Launch Control strategy

[Hugh]

Have been pondering how to get the best from the Syvecs launch control on my S6Plus and started looking for pointers to see how others had optimised their launches.

Watching Formula 1 cars do practise starts on TV, I noticed that the wheels did not spin at all, all the work was being done by the clutch.

I also found this article https://forums.ni.com/t5/LabVIEW-Studen ... -p/3538051 that shows a kind of S shape to the Revs as the rear wheels spin up and then settle down to match the front wheel speed.

I put a spreadsheet together that calculated an S-Curve that I applied back to engine revs between whatever RPM you wanted to launch at and the end RPM which is where the front wheel speed should match the rear wheel speed.

The graph at the bottom refers to the numbers directly above it, the graph to the lower right relates to the middle row of numbers.

The difference between the numbers was that way I applied the S-Curve numbers back to the RPM figures.

Have to say that the Rev increase looks OK to my eye, but the wheel speeds should be a coming together a bit more gently as the revs increase, so the S-Curve is not the looking like the best method to use.

The image is being cropped for some reason, you can open it up here https://drive.google.com/uc?export=down ... ZHRnEX-9hD



Given the popularity of drag racing round the world, also the number of race cars that launch from standstill, I assume this subject is well understood.

Any thoughts?

[emi]

intresting...

[stevieturbo]

If you can manage it all via the clutch...then yes that could work great. But you will need a very controllable clutch ( and one you are happy to replace often !! lol ) ( or a torque converter ! )

But the reality is with so many variables, tyres, surface, conditions etc it will be hard to find a single optimisation that suits every venue.

Ignoring clutch slip...I've found that 4wd cars just like to be launched bloody hard.

On a 4wd car maybe better using a launch ramp vs time, rather than trying to compare wheel speeds ? All wheel speeds F/R will tell you is if there is any slip between, them. Or try and compare to a GPS speed where there is no slippage.

But it's all going to take lots and lots of testing.

[Hugh]

Not quite got an F1 budget to play with Stevie.

Thought it might be better to break the launch down into three parts:

1----------Required RPM to get you off the line.
2----------RPM required to keep the engine on boost.
3----------S-Curve to blend the maximum engine RPM down to the correct wheel speed.

Clearly as soon as the tyres have grip, the above will not be in play, the Syvecs input Base Engine speed is the maximum RPM that the ECU will allow before reducing power.

A negative number in the Wheelspin line allows some degree of wheelspin before the ECU will cut back the power, so there might be a case for designing the spreadsheet to have a fixed offset, however, a fixed offset would potentially hold the engine revs below the boost threshold



The graphs on the above are:-

Top = S-Curve, have created a more sophisticated model that allows a better S and also the point that the S-Curve builds and the severity of the S

Left hand graph = S-Curve applied without the RPM hold in the lower revs.

Right hand graph = Launch RPM programmable on its own, followed by an RPM hold, followed by the S-Curve fit ( all points programmable )

Any other thoughts?

[stevieturbo]

But it's a bit more complex than that ?

I could launch all day with no wheelspin...but it wouldnt be vary fast. ie how you drive on the road every day.

So whilst you need enough rpm to achieve boost....does that also give you the power you need for a hard launch ? If you could maintain say 5000rpm and slip the clutch to maximise accel up until all drive is sent to the wheels...you'd be flying. But then that could potentially be very very hard on a clutch. On a 4wd car, it's probably easier on everything to have that slippage at the tyres.

And targeting say 10% slip...may not be good for all tyres, conditions or speeds.

I just dont think there is any easy solution other than solid testing to see what works best, and is zero slip the best for all tyres and surfaces ?


Same with traction control, I see a lot of resources online suggest around 10% slip should yield best grip. On drag radials etc on an airfield...with 10-% slip the entire 1/4, I destroy a set of tyres in a few passes !!

Although I do also seem to struggle with what is slip. On my car, with any tyre whether soft or a 35 series 888 with a hard sidewall, under acceleration the driven wheels do appear to rise in speed more than the undriven, even when I am totally sure there is no slippage. And when I let off, this slippage disappears. But it is definitely not the same as wheelspin which is on top of that again.
So whilst I can easily maintain slip targets pretty well.....just not sure what is real slip when we're talking about low levels. I assume the same applies during launch too ?

IMO setting a baseline of rpm rise vs time from testing to try and limit excessive rpm rise is a good starting point, or against an undriven wheelspeed source. But it just needs testing, and lots of it

[Ryan.g]

Hugh,

With a GTR the by far best way to get it off the line or in fact on most cars is to setup the Launch in Stage which is normally is by default on the GTR base maps. Here you can setup a RPM Limit based on Vehicle speed or time.

With 4wd if its likely you could spin the front wheels where Vehicle speed would be calculated from then the best way is to do based on GPSSpeed from our 50hz GPS unit then can plot the perfect RPM target back calculated from the gear ratio and max rpm for that gear to extract maximum Long G force.

[Hugh]

Thanks Ryan,

Think I have a good place to start with the settings.

Have set up Worksheets in SCal that have the relevant tables, so will hopefully get some practise in to improve the consistency on launches