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Data Analysis Fundamentals: Analysing the Time Delta / Lap Gain/Loss Channel - Basic Sensors

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Analysing the Time Delta / Lap Gain/Loss Channel - Basic Sensors


00:00 - When you're ready to start looking at performance, using the time variance plot relative to your reference lap is going to be your best tool to start with.
00:07 Here I'm going to go through a couple of examples looking at a professional vs an amateur driver in the same car on the same day and there's quite a big difference in performance which makes it a really good data set to look at to start with because it'll show lots of clear differences.
00:21 I'll take a look at the data a couple of different ways.
00:23 FIrst just assuming you've only got basic channels available with engine speed, vehicle speed, lateral and longitudinal G.
00:30 Then I'll look at exactly the same data set with a few more advanced channels added in as well.
00:35 Here on my laptop screen I've got the data loaded up, we've got the reference lap which is the fastest lap we have for this car in white and we have the latest lap which is from the amateur and the slower driver which is shown in the colour channels.
00:48 The points I want to concentrate on first are the areas where we've got the biggest dips in the variance channel.
00:53 Looking at the variance I've got a really big dip here at turn 1, I've got another one at turn 9 and I've got another one later in the lap around turn 10.
01:02 So these are the points I want to start with first and now we're going to dig into the actual log data and look at the reasons for why those dips are there.
01:08 When I look down through my detailed log data here, I've got engine speed at the top, then I've got my vehicle speed shown here, my longitudinal G force in red and my lateral G force in green.
01:19 These are the bare minimum log channels I'd expect you to have if you're logging data and these are what we're going to start doing this example with.
01:26 So if I just zoom into the first part of the lap, I'm looking here at this turn one section.
01:29 The first thing that's immediately obvious is the big difference in the speed trace.
01:34 So this is obviously a big part of where this time difference is coming from.
01:38 I also want to mention here in the reference data there's this big dip which is just a wheel lock up in this case which is giving us a dip in the speed trace.
01:47 I just want to ignore that, that's not something that's really too relevant to our analysis right now.
01:53 Looking through here the first thing if I look at the longitudinal G force, we can see here that the amateur driver is braking much quicker 'cause we can see that this dotted line here is the reference zero line.
02:05 So that's zero longitudinal G force.
02:08 So we can see it's dropping off a lot earlier, while the pro is still accelerating, the amateur is dropping off here and starting to brake much earlier.
02:16 So this initial lift here is just them lifting off the throttle and it's not until we get down this piece here, this lowest piece which is where the brake application's actually coming in.
02:26 So even just dropping off the throttle here, we're dropping below the zero longitudinal G force line because that's just the aerodynamic drag which is starting to retard the car at that point.
02:34 So that makes it really clear, this loss in the first place but the really strong part of the loss is actually happening much later in the corner, we can see the gradient really drops over here in the variance channel.
02:44 We can see that the longitudinal force, the peak longitudinal force for the pro is much higher here, that means they'll be using much more brake pressure than the amateur at this point in the braking zone so that's one important point to look at.
02:58 First there being the point where they're starting to do their braking, the second being the magnitude of the braking so this is a really good example of the difference, what you'll often see between a pro and an amateur, both in terms of braking point and in terms of the braking strength, how hard they're actually braking.
03:15 Later in the turn, the longitudinal force is actually quite similar but because the amateur has started braking so much earlier, we can see how much lower it sits in the line here.
03:23 There's quite a big difference in speed trace.
03:25 Really obvious thing here looking at the lateral G is how much combined lateral and longitudinal force the pro is holding compared to the amateur.
03:33 So we can see here that the amateur is driving the car much straighter.
03:36 So the lateral G force here is quite constant and then right as they approach the corner entry they turn in quite sharply whereas the pro is able to hold a lot more combined force so they're holding longitudinal and lateral at the same time.
03:51 So I'm just going to zoom back out and just look at the next point in the lap where I wanted to discuss which was the turn 9 section.
03:58 So I'll just zoom to this section here.
03:59 Again looking at the speed trace we can see that the amateur is losing the majority of their time in this second part of the braking phase.
04:09 So this is what I would generally refer to as the first part of the braking phase and then this later section here is what we'd call the late brake when you tend to be trailing into the turn.
04:19 And we can see that's where the gradient is strongest there in the variance.
04:23 It pretty clearly lines up with the difference in the speed traces there.
