Each parameter representing a specific aspect of the car (such as engine, tires or aerodynamics). This makes it easy to identify the effect that each parameter/sub-system will have on the vehicle's performance – something we believe helps you better understand what to focus your time and resources on. A simplified vehicle model however, has the downside that it doesn't allow you study the vehicle in great detail. For that we need increased fidelity, but in our experience, you have to make it useful before you make it complicated. And, with OptimumLap, the results are typically within 10% of reality.

We have built OptimumLap to encourage you and your team, to use simulation results (engineering data) to make engineering decisions. With the built-in tools you are able to study effects of engine power, gearbox characteristics, aerodynamics, tires and mass. The results will help you define the specifications for the detailed design of different sub-systems. For example: Do you need more longitudinal or lateral grip? How much drag can you wings add before they start to negatively affect performance? Which final drive ratio minimizes the number of gear shifts (and thus the size of your pneumatic tank)? How much energy do my batteries or fuel tank have to be able to store to complete endurance?

These are just some examples of how OptimumLap can be used and we are excited to see what types of analyses you will come up with! We are making OptimumLap available free of charge for anyone. If you want to get started already, we are currently in a beta testing phase (with the final release slated later this fall) and we invite you all to try it.

To sign-up for the beta:
1. Go to http://beta.optimumg.com/signup
2. Enter the invite code: FSAELap2012 (there are only 50 invites available at this time)
3. You will receive an email with a download link and your license key.

That's all for now, we would love to hear your thoughts and comments. We will of course update you here, on our facebook page on our website once we have an update!

For more information: http://beta.optimumg.com/introduction/

http://s3.amazonaws.com/backend_static/img/thumbs/gear.png (http://s3.amazonaws.com/backend_static/img/gear.png)

http://s3.amazonaws.com/backend_static/img/thumbs/panels.png (http://s3.amazonaws.com/backend_static/img/panels.png)

http://s3.amazonaws.com/backend_static/img/thumbs/traction.png (http://s3.amazonaws.com/backend_static/img/traction.png)

--

Best regards,

Rachel
rachel.trapp@optimumg.com
OptimumG
Vehicle Dynamics Solutions
http://www.optimumg.com

[jlangholzj]

My initial impression on this is great!

A lot of the car characterization tools/graphs teams may have available to them if they already purchased RDP (race data power). There are some added goodies however and I really like the vehicle report.

The real winner is tying all those tools into a track simulation. Acceleration/Skidpad have always been somewhat easier to figure out times/values and other things for but being able to put it into an autocross/endurance event is something awesome.

I got about half way through making the track for FSAEL-12 endurance and it crashed....lost everything on the track layout...and i went cross-eyed http://fsae.com/groupee_common/emoticons/icon_smile.gif I'll get back at it, just not tonight.

So far, another great tool from the optimum crew!

[OptimumG]

Yep, during this pre-release period our main focus is on stability and usability, so any feedback that you guys have is definitely appreciated! You can contact us directly or you can submit feedback through the software too (just hit "F2").

Also, inside that zip folder you have, you should also find some sample 2012 Lincoln (FSAE-West) and FSG tracks, among others. That may help you get up and running with some representative FSAE/FS Student tracks.

--

Best Regards,

Pete
pete.ringwood@optimumg.com
OptimumG
Vehicle Dynamics Solutions
http://www.optimumg.com

[mech5496]

Great! Lapsims have always been a huge concern for an FSAE team especially when deciding about major components on the design phase.... gonna give it a try!

[GO]

Just downloaded now. Thanks for making this available. I am commencing my own Lapsim project this coming year and hopefully this will help with some ideas.

You wouldn't happen to have this or last years FS Silverstone tack map would you?

Many Thanks

[Roundabout136]

Damn, already filled up!

[OptimumG]

Roundabout - During this prerelease/testing period we are releasing new program builds quite often. We will probably release some more invite codes as we get further into this testing period, so check back in a few days time and there may be some more here.

Go, If you have some logged data that you'd like to pass along, we can generate a Silverstone track map for you - as long as you don't mind us releasing it as a general "Sample track".

-

Pete
pete.ringwood@optimumg.com
OptimumG
Vehicle Dynamics Solutions
http://www.optimumg.com

[povelocj]

I was not able to find any tracks in the zip file. Would anyone be able to point me to where they are?

[NickFavazzo]

I found them in the extracted folder from the zip:
Optimum Lap Beta Release 1.1->Sample Tracks.

[povelocj]

Originally posted by NickFavazzo:
I found them in the extracted folder from the zip:
Optimum Lap Beta Release 1.1->Sample Tracks.

I think I have a different download than you

The zip file is named optimumLap.zip
And when extracted the folder is OptimumLap_V1.1.0.1

[Jakob]

Nice Program! Thanks!

Maybe it would be good to add "incl. Driver" to the Vehicle Mass description. At least when selecting Vehicle Type "FSAE".

I think some people will forget the driver otherwise.

Jakob

[povelocj]

Would someone be able to email me the circuit files? I made my own circuit and everything seems to be going well. My email is povs09@gmail.com

I will start making a list of possible bugs useful add ons.

[jlangholzj]

Originally posted by Jakob:
Nice Program! Thanks!

Maybe it would be good to add "incl. Driver" to the Vehicle Mass description. At least when selecting Vehicle Type "FSAE".

I think some people will forget the driver otherwise.

Jakob

if you mouse over the field it states "vehicle weight including driver"

[Cardriverx]

Any way I can still get an invite?

[NickFavazzo]

Has anyone managed to get a nice skidpad track working? I have managed to get the two loops but no entry or exit straights (it crashes).

