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Launch Control: Ground Speed Launch Control Tuning

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Ground Speed Launch Control Tuning

15.05

00:00 - We're going to look at setting the launch control up on our M1 now using ground speed based launch control.
00:06 Before I came on camera, what I've done is a little test, which we can just look at now where I've driven the car gently through first gear so that I can get a bit of a representation of our RPM versus ground speed, and you'll remember that from the body of the course that's going to be our zero slip point, if you like.
00:28 That's what we've got up on the screen now, and you can see RPM, I've increased that sort of right the way up to, in this case, 7,200 RPM.
00:37 Now, what you'll notice, though, is I don't actually have on this particular time graph, I don't have any representation of our ground speed, of course, what I can do is I can go back to our vehicle workbook, and on the time graph in the vehicle workbook, we've got our ground speed, our driven speed and our undriven wheel speeds, but that's not strictly useful because we have to swap backwards and forwards between them, so again something you, or anyone who's gone through our M1 software tutorial would have remembered is we can actually modify the functions, the channels being displayed on the time graph.
01:13 To do that, though, what we have to do is go to our layout and go to our layout editor, and we need to unlock the layout so that we can actually make changes to it.
01:24 You can see if we click on the Toyota 86 package there, and you can see the little padlock.
01:30 If we click unlock, that's going to let us make changes to the time graph.
01:34 We can press F5 and we can add a new group, and next we can click add channel, and what we're gonna do here is add wheel speed front drive, and that's going to give us a reference to our wheel speed right here on the time graph.
01:51 The aim is to set the RPM limit pretty well on the line of what RPM, engine RPM we're expecting based on the ground speed.
02:03 I'll click back up into our launch engine speed table and first of all, I'm going to open that up and I'm going to change that second point from zero to five kilometers an hour, so we want really something that's going to be nice and smooth.
02:17 What we can do is work our way through this particular table here.
02:23 Now, what we want to do is look at the ground speed, so in this case five kilometers an hour, this matches the first break point on our table.
02:33 You'll notice that the engine speed that we've used to achieve five kilometers an hour is 1,500 RPM.
02:39 This is what I was saying in the body of the course.
02:42 Clearly, if we set the target RPM here at 1,500, it's just going to drag the engine speed down.
02:48 The engine's not going to be producing any power there.
02:51 All it's gonna do is have a stall.
02:52 We don't want to do that, so there is sort of a smoothing that we need to apply.
02:57 We're going to leave that at the moment.
02:59 We know that we were launching cleanly with about 3,000 RPM, so if we click back down and we move through and we'll see what sort of RPM, what sort of ground speed we were getting with about 3,000, and you can see here 20 kilometers an hour we were getting around about 3,000 RPM.
03:24 Now, again, if we enter 3,000 RPM in here, that's going to be a zero slip state, so we really want to be able to provide a small amount of wheel slip, so generally somewhere around about five to 10%, again you can play with the values based on your acceleration testing, but what I'm going to do there is start by entering 3,150 RPM at 20 kilometers an hour.
03:50 Once we've done that, we can move through to 25 kilometers an hour, so it's just a case of moving through the table so at this point we were 3,500 RPM, so what I'm gonna do there is we'll enter 3,650 RPM as our target point, move through the table again, and our next break point is 30 kilometers an hour, so we'll see what we had there, and we've got about 4,200, so I'm going to enter 4,400.
04:25 Again, you're always better to start with the target RPMs in that table a little bit higher rather than a little bit lower.
04:33 It's going to make it easier on the drive train, and we're going to start with a little bit of wheelspin.
04:38 We can always pull that back if we want to.
04:41 Our next point is 35 kilometers an hour, and we're at about 5,000 RPM, there.
04:48 5,050, so I'll enter 5,250 there.
04:54 Lastly, our next break point is 4,000, and we've got 5,600.
05:00 I'll enter 5,800, and we actually extend past all the way up to 7,200.
05:08 We're at 50 kilometers an hour, so what we can do is we can add some more break points to this table, so we'll go 45, 50, and 55.
05:17 Really, we want to be covering the range of our speed that we can get in first gear, so regardless of where we shift from first into second, we've still got that covered.
05:28 We had entered up to 40 kilometers an hour, so at 45, we'll just come back here in the table, and we've got 6,400, so I'm going to enter 6,600, and the last point I had was about 50 kilometers an hour, 7,100 RPMs, so I'll enter that at 7,300, and then the last point, 55 kilometers an hour, we didn't quite get there.
05:57 You can obviously go and do a more thorough test just for the purposes of our demonstration, I'll enter 7,600, which is our main engine rev limiter.
06:06 Now this gives us this awkward position between our launch RPM at 3,000 and 20 kilometers an hour where we really start matching our engine RPM versus our ground speed.
06:20 What I'm going to do is I'm going to just bring the target RPM down on here, down a little bit to about 2,700.
06:29 What we're gonna do is we're gonna launch at 3,000 RPM.
06:31 It should give us a little bit of wheelspin and then once the car's wheelspinning, we don't need quite as much engine power to keep that up, so we can actually drop the RPM a little bit, and that's going to help the ground speed and wheel speed catch up.
06:45 If we just held it at 3,000 RPM or let it increase, it's gonna result in too much wheelspin.
06:51 We want to be able to bring the RPM down a little bit.
06:55 How much we can do that is going to depend a lot on your engine as well as the amount of traction.
07:01 A really big capacity V8 with a lot of low RPM torque, you aren't gonna be able to pull that down very low.
