# Launch Control: Ground Speed Launch Control Tuning

## Ground Speed Launch Control Tuning

### 14.10

00:00 | - Now that we've looked at how to set up a basic 2-step style launch control, we're going to look at how we can set up the ground speed based launch control limiting in the Link G4+ software. |

00:11 | Now remember that the first step of setting up the ground speed based launch control still requires us to find the launch RPM that works best for the car anyway, so we can still use what we've learned from the last module as a starting point for where we're going to launch the car. |

00:28 | Now if we drop into our software, the first thing we need to do here is change our launch mode to 2D Launch RPM Table, and it will give us access to the ground speed based RPM limit table. |

00:42 | So, if we wanted to include a multi-position switch so that we can alter the launch RPM depending on conditions, we can choose 3D Launch RPM Table, essentially exactly the same as what we're going to look at, but it just adds another access so we can adjust the launch RPM. |

01:01 | Once we've done that, it gives us a couple more parameters that we didn't have before. |

01:06 | First of all, we have our disarming speed, which is the ground speed above which the launch control system is deactivated, and what we want to do is see if there's somewhere around about the same point that we reach maximum speed in first gear. |

01:21 | We really only want the launch control functioning while we're in first gear. |

01:26 | And the other thing we now have access to is our Launch RPM Table. |

01:30 | So, if we double-click on that, it gives us access to a ground speed based launch RPM table. |

01:38 | Now, before we came on-camera, I did a little bit of logging which we can see here, and what I did was just drove along smoothly, and I logged the ground speed versus engine RPM, and remember, we want to get that correlation between ground speed and engine RPM that's going to be the basis for setting up this table, so I've got that data here, and you can also see that at the top of first gear, which we ended up getting all the way to 6800 RPM, we're assuming about 62 kilometers an hour. |

02:11 | So that makes a set point of 60 kilometers an hour it's probably about right for where we want to disarm the launch control. |

02:22 | So, what we want to do is basically move the RPM data from this log into our ground speed based launch control table. |

02:34 | So we'll just do that now, and if you look, We started, remember we found that the car launched reasonably well with a launch RPM of 2500. |

02:45 | Now if we look at our data log, and you look at the RPM, the engine RPM once the clutch is completely engaged, and down at this point 7.7 kilometers now, we're down at only 1200 RPM. |

02:59 | So, clearly, if we pull the engine RPM down that low, the car is just not going to launch well, it's probably going to have insufficient engine power and stall, so that's where it comes to getting a happy interpolation between our launch RPM, and a point in the table where we can lock our RPM target to the numbers that we're going to get from this table now. |

03:23 | So, let's look at a point where we reach around about the same RPM that we were using as our launch, and if we get down to say about 25 kilometers an hour, you can see here we're at 2800 RPM. |

03:40 | So we can put that into our table here at 2800, which is basically just the first point where we're actually above our launching RPM so at 25 kilometers an hour, we're at 2800 RPM. |

03:54 | Now if we go all the way through to the end of our log, and at 60 kilometers an hour, we're at about 6600 RPM, so we can put that into our final point, and because it is a linear correlation between ground speed and our engine RPM, what we can do is just highlight that table, and if we press between those two points we just entered, and if we hold down Control and press "i", we'll do an interpolation between those two points. |

04:28 | Before we move on, there's another part to this that is quite important to remember. |

04:33 | It's the way that the Link and ViPEC issues through the rev limiting. |

04:36 | If you got a 200 RPM control range, which is what we've got by default, what's going to happen is our launch RPM will actually start cutting or limiting 200 RPM prior to the values in this table. |

04:51 | So, remembering that the numbers we just got are our zero-slip RPM values, so if we leave these in our table now, we're actually going to end up pulling the engine RPM down below what we can achieve zero-slip with, so, it's gonna be completely counter-productive. |

05:09 | So what we want to do is start by increasing those values by 200. |

05:13 | So add 200 to all of those values. |

05:17 | Now what we want to do is get a smooth interpolation between our launch RPM and this point, somewhere around about 20, 25 kilometers an hour, and we can obviously adjust this after we've done some dialogue and seeing how the car performs. |

05:33 | What I generally find is that it works best if we pull the RPM down very slightly below our launch RPM, and then hold it reasonably flat before starting to increase it. |

05:46 | so what I'm going to do is pull the RPM down at five and 10 kilometers an hour down to 2400 RPM. |

05:54 | So, what this does is it holds the rear wheel speed relatively constant, while it allows the car to start moving and catch up. |

06:02 | And then what we're going to do is we'll increase those values up to 3000 RPM at 25 kilometers an hour. |

06:11 | Now, again, remembering at this point, this is going to give us our zero-slip target, or as close as we can hope to achieve. |

06:20 | What we're really going to want to do though, is add a little bit of wheel slip in here. |

06:26 | So with the Link G4+ it's reasonably easy to do. |

06:31 | What we can do is highlight the values in the table, and for right now, I'm going to again just do this in the 25 kilometer an hour and above range, where we're sort of got back to that point where we're trying to actually target the table values. |

