Data Analysis Fundamentals: Analysing the Time Delta / Lap Gain/Loss Channel - Advanced Sensors
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Analysing the Time Delta / Lap Gain/Loss Channel - Advanced Sensors
14.15
| 00:00 | - In that previous example, I was making the assumption that it was just a really basic logging system with the absolute bare minimum channels but I think you can see pretty quickly already with those basic channels you can already start to learn quite a lot about the differences in the way the car's been driven. |
| 00:13 | Now I want to take a look at the exact same data but I want to take it from the perspective of having a few more advanced sensors so the sensors that I've got added into this system are throttle position, brake pressure, steering angle and gear position. |
| 00:28 | So here looking at the exact same log data we were before, but as I was talking about in green here we have the throttle position, in red I have the brake pressure, in orange I have the steering angle and in purple down the bottom I have the gear position. |
| 00:42 | I tend to have the throttle and the brake traces overlapped, it just helps me have a little bit more vertical space and because you've usually only got braking or accelerating happening at one time or the other, it means that you can usually overlay it quite effectively. |
| 00:53 | So I want to start by zooming into the same areas we discussed before. |
| 00:57 | So I'm just going to look at that loss at turn one. |
| 00:59 | So to start with, looking at the throttle trace, it's really clear that the pro driver is going much much deeper on the throttle so I can have a look at the difference in the distance scale at the bottom to work out how far that distance is. |
| 01:13 | I can also see the difference in brake pressure. |
| 01:17 | So there's an enormous difference in brake pressure between the two drivers here. |
| 01:20 | We can see we're approaching double the brake pressure that the pro is using. |
| 01:24 | We can also actually see here a little bit of a crossing where in the white data the pro is getting onto the brakes before they're actually fully off the throttle. |
| 01:31 | Crossing of the accelerator and the brake isn't something you really want to be seeing. |
| 01:35 | It tends to use more fuel, it's harder on the car, it's harder on the brakes. |
| 01:39 | It's something you tend to be discouraging out of drivers. |
| 01:42 | It is something you'll often see with a left foot driver. |
| 01:45 | And again in that brake pressure trace of the pro, I wouldn't say it's perfect but looking at this it's a much more consistent bleed where that brake pressure's dropping off all the way as they trail into the corner and then there is a much faster bleed right at the end here. |
| 02:00 | The ideal shape of that brake trace will depend on the specific car and in particular the type of corner and the track layout. |
| 02:07 | It's not always a case of the ideal perfect bleed from peak pressure all the way to zero at the apex. |
| 02:13 | This is an example of where that particular technique doesn't work so well. |
| 02:17 | But using the professional as the reference here you can see they are bleeding pretty consistently all the way to the apex where with the amateur while there is some amount of bleed it's really much more of a tabletop so once they get to pressure, they are pretty constant all the way until they get the apex and it drops off really quickly which isn't typically something that we want to see. |
| 02:36 | We can also see the rate at which the amateur is ramping up on the brakes which is really slow, it's taking them a long time to get from starting braking to get to full brake pressure. |
| 02:46 | Here I'm using the pro version of MoTeC's i2, one of the advantages that the pro version does is it allows you to use a delta function. |
| 02:53 | So if I put the cursor here, press spacebar, and put the cursor somewhere else, in this case I can see that the amateur is taking 10 metres difference between when they lift off the accelerator to get onto the brake. |
| 03:05 | If you don't have the pro version or you're using a software that doesn't have that function you can also use the distance scale at the bottom here and just read off the distance difference between putting the cursor in two different places like that. |
| 03:15 | It can help to zoom in a little bit further if you want to read that off a bit more clearly. |
| 03:19 | Looking at the difference between the points that both drivers are lifting, if I check that distance there, that is 30 metre difference between when the two drivers are doing their lifts. |
| 03:30 | And a similar idea, if I hold my cursor over the points of interest on the brake pressure, I can see here the difference in brake pressure between them. |
| 03:37 | So the amateur driver's using about 60 bar and the pro is using about 105 bar there so a huge difference in peak brake pressure. |
| 03:44 | At corner exit again a really big difference in the throttle aggression. |
| 03:48 | So this is something we see here with the amateur driver really slowly getting onto the throttle, being really really slow on the ramp and then once they've comfortable, they're going to full throttle really quickly whereas the pro is lifting the throttle, getting to full throttle much much quicker, much more aggressively, they are having to do a lift here as they're probably feeling something a little bit unsettled with the car before they get to full throttle but that is making quite a big difference. |
| 04:13 | You can see here in the speed trace how much more aggressively the speed trace rises out of here compared to the amateur and that's really because of the difference here in the throttle application. |
| 04:23 | In the steering trace at the bottom here it's a much clearer example of the way the pro and amateur are driving the ccar. |
| 04:29 | So we can see here in the coloured where the amateur is driving the car much straighter, so big consistent brake pressure. |
| 04:35 | You can see in the steering angle they're driving it much straight as it's sitting closer to that zero line and then really at the last minute they're doing a big aggressive steering input to get through the corner. |
