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Launch Control: Two Step Launch Control Tuning

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Two Step Launch Control Tuning

10.05

00:00 - Now we can actually get to the nuts and bolts of tuning the launch control system, and we're going to look at this in three separate ways.
00:09 We're going to start by treating the system as a simple two-step launch control function.
00:14 Really with the M1, once you've got the wheel speed set up and put to the ECU, there's probably no real advantage or reason for you to treat it like this.
00:23 But for those who wanted to, we'll look at a really basic setup which is really how I've got the setup done now.
00:31 If we move into our launch control worksheet and look at our engine RPM table.
00:37 We've already seen this before.
00:39 You can see I've got the zero ground speed RPM limit set to 3000.
00:44 And what I've done is I've set the first point in the table at one kilometer an hour.
00:50 So, as soon as the ECU registers any speed at all from the wheels, the engine RPM limit is going to be lifted to 8,000 RPM.
01:00 I'll just quickly talk about the interaction with the RPMs as well.
01:05 With the MoTeC M1, the ECU will always use the lowest requested RPM limit from any of the available sources.
01:11 So, while I've set this to 8,000 RPM, my main engine rev limiter function is actually set to 7,600, so that is the one that will function.
01:21 Basically, I'm using 8,000 just to get it out of the way and make sure it's not going to do anything.
01:26 Now, again if we want to make any changes to this, we can press the A key so we can adjust the axis vehicle speed.
01:35 Also if we wanted to, I could disable the driver launch aim switch all together if I wanted.
01:42 So we'll leave that setup, and I mentioned in the body of the text that if I had no prior knowledge of a car, unless it had a very very large turbo, I'm going to probably start with an engine launch RPM of around 5,000.
01:57 So, let's just do that to show you exactly what happens.
02:02 I'll just shrink that back down.
02:03 Things we've got to look at here, we've got our time graph, which is going to show us most of the details that we're going to be interested in.
02:13 I'll fullscreen there and just pause it.
02:14 So, I've got our engine RPM and our launch RPM speed here, our throttle position.
02:19 We can see our ignition timing which is going to be quite key if we are adjusting or targeting a retarded ignition timing.
02:26 We've got our ignition output cut count, now this is quite unique on the MoTeC M1.
02:31 It registers every single time the ignition cut occurs, so we can actually see this counting up the more often the ECU cuts the ignition.
02:42 We've got our boost aim and our current boost pressure.
02:46 We've got our exhaust lambda and our measured and our target exhaust lambda.
02:51 And we've got our launch state which at the moment is saying disabled.
02:54 That's what we're going to be using to test and setup the system.
02:59 So what we'll do now is we'll just do a quick launch with those parameters configured and we'll see what we end up with.
03:06 (car revving) Okay, so if we just come back to a stop there after that first launch and what we'll do is we'll pause the time graph and we will expand that to have a look at what actually happened.
03:23 Now, you can see here, I'll just zoom in so that we're looking at the area of the launch occurring.
03:32 So you can see that we went to full throttle, and you can see the engine RPM increase and it sits at 5,050 RPM, give or take, which is essentially the target launch RPM plus our margin if you remember.
03:47 So that's what's happening there, it's moving up and down.
03:50 You can see at this point here this is where I actually let go of the clutch, released the clutch and you can see that our engine RPM limit increases up to 8,000.
04:01 And you can see the actual engine speed starts to increase.
04:05 Now just before I talk about that, remember I mentioned that when we're on launch control we're not going to have any really usable reading from our lambda sensor.
04:15 And you can see exactly that, the yellow line here and our exhaust lambda is the measured lambda and the orange is our target.
04:24 You can see pretty much as soon as we hit the launch limiter and the ignition cuts starts becoming active, our exhaust lambda is starting to read exceptionally late.
04:33 So that's again, that's just what I was saying, we're not going to get a usable reading.
04:37 Now, as soon as I let go of the clutch there, what I ended up with was an excessive amount of wheel spin, because 5,000 RPM for this car, with a small turbo is way more than we really need to get the car moving.
