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Professional Motorsport Data Analysis: Damping Histogram

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Damping Histogram

14.24

00:00 - A histogram of the damper velocities is a commonly used tool for understanding damping.
00:06 This is because we know that the dampers primarily produce their force in response to velocity.
00:11 And therefore it makes sense that we would want to look at which velocities are being used by each damper.
00:17 In a similar way to how we use the throttle histogram in a previous section of the course, the damper velocity histogram is telling us how much time each damper is spending in each velocity range.
00:28 Here's an example of a set of histograms, one for each corner of the car.
00:33 Looking at all 4 corners together at the same time is common practice.
00:37 And the settings we use for the histograms are application dependent depending on the sort of racing we're doing.
00:44 For road racing, the typical velocity range is between positive 250 mm/s and -250 mm/s.
00:53 For these examples, positive velocities will represent compression and negative velocities will represent rebound.
01:00 For this range of velocities a bin width of around 20 mm/s is about right to capture enough detail to break down the different damper speed ranges.
01:09 In some data analysis software, we have the option to show histograms in either bar format as shown here or line format.
01:17 I prefer line format as I find it easier to see differences when using overlays of different cars or damper settings but you should experiment with both.
01:27 One other thing to mention with histogram setup is the direction convention.
01:31 This just means you need to tell the software if positive damper values of velocity indicate compression or rebound for your setup.
01:39 For these examples, positive values indicate compression.
01:43 As with the throttle histogram, these are normally zoom linked.
01:47 And in most cases it only makes sense to look at a damper velocity histogram over at least one full lap.
01:54 So be careful this is what you have selected.
01:56 It's certainly valid to set the zoom to include multiple laps, just ensure you're only including whole and only fast laps.
02:05 You wouldn't want to include any in or out laps or safety car laps as this will skew your data.
02:11 As we discussed earlier in the module, the histogram is telling us how much time each damper is spending in each speed range.
02:18 The areas close to the central axis represent each damper working at lower speeds and as we move away from the centre, the damper is working at higher speeds either in rebound or compression.
02:32 In this case, adding some overlays really helps to explain these plots.
02:36 Let's say we were to increase both the low speed rebound and compression damping together on the front axle.
02:43 Looking at the damper force plot from the damper data, let's assume that we're going from our baseline curve shown here in black to the new curve shown in red.
02:52 This is showing us how much force change we'll get for a given adjustment.
02:57 With this change, we'd expect to see a spike in the middle of the histogram.
03:01 This is because we've added low speed damping, therefore, the damper will spend more of its time in the low speed region in both the compression and rebound directions.
03:11 Looking at the damper histograms from the logged data, after running the car on track with this adjustment, this is exactly what we see.
03:19 The original logged data histograms are shown in colour and the new data from the damper adjustment is shown in white.
03:25 We can see that the front dampers are spending more of their time in a lower speed range which is exactly what we expected to see.
03:32 Because we're looking at the percentage of the lap for the damper speeds and because we're spending more time at lower damper speeds, we must have also spent less time at higher speeds as a proportion of the entire lap.
03:45 This is why we see this difference on both the rebound and compression sides in the higher speed ranges in the overlaid data.
03:53 This doesn't mean we have less high speed damping now with this adjustment.
03:57 It just means that we've biased the damping forces towards low speed.
04:01 Everything with these histograms is relative.
04:04 We can break down the different velocity ranges into different handling regimes to understand a little bit more about what they mean.
04:11 This is a broad general discussion relevant to most road racing situations for something like a club racing saloon, touring or a GT car.
04:20 Using these rough damper velocity boundries can help us focus on the relevant parts of the histogram depending on what sort of behaviour of the car we're looking to change.
04:30 The 0-5 mm a second speed range highlighted here is where the friction forces, both inside the damper and within the rest of the suspension tend to dominate.
04:40 Generally the behaviour in the speed range is dominated more by the components we use rather than any adjustments we make to the car.
