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Professional Motorsport Data Analysis: Damper Fundamentals

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Damper Fundamentals

12.37

00:00 - To maximise the available mechanical grip from any chassis and tyre combination, getting the damping right is critical.
00:07 It often seems that within some parts of the motorsport community there's a lot of confusion and general misunderstanding of the purpose and implementation of damping.
00:17 This is an enormous subject and properly diving into it would require its own dedicated course.
00:23 But with that said, it's entirely possible to find and make gains using logged data even with a relatively basic understanding of the subject.
00:34 In this section we're going to focus on exploring how we can use some simple tools to understand and find improvements in our damping settings.
00:42 To make use of the techniques we'll cover in this section, you're going to need damper potentiometers fitted to your suspension.
00:48 As this damper position data is what we'll use as the basis for the analysis.
00:53 The damping we'll discuss in this course will be limited to what the dampers provide, not any other components.
01:00 Before we discuss analysing dampers, it's worth reviewing a few fundamentals.
01:05 Everything we discuss in this section is idealised in that we will ignore some of the more complex phenomena.
01:11 We will stick to discussing the fundamental principles in a practical way instead of getting bogged down in the different complexities.
01:18 Fundamentally, elastic elements in a suspension like springs and anti roll bars produce a force in response to displacement.
01:27 In the case of a linear spring, the force it reacts with is proportional to its displacement.
01:33 The principle of damping is that forces produced in response to the speed of the displacement, meaning how fast you move it.
01:40 This basic principle is the most critical point to get across when considering why a spring and damper produce force through completely different physics.
01:49 Here's a graphic to help visualise how the force response differs between a spring and a damper.
01:54 On the left side, we have a linear spring and on the right, a damper.
01:59 Both of these are attached to a common element that will drive them at the same speed and displacement.
02:05 Underneath is a pair of plots that will represent the force in the spring and damper respectively over time as we vary the input.
02:14 If we start driving the system with a slow but constant sinusoidal input, we can see the force response in both the spring and the damper.
02:22 As we begin to increase the speed of the input, we can see that the force response of the spring is the same as it was at low speed while the force to drive the damper has increased.
02:33 Continuing to increase the speed even more, we see that the damper force continues to increase while the spring force again remains the same as with the original speed.
02:43 This is because the amount of displacement isn't changing but the speed is.
02:47 I think this is quite a good illustration of the fundamental difference in the working principle of a spring vs a damper.
02:54 So the takeaway here is that for elastic elements like springs and anti roll bars, we care about how far they've been displaced, bent, squashed or twisted, for a damper we care about how fast it was displaced.
03:08 The primary purpose of elastic elements like springs, bump rubbers and anti roll bars is for us to control the stiffness of different parts of the suspension.
03:17 We use them for things like supporting the weight of the car, controlling how far the suspension deflects when subjected to downforce, how much each end of the car rolls during cornering and how much the car squats during acceleration.
03:31 The primary purpose of a damper is to damp out oscillations in the suspension.
03:36 The source of the oscillations is energy that's stored both within and imparted to the suspension.
03:43 The energy that's stored and released within the suspension is in elastic elements such as the springs, anti roll bars, bump rubbers, tyres, suspension members and even the chassis itself.
03:56 The energy that's imparted to the different elements of the suspension, primary comes from irregularities in the road surface and the driver inputs.
04:04 Here's an animation of what is typically referred to as a quarter car model.
04:09 Simplifying the suspension down to a single corner of the car makes it simpler to understand the relative effects of the different parts of the system.
04:17 In this example, we're only considering a single spring and damper to represent the suspension with a mass on top representing one quarter the mass of the chassis.
04:27 In reality, the tyre also has its own stiffness and damping properties but for now we'll ignore that.
04:34 Here we have a tyre following a non smooth road surface and to start with, we'll deactivate the damper which means we have a 0 damping.
04:43 We can see that the tyre is spending a lot of its time not in contact with the road.
04:48 This is because of the energy that's being stored in the spring, is released after it gets to full compression on each cycle, causing it to jump even further off the road surface.
04:58 Clearly, we can't generate much tyre grip in this case with the tyre not spending much time on the road.
05:05 Now if we add some damping, we can see the tyre is starting to spend a little more time in contact with the ground.
05:11 As we continue to increase the level of damping, the tyre is beginning to follow the road surface more closely.
05:19 There's a point where for a given road surface profile, the level of damping will be too high and continuing to increase the level of damping will essentially make the suspension behave as if it were close to solid.
05:31 This means we start to increase the deflection of the sprung mass by adding too much damping.
05:35 We have made the vertical load variation on the tyre worse.
05:40 For a given road profile and spring stiffness, there's an optimum level of damping.
05:44 In practice, this means each spring stiffness has a different optimum damping setting for each circuit we run at.
05:52 The takeaway here is that too little damping is bad, as is too much damping.
05:56 It's our job to find the right balance for the given conditions.