| 04:45 | This is quite different from what's happening with the pro. |
| 04:47 | With that, they're getting the steering input on probably even more aggressively but they are getting more of it on earlier. |
| 04:55 | So one of the things about the steering trace, it's quite useful for understanding balance. |
| 04:59 | Initially looking at the steering trace, it could seem like one driver has a lot more understeer than the other because there is a lot more steering input. |
| 05:07 | Because the pro is carrying more speed through the corner than the amateur, that means they need more steering input in order to have more lateral acceleration so they can take a similar path with more speed through the same corner. |
| 05:17 | So in this particular case, having more steering input here isn't necessarily a case of understeering the chassis, it's really more of a function of the more speed being carried into that corner entry. |
| 05:28 | So let's look at another point in the lap here, the same points we were looking at before. |
| 05:34 | Again it's really in the second part of the braking phase that most of the damage is being done to the amateur here, we see the variance is dropping off in this little ramp here. |
| 05:42 | So again we can see the difference between amateur and pro as far as the point they're lifting so let's check what that is. |
| 05:47 | It's 10 metres there at the point they're lifting. |
| 05:49 | Really clear thing about the brake trace here is how slowly the amateur is getting to their peak brake pressure versus the pro. |
| 05:57 | So there's not a lot of crossover in this braking zone for the pro but they are ramping to peak pressure much quicker. |
| 06:04 | The actual peak pressure was really essentially almost the same, it's just that the pro is getting much more retardation done earlier in the braking zone. |
| 06:10 | There is this other little feature I just want to mention here, it's this little spike in the brake pressure, this is the pro just tapping the brake pedal with the left foot while they're still accelerating down the straight. |
| 06:20 | That little spike in the brake pressure that we see there while the car's still accelerating is due to something we call knock off. |
| 06:26 | That brake knock off is something you'll usually see, particularly on rough circuits but it's where essentially the pistons and the brake callipers are getting forced back in, that means when it comes to the braking zone, the pistons have got to take out the initial slack because they've been pushed back into the callipers. |
| 06:41 | When it comes to the braking zone, some of the pedal will be taken up by initially just getting the pistons back onto the back of the pads against the discs and then at that point you can start to pump up the brakes. |
| 06:51 | So this is often something you'll see drivers doing when they're heading down the straight if you've got a car that's suffering from knock off which can either be from compliance in the system or loose wheel bearings or particularly on bumpy circuits where all of those problems tend to get compounded and the discs end up rocking against the brake calliper pistons. |
| 07:09 | You'll often see someone that's using their left foot to put a little tap on the brake pedal so that means once the pistons are out and they get to the braking zone and the pedal is nice and hard and they can start braking without any fear of hitting a long pedal when they go to hit the brakes at the end of that straight. |
| 07:22 | Now that I've dealt with that, I just want to look at the rest of this braking zone. |
| 07:25 | So you can see where the rest of the damage is done here where the speed traces really start diverging and that's again through this pretty poor braking effort here where they're taking a long time to get to peak pressure and then once they're at it it's really like a tabletop and that tabletop is really constant and it's not until this point where the speeds are really already quite diverged that they've realised they've overslowed and they start aggressively tapering off the brake pedal. |
| 07:49 | So when you look a the pro, it's much closer to being a quick build and then a constant, there is definitely a second application here which is not perfect but if you look at the whole trend compared to the amateur braking there's quite a big difference in the middle here and that's really where a lot of that time delta's coming from. |
| 08:05 | Again you can see the pro using much more steering angle on the corner entry here and that's really again because they're asking for more lateral acceleration the whole way into the corner because they're carrying more speed. |
| 08:17 | There is this quite interesting feature at the end where we see some oversteer. |
| 08:20 | So whenever you see a feature in the steering trace like this where the steering has been applied and then you can see here where we expect it to smoothly carry on to be removed from the car as you go through corner exit, we've got this really quick snap here. |
| 08:34 | This is a situation where the driver's turned into the corner, then there's been a snap at the rear of the car and they've used an opposite lock correction and that's something you'll often see at corner exit in the steering channel. |
| 08:43 | So we can see here the difference in your throttle trace is quite different. |
| 08:46 | While the am has gone to a small amount of constant throttle and sort of held it there, and very very slowly started to apply it and then more aggressively right when the car is much straight they've got to full throttle, we've got the pro here which is waiting a little bit longer and then more aggressively getting onto it and we can see it really clearly lines up the point where the steering starts going back to opposite lock is the point where they're really starting to aggressively stab the throttle here. |
| 09:10 | So we can see as we move through, get on the throttle, the car snaps there into a big opposite lock correction, they lift out of the throttle and then as the car returns to going more straight and the steering wheel starts straightening up again they get back to full throttle. |