04:48 The 5-25 mm/s range highlighted here is the speed range we're typically tuning to control the transient corner entry and exit balance as well as heave, pitch and roll movements of the sprung mass.
05:03 In other words, to influence the transient vertical load on each tyre during driver inputs as well as the motion of the chassis.
05:11 When we talk about making a low speed damping change, this is the range we're talking about.
05:16 Because this is the range that tends to have the most influence on chassis movement.
05:20 When you're tuning for aerodynamics, this is the range you're often also concentrating on.
05:26 In the case where we have a set of dampers that have only low speed adjustment, this is the speed range with which we can expect the adjusters to have most influence.
05:35 The 25 -200 mm/s range highlighted here is largely the result of bumps and irregularities in the track surface.
05:43 This is the range we're tuning to change the behaviour of the car over bumps on a rough track surface such as a street circuit.
05:50 At a particularly smooth racetrack, we wouldn't expect to see the dampers spend much time in this speed region.
05:57 This is the range we'd normally consider high speed.
06:00 In the case that we have dampers with high speed adjustment, this is the speed range over which we can expect them to have the most influence.
06:07 At 200 mm/s and greater, we're looking at the range for which we're hitting curbs and is where the damper is subject to violent speeds in accelerations.
06:16 Some high end dampers have an adjustment for what is often called blow off settings and this is the sort of speed range they typically affect.
06:24 We can use blow off settings to help the car ride the curbs better by reducing the damper force at extremely high velocities.
06:31 This allows the unsprung mass to ride the curb without upsetting the sprung mass as much.
06:36 From a reliability perspective, we can use the histogram to determine if our dampers are behaving relatively consistently from side to side.
06:45 We're looking for a similar speed distribution for both sides of each axle.
06:49 Even for 2 dampers that are behaving identically we expect the histogram to not be completely identical as both sides of the car are operating on slightly different parts of the track.
06:59 There are a number of other sources of errors but in simple, practical terms, these are out of our control so we don't get too hung up on histograms that don't match exactly.
07:09 We can expect individual dampers of identical spec with the same settings to behave slightly differently.
07:15 This is due to the nature of hydraulics that determines the response of modern dampers.
07:21 Where the tolerances of the components are critical and very small variances in manufacturing and assembly cause measurably different behaviour of the damper.
07:30 The best way to see these is on a damper dyno.
07:32 Dampers are one of the components where you really get what you pay for due to the tight tolerancing required in manufacture.
07:39 Even in very high end dampers that are carefully built by experts, it's normal to have a small but measurable difference in performance from one set to another.
07:49 This is where we make use of a damper dyno to equalise the performance to a known baseline behaviour.
07:55 This will result in each damper having a different setting or number of clicks to achieve similar behaviour.
08:02 In the case you suspect something is wrong with your dampers or the adjusters aren't affecting the histograms in the way you'd expect or maybe you can't get each side of the car to match very well, the only way to check them is on a damper dyno.
08:16 This is an example of a set of histograms from where the car, track damper set and damper settings are all the same with the data being from back to back runs in the same session.
08:29 The differences we see here in the overlay are reasonable, there's nothing wrong with these dampers or the sensor setup, this is an expected level of variation.
08:38 Once we've made a damping adjustment or a damper change, we should have in our head, the change in our histograms we'd expect to see.
08:46 One the different settings or dampers have done a run, we should check the histograms to make sure they look as expected.
08:53 For example, if we increased low speed rebound on the rear axle, we should expect to see this reflected in the histogram as more time being spent in low speed rebound in the rear.
09:04 We can often catch errors in mechanic's adjustments and problems with dampers by quickly running our eye over the histograms throughout the race weekend.
09:12 If we consider just from a theoretical perspective, the mechanical aspects of maximising grip around a full lap of the circuit, the baseline starting point is to aim for a symmetrical histogram between compression and rebound on each corner of the car individually.