04:27 We can see that the pro is going a little bit later on the brakes when they start their braking but that's not the most prominent part here, it's really the speed at which they're able to build up the maximum braking force, so this line here is much much more aggressive whereas for the amateur, taking them much more time to get to that constant brake force.
04:44 We can see the pro here is much more aggressive with getting to the peak brake force which is why this line is much closer to vertical, the white line.
04:50 Whereas the amateur is taking a lot more time to reach peak brake force which doesn't happen until down here.
04:56 So that's the start of the braking zone.
04:58 Then you can see this diversion here in the longitudinal G there the pro is beginning to already lift off the brake pedal and that's really where you see this difference here where the longitudinal force drops off, there's a constant bleed off of the pressure here in the white line and that's really where this divergence happens in the speed trace at the same time.
05:20 And once that happens, it really just continues all the way to the apex of the corner.
05:25 So if we just zoom back out again I just want to go to the final portion of the lap and look at this.
05:30 And what we actually see here in this case is the amateur braking with more pressure than the pro.
05:36 So this is a case where the amateur is over slowing the car where you don't need to be over slowing the car as much and as a result, we can see how much more speed the pro is carrying into this section of corners here.
05:48 We can see we've got a bit of a section of corners quite close together here with these two dips in the speed trace and this little ramp in between.
05:54 So this is obviously coming up to a little complex of corners and we can see even though the braking point and even the approximate ramp time to get to full brake pressure is pretty similar, definitely a little more, a little quicker for the pro but it's more similar than the previous example we looked at.
06:10 In this case of the way the brake is being bled off, you can see that the pro is relatively consistent once they get to peak brake pressure, it's pretty constant bleed off, the pressure.
06:20 Whereas the amateur is using more pressure and they've realised that they're going too slow and that's why we see this kink here in the speed trace so they've overslowed the car, realised they've overslowed it, all of a sudden jumped off the brake pedal and then tried to pick up that speed again.
06:33 This style of braking is something you don't want to be doing because it can often upset the car.
06:38 You don't want to be having the car nose dropping and then coming up and dropping.
06:42 You want to have the car sitting down on the nose and it to be pretty consistently down until you get to the apex and as you lift on the throttle and come out, that's when the nose comes up.
06:51 You don't want to have any porpoising of the front, it's bad for grip, it's bad for aerodynamics, it's really something you want to avoid.
06:56 That's an example of analysing the points of maximum loss just looking at those 4 channels of engine speed, car speed, longitudinal and lateral G.
07:05 Now I just want to add a XY plot and a track map just to show you how you can exploit those to understand what's going on with the car as well.
07:12 So moving across to a slightly different view.
07:14 I've got the exact same log data shown here, the only addition is I've got my lat/long G plot shown here and a track map for a little bit of context.
07:22 So if we just zoom back in to the initial point, I'm just going to turn the delta back on, the variance channel so that we can see where we're looking again.
07:30 Going to go back to turn one and have a look.
07:32 So the point I was making initially about both this peak in brake pressure, so you can see here we're on the XY plot where the white part of the cursor is on the traction circle, versus where it is on the amateur parts of the track and traction circle, we're getting much more braking, peak braking force on the reference lap, on the pro lap.
07:54 But the point I really want to make using this traction circle here is if we bring the cursor along to the point where we've got a lot of combined load.
08:03 So we can see the pro is starting to ramp up their lateral load while they've still got quite a lot of longitudinal load, that becomes really clear in this difference in the traction circle here.
08:12 One of the things about a traction circle is it can be quite overwhelming if you're looking at it over an entire lap.
08:17 It often becomes a lot clearer what's going on if you zoom into a specific section of track, maybe one left, one right hand corner.
08:24 Otherwise it's just too many points to overlap with each other and it tends to be much more difficult to see the trends.
08:29 So in the same way that we can see with the log data produced on this time/distance plot here, if we look at it on the traction circle, it's really clear that the pro is able to ride that edge of the traction circle much closer so you can see from the point of maximum lateral acceleration to maximum braking, it's a much more pronounced outward line whereas the amateur is much more of a straight line and they're using much less of the envelope of the car.
08:57 Looking at the example in that late section of the lap we can see something really similar here on the traction circle where the pro is able to exploit much wider in the traction circle than the amateur.
09:10 So the amateur's really sitting on this line here and the pro is using much more of this combined area.
09:15 So being able to exploit that traction circle at the edges or getting much closer to something that ideally runs a curve between the maximum lateral and the maximum longitudinal, that's what we're aiming for.