06:46 | We're going to highlight those values and what I'm going to do is multiply those values by 1.05, which is 5-percent, so this will give us around about a 5-percent target slip. |

06:58 | Now that we've got those values in there, what we can do is do a launch, and we'll log it, and we'll see how that responds. |

07:06 | (engine starting) (revving engine intermittently) Okay, so now that we're done our first launch there, we can have a look at the data and see how well that performed. |

07:28 | Now, there's a couple of things we can note straightaway, is with the launch RPM set up like that, a ground speed based launch RPM table, you can see that right through the whole launch, right to the point where I backed off the throttle at the top of first gear because we were on the rev limiter, I managed to stay right at full throttle, so that's where it's exceptionally well. |

07:52 | What you can also see is driven wheel versus non-driven wheel speed here, and you can see that we still have quite a bit of wheel spin right up to the end of our dialogue, so that suggests to me that we actually had too much wheel spin, we had too much RPM in our table. |

08:13 | So what we can do is, we can start reducing that, and if we look, Basically, the point where we want to start reducing, that would be the point where we're sitting at around about that 5-percent wheel slip, so in that case, anywhere down below about 55 kilometers an hour, what I'm going to do is reduce the values in that table, and then we'll try again and see how we go. |

08:46 | Now, this is a trial and error set-up. |

08:49 | We don't have any rock solid numbers that we can apply right from the get-go, so it is a case of starting with some values in the table as we looked at, then assessing how the cars responded, and then making some changes. |

09:02 | So in this case, we know that we've got too much wheel spin, so we're going to reduce the values in the table, and then we'll see how that works. |

09:10 | So, what I'll do is I'll highlight from five kilometers-an-hour up to 55, and we will multiply that by .95, so that takes five percent out of the table values, and we'll store that, and I'll do another launch and see how that works. |

09:31 | (engine starts) (revving engine) So we'll start our data logging up All right we'll shut the car down again, and just have a look at what's going on there, and just from the seat of the pants there, that felt like a much better launch. |

09:55 | And you can see that while we've got some wheel spin, that wasn't anywhere near as dramatic as in that last test, and you can see now, from about 55 kilometers an hour, our front and rear wheel speeds are relatively matched. |

10:11 | So that means we've got traction at that point. |

10:15 | What I'll do, we've still got more wheel spin than we'd like, so if we look at, for example, at 25 kilometers an hour, we actually had a rear wheel speed of 48 kilometers an hour, so way, way more wheel spin than we'd really like to see. |

10:32 | So, what I'll do is a -- change Again we want to allow around about that sort of, five, maybe 10 percent wheel spin, so we want to look at the dialogue we've got there, at any point where we've got an excessive amount way more than that five to 10 percent of wheel spin, we want to start reducing our values, and our launch RPM table even further. |

10:57 | So what I'll do there, is from a ground speed of about 45, let's say 50 kilometers an hour, we will reduce it even further, and, I'll go from five kilometers an hour. |

11:14 | Now, this becomes a point you'll need to test. |

11:17 | You can see, we launch from 2500 RPM, and my first point on the table is now 2300. |

11:24 | So, this is really going to depend on the torque output of the engine as to whether or not we could pull this down further. |

11:32 | With our high RPM turbo-charged engine, we might find that if we pull the RPM down too low, the engine will fall off boost, fall off its power band, and then it will become detrimental to our launch. |

11:45 | In this case, what I'll do though, is we'll highlight the values up to 50 kilomenters an hour, and I'll take 10 percent out and I'll multiply it by .9, and we will store that, and try again and see how that works. |

12:00 | (engine revving) (shifts gears) All right, if we look at that dialogue, you can see now where it's starting to reduce the amount of wheel spin up at higher ground speeds, so now above about 45 kilometers an hour, we've got control of that wheel spin. |

12:19 | If anything, we could probably do to increase our rev limiter above about 50 kilometers an hour a little bit just to allow that small amount of wheel spin. |

12:30 | In the bottom end, though, we've still got quite a lot of wheel spin, and it becomes a balancing act between having enough engine power to get the car off the line and moving, and stopping it from bogging. |

12:41 | What I would probably, I would be a little hesitant to reduce the RPM down in that five and 10 kilometer an hour areas too much below what we've got at the moment, but what we could do so if we look at 10 kilometers an hour, we have rear wheel speed of 43 kilometers an hour. |

12:58 | So that's quite a lot of wheel spin. |

13:00 | We could reduce that potentially slightly, and just test until we find that point where the car starts bogging, but above 10 kilometers an hour probably up to about 40 kilometers an hour, we could make a further adjustment and reduce that engine RPM limit down to help reduce that wheel spin. |

13:21 | So it just becomes an---- of testing using your data logging to test the acceleration until you find out where the particular sweet spot is for your car, and your tire, and the current track conditions. |

13:39 | But using the dialogue makes it very easy to see exactly how the car is performing, and what changes you need to make next. |

13:47 | Now, if we were using the 3D table with a load access, you could then make further changes to another point in that table, based on a weird weather condition if you wanted to. |

13:58 | If you do have any further questions that have come up that you want to know more information about, please post in the forum, and I'll be happy to answer your questions there. |