06:01 In a motorsport context, there are 3 main reasons we use dampers and spend time tuning them.
06:07 First we want to maximise the consistency of the tyre vertical contact patch force.
06:13 Secondly, we can tune the speed of transient handling events such as the pitch and roll behaviour.
06:19 Lastly we want to maintain a consistent chassis platform for aerodynamic reasons.
06:24 We already understand that the vertical force the tyre experiences at the contact patch is directly related to the longitudinal and lateral forces we rely on to accelerate the car.
06:36 In a steady state case, with a completely smooth road surface and no imperfections, the vertical load on each tyre contact patch would theoretically be constant.
06:47 In this situation, we don't have much need for any damping.
06:51 The physics are dominated by the simple elastic elements like our springs and anti roll bars.
06:57 In a steady state situation like this, the energy level is constant so we don't have any oscillations to damp out.
07:04 When we introduce bumps, undulations and non constant inputs to the car, as we have in the real world, the dynamics of a system become more important as the vertical load on each tyre is now not steady.
07:17 It's varying over time.
07:19 This variation in force is influenced by a huge number of factors but for simplicity, we can consider the energy stored in the elastic elements, the road profile, the unsprung mass, as well as the kinematics of the suspension to be dominant.
07:35 In simple terms, the minimum vertical load we apply to each tyre through any section of the track is going to be the limiting factor for our longitudinally and lateral accelerations.
07:46 High grip tyres and a lot of downforce are negated by variation in the vertical load applied to the tyres.
07:53 As we see in this example, where the vertical load applied to a given tyre is varying over time, the main shape of the variation of the vertical load profile is from weight transfer throughout the lap as well as the downforce which is indicated by this line.
08:08 However, zooming into one section of track we can see these higher frequency changes in vertical load more clearly.
08:15 These are mainly due to the uneven profile of the road surface and the suspension's response to these unsteady inputs.
08:22 Tracing a line through the points of minimum force shows us the limiting factor for grip.
08:27 These other areas of high vertical load can't be fully exploited because of the minimums we see here.
08:35 The important point to take away here is that even if we have a high force potential, we're limited by these transient points of minimum load.
08:43 These are what's limiting our performance and preventing us from exploiting the theoretical performance envelope of the car.
08:51 We use dampers to tune the response of each corner of the suspension to try to even out the load variation as much as possible.
08:58 Reducing these minimums is what will gain us grip overall.
09:02 The dampers are the primary tool we'll be using to minimise this variation in load in the higher frequency ranges.
09:09 They exist to damp the oscillations induced by road irregularities and driver inputs.
09:15 The actual mechanics of how different types of dampers work and the maths behind it is outside the scope of this course and it's safe to say that understanding damping completely, is a pretty big undertaking.
09:27 With that said, you don't need to be an expert in damping to use the data to your advantage.
09:32 Put simply, the operating principle of modern dampers is about providing a force in response to different speeds by forcing fluid through different sized and shape orifices.
09:43 A side effect of doing this is the conversion from the kinetic energy imparted to the fluid, to thermal energy.
09:50 We can think of this as losing or dissipating the kinetic energy as heat.
09:54 This energy conversion is why dampers get hot in operation and is also the main cause of the fluid degradation that happens over time inside the dampers, requiring them to be serviced.
10:05 As I mentioned before, another important way we make use of damping is to control the speed of suspension displacements in transient handling manuevers.
10:13 Often we're exploiting this to change the behaviour of one end of the car, relative to the other by changing the rate of displacement.
10:21 For example, to change the speed that the car rolls at on the front axle, relative to the rear or to change the speed that the front of the car pitches during braking.
10:30 To put it another way in broad terms, when we're talking about transient handling, such as what's happening when we first start braking or first turn into a corner, if we want to change how far something in the suspension is going to move, we do that with an elastic element such as springs, anti roll bars and bump rubbers.
10:50 If we want to control how fast it happens, we make use of the dampers.
10:55 As mentioned earlier, in applications where we have significant down force, we'll often make use of the dampers to control the behaviour of the sprung mass.
11:04 Many modern race cars generate most of their downforce with the floor of the car.
11:08 The aerodynamics of vehicle floors mean proximity and angle to the ground become the dominant parameters.
11:16 In some situations a lot of damping is used simply to keep the floor of the car within a certain aerodynamic window.
11:23 In high downforce applications, the amount of damping required to control the sprung mass to keep it within the required pitch, roll and ride height windows is usually at odds with the optimum damping level to achieve peak mechanical grip.
11:38 In high downforce cars, we often end up over damped.
11:41 Particularly in rebound in order to keep the platform stable.
11:46 Each situation will be different but in some cases this tradeoff will mean faster lap times through optimising downforce at the expense of pure mechanical grip.
11:55 It's also worth mentioning that the level of damping in the suspension also plays a roll in the way temperature is built up in the tyres.
12:04 This comes from varying the amount of energy that's absorbed by the suspension relative to the tyres.
12:10 You can think of this as a simple energy exchange where if more energy is absorbed by the dampers they get hotter.
12:17 Alternatively, if a higher proportion of the same energy could be absorbed by deforming the construction of the tyres, the tyres would instead get hotter.