[mech5496]

I was thinking of trying it sometime yesterday, but it was soooo hot that I preferred to take a swim... I was thinking that it would be useful to upload any FSAE-specific tracks here (something like a shared FSAE track library), or send them to the OptimumG guys to include in future releases. Skidpad and acceleration is common ground to all competitions and I would love to have tracks such as FSAEM or FSUK included on the sample tracks, although FSG works just fine for me! http://fsae.com/groupee_common/emoticons/icon_biggrin.gif What do you guys think?

[NickFavazzo]

Definitely up for a shared tracks, after playing with the create a track for a while now I can really appreciate a good track as opposed to my roughies..

@OptimumG do you have a program that extracts track information straight from data or have you made the FSAE tracks by hand?

[OptimumG]

To those who missed out on the first round of the beta release, we are working hard towards releasing new versions quite regularly - we've already had some great feedback and addressed those issues, so we expect to expand the beta in the coming days.

Regarding the track maps, we are also working on having a database where you can access download/upload/share tracks. Having pre-built tracks makes it much easier to get up and running, so that is something we are looking at improving.

Nick, Our current sample tracks are generated from logged acceleration and velocity information but we are looking at being able to import logged data straight into OptimumLap (to help with both track generation and model validation). As Harry mentioned, if you guys want to send through some comp data in the meantime, we are happy to generate a track from it and include it in future releases.

Attached here is a zip file of a few sample tracks to keep you going: http://downloads.optimumg.com/...ta-Sample-Tracks.zip (http://downloads.optimumg.com/OptimumLap-Beta-Sample-Tracks.zip) (It contains Nebraska, FSG and Australia; as well as some other no FSAE ones).

We do expect to have a new beta release out soon, so stay tuned, and we look forward to your feedback.


--
Pete
pete.ringwood@optimumg.com
OptimumG
Vehicle Dynamics Solutions
http://www.optimumg.com

[jlangholzj]

Also, It would be great to have e85 included instead of just "gasoline:

[NickFavazzo]

I'm liking the additions in the update.
Has anyone been able to get a skidpad track to match their actual times? I have matched UWAM times on the FSAE-A track but cannot tweak to also match skidpad times.

Also is anyone else having trouble setting sectors for a skidpad track? I cannot seem to get one loop to match correctly given I know the sector length...

*EDIT* has anyone tried an accel sim yet? I cannot make it start from a stop... am I missing something simple here?

[Jakob]

Originally posted by NickFavazzo:


Also is anyone else having trouble setting sectors for a skidpad track? I cannot seem to get one loop to match correctly given I know the sector length...

Why not just use an simple circle (Track Configuration: Closed Circuit) as skidpad simulation.
Don't you just want the time for one lap (left/right doesn't make a difference here)?
Is there a benefit simulating the "inlaps" and straights?




*EDIT* has anyone tried an accel sim yet? I cannot make it start from a stop... am I missing something simple here?

I guess:
Track Configuration: Open Circuit

.

[NickFavazzo]

for the skidpad, I'm not necessarily concerned with straights but I cannot seem to get the sectors to match up with track geometry, I am trying to set a full skidpad layout as a relatively simple track to learn with.

I'll double check the open circuit bit for the accel track but I am pretty sure I have played with it already..

[Fantomas]

@Rachel:
It would be great to give the organizers of the various events access to this together with a "standard" car model. Maybe they are then able to set up track layouts which are rules compliant.

Fantomas

[Jakob]

Originally posted by NickFavazzo:

I'll double check the open circuit bit for the accel track but I am pretty sure I have played with it already..

http://www7.pic-upload.de/09.08.12/42qd56lg15q.jpg

But the speed is not starting from zero?!

.

[NickFavazzo]

Managed to sort the accel problem, turns out I was changing the wrong setting for open/closed track. In the update email the launch problem was mentioned as a known problem, I take it will be fixed eventually.

[Jakob]

Originally posted by NickFavazzo:
... In the update email the launch problem was mentioned as a known problem, I take it will be fixed eventually.

You're right, I read the e-mail straight.

Launching a vehicle with a sequential gearbox will start from the lowest rpm in the lowest gear. No Launch control strategy.

So I just added a point with low rpm (500 1/min) with the same Torque (50.3 Nm) like the next higher point (6119 1/min) to the engine data. I think that's fine because the tire is the limit there.

http://www7.pic-upload.de/09.08.12/kb5jfco43yw.jpg

[NickFavazzo]

Has any one come across having two identical vehicle settings producing different laptimes? I'm not sure if I have changed something but I cant figure out for the life of me what is different between the two..
If anyone wants to look at the project file let me know and I will email it across..

*EDIT* I found that the "at kg" box for the lateral coefficient of friction has been at the value in the final drive ratio box and is not actually what is in the box, eg. friction at 200kg, final drive 6.9. In the calcs it has been using the 6.9 for some reason. report sent.

[The Neck]

Any news on more releases for people that missed out on the first round of OptimumLap?

[OptimumG]

We've had some great preliminary feedback from a whole range of teams. Notably UWA Motorsports, USF Racing, KA-Racing, Bearcat Motorsports, TU Graz Racing, McGill Racing and Uni Patras - a big thank you to you guys, and to many more.

We've just rolled out a new 1.2.1 beta version, which addresses most of the issues we have found to date, and which focuses heavily on stability and usability improvements. As such, we are opening up the beta again, with the following details.

Invite Code: FSAELap2012
Signup Page: http://beta.optimumg.com/signup

There is another 75 spots, so get in quick!

In the coming weeks we hope to roll out a track database to ease the issues of building your own track. Among other things, we are also looking at how we model vehicle launches and at incorporating an automatic sensitivity study tool, to help really focus on where the vehicle performance lies.

During this beta period OptimumLap is still under full time development and testing, so please keep the feedback and suggestions coming. We are really quite interested to see how you guys are using this, so please let us know.