04:50 So you can see what I've done there is with the throttle, as soon as the car has really started moving I've dropped the throttle back to 65-68%, all the way back and to try and manually control that wheel spin.
05:06 Again, the reason for that is as soon as we actually engage the clutch and the car starts moving, there's nothing this particular setup can do for us to help control that wheel spin so that still has to be done manually.
05:20 The advantage though, is we still get a consistent launch RPM and a consistent amount of power every time.
05:27 Okay, so let's look at setting that up a little bit more realistically.
05:32 In this case, as I said, 5,000 RPM is way too much, so let's bring it down to 3,000 RPM, which I know is a much closer point.
05:41 Now, of course this is still going to depend a little bit on the track conditions of the day, the tires that we're running and how much temperature there is in the tires.
05:50 But let's try 3,000 RPM for a launch.
05:53 and we'll see what that gives us.
05:55 (car revving) Okay, so that was pretty close to ideal there, we'll have a look at the time graph to see what we can see there.
06:14 First of all, you can see that we're sitting at about 3,000-3,100 RPM, the RPM is just bouncing around about that set point based on our control range and our set point.
06:28 You can see that as soon as I let go of the clutch, our RPM doesn't just jump up here, I'll just zoom in a bit so we can see it a bit better.
06:37 We actually get quite a smooth increase in our RPM which is really what we want to achieve, and you can see that that's resulted in less wheel spin, simply because you can see that I've stayed at full throttle for quite a lot longer.
06:52 I've been able to stay at full throttle.
06:53 Once the RPM starts to increase and the boost increases and we get more engine power, then, obviously the wheel spin will start taking over and that's at the point you can see that I've started to back out of the throttle.
07:04 But for this particular car that point 3,000 RPM on this day, these conditions, it's a pretty good place to be.
07:13 We just want that little amount of initial wheel spin to let the car move off, and what we're going to do now is we'll go a little bit further and we'll drop the RPM to show you what happens when we go a little too far.
07:27 So lets try 2,700, which I'm going to expect is probably going to be a little bit too low.
07:34 (car revving) Okay, that actually still got off the line, but there wasn't as much bite, the engine was being dragged down.
07:48 Let's just have a look at our throttle trace and our time graph, you can see that I've actually stepped off the throttle pretty quickly in that one.
07:59 But you can see that initially the RPM actually drops a little bit and that would indicate to me that I'd probably want just a little bit more engine power.
08:10 I'll try to make it a little bit more obvious by dropping the RPM, the launch RPM, further down to 2,400.
08:18 So this should probably just result in us stalling.
08:22 (car revving) (laughs) And there's the beauty of a car with a really small turbo, even from 2,400 RPM we're actually still getting a reasonably good launch.
08:36 But what you can see here in the time graph is again, as I step off the clutch and the car starts moving, so you can see that our RPM has dropped down to 2100 RPM while I'm still at full throttle.
08:50 We're really in danger there, while the car has moved off, that's probably a little bit too low and we're risking the engine falling off the power band.
09:00 And it's not going to give us the results we want, so what we really want to see here is the RPM from where we jump up the clutch and the car initially starts moving, we wanna see the RPM either stay flat or very slightly increase, if we're seeing the RPM jump straight up, that means we've got too much RPM, too much engine speed, too much engine power and the car is breaking straight into wheel spin.
09:25 If we're starting to see the RPM drop when we get off the clutch, that suggests we don't have enough, so there's that little sweet spot where the RPM just stays flat and starts smoothly increasing, that's what we want to achieve.
09:39 Okay, so that covers how we would go about setting up a simple, essentially a two step base launch control where we've got no reference to ground speed in there.
09:50 We can't do that as I've said in the M1 with a clutch switch, but this is the next best thing.
09:55 Now we're going to have a look at how we can set that up with a proper ground speed based launch control strategy.