09:29 This comes simply from the concept of an energy balance that means the damper should be absorbing a similar amount of energy between compression and rebound in both low and high speed regimes.
09:40 In many situations, this isn't the actual optimum.
09:43 But it's a sensible starting point for getting yourself in the performance window, particularly if you're just getting started with your damping setup.
09:51 Let's look at a set of histograms for a car we've just fitted and set up damper pots to for the first time.
09:57 Here we're zoomed over our single fastest lap so far.
10:01 We've overlaid a typical distribution as a guide for getting the sort of symmetry we should be aiming for.
10:08 We can see that we don't have particularly good symmetry in low speed on the front axle.
10:11 The front left and front right need different levels of correction but we can see that for both sides in the low speed range we either need more compression stiffness or less rebound stiffness.
10:25 Let's say because the track we're running on is relatively rough, we prefer not to do anything that will reduce our suspension compliance so we'll reduce low speed rebound stiffness from both sides on the front and leave the compression settings alone.
10:39 The actual amount of adjustment we need to get the effect we want on the histogram will depend on the model of dampers we're using.
10:47 In some dampers, one click will show up, in others you might need 20 clicks.
10:52 It's just something we have to experiment with for the hardware we have.
10:56 We can see that the front left is more skewed than the front right.
11:00 So we'll make a slightly larger adjustment on the front left than we will on the front right.
11:05 Now after running the car on track with the new settings, let's look at the data from after that adjustment.
11:12 The original is shown in white and the new data in colour.
11:16 We can see it went in the right direction but we still need more of a correction in order to improve the symmetry.
11:23 Making another pass with more of the same adjustment and running the car again, we can see the histograms have a much more symmetric distribution that I'd call acceptable.
11:34 It should go without saying that driver feedback and lap times should be guiding our decisions as we go through different damping changes as well.
11:42 The histogram is only telling us part of the story.
11:45 Once we've got a feel for how large a change needs to be in order to affect the histograms, we can start designing a matrix of tests to try different damping levels.
11:54 You can try both increasing and decreasing overall levels of damping while maintaining symmetry of the histograms as well as trying different levels of skewed between rebound and compression at both ends of the car.
12:08 Unless you're running on an oval you wouldn't normally run asymmetric damping from one side of the car to the other so you should aim to keep the left and right sides of each axle the same.
12:18 One common exception to a symmetrical histrogram target is aerodynamics.
12:23 As we discussed earlier, cars that are generating a significant proportion of their downforce with the floor are sensitive to changes in the attitude of the chassis.
12:32 The downforce is primarily sensitive to heave, pitch and roll.
12:36 In the case where a car is generating a lot of downforce and maybe they're trading off some of the mechanical grip in order to control the chassis platform, is worthwhile.
12:45 Controlling that chassis platform allows us to keep the attitude of the chassis in a way that maximises our downforce.
12:53 This usually means running more low speed rebound than we otherwise would as it tends to keep the chassis platform in a more consistent attitude.
13:01 You'll need to evaluate for your own situation for each circuit how much emphasis you need to put on aerodynamics vs mechanical optimisation.
13:10 A good guide that can help decide how large of a change to make in the damping settings, is that we should be able to consistently see the difference in the histograms over top of the natural noise that will always cause differences.
13:23 If we can't see the difference from one run to another after an adjustment, then the change probably wasn't big enough.
13:30 With the number of combinations of different damping settings available, plus different combinations of front and rear damping, you can see how quickly you can run out of track time and tyres when trying to find the best settings.
13:44 However even when backed up by a lot of pre testing simulation, running the different settings on track, gathering the driver feedback and reviewing the data is the only solution, regardless of the type of racing you're doing.
13:57 As we mentioned before, the range of adjustment of each damper and the amount of damping change you'll get with each click is going to depend on its design and build spec.
14:08 The ideal damping behaviour is going to be specific per circuit, setup, tyre and driver preference among other things.