--

Best Regards,

Pete
pete.ringwood@optimumg.com
OptimumG
Vehicle Dynamics Solutions
http://www.optimumg.com

[Charles Kaneb]

What load sensitivity are you guys using? I can get a fairly close match for my team's laptimes over a broad span, but I only have one data point and don't know anyone else's car well enough to simulate it.

FWIW I'm using .002 most of the time.

[NickFavazzo]

I have a few UWAM vehicles on GoodYears using .004, .005 for the sensitivity, I havent began playing with it to intensely but I will be trying to match TTC and testing at some point.

[SNasello]

I just noticed a few things in the latest version which seem a bit odd. Why is there no longer a weight distribution or load sensitivity parameter? Although this has no effect in the corners, it makes a big difference on braking and acceleration performance. The load sensitivity is also very important for aero cars.

[OptimumG]

Stefan, the load sensitivity options are still there, but you will have to go File > Options > Advanced and enable the check box there.

Running with this load sensitive option is essential for formula student applications, as a typical formula student tyre is highly load sensitive. It is still advised (but less critical) to run the load sensitive model for other types of vehicles.

The values that Nick and Charles mention above are in the right ballpark, but TTC data will confirm the proper value for a specific tyre.


Why is there no longer a weight distribution?

We have simplified the "weight on driven wheel" concept down to just two-wheel-drive or four-wheel-drive inputs. The weight on driven wheel input represented how much vehicle weight is on the driven tyres, which does differ from the weight distribution. We only used this value to determine the traction limit available under positive (forward) longitudinal acceleration, so values of 100% would always result in the quickest lap times, representing all four wheels being driven. Selecting the two wheel drive option is now equal to a weight on driven wheel of 50%, and four wheel drive is the same as 100%. For formula student cars which are commonly traction limited for so much of their operating range, this input had a very large influence on the simulated results.

With the simplified point mass model, we can't effectively model weight distribution or weight transfer (which is also why there are no wheelbase, track width or center of gravity inputs). Having the option to input a percent weight gave the impression that we were doing this, so apologies for any confusion on that front.

I'm interested to hear any of your thoughts on this, as internally here at OptimumG we've had a lot of discussions on complexity vs simplicity (and how they relate to usefulness) whilst developing this program.

--

Pete
pete.ringwood@optimumg.com
OptimumG
Vehicle Dynamics Solutions
http://www.optimumg.com

[SNasello]

Thanks for the tip on the load sensitivity, I didn't look into the options in this version.

I have written my own point mass lap sim which does include weight transfer effects. It is still not perfect, but gives a better idea of how much cornering power is available depending on CG height, track width, and of course tire load sensitivity. Essentially I just assumed a load transfer distribution equal to the weight distribution of the car, which gave pretty decent results for maximum cornering speed and lateral acceleration. The fact that the corners and straights are calculated separately means you can just switch between a lateral and longitudinal load transfer calculation. The biggest problem is you add another iteration loop, which costs calculation time.

Some interesting results come out however, in terms of CG height and track width influence. The most interesting effect of track width however is the line that can be driven through a given course. This is a little bit trickier to simulate however.

[Ben A]

Hello,

I would appreciate it even if there was the ability to specify wheelbase and track width and center of gravity, too. So we can better learn about chosing wheelbase and track width and there interaction. Is That an option to implement?

[SNasello]

I have made a comparison between OptimumLap and my own lap time simulation which includes load transfer, using the same vehicle parameters on the same track. Just to give an idea of how the load transfer affects that lap time and speed profile.

http://img692.imageshack.us/img692/3961/lapsimcomparison.jpg (http://imageshack.us/photo/my-images/692/lapsimcomparison.jpg/)

The load transfer reduces the amount of time when the car is traction limited under acceleration and makes for a slightly earlier braking point. The reduced cornering speeds have a large effect on the braking points as well. In the end the lap time discrepency is close to 5%, which could be significant for some design decisions.

Here is another one showing the effect on an acceleration event.

http://img513.imageshack.us/img513/7887/accelerationcomparison.jpg (http://imageshack.us/photo/my-images/513/accelerationcomparison.jpg/)

[SteveOr]

I want to try some simulations, but, i have no experince of Aero. Can any one give me a few examples for drag, down force coef. and front area for FSAE Cars?

What are Numbers perhaps for the actual Monash, Gobal, Erlangen, Esslingen, HAWKS and KIT Cars?

I would be nice to get a few numbers to get better results for the simulation.

Thank you

[SNasello]

SteveOr,

I would love to help you out with your question, but have to say that we (Esslingen) also didn't have any idea of typical numbers when we started. The question you should ask, is how much aero do I need, and is it worth the weight/drag penalty.

That is the beauty of the this type of simulation, that you can answer such questions without knowing where to start, just run a 2 parameter sweep of Cl and Cd, set Frontal aero to 1 for simplicity. Go from say CL of 0 up to 6 or so (probable still achievable) and Cd from 0.5 to 2.

I won't say exactly where we lie in that range.

[SteveOr]

Ok Thank you,
I did this simulation with the sweep. The Result is a 3d diagram. But what can i see here?, ok thats clear that the Laptime goes down with lower drag and more downforce but how help me that with the decision of aero or no aero or what aero coef. goals has the designer has to go for?
https://dl.dropbox.com/u/1713950/Drag_1.jpg

https://dl.dropbox.com/u/1713950/drag2.jpg

https://dl.dropbox.com/u/1713950/drag3.jpg

Before this i analysed the effect of weight reduction on Laptime.

So i see me best Laptime with the lowest weight was 89,2.

It would be glat i anyone could show me the right way in that sector of Aero and Laptime simulation.

Thank you.

[OptimumG]

Stefan, Thanks for sharing those comparisons.

Without a doubt, including the effects of load transfer (or other additional vehicle model inputs) into a simulation will yield more accurate results, with the downside being the additional time to obtain the results.