07:07 A small capacity engine with a large turbo that's quite peaky, you're probably not gonna be able to do that, or you're going to risk stalling, but you can easily play with those numbers and see the result through the data logging.
07:20 So, now we've done that, I'll start the car, and we'll actually try a launch and see how that actually, how that works for us.
07:30 (motor running) (tires screech) Okay, so what I'll do is we'll just pause that time graph, and we'll have a look at what happened there.
07:50 I know from the driver's seat, I know that that was far from ideal and we didn't end up getting a really smooth or fast launch, but let's have a look at the data, and see what that shows us.
08:03 We'll just zoom in.
08:09 Okay, so you can see first of all, if we look at our engine RPM versus our launch engine speed, you can see that we've sat basically on that limiter the whole time, and you can see that the entire way through our launch control, we've got our ignition output cut as increasing.
08:32 Now, the first thing you can also notice is the whole way through that launch, I was staying at full throttle, and you remember at our last test, we were just using the two-step method that wasn't possible.
08:43 That's one positive.
08:45 We've been able to stay on the throttle and allow the ECU to do all of the control.
08:51 What I'm going to do now is we're going to increase the RPM targets and have a look and see how that affects our launch.
09:00 Before we do that, though, let's just have a quick look back at our vehicle worksheet, and if we look at our time graph here, you're going to be able to see the wheelspin, so it is quite important to be able to reference both of these worksheets and see exactly what's going on.
09:21 If you look at this particular group here, we've got our front wheel speed, this is our rear wheel speed.
09:27 You can see there initially we get quite a lot of wheelspin, which is what we know, and then at about this point, the front and rear wheel speeds are clamped, so that's about 20 kilometers an hour.
09:38 Chances are what we can actually do is increase our engine speed targets from probably somewhere around about 15 kilometers an hour to carry some of that wheelspin, because what you can see is we're effectively clamped on our front and rear wheel speeds being the same.
09:56 that doesn't give us that wheel slip, and you'll remember again from the course we really will get an improvement in our acceleration with a small amount of wheel slip.
10:04 What I'm gonna do now is from 15 kilometers an hour, we're going to increase our RPM targets by let's add five percent.
10:17 We can just go 1.05 times, and we will see how that affects our launch, and we'll do another launch now.
10:28 (engine revs) (tires screech) Okay, so that's our second launch there, and even from the driver's seat, it felt much, much smoother and much faster, and the traction was much better, so I know just from a seat of the pants feel that was a step in the right direction.
10:51 Obviously, we've got the ability to use our data logging as well to measure out zero to 100 kilometer an hour times or in this case, maybe zero to 50, to the top of first gear, and get a real accurate answer as to whether it was a move in the right direction or a move in the wrong direction.
11:08 For the purposes of our quick demonstration, though, let's just have a look at our time graphs here.
11:15 If I again zoom in, you can see this time here, the engine speed versus launch speed, and this is also demonstrated by the cuts.
11:26 You can see that for the most part, once we've actually got the car launched, the engine RPM is not sitting on that limiter anymore.
11:35 This part through here, we're actually not sitting on a limiter, so the engine is accelerating cleanly.
11:41 We're not artificially clamping the engine down and we're not getting any wheelspin.
11:46 If, however, traction was an issue at this point and the RPM bounced up, it would hurt the limiter, and we wouldn't end up just breaking out into a large amount of wheelspin.
11:57 You can see that as soon as the car is pretty much moving, we're sitting off that limiter.
12:05 We do hit it just here, I think just a little bit right there.
12:10 Actually, no we don't because our ignition cut output still has an increase.
12:15 That's probably a pretty good indication of where we're on the right track.
12:20 We've moved in the right direction.
12:22 What I could do is one more test where we could increase the RPM through this initial stage of the launch where we're just moving from the launch RPM to a transition into the car moving.
12:36 I would probably now try adding 10% to that and just see what sort of result that gives us.
12:43 Let's just try that, and we will see if we're getting an improvement.
12:48 In our launch engine speed table, I'm going to just highlight the cells from zero to 15 kilometers and hour, and I'm going to multiply those by 10%, so 3,300 RPM is going to be a little bit more aggressive on our launch, and that may be more than we actually need, but I want to just give a demonstration of both sides of the correct points, so we've already seen what happens when it was too low.
13:17 We've seen something that was pretty good in our last test.
13:19 Now we're going to look at something that may be a little bit high.
13:33 Okay, so that's our third test done there.
13:35 We'll again have a look at the time graph.
13:37 That actually again felt pretty good from the driver's seat, but the data will show us what's really going on.
13:44 Now, if anything, I think looking at that data without actually doing an analysis of the acceleration was probably a better result, all things considered.
13:55 You can see that again in the later part of the launch because this car isn't overly powerful, we have stayed off the limiter, so pretty much that the powerful aspect of the launch control for this car is that zero to about 20 kilometers an hour.
14:12 Once we've got through that, the car's actually got traction, and it is hooked up, so we don't need to really worry the launch control's not as useful for this car, in that respect.
14:23 If we had a lot more power or the track was wet, that's when it would really come into its own, but what we can do is using the time graph analysis, we can look at the acceleration data and base our decisions on whether or not we've got an improvement or we've gone backwards.
14:41 It's very easy to make small changes to the launch control and iteratively test that and see when we've got exactly the optimal results for this particular combination of car and tire and race track.