| 09:25 | And they're on their way on the corner exit. |
| 09:27 | Looking at the last section of the lap, we have the, actually the point where the pro and am are lifting off the throttle is actually pretty similar. |
| 09:34 | We can see the pro's carrying a little bit speed with the white line being on top of the blue line there. |
| 09:40 | You can actually see in the delta, there's about 3 km/h difference so it's pretty close really. |
| 09:44 | The point they're lifting off the accelerator is pretty similar but the big difference happens here in the braking trace. |
| 09:50 | Probably some of the best braking we've seen from the amateur over a lap so far in terms of having enough brake pressure. |
| 09:57 | This is actually a little bit of a reversal in the difference between the brake pressures between the pro and the am. |
| 10:03 | In this case we've got the amateur using more brake pressure than the pro. |
| 10:05 | They're also ramping to peak pressure pretty well, certainly compared to the other points we looked at in the lap. |
| 10:12 | The problem in this case, you see the big divergence in the speed trace here, and that's really just indicating that the amateur, while they're getting to peak pressure much better than they did earlier in the lap, they are holding too much pressure so in this case the pro is not braking the car as heavily and as a result is carrying more speed into the corner. |
| 10:31 | So this big difference in the brake pressure here is really having a huge detrimental effect on the amount of speed that's being carried into the corner. |
| 10:38 | You can also see here what's really clear is how much the, on the reference lap, the pro driver in the white is fighting the car all the way in so this really jagged line all the way through in corner entry and corner exit, it's not necessarily something you want to see, a really sawtooth pattern on here, it can be quite hard on the tyres, can be quite hard on the car, it's not a very good way to drive a car if you're looking for stability but it is something sometimes you'll see with a really aggressive pro driver where they're sawing at the wheel the whole way through here. |
| 11:07 | A little bit of that style, a little bit of that is them being closer to the limit of the car. |
| 11:13 | So in this section we can see we've actually got two corners linked together so this is an apex here and an apex here. |
| 11:18 | With this little short shoot between them. |
| 11:20 | We can actually see that the amateur is getting to full throttle earlier than the pro in this case but unfortunately that's really because they're going a lot slower at this first apex here so they're able to be more aggressive on the throttle. |
| 11:34 | So at first glance it looks like the amateur's actually doing a better job through here just looking at the throttle trace alone but if you look at the speed trace it shows you how much more they've slowed the car on entry which is allowing them to use more throttle to accelerate the car out. |
| 11:48 | Just going to flick across to another view here that I've got set up which is exactly the same, just looking at the traction circle as well as the time/distance graph as well as a track map which is a way I typically have my log system set up if I was doing a little bit of driver analysis but in this case we're looking at it with the more advanced channel of the throttle, the brake, the gear and the steering as opposed to just the lat and long G. |
| 12:09 | I just want to dig into a couple more sections of this lap where I'm seeing some differences. |
| 12:12 | So one of those places is through here and looking at the gear trace. |
| 12:17 | So one of the things that are quite clear here is looking at the difference in the gear position so at this hairpin corner so we can see where we are on the track map in the top right here. |
| 12:26 | The pro is using first gear, the amateur is using second, you can see that in the legend up the top there. |
| 12:31 | One of the things you'll often see with a pro vs am is an am staying in a higher gear where they're a little bit more comfortable they're often doing that because they don't want the car to snap on them, they're a little bit nervous about the car being loose on exit whereas the pros tend to be more comfortable with a looser car and as a result, they can take advantage of using a lower gear which gives them a higher drive out of the corner at the expense of being a little looser and a little less stability. |
| 12:56 | So that's actually something that's really clear in this corner, the pro driver is using first gear and they are getting better drive out of the corner. |
| 13:03 | This is partly because they're using more accelerator on corner exit here but they will definitely be getting better drive because they're using a lower gear and then we see this snap in the steering here and that snap as we discussed before, that's about the car snapping in the rear and the driver doing a correction on the steering. |
| 13:21 | On the traction circle on the right hand side here, we can again see the way that the pro is able to carry more speed through the corner, so looking at those cursors, just going back through this late part of corner entry you can see how much more combined force the pro is using and really being much closer to the edge of that traction circle than where the amateur is sitting through there. |
| 13:42 | Hopefully that example's clear where you start with the variance, you look for the areas of greatest loss which are going to be in those areas where you've got the steepest gradient. |
| 13:49 | Then you can take your cursor and line it up with those areas of steepest gradient those biggest losses, and you can look for the reasons why. |
| 13:56 | Looking at that example of the more advanced channels with the throttle, the brake, the steering and the gear, hopefully that becomes a little clearer on how you can make use of those channels, you can see a little more detail about why you're getting those differences, what the driver's doing to induce the car to do something specific. |