In this case, the additional resources may be the time taken to tilt the car and measure the center of gravity location. In the case of incorporating a more accurate tyre model, the trade off is the time required to run the tests, fit the models (and then validate them). More and more resources must be devoted for each additional bit of accuracy, but surely there must be a limit? How accurate do you need to be before the results start becoming actionable, useful results?.

We believe that the relationship between accuracy and usefulness is definitely not linear, and that the overall usefulness is strongly related to the problem that you are trying to solve. If you can't apply the results, then increased accuracy offers no actual advantage. Damian Harty explores this concept well in his Paper "The Myth Of Accuracy" - I encourage anyone interested to seek it out.

If you are trying to determine where to allocate development resources - to determine if mechanical grip, aerodynamics or vehicle power is more important for your use case - OptimumLap allows for a very broad study of this, and this is what we were going for when we developed it. If lateral acceleration performance turns out to be critical for your application, then it would be worth investigating what can be done to focus on that aspect. Whether you do this by investing resources to drop the vehicle center of gravity, focusing on suspension development to improve kinematics or tyre temperature control - or numerous other possibilities - is not what OptimumLap was designed to do.

OptimumLap has been designed to tell you not whether this investment will be useful, but whether it will be more useful than power-train development or development of a completely different vehicle sub system all together. OptimumLap is at the start of the simulation tool chain - it won't provide you the end result answers, but hopefully it will tell you which questions to ask.


--

Pete
pete.ringwood@optimumg.com
OptimumG
Vehicle Dynamics Solutions
http://www.optimumg.com

[SNasello]

Thanks for the reply Pete. I definitely have to agree with you, just wanted to point out where the simulation falls short. I can understand also from a programming and computing time standpoint, my simulation would have been written much quicker if I didn't include load transfer and would calculate much faster as well.

SteveOr: The lap time simulation alone won't grab you all of the answers, nor will someone just give them to you. Like Pete just mentioned, it is designed to give you a direction.

If anything the lap time sim should have showed you, maybe we should really look into aero? The questions you need to answer in addition are, Do we have the manpower and time to manufacture the wings? Can we afford the additional setup time? Can we validate that the wings actually do improve performance?

Is 50kg of downforce and just as much drag @50km/h worth 50kg of additional weight? (You can build an aero package with much less weight and much less drag than this).

[OptimumG]

Originally posted by SteveOr:
I want to try some simulations, but, i have no experince of Aero. Can any one give me a few examples for drag, down force coef. and front area for FSAE Cars?

What are Numbers perhaps for the actual Monash, Gobal, Erlangen, Esslingen, HAWKS and KIT Cars?

I would be nice to get a few numbers to get better results for the simulation.



SteveOr,

To add to what Stefan has said, there are some SAE papers (2006-01-0808 and 2006-01-0806) by Scott Wordley and Jeff Saunders (both Ex-Monash guys) on this very topic, with actual values from previous Monash vehicles.

The Formula Student aero rules may have changed slightly in that time, but the results should still be pretty indicative. Scott is still active on these forums, so maybe he can chime in on how aero has evolved over the years.

As a a start, you may want to create two different vehicles within OptimumLap (a low downforce and high downforce configuration) and compare the speed traces and fuel consumption between them. From there you can decide if it is worth studying the effects of angle of attack, size, location (and much more) in greater detail.

As Stefan mentioned, once you have one answer, many more questions will come up - This is never stops.

--

Pete
pete.ringwood@optimumg.com
OptimumG
Vehicle Dynamics Solutions
http://www.optimumg.com

[SteveOr]

Thank you for this.

Would you tell me Stefan how much of the down forces come from the undertray on your car in percent? I saw you have a very long undertray. That would be nice to know. Thank you.

Is there a way to get the SAE Paper in germany for free?

[SteveOr]

Hello,

i found the SAE Paper.

i did a simulation with the Monsh Drag and lift coef. And what i see is that with the high down forces setting and 15kg more weight the Accel. time is 0,07 sec. faster then no aero, the low drag setting is a littel bit (0,01) slower than without aero. That is a littel bit confused for me. So the Aero package generates the so much doen force at higher speed that grip potenzial is higher than the drag?

[JulianH]

Originally posted by SteveOr:
Hello,

i found the SAE Paper.

i did a simulation with the Monsh Drag and lift coef. And what i see is that with the high down forces setting and 15kg more weight the Accel. time is 0,07 sec. faster then no aero, the low drag setting is a littel bit (0,01) slower than without aero. That is a littel bit confused for me. So the Aero package generates the so much doen force at higher speed that grip potenzial is higher than the drag?

At least, there was one team running a full downforce rear wing in the FSG Acceleration http://fsae.com/groupee_common/emoticons/icon_smile.gif

It depends on the power of the car, if you have enough (traction limit) then rear downforce helps you while accelerating.

The Monash numbers from 2002 (cD*A = 1.8 and cL*A= 3.41) are very "draggy". With the new aero-rules, it is possible to have a cL*A of roughly 3.8 while having cD*A = 1.3.

The question is now, how much weight equals a higher Lift coefficient. It is not linear and I think it is only possible if you do CFD simulations, what is possible with which setting to find that.

[Thibault HUGUET]

I want to say if anyone have a problem to import the FSG track in OptimumLap?

I downloaded the file ont the online track database in OptimumG website but when I try to import it, the track doesn't appaer in the design menu. So I can't laucnh simulation. Other track as Nebraska works fine.

Thanks OptimumG for this Software!

[OptimumG]

Thibault,

Apologies about that one - if you download it now it should be fine. The previous track was mirrored to reality, and when we flipped it back, it didn't upload cleanly.

