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Professional Motorsport Data Analysis: GG Diagram

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GG Diagram


00:00 - So far in this section, we've only looked at things from the single tyre's perspective.
00:04 Now it's time to shift towards looking from a full vehicle perspective with the data we log.
00:09 A helpful display for understanding tyre, chassis and driver behaviour and utilisation is the GG diagram.
00:18 Also referred to as the traction circle.
00:21 This is a plot of the accelerations logged by the onboard accelerometer.
00:26 It's called a GG diagram as often the acceleration is plotted as longitudinal vs lateral G force.
00:33 In principle, the GG diagram is showing us something similar to what we're looking at with the friction ellipse in the previous module.
00:41 Where the friction ellipse gives us an understanding of how a single tyre should behave with combined loading, the GG diagram is telling us how the car and driver is exploiting the tyres from an entire vehicle perspective.
00:54 It's showing us something of a performance envelope of the car.
00:58 The extent of this envelope is defined by the vehicle characteristics, tyres and setup.
01:04 How close the car is driven to the edge of the envelope is up to the skill and commitment of the driver.
01:10 Looking at the axes of the GG diagram, this is the convention we'll use.
01:14 With braking at the bottom, drive at the top and cornering horizontally.
01:18 If we now add some raw data to the plot, the first thing we see is that it's quite messy which is pretty typical.
01:26 While there's a lot of scatter in the data, we can still see some trends quite clearly.
01:31 These concentrated clusters of data along the centreline of the plot are braking and accelerating in a straight line and these areas at the far left and right show us the pure lateral cornering forces near the mid corner.
01:44 The areas that link the pure lateral and longitudinal extents of the GG diagram, is what we're often interested in with the GG diagram from a driving perspective.
01:52 These are the areas that represent the combined loading of the tyres that we want to make sure we're maximising.
01:58 Looking at some data here and zooming into a specific area of the circuit, we can use the replay function at half speed and can see how the plot captures the transition from acceleration to braking, to corner turn in, mid corner, corner exit and back to straight drive again.
02:17 Looking at the GG diagram next to the driver inputs, we can see how the unsteady steering inputs result in quite large changes in the lateral acceleration during the turn in phase.
02:27 In this example, I'm just going to use MoTeC's i2 software to walk through looking at the GG diagram, we're going to do a walkthrough of an entire lap and I'm just going to point out the features I see both on the time/distance plot and the correlation with the lat/long or GG plot.
02:44 So over on my laptop screen, you'll see I've got a basic layout of a time/distance plot here so we've got our engine RPM, speed, throttle and brake traces overlaid, I've got the brake bias, the steering and also the gear position here as well.
02:57 On the right hand side I've got our lateral and longitudinal G force plotted on top of each other.
03:03 In this particular case, everything that is shown in colour is for the faster lap and everything that's shown in white is for the slower lap from the slower driver.
03:11 One of the things that's really important to understand about using a GG plot is using the zoom linking feature.
03:16 What I mean by that is that the period of distance that we're looking at on the time distance plot also should be linked with what's shown on the GG diagram.
03:25 That's really important because it gets rid of a lot of the clutter and you'll see as we go through this example how important that is.
03:30 So I'm going to zoom into one particular section of track here and we see straight away as soon as I zoom in like that, if I just zoom in and zoom out, you can see a different amount of data is shown on the GG diagram.
03:42 Now that's really important because if you look at a full lap like this, it's really overwhelming, we've got the entire lap showing and while I can see some trends here, I can see that the coloured driver here is generally exploiting more of the GG diagram in general, they've got a bigger performance envelope they're using there.
03:57 It's showing us the whole lap, it's really difficult to see what's happening at what point on track so that's what I mean by the zoom linking and why it's so important so again if we just zoom back into a particular area of track here, and what you'll also see is as I move through, forward and back through the lap, you can see everything updates there.
04:16 So the first thing I notice, I can see how much more speed the faster driver is carrying here than what the slower driver is using.
04:25 As I move the cursor through this position you can see how much further out or how much wider on the GG diagram the coloured driver is getting the car to.
04:37 So if I just scroll through this section you can just see really clearly this area of the GG diagram where there are much more combined load which is what's really what's giving us, this is the trend you'll see between say a professional driver or a really strong driver vs maybe someone a little bit weaker and that's exactly the situation we've got here.
04:56 We can see this is the sort of region that the amateur is operating in and this is the sort of region that the pro is operating in so if we just keep scrolling through here, we can see a similar trend towards the end of the braking zone here where they're actually doing a flip flop and they're changing direction.
05:11 And it's the same thing, the pro is just, it's not maybe quite as clear on this one but there is definitely a trend and more combined braking and cornering in this section of the corner so if we just move further through the lap, let's try and find some cleaner examples of this.
