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Professional Motorsport Data Analysis: Logging Damper Data

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Logging Damper Data

04.58

00:00 - Using some type of damper potentiometer or damper pot for short, the position data itself is useful but we can also use some simple maths to calculate the velocity and acceleration of the damper over time as well.
00:14 In many cases, the logging rate required for the damper position to analyse the actual damping behaviour will be the highest of any sensor we have on the car.
00:23 This is because to calculate the velocity and acceleration accurately from a position signal we need to have a relatively high logging rate.
00:32 In mathematical terms, we're talking about taking the derivative of the displacement over time to calculate the velocity.
00:39 In practical terms, we're taking the slope or difference between two measured damper positions to calculate the velocity.
00:47 The calculation being the change in position over a known time step.
00:53 As we're taking the slope of a typically very unsteady signal, if we want an accurate calculation of damper velocity we need to ensure we're logging the displacement quickly enough that we're capturing all of the required features.
01:06 Here's an example of some logged damper position data for the front left corner of a car.
01:11 We have the same data shown but logged at 4 different frequencies.
01:15 The original signal at the top is logged at 500 Hz which is pretty typical.
01:21 Below that we have 100, 50 and 10 Hz.
01:25 Remember this is the position data and what we need to do to calculate the velocity from position is divide the difference in displacement over a known time step.
01:35 As this position data is logged in millimetres, that gives us the resultant unit of mm per second for the velocity.
01:43 Another way to think about it is that we're drawing a small line between each data point and the slope or gradient of that line is the calculation of the damper speed at that point in time.
01:53 Now if we want to show the resultant speed calculation using these different frequency logged channels, we can start to see the importance of logging rate for a velocity calculation.
02:03 Comparing to the 500 Hz calculation we can see that the 100 Hz does follow a similar form but looking at some of these peak values, the magnitude is a long way off.
02:15 Massively underestimating the velocity.
02:17 Moving to the 50 Hz calculation we can see that we're missing even more detail and by the time we get to 10 Hz the calculation is clearly useless.
02:28 It doesn't resmble anything close to the original calculation of velocity at the full 500 Hz logging frequency.
02:35 For this reason, in practice for the average road racing car, this generally requires a minimum logging rate between 250 and 500 Hz for damper position.
02:45 This is an important consideration when selecting a logger if you plan to analyse your damping as some entry level loggers may not support such high logging rates.
02:56 Another consideration is the amount of logging memory we'll have available.
02:59 As logging at such high frequency consumes more of our logging memory.
03:03 The type and length of competition you're taking part in and how often you're clearing memory will determine how much space is needed in the logger.
03:13 Even though we won't refer to it much here in this section, we can make a lot of use of the position data in other types of analysis as we did in the previous section when looking at the roll gradients.
03:24 Like we covered earlier, we calculate the damper speed from its change in position over time.
03:31 This is sometimes handled and calculated for us with some predefined math in either the logger or the data analysis software.
03:37 We know the dampers are fundamentally most sensitive to velocity so this is the primary metric we're inerested in for most damping analsyis.
03:46 Whereas the velocity was calculated from the change in displacement over time, the acceleration is calculated from the change in velocity over time.
03:55 For basic damping analysis, we aren't typically making a lot of use of damper acceleration.
04:00 One thing the acceleration is helpful for though is identifying any large impact the suspension has experienced during a lap.
04:08 The largest impact loads will generally be seen when running over curbs.
04:12 In the case of identifying a structural tyre, or suspension failure, it can sometimes be traced to a large impact and acceleration is the best way to identify this in the data.
04:23 A good way to use the damper acceleration data is with a report table as shown here.
04:28 After a run, we can quickly look through the maximum values to see if anything stands out.
04:32 Over time, you'll get familiar with what sort of acceleration values you can expect from your car at each circuit.