You can find the FSG track (and many others) over here: http://share.optimumg.com/tracks/

--

Pete
pete.ringwood@optimumg.com
OptimumG
Vehicle Dynamics Solutions
http://www.optimumg.com

[Thibault HUGUET]

thanks, FSG track works fine now.

Now, I must find the same results with my simulation than the reality. Actually, the gap is more than 10s...

[SNasello]

Thibault,

The FSG track from OptimumG is not the same one that was built at the event. I have built up a version of the FSG track from my team's logged data, I will see if I can upload it. I am still working on the autocross track.

[Thibault HUGUET]

Ok, so it's normal that I have this Gap.
If you can upload your FSG track, I'm very interested because I haven't data which can help me to make my own OptimumLap track.

[Turns]

Does it take into account shift time since this would be important?

[SNasello]

I don't see a way to upload track maps to the online database. If you would like my version of Hockenheim Endurance 2012 send me a PM with your e-mail address.

One of the reasons that you could be getting a 10 second difference in lap time is that the FSG track was only about 1.23km long, and the one in Optimum lap is 1.42km long.

Are you just trying to validate this based on your lap time at the event or also looking at velocity traces? If you measured lateral acceleration and velocity at the event then you can create your own track map.

[OptimumG]

Stefan - We are in the process of opening up the track database to allow anyone to submit tracks to it, or to convert their own logged data to an OptimumLap track. We'll also be adding the ability to search for tracks and so on, so that on the whole, everything is a bit easier to use. (I'll put a post up here when that one is live).

Turns, the vehicle model in OptimumLap is deliberately simple - we don't take into account the time taken to shift gears, even though yes, in reality, that does affect the outputs. The reason we don't model the shift times is that OptimumLap is intended as a "concept level" simulation tool, designed to find which section of the car is most relevant to work on. If the OptimumLap results turn up that longitudinal acceleration is more important than lateral acceleration, then that points you in the direction of looking at power-train development - focusing on the shift system (either by reducing the time between shifts, or reducing the total number of shifts) is just one way to achieve this.


--

Pete
pete.ringwood@optimumg.com
OptimumG
Vehicle Dynamics Solutions
http://www.optimumg.com

[SNasello]

Thanks Pete, I suspected this would be the case.

Just out of curiosity, what type of logged data will be required to generate the track map? I assume just vehicle speed and lateral acceleration from one lap?

I think an interesting feature would be to allow import of an excel table of the sector length, corner radius and direction flag. Such a feature would have saved me quite a bit of time already.

[Paul Achard]

Hi,

Pretty basic concerns, but the help file doesn't really address this:
-Is the torque input supposed to be at the wheel, or at the crank?
-Can I avoid copying the torque data line-by-line, i.e. copy the entire curve at once?

Thanks!

[Thibault HUGUET]

Stefan, I have send you a PM.

I'm interested by the Paul question with the torque input.

Also, I haven't real idea of value for aero data for a FSAE car without aero package. The value in help message are for a basic passenger car. For example, 2m² in front area, but i think it's less for an FSAE ( 0,7 m²?).

[Turns]

Originally posted by SNasello:
I don't see a way to upload track maps to the online database. If you would like my version of Hockenheim Endurance 2012 send me a PM with your e-mail address.

One of the reasons that you could be getting a 10 second difference in lap time is that the FSG track was only about 1.23km long, and the one in Optimum lap is 1.42km long.

Are you just trying to validate this based on your lap time at the event or also looking at velocity traces? If you measured lateral acceleration and velocity at the event then you can create your own track map.

That's fair enough. The main problem i was having without shift times was modeling drag racing times, as this can have quite a large imapct depending on where you shift. Such as whether to shift or overrev the gear if youre changing near the finish line.

[OptimumG]

-Is the torque input supposed to be at the wheel, or at the crank?
-Can I avoid copying the torque data line-by-line, i.e. copy the entire curve at once?

Paul - the engine torque is given at the crank. If you've gathered this data on a chassis dyno (at the wheel), you'll want to set your drive efficiency to 100%, as your measurements will already include the losses.

Regarding the torque curve, if you copy two columns from excel (rpm and torque), you can click on the engine data table and hit Ctrl-V to paste it in directly - It's not so obvious, but it does help when you already have a detailed curve.

I'll make sure that both of these suggestions are included in the tutorial/help file too.

--
Pete
pete.ringwood@optimumg.com
OptimumG
Vehicle Dynamics Solutions
http://www.optimumg.com

[OptimumG]

Just an update, you can now head to our website and convert your logged data (speed and lateral acceleration) to an OptimumLap track format. We also greatly encourage you to upload your vehicles and tracks to the online database, to help aid others with their understanding.

How the database works is that we will publish selected (not all) tracks and vehicle for everybody, with the idea being to help promote understanding of different circuits and vehicles. We hope that this will allow those just getting started with simulation to get a feel for the typical values of different vehicle concepts.

The logged data conversion requires speed and lateral acceleration data at a fixed frequency (ideally around 5 to 10 Hz).

To get started with this you can either head to the the main OptimumLap page (http://www.optimumg.com/software/optimumlap/) and follow the links to the account login section, or head directly to the OptimumLap login section (http://share.optimumg.com/accounts/profile) (Note, you will need to set yourself up with a password to get started).

Below are a couple of screenshots outlining what's new:

http://www.optimumg.com/images/software/thumbs/oLap_user_panel.png (http://www.optimumg.com/images/software/oLap_user_panel.png)

http://www.optimumg.com/images/software/thumbs/oLap_track_database.png (http://www.optimumg.com/images/software/oLap_track_database.png)

http://www.optimumg.com/images/software/thumbs/oLap_vehicle_database.png (http://www.optimumg.com/images/software/oLap_vehicle_database.png)

Hopefully this will allow you guys to validate your models at your usual test tracks, rather than based off a single competition run. Let us know how you go!