05:30 This is a really clean example here so we've got the slower driver in white lifting off the gas earlier, the point they break is actually quite similar.
05:38 But as they move through the corner we can see the areas that are being used on the traction circle here on the GG diagram.
05:47 It's really distinctly different so we've got the pro here operating right out using all of this extra acceleration on the car whereas the amateur is really a perfectly straight line between their maximum braking force and their maximum lateral.
06:02 So we can see, there's a couple of things going on here, one of them is that the pro is getting a little more longitudinal acceleration.
06:08 It's not massive, not interesting, not compared to how much more brake pressure they're using here, you can see in this section how much more brake pressure, much more peak brake pressure they're using.
06:19 We're not actually seeing that reflected so much in the longitudinal acceleration here but what we are seeing is this combined load, the way it's transitioning from braking in to cornering and also how much more lateral acceleration is being carried through the corner here.
06:31 Then if we just keep moving forward, let's see what other parts of the track we can analyse here.
06:43 So this is into a relatively slow part of the track.
06:47 While we see some difference down here in the combined load, one of the things that's quite clear is in the drive phase here, so if we just bring the cursor through, because anything on the top axis here, anything above the 0 line is obviously drive, or acceleration.
07:01 So one of the really nice features that you'll see a lot of data analysis software packages do is that as you move the cursor through, because it highlights on the GG diagram exactly where we're looking, you can actually do the same thing, you can actually come here and click on any of these points, you can in i2 anyway and it'll update the cursor position, which can be a really nice feature if you're looking for something specific in the GG diagram.
07:23 But essentially what it looks like is happening here is that we've got our 0 line here on the lateral.
07:29 So we know anything over here is in combined drive.
07:33 We can see the coloured driver getting a lot more heavily loaded drive acceleration out of the corner and that's, we see the reason for that here in all of this extra throttle.
07:44 So as they exit the corner the position these 2 drivers are picking up the throttle is totally identical, it's just that the colour driver is getting to full throttle much much more aggressively and much earlier and holding it and that's really what we're seeing reflected in this area of the GG diagram.
07:59 Let's look at a few more, here we've got something similar going on that we saw in the previous one, it's really in this drive section on the corner entry, actually the white driver's doing a very similar and in fact better job from some points of the combined load through here.
08:15 But it's really in the drive phase that the big difference is happening so we can see how much more aggressively the colour driver is getting onto the throttle here, we see that really clearly in the speed trace and then we see that reflected here in the GG diagram.
08:30 So that was just a walkthrough of a couple of the corners in this particular data set to show you guys the correlation between what we see in the time/distance plot and what we see in the GG diagram and what that means for both of them.
08:42 From going through that example you can see how using the GG diagram in conjunction with the logged driver inputs can quickly expose differences in how the car is being driven which is vital information that can be used to coach yourself or your driver.
08:58 Before moving on, we do need to have a look at something that can have a big effect on the size and shape of the GG diagram.
09:05 And that's downforce.
09:07 Looking at a theoretical case of a car that produces moderate downforce levels with all other factors equal, here the GG diagram for high and low speeds are shown.
09:19 As the downforce level increases with speed, the vertical load on the tyre increases which increases the maximum forces they are capable of producing.
09:28 We typically get higher gains in braking and cornering simply because these tend to be happening at higher speeds.
09:35 At lower speeds we have little downforce and often an excess of engine torque while at high speeds we are typically power limited and the extra downforce doesn't gain us as much in acceleration.
09:47 Looking at some logged data of the same car at the same track but one at a high speed and the other in a low speed section, we can clearly see the different accelerations the car is capable of producing with additional downforce.
10:00 The red data is from the high speed area of the circuit and the white the low speed.
10:04 We can see how the performance envelope of the car gets larger with the addition of downforce at higher speeds.
10:12 The point being when we're using the GG diagram, road speeds need to be taken into consideration.
10:18 Most data analysis systems give you the option of colour the data points on a scatter plot but a third channel, this allows you to visualise with the third dimension, even though the plot remains only 2D as we saw earlier in the course.
10:33 If we select road speed as the channel to colour the data by, using the same data we've just looked at, it helps visualise the effect of speed available on the G force envelope.
10:43 The colour legend shows us high speeds are shown in orange and red with low speeds in blue.
10:48 We can see the most striking differences in the increase in lateral acceleration we get in high speed corners for this car.

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