--
Pete Ringwood
pete.ringwood@optimumg.com
OptimumG
Vehicle Dynamics Solutions
http://www.optimumg.com

[SNasello]

Pete,



**EDIT** Works now.

On the other hand, i am only able to export data from my data logging software at 6.25hz and 12hz (For some reason it is based on multiples of the base sampling rate, which is 800Hz). The 6.25hz would not be a problem except that when I try to convert the track it doesn't accept decimal places. This screws up the integration of the distance and I end up getting an incorrect track length.

Is is possible to allow up to a higher frequency (12Hz) or allow for a frequency such as 6.25Hz?

[OptimumG]

Stefan - Oops. Apologies about that one, it's fixed now: http://share.optimumg.com/tracks/convert/

--
Pete
pete.ringwood@optimumg.com
OptimumG
Vehicle Dynamics Solutions
http://www.optimumg.com

[SNasello]

Thanks Pete,

Works great now. I will get some track maps from some previous events posted for everyone to use.

[peterPan]

Hi, which weight distribution is assumed for the car?

Its not 50:50, since an acceleration run on a straigth track does not give me a longitudinal Acceleration of 50% * TireLongG in the traction limited Zone (Aero set to 0).

[Thibault HUGUET]

I have a problem to import FSAE non aero car.
I can import other car of the online database.
I'm the only one with this problem ?

[Surjan Singh]

Hello, I probably missed something really obvious but I'd appreciate some help. I was playing around with OptimumLap and ran a batch run on the FSAE No Aero Car at the Michigan track. The program is showing that a heavier car is faster. Thanks in advance for the help.https://dl.dropbox.com/u/14060418/optimumlap.jpg

[SNasello]

Are you using the advanced tire model with normal load sensitivity? Do you have a negative downforce coefficient (lift)?

These are the only two reasons I could think of why more weight would help.

This shows once again the limitations of the software, which you need to understand if you want to use it. Without load sensitivity and load transfer effects you get some incorrect results.

[Surjan Singh]

Ah, I missed the load sensitivity posts. That fixed the issue. Thanks for the help.

Surjan

[OptimumG]

Originally posted by Surjan Singh:
Hello, I probably missed something really obvious but I'd appreciate some help. I was playing around with OptimumLap and ran a batch run on the FSAE No Aero Car at the Michigan track. The program is showing that a heavier car is faster. Thanks in advance for the help.

Surjan, As Stefan mentioned, in this case it relates to the load sensitivity of the model. Running a sweep of simulations and changing the mass for each one - without updating the tyre grip levels - will often give better lap times for FSAE based application (due to how frequently they are traction limited).

However, adding more weight to a vehicle will typically reduce the normalised grip that the tyres provide, lowering overall corner speeds.

I've attached a few examples here, but we'll also be putting together some tutorial style pdfs to further demonstrate this. In the first example the vehicle can corner at the same speed, even with the added weight, as the grip coefficient remains unchanged with mass. Here, the results say that the added mass is no real detriment (due to being severely traction limited.)

http://www.optimumg@optimumg.com/images/software/forum_hosting/non_sensitive.png

In this second example, the normalised force that that a tyre can provide changes with the vehicle weight, resulting in a heavier vehicle taking a much larger performance hit. Here, each simulation point has a different mass, -and- a different level of grip.

http://www.optimumg@optimumg.com/images/software/forum_hosting/load_sensitive.png

It's up to you guys to determine both the load sensitivity of your tires and how to incorporate this information into your vehicle design, but we hope that OptimumLap provides a tool to quickly quantify these global, high-level effects.

--
Pete
pete.ringwood@optimumg.com
OptimumG
Vehicle Dynamics Solutions
http://www.optimumg.com

[OptimumG]

Originally posted by peterPan:
Hi, which weight distribution is assumed for the car?

Its not 50:50, since an acceleration run on a straigth track does not give me a longitudinal Acceleration of 50% * TireLongG in the traction limited Zone (Aero set to 0).

The assumed vehicle weight on the driven tyres is 50% for "2WD" and 100% for "AWD". Aero is one factor that needs to be zeroed if you are looking to get a longitudinal acceleration 50% * TireLongG, but you'll also need to set the rolling resistance of the tyres to zero, and the gearbox efficient to 100%. In the attached screenshot, the longitudinal grip level parameter was 1.4, yielding 1.4g of longitudinal acceleration for an AWD vehicle in the traction limited zone, and 0.7g for a 2WD drive vehicle.

http://www.optimumg@optimumg.com/images/software/forum_hosting/weight_dist.png

We previously allowed any value for this parameter in early beta builds, but with this parameter we are modelling the weight on the driven wheels, not the weight distribution. Similar to the above question regarding tyre load sensitivity, where you can make a heavier vehicle yield better lap times, we are only using this parameter for longitudinal acceleration, not lateral acceleration. This meant that increasing the weight on driven wheels always yielded better lap times, and for a 2WD vehicle it isn't that simple.

This is one of many simplifications we've made to characterise vehicle performance, and now that OptimumLap has been out for a little while, I'd welcome your thoughts on how useful you've found the simplified model, and how you've managed to utilise the results.

--
Pete
pete.ringwood@optimumg.com
OptimumG
Vehicle Dynamics Solutions
http://www.optimumg.com

[H.Mach]

Thibault HUGUET
I have a problem to import FSAE non aero car.
I can import other car of the online database.
I'm the only one with this problem ?

I have the same problem. Can you help us please ?

[OptimumG]

Originally posted by H.Mach:
I have a problem to import FSAE non aero car.


We're looking a fix right now, we should be able to get one out by the end of the day.

* Edit *
Just an update, we've fixed this, we'll roll out an update first thing tomorrow morning.

* Edit *
An update is available which fixes this issue, as well addressing a few more. This is the last update which will require reentering your licence key on upgrade too - we've fixed that one now.


Cheers,

--
Pete
pete.ringwood@optimumg.com
OptimumG
Vehicle Dynamics Solutions
http://www.optimumg.com

[Thibault HUGUET]

The problem is present with the new version too.
If you want, i can send you the error message.

[OptimumG]

Originally posted by Thibault HUGUET:
The problem is present with the new version too.
If you want, i can send you the error message.

Yes please, we can't replicate it on our end - if you could contact me directly on pete.ringwood@optimumg.com, we can get this sorted out.

[FsaeSpec]

Saw a member of my old FSAE team use this in the lab the other day, pretty neat software! Good work OptimumG!!

[Claude Rouelle]

FSAE Spec,

Thank you for your kind words. Well appreciated. Especially from you as you went through the same pain in designing your own software.

OK, now teams have all the tools to decide what the ideal, winning car concept is and to present their arguments to design judges... http://fsae.com/groupee_common/emoticons/icon_smile.gif

Some students who already know vehicle dynamics well are asking for more; a real car with 4 wheels, kinematics, compliance, aero, etc.. .. That is what OptimumDynamics (that we call CVD before) is for. For the moment we only use OptimumDynamics with our consulting customers but we may put the software on the market one day. Maybe there will be a low price version of it for students. Too early to decide.

Students often have access to very sophisticated vehicle dynamics software mainly used in the passenger car industry but it seems they like the decision making simplicity, the usefulness and the user friendly aspects with which OptimumG software packages are designed. That is probably because we are race engineers, we are customers oriented and we think with the end in mind.

The fact is that it does not make sense to go for the vehicle dynamics "full Monty" before some basic, compared influence of weight, grip, aero, power, energy used and track configuration on performance are understood. In fact I regret that a software like OptimumLap was not created before we went through OptimumKinematics and OptimumTire development. I guess we too had to make or own intellectual m... gymnastic.

There could be a few updates or upgrades in OptimumLap in the future. In fact your suggestions will be welcome and appreciated. But as a mass-point, free of charge lap time simulation software I think using it as it is can already give students a lot of decision help in the car initial concept.

Again thank you for your encouraging words that will be well appreciated by the OptimumG team.

[kcouranz]

I am wondering how OptimumLap calculates fuel consumption. Is it simply the energy required to get around the track combined with the thermal efficiency?

Also is there the potential to revert the 2WD/AWD input to percentage weight on driven wheels (possibly an advanced option to do so)? Currently my simulations overestimate the traction limited zone when 2WD is used, and underestimate the traction limited zone when AWD is used. For example, I know a car can do 1g forward acceleration, if I want my 2WD model to achieve this I need to set the longitudinal tire friction to 2.0, despite what my tire data is. If I use AWD then my model car will have more traction than is realistic. I know the aim of this simulator is not to model cars accurately, but to see the effects of changes. But in using the simulator to see when diminishing returns occur from adding power, traction limit and therefore weight on driven wheels is very important.
Cheers.

[OptimumG]

kcouranz: Yes, you're correct - the fuel consumption metric is based off the energy used, the thermal efficiency and the energy density of the chosen fuel. We're only calculating this energy used value under acceleration and cornering (not braking), so correspondingly there is no fuel consumption under braking. This will slightly underestimate the total consumption depending on if you have an overrun fuel cut set up or how your engine is mapped, but we've seen good correlations (within 5%) of the predicted consumption per lap from OptimumLap and logged data at tracks all the way up to Le Mans/Sarthe (13+ km in length).

Again, 5% correlation isn't going to be enough to determine your race day strategy, but it will give you an idea how sensitive the fuel is to both aero changes and engine power, and it is these sensitivities (among others) which OptimumLap is built for.

Regarding the 2WD/AWD question - we definitely agree with your point, and are looking at either reintroducing it as an "advanced" option or at other ways to decouple the positive/negative longitudinal capabilities (for example, adding a simple driver skill level model, so that the vehicle doesn't always operate on the limit, but rather within a smaller friction ellipse).

When we release a new version, we should have an answer on this front, as well as a few more bug fixes and some brand new features. We don't currently have a date planned for the next release, but we'll post back here when we do.


--
Pete
pete.ringwood@optimumg.com
OptimumG
Vehicle Dynamics Solutions
http://www.optimumg.com

[OptimumG]

Just to add a little further to my previous post - still no ETA on a new update of OptimumLap, but we have put together a bit of a case study on the upcoming USGP F1 race at the Circuit of the Americas.

Being a new circuit, we thought it would be a good idea to show how OptimumLap can be used to characterise a track and help understand which vehicle aspects are most crucial.

It's up on our blog: http://www.optimumg.com/techni...d-states-grand-prix/ (http://www.optimumg.com/technical/simulating-the-united-states-grand-prix/) and we very much welcome feedback on it.



--
Pete
pete.ringwood@optimumg.com
OptimumG
Vehicle Dynamics Solutions
http://www.optimumg.com

[NickFavazzo]

Very good read, I look forward to seeing how they correlate. Interesting to see the CVT vs gears, I had not thought to look at that before.

[FsaeSpec]

Originally posted by OptimumG:
Just to add a little further to my previous post - still no ETA on a new update of OptimumLap, but we have put together a bit of a case study on the upcoming USGP F1 race at the Circuit of the Americas.

Being a new circuit, we thought it would be a good idea to show how OptimumLap can be used to characterise a track and help understand which vehicle aspects are most crucial.

It's up on our blog: http://www.optimumg.com/techni...d-states-grand-prix/ (http://www.optimumg.com/technical/simulating-the-united-states-grand-prix/) and we very much welcome feedback on it.



--
Pete
pete.ringwood@optimumg.com
OptimumG
Vehicle Dynamics Solutions
http://www.optimumg.com

Link doesn't work, would like to read http://fsae.com/groupee_common/emoticons/icon_smile.gif

[Lorenzo Pessa]

Originally posted by FsaeSpec:
Link doesn't work, would like to read http://fsae.com/groupee_common/emoticons/icon_smile.gif

You can find some stuff here: http://blog.axisofoversteer.co...p-will-be-13753.html (http://blog.axisofoversteer.com/2012/11/pole-at-austin-gp-will-be-13753.html)

[HksUsa]

Hello,

How are the downforce/lift and drag calculated if the only inputs are the lift and drag coefficients ? Wouldn't OL need the total area of the car to be able to calculate these values ?

Thank you, Kevin

[OptimumG]

Hi Kevin,

You are correct, indeed we do. The aerodynamic inputs for OptimumLap are constant downforce and drag coefficients, as well as the total frontal area (reference area) and the air density.

All of these inputs are located together under the heading of "Aero Inputs".


--
Pete
pete.ringwood@optimumg.com
OptimumG
Vehicle Dynamics Solutions
http://www.optimumg.com

[HksUsa]

Thank you Pete for your answer.

I was aware of the frontal area input, but I have trouble figuring out how you can calculate the downforce/drag of a whole car by simply using its frontal area ?

When calculating these numbers for a wing, you need the total area of the wing, wouldn't it be the same for a car ?

[Claude Rouelle]

HksISA,

Just to be sure you understand (because I have seen students being confused), in simple terms, we are speaking about the area of the car (or the wing) PERPENDICULAR to the direction of the movement.

For a car that is the frontal area, we do not worry about the top view area. That is unless you want to car to move up and down like aircraft do.

[HksUsa]

Originally posted by Claude Rouelle:

Just to be sure you understand (because I have seen students being confused), in simple terms, we are speaking about the area of the car (or the wing) PERPENDICULAR to the direction of the movement.

For a car that is the frontal area, we do not worry about the top view area. That is unless you want to car to move up and down like aircraft do.

Well I'm not sure I understand... An aircraft also moves forward, just like a car does and we do consider the top view area of the wings for the lift/drag calculation, even at an angle of attack of zero degree.

Based on what you said, we should only consider the leading edge (Bord d'attaque) area to calculate the lift and drag for a wing, which would be incorrect.

[Claude Rouelle]

An aircraft moves backward?

Fortunately not the one I am flying in....!!

[JulianH]

HksUsa,

it doesn't matter which area you use. It is just a convention to use the frontal area of a car to calculate the aerodynamic forces (for an aircraft you use the area of the wings, I guess).

If you go to a wind tunnel and measure the downforce of the car, you get the force, now you divide by the dynamic head and your result is cLift * Area. If you change the area to only the drivers head or so, than your cLift must change too but the force stays the same.


Just accept that for calculations in cars, the frontal area is used and then calculate the coefficients cLift and cDrag from the forces and the surroundings (density of air and velocity of the car).

Regards,

Julian

P.S. Claude, a team member of our 2012 team desgined and tested an model aircraft that could fly forwards and backwards and won a lot of prices with it http://fsae.com/groupee_common/emoticons/icon_smile.gif

[HksUsa]

Julian

Thank you for your answer. My concern here is only about the mechanics behind de OL aero calculation method.

So, if I understood correctly, it says frontal area in OL, but it is totally arbitrary ? I can use the area I want ? (As long as I have the corresponding Cl/Cd of course)

[OptimumG]

Originally posted by HksUsa:
So, if I understood correctly, it says frontal area in OL, but it is totally arbitrary ? I can use the area I want ? (As long as I have the corresponding Cl/Cd of course)

Kevin, that is correct. You can use which ever values you like, although it is common to set the frontal area to 1 and to just use the corresponding Cl*A / Cd*A values.

As Julian mentions, as long as you account for it, it will be fine. It's the total lift force and drag force that is important for this simplified point mass vehicle model.


--
Pete
pete.ringwood@optimumg.com
OptimumG
Vehicle Dynamics Solutions
http://www.optimumg.com

[HksUsa]

Alright !

Thank you for your answers. It's really appreciated.

[kevin_c]

Hello,

My name is Kevin, I'm a first year student at Sheridan College in Brampton. I'm the drivetrain design lead for our FormulaSAE team.

I'd like to first say thank you for making Optimum Lap available for free. It's been immensely helpful for giving students ideas and direction for design.

When I created a 75m drag strip to help select our final drive ratio for the acceleration event, I ran into something interesting.

As I created more cars with smaller and smaller FD, the lap times continued decreasing. I thought it was a bit strange, then I looked at the plot for Speed vs Time. It looks like at Time = 0, the car already had a speed, and that is the speed that kept increasing.

Is this something I had missed during setup? Or perhaps a bug? How do I manually set initial velocity = 0 when time = 0? Any information would be greatly appreciated.

Here's a screenshot:
http://i.imgur.com/S8RuNpj.png (http://imgur.com/S8RuNpj)

Thanks,
Kevin

[BenMueller]

Hey Kevin,

I looked at my data and I also have an offset, but all different setup's have nearly the same! The offset is between 17-20 km/h.
What about your engine data - at which rpm do you started?

[TiJei]

Hi Guys,

in the manual it is written, that in case of open tracks the car starts with "minimum" velocity. The minimum velocity thereby depends from minimum speed entered in your engine map, the transmission ratio and tire diameter.
To overcome this problem you need to do an estimation of transmitted torque between 0 speed and minimum speed. This is the area were either the clutch is not fully engaged or the wheels are spinning.

The minimum engine speed I was able to enter is 1 rpm. This reduces your start speed to neglectable numbers with respect to the rest of the simplifications within OptimumLap.

Regards